Non-destructive testing methods

Abstract

To provide a nondestructive inspection method that can accurately estimate presence or absence of damage to a reinforcing bar provided in a concrete structure.SOLUTION: A nondestructive inspection method includes: measuring magnetic flux density in a first direction of an object to be inspected P at a plurality of measurement positions arranged side by side along a second direction parallel to a surface CF of a concrete structure C and orthogonal to the first direction; forming, for each of the measurement positions, a first direction fluctuation curve indicating fluctuations along the first direction of the magnetic flux density in the first direction measured at the plurality of measurement positions; forming a first direction differential curve obtained by performing first-order differentiation of the first direction fluctuation curve at each measurement position; calculating, for the first direction differential curve at each measurement position, a difference ΔdBx between a maximum value and a minimum value across a position where the first direction differential curve becomes 0 and / or the difference ΔdXx between a position of the maximum value and a position of the minimum value across the position where the first direction differential curve becomes 0; and determining presence or absence of fracture of the object to be inspected P on the basis of the difference ΔdBx and / or the difference ΔdXx.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-destructive inspection method, and more particularly to a non-destructive inspection method for detecting fractures in reinforcing bars, steel rods, steel wires, etc. installed in concrete structures using a magnetic flux leakage method. [Background technology]

[0002] Conventionally, magnetic leakage flux methods have been used as non-destructive testing methods for detecting damaged areas in reinforcing bars, steel rods, steel wires, etc. (hereinafter referred to as reinforcing bars, etc.) installed within concrete structures. In this magnetic leakage flux method, a magnet such as a permanent magnet is moved along the surface of the concrete to magnetize the reinforcing bars, etc., and then the magnetic flux density leaking from the surface of the concrete is measured. Then, the presence or absence of damage to the reinforcing bars, etc. is detected based on the results of the magnetic flux density measurement. Technologies for detecting damaged areas in reinforcing bars, etc. using this magnetic leakage flux method are disclosed in Patent Documents 1 to 6. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3734822 [Patent Document 2] Patent No. 5946638 [Patent Document 3] WO2020 / 027028 publication [Patent Document 4] WO2020 / 027043 publication [Patent Document 5] Patent No. 6305860 [Patent Document 6] Japanese Patent Publication No. 2020-148565 Summary of the Invention [Problem to be solved by the invention]

[0004] By using the techniques disclosed in Patent Documents 1 to 6, it is possible to detect damaged parts such as reinforcing bars with a certain degree of accuracy, but there is a need for a method that can more accurately determine damaged parts.

[0005] In view of the above circumstances, an object of the present invention is to provide a non-destructive inspection method that can accurately estimate the presence or absence of breakage of reinforcing bars or the like provided in a concrete structure.

Means for Solving the Problems

[0006] <X-axis direction> The non-destructive inspection method of the first invention is a method of measuring the magnetic flux density of an inspection object extending in a first direction embedded in a concrete structure outside the concrete structure along the first direction of the inspection object, and estimating the presence or absence of breakage of the inspection object based on the variation of the measured magnetic flux density. The magnetic flux density in the first direction is measured at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and orthogonal to the first direction of the inspection object. A first-direction variation curve showing the variation of the magnetic flux density in the first direction measured at a plurality of measurement positions along the first direction is formed for each measurement position. A first-direction differential curve obtained by differentiating the first-direction variation curve of each measurement position is formed. For the first-direction differential curve of each measurement position, the difference ΔdBx between the maximum value and the minimum value sandwiching the position where the first-direction differential curve becomes 0, and / or the difference ΔdXx between the position of the maximum value and the position of the minimum value sandwiching the position where the first-direction differential curve becomes 0 are calculated respectively ,each R which is the inverse cube of the distance R from the measurement position to the inspection object -3 A linear approximation formula representing the relationship between R and the difference ΔdBx calculated from the first-direction differential curve of each measurement position, and / or R which is the square root of 1 / 2 of the distance R from each measurement position to the inspection object 1 / 2 A linear approximation formula representing the relationship between and the difference ΔdXx calculated from the first-direction differential curve of each measurement position is created, and it is determined that breakage has occurred in the inspection object when the difference ΔdBx calculated from the first-direction differential curve of each measurement position and / or the difference ΔdXx calculated from the first-direction differential curve of each measurement position satisfies the linear approximation formula. Second InventionThe non-destructive testing method is A method for estimating the presence or absence of a fracture in an object to be inspected based on a variation in the measured magnetic flux density, the method comprising: measuring the magnetic flux density in the first direction of an object to be inspected that is embedded in a concrete structure, outside the concrete structure along the first direction of the object to be inspected; measuring the magnetic flux density in the first direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be inspected; forming a first direction variation curve for each measurement position that indicates the variation in the magnetic flux density in the first direction measured at the plurality of measurement positions along the first direction; forming a first direction differential curve by first-order differentiating the first direction variation curve for each measurement position; and calculating, for the first direction differential curve at each measurement position, a difference ΔdBx between a maximum value and a minimum value that sandwich a position where the first direction differential curve is zero, and / or a difference ΔdXx between a position where the first direction differential curve is zero and a position where the maximum value and a position where the first direction differential curve is zero; In a test structure simulating a concrete structure, which has a test object having a fracture that is a component equivalent to the inspection object, a magnetic flux density in a first direction is measured along the first direction of the test object at a plurality of measurement positions arranged along a second direction parallel to the surface of the test structure and perpendicular to the first direction of the test object, a first direction variation curve indicating a variation along the first direction of the magnetic flux density in the first direction measured at the plurality of measurement positions is formed for each measurement position, a first direction differential curve is formed by first-order differentiating the first direction variation curve at each measurement position, and for the first direction differential curve at each measurement position, a difference ΔdBx between the maximum value and the minimum value sandwiching a position where the first direction differential curve is 0, and / or a difference ΔdXx between the position of the maximum value and the position of the minimum value sandwiching the position where the first direction differential curve is 0 is calculated, and a value R is calculated which is the inverse cube of the distance R from each measurement position to the test object. -3 and a first-order approximation formula representing the relationship between the difference ΔdBx calculated from the first direction differential curve at each measurement position and R, which is the 1 / 2 power of the distance R from each measurement position to the test object. 1 / 2 and the difference ΔdXx calculated from the first direction differential curve at each measurement position, and if the difference ΔdBx and / or the difference ΔdXx calculated from the magnetic flux density measured in the concrete structure satisfy the first order approximation formula, it is determined that a fracture has occurred in the object to be inspected. Third Invention The non-destructive testing method is A method for estimating the presence or absence of a fracture in an object to be inspected based on a variation in the measured magnetic flux density, the method comprising: measuring the magnetic flux density in the first direction of an object to be inspected that is embedded in a concrete structure, outside the concrete structure along the first direction of the object to be inspected; measuring the magnetic flux density in the first direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be inspected; forming a first direction variation curve for each measurement position that indicates the variation in the magnetic flux density in the first direction measured at the plurality of measurement positions along the first direction; forming a first direction differential curve by first-order differentiating the first direction variation curve for each measurement position; and calculating, for the first direction differential curve at each measurement position, a difference ΔdBx between a maximum value and a minimum value that sandwich a position where the first direction differential curve is zero, and / or a difference ΔdXx between a position where the first direction differential curve is zero and a position where the maximum value and a position where the first direction differential curve is zero;In a test structure simulating a concrete structure, which has a test object having a fracture that is a component equivalent to the inspection object, a magnetic flux density in a first direction is measured along the first direction of the test object at a plurality of measurement positions arranged along a second direction parallel to the surface of the test structure and perpendicular to the first direction of the test object, a first direction variation curve showing the variation along the first direction of the magnetic flux density in the first direction measured at the plurality of measurement positions is formed for each measurement position, a first direction differential curve is formed by first-order differentiating the first direction variation curve at each measurement position, and For the differential curve, the difference ΔdBx between the maximum value and the minimum value on either side of the position where the first direction differential curve becomes 0, and / or the difference ΔdXx between the position of the maximum value and the position of the minimum value on either side of the position where the first direction differential curve becomes 0 are calculated, and a diagnostic map having a fracture region for estimating fracture of the inspection object is formed, with the difference ΔdBx as the first axis and the difference ΔdXx as the second axis, and the presence or absence of a fracture of the inspection object is estimated based on whether the difference ΔdBx and the difference ΔdXx calculated from the magnetic flux density measured in the concrete structure are located in the fracture region of the diagnostic map. Fourth Invention The non-destructive testing method is A method for estimating the presence or absence of a fracture in an object to be inspected based on a variation in the measured magnetic flux density, the method comprising: measuring the magnetic flux density in the first direction of an object to be inspected that is embedded in a concrete structure, outside the concrete structure along the first direction of the object to be inspected; measuring the magnetic flux density in the first direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be inspected; forming a first direction variation curve for each measurement position that indicates the variation in the magnetic flux density in the first direction measured at the plurality of measurement positions along the first direction; forming a first direction differential curve by first-order differentiating the first direction variation curve for each measurement position; and calculating, for the first direction differential curve at each measurement position, a difference ΔdBx between a maximum value and a minimum value that sandwich a position where the first direction differential curve is zero, and / or a difference ΔdXx between a position where the first direction differential curve is zero and a position where the maximum value and a position where the first direction differential curve is zero; When there are no buried rebars other than the one being inspected in the concrete structure, R is the 1 / 2 power of the distance R from each measurement position to the inspection target. 1 / 2 and the difference ΔdXx calculated from the first-direction differential curve of each measurement position, and a linear approximation equation is created, where the position difference from the inspection object to the measurement position in the second direction is defined as position difference Y, the distance from the inspection object to the measurement position is defined as distance R(Y), and the difference ΔdXx in the case of position difference Y is defined as the value ΔdXx(Y) estimated by the linear approximation equation, and the relationship between ΔdXx(Y) / ΔdXx(0) and (R(Y) / R(0)) 1 / 2 and estimates the fracture gap of the object to be inspected based on the slope of the relative value linear approximation formula. R(0): The distance from the measurement position to the test object on a third direction line perpendicular to the first and second directions is the same as the measurement position, and the measurement position is on the third direction line of the test object. <Y-axis direction> Fifth Invention The non-destructive inspection method is a method for measuring the magnetic flux density of an inspection object extending in a first direction embedded in a concrete structure outside the concrete structure along the first direction of the inspection object, and estimating the presence or absence of breakage of the inspection object based on the fluctuation of the measured magnetic flux density. The method includes measuring the magnetic flux density in a second direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and orthogonal to the first direction of the inspection object, respectively forming second-direction fluctuation curves showing the fluctuation along the first direction of the magnetic flux density in the second direction measured at the plurality of measurement positions, respectively forming second-direction differential curves obtained by second-order differentiating the second-direction fluctuation curves at each measurement position, for the second-direction differential curves at each measurement position, calculating the difference Δd2By between the maximum value and the minimum value sandwiching the position where the second-direction differential curve becomes 0, and / or the difference Δd2Xy between the position of the maximum value and the position of the minimum value sandwiching the position where the second-direction differential curve becomes 0 ,each R which is the inverse cube of the distance R from the measurement position to the inspection object -3 A linear approximation formula representing the relationship between the value Δd2By / β obtained by dividing the difference Δd2By calculated from the second-direction differential curve at each measurement position by the correction coefficient β, and / or R which is the square root of the distance R from each measurement position to the inspection object 1 / 2 Create a linear approximation formula representing the relationship between the value Δd2Xy·α obtained by correcting the positive or negative sign of the difference Δd2Xy calculated from the second-direction differential curve at each measurement position and R which is the square root of the distance R from each measurement position to the inspection object. When the value Δd2By / β calculated from the second-direction differential curve at each measurement position and / or the value Δd2Xy·α calculated from the second-direction differential curve at each measurement position satisfy the linear approximation formula, it is determined that breakage has occurred in the inspection object. α: SIGN(Y) β: Y / Za·SIGN(Δd2Xy) Y: The difference in the second-direction position from the inspection object to each measurement position SIGN(A): Depending on the positive or negative sign of A, when A is a positive number or 0, the value is “+1”, and when A is a negative number, the value is “-1” Za: The distance from each measurement position to the inspection object in a third direction orthogonal to the first direction and the second direction Sixth Invention The non-destructive testing method is A method for estimating the presence or absence of a fracture in an object to be inspected based on a variation in the measured magnetic flux density, the method comprising: measuring the magnetic flux density of an object to be inspected that is embedded in a concrete structure and extends in a first direction outside the concrete structure along the first direction of the object to be inspected; measuring the magnetic flux density in the second direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be inspected; forming second direction variation curves that indicate the variation in the magnetic flux density in the second direction measured at the plurality of measurement positions along the first direction; forming second direction differential curves by second-order differentiating the second direction variation curves at each measurement position; and calculating, for the second direction differential curve at each measurement position, a difference Δd2By between the maximum value and the minimum value that sandwich a position where the second direction differential curve becomes zero, and / or a difference Δd2Xy between the position of the maximum value and the position of the minimum value that sandwich the position where the second direction differential curve becomes zero; In a test structure simulating a concrete structure, which has a test object having a fracture that is a component equivalent to the inspection object, a magnetic flux density in a second direction is measured along the first direction of the test object at a plurality of measurement positions arranged along a second direction parallel to the surface of the test structure and perpendicular to the first direction of the test object, a second direction variation curve indicating the variation along the first direction of the magnetic flux density in the second direction measured at the plurality of measurement positions is formed for each measurement position, and a second direction differential curve is formed by second-order differentiating the second direction variation curve at each measurement position, and for the second direction differential curve at each measurement position, a difference Δd2By between the maximum value and the minimum value sandwiching a position where the second direction differential curve becomes 0, and / or a difference Δd2Xy between the position of the maximum value and the position of the minimum value sandwiching the position where the second direction differential curve becomes 0 is calculated, and a value R which is the inverse cube of the distance R from each measurement position to the inspection object is calculated. -3 and a value Δd2By / β1 obtained by dividing the difference Δd2By calculated from the second direction differential curve at each measurement position by a correction coefficient β1, and / or R, which is the 1 / 2 power of the distance R from each measurement position to the test object. 1 / 2 and a value Δd2Xy·α1 obtained by correcting the positive or negative sign of the difference Δd2Xy calculated from the second direction differential curve at each measurement position, and it is determined that a fracture has occurred in the inspection object when the value Δd2By / β and / or the value Δd2Xy·α calculated from the magnetic flux density measured in the concrete structure fall within the range of the first-order approximation formula. α:SIGN(Y) β:Y / Za·SIGN(Δd2Xy) Y: Difference in the position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, if A is a positive number or 0, the value is "+1", and if A is a negative number, the value is "-1". Za: Distance from each measurement position to the inspection object in the third direction perpendicular to the first and second directions α1:SIGN(Y1) β1:Y1 / Za1·SIGN(Δd2Xy) Y1: Difference in position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, if A is a positive number or 0, the value is "+1", and if A is a negative number, the value is "-1". Za1: Distance from each measurement position to the test object in the third direction perpendicular to the first and second directions Seventh Invention The non-destructive testing method is A method for estimating the presence or absence of a fracture in an object to be inspected based on a variation in the measured magnetic flux density, the method comprising: measuring the magnetic flux density of an object to be inspected that is embedded in a concrete structure and extends in a first direction outside the concrete structure along the first direction of the object to be inspected; measuring the magnetic flux density in the second direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be inspected; forming second direction variation curves that indicate the variation in the magnetic flux density in the second direction measured at the plurality of measurement positions along the first direction; forming second direction differential curves by second-order differentiating the second direction variation curves at each measurement position; and calculating, for the second direction differential curve at each measurement position, a difference Δd2By between the maximum value and the minimum value that sandwich a position where the second direction differential curve becomes zero, and / or a difference Δd2Xy between the position of the maximum value and the position of the minimum value that sandwich the position where the second direction differential curve becomes zero; In a test structure simulating a concrete structure, which has a test object having a fracture that is a component equivalent to the inspection object, a magnetic flux density in a second direction is measured along the first direction of the test object at a plurality of measurement positions arranged along a second direction parallel to the surface of the test structure and perpendicular to the first direction of the test object, a second direction variation curve showing the variation along the first direction of the magnetic flux density in the second direction measured at the plurality of measurement positions is formed for each measurement position, a second direction differential curve is formed by second-order differentiating the second direction variation curve at each measurement position, and a position at which the second direction differential curve at each measurement position becomes 0 is determined. The present invention is characterized in that a value Δd2By / β1 obtained by dividing the maximum and minimum values ​​sandwiching the position where the second directional differential curve becomes 0 by a correction coefficient β1 and / or a value Δd2Xy·α1 obtained by correcting the positive or negative sign of the difference Δd2Xy between the positions of the maximum and minimum values ​​sandwiching the position where the second directional differential curve becomes 0 are calculated, and a diagnostic map having a fracture region for estimating a fracture of the inspection object is formed, with the value Δd2By / β1 as the first axis and the value Δd2Xy·α1 as the second axis, and the presence or absence of a fracture of the inspection object is estimated based on whether the value Δd2By / β and the value Δd2Xy·α calculated from the magnetic flux density measured in the concrete structure are located in the fracture region of the diagnostic map. α:SIGN(Y) β:Y / Za·SIGN(Δd2Xy) Y: Difference in the position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, if A is a positive number or 0, the value is "+1", and if A is a negative number, the value is "-1". Za: Distance from each measurement position to the inspection object in the third direction perpendicular to the first and second directions α1:SIGN(Y1) β1: Y1 / Za1 · SIGN(Δd2Xy) Y1: The difference in position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, when A is a positive number or 0, the value is "+1", and when A is a negative number, the value is "-1" Za1: The distance from each measurement position in the third direction orthogonal to the first and second directions to the test object Eighth Invention The non - destructive inspection method is A method for estimating the presence or absence of a fracture in an object to be inspected based on a variation in the measured magnetic flux density, the method comprising: measuring the magnetic flux density of an object to be inspected that is embedded in a concrete structure and extends in a first direction outside the concrete structure along the first direction of the object to be inspected; measuring the magnetic flux density in the second direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be inspected; forming second direction variation curves that indicate the variation in the magnetic flux density in the second direction measured at the plurality of measurement positions along the first direction; forming second direction differential curves by second-order differentiating the second direction variation curves at each measurement position; and calculating, for the second direction differential curve at each measurement position, a difference Δd2By between the maximum value and the minimum value that sandwich a position where the second direction differential curve becomes zero, and / or a difference Δd2Xy between the position of the maximum value and the position of the minimum value that sandwich the position where the second direction differential curve becomes zero; In the case where there is no embedded reinforcing bar other than the inspection object in the concrete structure, R which is the square root of the distance R from each measurement position to the inspection object 1 / 2 Create a linear approximation formula representing the relationship between R and the value Δd2Xy·α calculated from the second - direction differential curve of each measurement position. Let the difference in position in the second direction from the inspection object to the measurement position be the position difference Y, and the distance from the inspection object to the measurement position be the distance R(Y). Let the value Δd2Xy·α at the position difference Y be the estimated value Δd2Xy(Y)·α(Y) by the linear approximation formula. And create a relative - value linear approximation formula representing the relationship between (Δd2Xy(Y)·α(Y)) / (Δd2Xy(0)·α(0)) and (R(Y) / R(0)) 1 / 2 And estimate the fracture gap of the inspection object based on the slope of the relative - value linear approximation formula. <00001⑧7>α: SIGN(Y) β: Y / Za · SIGN(Δd2Xy) Y: The difference in position in the second direction from the inspection object to each measurement position SIGN(A): Depending on the sign of A, when it is a positive number or 0, the value is "+1", and when it is a negative number, the value is "-1" Za: The distance from each measurement position in the third direction orthogonal to the first and second directions to the inspection object R(0): The distance from the measurement position to the inspection object when the distance from the inspection object on the third - direction line orthogonal to the first and second directions is the same as the distance of the measurement position and the measurement position is on the third - direction line of the inspection object <Z - axis direction> The ninth inventionThe non-destructive testing method measures the magnetic flux density of an object to be tested that is embedded in a concrete structure and extends in a first direction outside the concrete structure along the first direction of the object to be tested, and estimates the presence or absence of a fracture in the object to be tested based on fluctuations in the measured magnetic flux density, the method comprising: measuring the magnetic flux density in a third direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be tested; forming third direction fluctuation curves that indicate fluctuations along the first direction of the magnetic flux density in the third direction measured at the plurality of measurement positions; forming third direction differential curves by second-order differentiation of the third direction fluctuation curves at each measurement position; and calculating, for the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value that sandwich a position where the third direction differential curve becomes zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value that sandwich the position where the third direction differential curve becomes zero. ,each R, which is the inverse cube of the distance R from the measurement position to the inspection object -3 and a linear approximation formula expressing the relationship between the difference Δd2Bz calculated from the third direction differential curve of each measurement position and R, which is the 1 / 2 power of the distance R from each measurement position to the inspection object. 1 / 2 and the difference Δd2Xz calculated from the third direction differential curve at each measurement position, and it is determined that a fracture has occurred in the test object when the difference Δd2Bz calculated from the third direction differential curve at each measurement position and / or the difference Δd2Xz calculated from the third direction differential curve at each measurement position satisfies the linear approximation equation. A non-destructive testing method of a tenth aspect of the present invention is a method for measuring a magnetic flux density of an object to be tested that is embedded in a concrete structure and extends in a first direction outside the concrete structure along the first direction of the object to be tested, and for estimating the presence or absence of a fracture in the object to be tested based on a variation in the measured magnetic flux density, the method comprising: measuring the magnetic flux density in a third direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be tested; forming third direction variation curves that indicate the variation along the first direction of the magnetic flux density in the third direction measured at the plurality of measurement positions; forming third direction differential curves by second-order differentiating the third direction variation curves at each measurement position; and calculating, for the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value that sandwich a position where the third direction differential curve becomes zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value that sandwich the position where the third direction differential curve becomes zero;In a test structure simulating a concrete structure, which has a test object having a fracture that is a component equivalent to the inspection object, a magnetic flux density in a third direction is measured along the first direction of the test object at a plurality of measurement positions arranged along a second direction parallel to the surface of the test structure and perpendicular to the first direction of the test object, a third direction variation curve indicating a variation along the first direction of the magnetic flux density in the third direction measured at the plurality of measurement positions is formed for each measurement position, and a third direction differential curve is formed by second-order differentiating the third direction variation curve at each measurement position, and for the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value sandwiching a position where the third direction differential curve becomes 0, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value sandwiching the position where the third direction differential curve becomes 0 is calculated, and R is the inverse cube of the distance R from each measurement position to the inspection object. -3 and a first-order approximation formula representing the relationship between the difference Δd2Bz calculated from the third direction differential curve at each measurement position, and / or R, which is the 1 / 2 power of the distance R from each measurement position to the test object. 1 / 2 and the difference Δd2Xz calculated from the third direction differential curve at each measurement position, and if the difference Δd2Bz and / or the difference Δd2Xz calculated from the magnetic flux density measured in the concrete structure satisfy the first-order approximation formula, it is determined that a fracture has occurred in the object to be inspected. A non-destructive testing method of an eleventh invention is a method for measuring a magnetic flux density of an object to be tested that is embedded in a concrete structure and extends in a first direction outside the concrete structure along the first direction of the object to be tested, and estimating the presence or absence of a fracture in the object to be tested based on fluctuations in the measured magnetic flux density, the method comprising: measuring the magnetic flux density in a third direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be tested; forming third direction fluctuation curves that indicate fluctuations along the first direction of the magnetic flux density in the third direction measured at the plurality of measurement positions; forming third direction differential curves by second-order differentiating the third direction fluctuation curves at each measurement position; and calculating, for the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value that sandwich a position where the third direction differential curve becomes zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value that sandwich the position where the third direction differential curve becomes zero;In a test structure simulating a concrete structure, the test object has a fracture that is a component equivalent to the inspection object, and the magnetic flux density in a third direction is measured along the first direction of the test object at a plurality of measurement positions arranged along a second direction that is parallel to the surface of the test structure and perpendicular to the first direction of the test object, and a third direction variation curve that indicates a variation along the first direction of the magnetic flux density in the third direction measured at the plurality of measurement positions is formed for each measurement position, and a third direction differential curve is formed by second-order differentiating the third direction variation curve at each measurement position, and the third direction differential curve at each measurement position is formed For the line, the difference Δd2Bz between the maximum value and the minimum value on either side of the position where the third direction differential curve becomes 0, and / or the difference Δd2Xz between the position of the maximum value and the position of the minimum value on either side of the position where the third direction differential curve becomes 0 are calculated, and a diagnostic map having a fracture region for estimating fracture of the inspection object is formed, with the difference Δd2Bz as the first axis and the difference Δd2Xz as the second axis, and the presence or absence of a fracture of the inspection object is estimated based on whether the difference Δd2Bz and the difference Δd2Xz calculated from the magnetic flux density measured in the concrete structure are located in the fracture region of the diagnostic map. A non-destructive testing method of a twelfth aspect of the present invention is a method for measuring a magnetic flux density of an object to be tested that is embedded in a concrete structure and extends in a first direction outside the concrete structure along the first direction of the object to be tested, and for estimating the presence or absence of a fracture in the object to be tested based on a variation in the measured magnetic flux density, the method comprising: measuring the magnetic flux density in a third direction at a plurality of measurement positions aligned along a second direction that is parallel to the surface of the concrete structure and perpendicular to the first direction of the object to be tested; forming third direction variation curves that indicate the variation along the first direction of the magnetic flux density in the third direction measured at the plurality of measurement positions; forming third direction differential curves by second-order differentiating the third direction variation curves at each measurement position; and calculating, for the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value that sandwich a position where the third direction differential curve becomes zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value that sandwich the position where the third direction differential curve becomes zero; When there are no buried rebars other than the one being inspected in the concrete structure, R is the 1 / 2 power of the distance R from each measurement position to the inspection target. 1 / 2 and the value Δd2Xz calculated from the third-direction differential curve of each measurement position, and a linear approximation formula is created, where the position difference from the inspection object to the measurement position in the second direction is defined as position difference Y, the distance from the inspection object to the measurement position is defined as distance R(Y), and the difference Δd2Xz in the case of position difference Y is defined as the value Δd2Xz(Y) estimated by the linear approximation formula, and the equations Δd2Xz(Y) / Δd2Xz(0) and (R(Y) / R(0)) are 1 / 2 and estimates the fracture gap of the object to be inspected based on the slope of the relative value linear approximation formula. R(0): The distance from the measurement position to the test object on a third direction line perpendicular to the first and second directions is the same as the measurement position, and the test object is located on the third direction line. 13th InventionThe non-destructive inspection method is 1st to 12th inventions in which, at the measurement position where Ya / Za indicating the relationship between the distance Ya from the inspection target to the measurement position in the second direction and the distance Za from the surface of the concrete structure to the inspection target is 0 to 1.5, the difference between the maximum value and the minimum value of the differential curve obtained from the fluctuation of the magnetic flux density measured at the measurement position and / or the difference between the position of the maximum value and the position of the minimum value of the differential curve are used to estimate the presence or absence of breakage of the inspection target. 14th Invention The non-destructive inspection method is 13th Invention in which, when the distance Za is 100 mm, the distance Ya is 0 to 150 mm.

Advantages of the Invention

[0007] <X-axis direction> First Invention According to, based on the measured magnetic flux density, breakage of the inspection target embedded in the concrete structure can be detected. Second and third inventions According to, even if there is an obstacle between the concrete structure and the inspection target, the accuracy of detecting breakage of the inspection target based on the measured magnetic flux density can be increased. Fourth Invention According to, when there is no obstacle between the concrete structure and the inspection target, the breakage gap of the inspection target can be estimated. <Y-axis direction> Fifth Invention According to, based on the measured magnetic flux density, breakage of the inspection target embedded in the concrete structure can be detected. Sixth and seventh inventions According to, even if there is an obstacle between the concrete structure and the inspection target, the accuracy of detecting breakage of the inspection target based on the measured magnetic flux density can be increased. Eighth Invention According to, when there is no obstacle between the concrete structure and the inspection target, the breakage gap of the inspection target can be estimated. <Z-axis direction> 9th InventionAccording to the present invention, it is possible to detect a fracture in an inspection object buried in a concrete structure based on the measured magnetic flux density. 10th and 11th inventions According to this method, even if there is an obstacle between the concrete structure and the inspection object, it is possible to increase the accuracy of detecting a fracture in the inspection object based on the measured magnetic flux density. 12th Invention According to the method, when there is no obstacle between the concrete structure and the inspection object, the fracture gap of the inspection object can be estimated. 13th and 14th Inventions According to this, the accuracy of fracture evaluation of the inspection object can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] 1A and 1B are schematic explanatory views of a nondestructive inspection device 1 used in the nondestructive inspection method of the present embodiment, in which (A) is a side view and (B) is a plan view. [Figure 2] FIG. 2 is a schematic explanatory diagram of a cross section taken along line II-II in FIG. 1(A). [Figure 3] 1 is a schematic block diagram of a nondestructive inspection device 1 used in the nondestructive inspection method of the present embodiment. [Figure 4] 1A and 1B are schematic explanatory diagrams of a test structure TM, in which (A) is a schematic cross-sectional view taken along line AA in (B), and (B) is a schematic cross-sectional view taken along line BB in (A). [Figure 5] (A) is a graph showing a first direction fluctuation curve, and (B) is a graph showing a first direction differential curve. [Figure 6] 10A is a graph of a linear approximation formula showing the relationship between the difference ΔdBx and R−3, and FIG. 10B is a graph of a linear approximation formula showing the relationship between the difference ΔdXx and R1 / 2. [Figure 7](A) is a graph comparing the first-order approximation formulas that represent the relationship between the difference ΔdXx and R1 / 2 when the concrete structure C has crossing rebars such as horizontal and vertical rebars and when there are no crossing rebars when the inspection object is PC stranded wire, and (B) is a graph comparing the first-order approximation formulas that represent the relationship between the difference ΔdXx and R1 / 2 when the concrete structure C has crossing rebars such as horizontal and vertical rebars and when there are no crossing rebars when the inspection object is PC steel bars. [Figure 8] (A) is a graph showing a second direction fluctuation curve, and (B) is a graph showing a second direction differential curve. [Figure 9] (A) is a graph of a linear approximation formula showing the relationship between the value Δd2By / β and R-3, and (B) is a graph of a linear approximation formula showing the relationship between the value Δd2Xy·α and the calculated R1 / 2. [Figure 10] (A) is a graph comparing the linear approximation formula that shows the relationship between the value Δd2Xy·α and R1 / 2 when the concrete structure C has crossing rebars such as horizontal and vertical rebars and when there are no crossing rebars when the inspected object is PC strands. (B) is a graph comparing the linear approximation formula that shows the relationship between the value Δd2Xy·α and R1 / 2 when the concrete structure C has crossing rebars such as horizontal and vertical rebars and when there are no crossing rebars when the inspected object is PC steel bars. [Figure 11] (A) is a graph showing a third direction fluctuation curve, and (B) is a graph showing a third direction differential curve. [Figure 12] 10A is a graph of a linear approximation formula showing the relationship between the difference Δd2Bz and R-3, and FIG. 10B is a graph of a linear approximation formula showing the relationship between the difference Δd2Xz and R1 / 2. [Figure 13] (A) is a graph comparing the first-order approximation formulas that represent the relationship between the difference Δd2Xz and R1 / 2 when the concrete structure C has crossing rebars such as horizontal and vertical rebars and when there are no crossing rebars when the inspection object is a PC stranded wire, and (B) is a graph comparing the first-order approximation formulas that represent the relationship between the difference Δd2Xz and R1 / 2 when the concrete structure C has crossing rebars such as horizontal and vertical rebars and when there are no crossing rebars when the inspection object is a PC steel bar. [Figure 14] 10A is a schematic diagram of a diagnostic map MP using the difference ΔdBx and the difference ΔdXx; (B) is a diagnostic map MP using the value Δd2By / β and the value Δd2Xy·α; and (C) is a diagnostic map MP using the difference Δd2Bz and the difference Δd2Xz. [Figure 15] 10 is a graph showing the relationship between the fracture gap Gap of the fracture GA and the slope of the linear approximation equation. DETAILED DESCRIPTION OF THE INVENTION

[0009] The non-destructive testing method of this embodiment is a method of estimating fractures in an object to be tested that is buried inside a concrete structure using a leakage magnetic flux method, and can improve the accuracy of detecting fractures in the object to be tested, which is an object that extends in one direction, such as reinforcing bars, steel rods, steel wires, etc.

[0010] The concrete structure in which the inspection target to be inspected by the non-destructive inspection method of this embodiment is buried (hereinafter, sometimes simply referred to as the concrete structure to be inspected) is not particularly limited. For example, bridge girders, piers, deck slabs, etc. of roads and railways can be cited as concrete structures to be inspected by the non-destructive inspection method of this embodiment.

[0011] The concrete structures inspected by the non-destructive inspection method of this embodiment are not limited to those with flat surfaces, but also include those with cylindrical surfaces. For example, a columnar body having a cylindrical surface can also be listed as a concrete structure inspected by the non-destructive inspection method of this embodiment.

[0012] The object to be inspected by the non-destructive inspection method of this embodiment is not particularly limited, and may be any object extending in one direction parallel to the surface of the concrete structure to be inspected, and which may be subject to damage such as fracture. For example, the object to be inspected may be a steel material such as prestressing steel rods (high-strength steel with a diameter of 10 mm or more), prestressing steel wires (high-strength steel wires with a diameter of 8 mm or less), prestressing steel strands (twisted prestressing steel wires), or a steel bar for reinforced concrete.

[0013] In the following, a case where the surface of a concrete structure to be inspected by the non-destructive inspection method of this embodiment is a flat surface will be described as a representative example.

[0014] In the following description, the surface of the concrete structure to be inspected includes the tangent plane of a cylindrical structure (curved concrete structure). In the case of a cylindrical curved concrete structure, the reinforcing bars to be inspected extend along the axial direction of the surface of the curved concrete structure (the central axis direction of the cylindrical surface). Therefore, the device used in the non-destructive inspection method of this embodiment measures the magnetic flux density while moving along the axial direction of the surface of the curved concrete structure. Furthermore, the magnetic sensor (described later) that measures the magnetic flux density measures the magnetic flux density while moving while maintaining a state parallel to the tangent plane of the surface of the curved concrete structure when the device moves along the axial direction of the surface of the curved concrete structure. Therefore, in the following description, when the surface of the concrete structure is used as a reference, it means that in the case of a curved concrete structure, the tangent plane of the surface of the concrete structure is used as the reference.

[0015] <Concrete Structure C> First, a concrete structure C to be inspected by the non-destructive inspection method of this embodiment will be briefly described.

[0016] The concrete structure C to be inspected is, for example, a structure such as a bridge girder, pier, or deck slab, and has an inspection object P, such as rebar, steel rod, or steel wire, buried inside the structure (see Figure 1). Specifically, the concrete structure C to be inspected has a planar surface CF, and the inspection object P is buried so as to extend in one direction parallel to this surface CF. The direction in which this inspection object P extends, that is, the axial direction of the inspection object P (the left-right direction in Figure 1), will be referred to as the first direction of the inspection object P below.

[0017] In the following, the first direction of the inspection object P may be referred to as the X-axis direction, the direction parallel to the surface CF of the concrete structure C and perpendicular to the X-axis direction as the Y-axis direction, and the normal direction of the surface CF of the concrete structure C as the Z-axis direction (see Figure 1). The Y-axis direction is the second direction and the Z-axis direction is the third direction in the claims.

[0018] In addition, the concrete structure C to be inspected may have embedded therein components other than the inspection object P, such as reinforcing bars for reinforcing bars, spacers, etc.

[0019] Furthermore, the concept that the surface CF of the concrete structure C and the inspection object P are parallel not only refers to the case where the two are completely parallel throughout the entire inspection object P, but also includes the case where part of the inspection object P is slightly inclined relative to the surface CF of the concrete structure C being inspected.

[0020] <Non-destructive inspection device 1 of this embodiment> Next, before describing the nondestructive inspection method of this embodiment, a nondestructive inspection device 1 used in the nondestructive inspection method of this embodiment will be described.

[0021] <Mobile object 2> As shown in FIG. 1, the non-destructive inspection device 1 has a moving body 2. This moving body 2 is structured so that it can move smoothly in one direction along the surface CF of the concrete structure C to be inspected. More specifically, the moving body 2 is structured so that it can move linearly along the direction of its central axis B (see FIG. 1(B)). Moreover, the moving body 2 has the function of being able to move while maintaining a constant distance H between the surface CF of the concrete structure C to be inspected and a magnetic flux measuring unit 5, which will be described later. Note that hereinafter, the direction of the central axis B of the moving body 2 (i.e., the direction of movement of the moving body 2) may be referred to as the x-axis direction (see FIG. 1).

[0022] Specifically, the moving body 2 includes a main body 2a and a plurality of wheels 2r rotatably attached to the main body 2a (see FIG. 1(A)). The plurality of wheels 2r are arranged so that their rotation axes are perpendicular to the central axis B of the moving body 2. Furthermore, the plurality of wheels 2r are arranged so that their rotation axes are parallel to the surface CF of the concrete structure C to be inspected when the moving body 2 is placed on the surface CF of the concrete structure C to be inspected. Note that, hereinafter, the direction parallel to the rotation axes of the plurality of wheels 2r may be referred to as the y-axis direction, and the direction perpendicular to the x-axis and y-axis directions may be referred to as the z-axis direction (see FIG. 1). When the moving body 2 is placed on the surface CF of the concrete structure C, the z-axis direction is parallel to the normal direction of the surface CF of the concrete structure C (the Z-axis direction described above).

[0023] Furthermore, the multiple wheels 2r are provided so that they can move while maintaining a constant distance H (distance in the Z-axis direction) between the magnetic flux measuring unit 5 (more specifically, the magnetic sensor 6) and the surface CF of the concrete structure C to be inspected. In other words, by rolling the multiple wheels 2r while they are in contact with the surface CF of the concrete structure C to be inspected, the mobile body 2 can be moved along the X-axis direction on the surface CF of the concrete structure C to be inspected while maintaining a constant distance H in the Z-axis direction between the magnetic flux measuring unit 5 and the surface CF of the concrete structure C to be inspected. In the following, when the mobile body 2 is moved, the description will be given on the assumption that the direction of movement is along the X-axis direction.

[0024] There is no particular limitation on the number of wheels 2r provided on the moving body 2. As described above, as long as the moving body 2 can be moved in the X-axis direction while maintaining a constant distance in the Z-axis direction between the magnetic flux measuring unit 5 and the surface CF of the concrete structure C to be inspected, the number of wheels 2r may be three, or may be four or more.

[0025] Furthermore, the structure of the mobile body 2 is not particularly limited as long as it can maintain a constant distance H in the Z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected and can move smoothly along the X-axis direction on the surface CF of the concrete structure C to be inspected. In the above example, the mobile body 2 has wheels 2r, but the above function can also be achieved by laying a guide rail or the like parallel to the surface CF of the concrete structure C to be inspected along the X-axis direction and moving the mobile body 2 along this guide rail. Note that maintaining a constant distance H in the Z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected also includes the case where the distance H between them varies by about 20 mm when the mobile body 2 moves along the surface CF of the concrete structure C.

[0026] Furthermore, if the surface CF of the concrete structure C to be inspected is uneven, an imaginary plane obtained by averaging the surface unevenness in an area corresponding to the width of the area where the magnetic sensor 6 is provided in the magnetic flux measurement unit 5 (area of ​​width W in Figure 1(B)) corresponds to the surface CF of the concrete structure C to be inspected. Therefore, if the surface CF of the concrete structure C to be inspected is uneven, the distance H in the Z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected is the distance from the imaginary plane in the Z-axis direction to the magnetic flux measurement unit 5. Note that, hereinafter, the term "surface CF of the concrete structure C to be inspected" also includes the imaginary plane obtained by averaging the surface unevenness in the area corresponding to the magnetic flux measurement unit 5.

[0027] Furthermore, when a cylindrical pillar-shaped surface is used as the concrete structure to be inspected (corresponding to the curved concrete structure described above), the distance between the magnetic flux measurement unit 5 and the surface of the concrete structure varies depending on the position in the direction perpendicular to the pillar's axial direction. However, the mobile body 2 of the nondestructive inspection device 1 has a function that allows it to move while maintaining a constant distance between each magnetic sensor 6 of the magnetic flux measurement unit 5 and the surface CF of the concrete structure C when the mobile body 2 is moved in the pillar's axial direction (i.e., the axial direction of the object to be inspected, which corresponds to the first direction of the object to be inspected in the claims). For example, if a tangent plane is set that is tangent to the intersection of a plane passing through the central axis B of the mobile body 2 and the central axis of the pillar with the surface of the pillar, the mobile body 2 of the nondestructive inspection device 1 has a function that allows it to move while maintaining a constant distance between this tangent plane and each magnetic sensor 6 of the magnetic flux measurement unit 5.

[0028] <Magnetic flux measuring unit 5> The magnetic flux measuring unit 5 measures the magnetic flux density on the surface CF of the concrete structure C to be inspected, and is equipped with a magnetic sensor 6. The magnetic sensor 6 is capable of measuring the magnetic flux density in three axial directions, and is disposed on the base member 5a of the magnetic flux measuring unit 5 (see FIG. 1(B)). Note that the magnetic sensor 6 may be any known magnetic sensor as long as it can measure the magnetic flux density in three axial directions. For example, a Hall element sensor, an MR sensor, an MI sensor, a TMR sensor, etc. may be used as the magnetic sensor 6.

[0029] A plurality of magnetic sensors 6 (eight in FIG. 1(B)) are provided on the base member 5a of the magnetic flux measuring unit 5 so as to be spaced apart along the y-axis direction. Specifically, when the moving object 2 is placed on the surface CF of the concrete structure C to be inspected, the magnetic sensors 6 are arranged so as to be spaced apart along the y-axis direction so that the magnetic flux densities of the inspection object P in the X-axis, Y-axis, and Z-axis directions can be measured.

[0030] The multiple magnetic sensors 6 are preferably arranged so that the measurement axes of all the magnetic sensors 6 are aligned in the same plane. Here, "aligning the measurement axes of all the magnetic sensors 6 in the same plane" refers to cases where the measurement axes of all the magnetic sensors 6 are aligned completely in the same plane, as well as cases where there is a slight misalignment between the measurement axes of the magnetic sensors 6. The misalignment between the measurement axes of the magnetic sensors 6 in the same direction refers to both cases where the measurement axes of the magnetic sensors 6 are misaligned within approximately ±20 mm in a direction perpendicular to the measurement axes, and cases where there is a slight tilt between the measurement axes. For example, in the case of the measurement axis in the x-axis direction, this includes cases where the measurement axes of the x-axis sensors 6 are misaligned within approximately ±20 mm in the y-axis and / or z-axis directions, cases where the inclinations relative to planes parallel to both the x-axis and y-axis directions are different, and cases where the inclinations relative to planes parallel to both the x-axis and z-axis directions are different.

[0031] When multiple magnetic sensors 6 are provided, there are no particular limitations on the spacing between the magnetic sensors 6 or the width W of the area in which the magnetic sensors 6 are provided. The spacing and width W of the area may be set appropriately depending on the depth at which the inspection object P is buried, the spacing, etc. For example, if the distance in the third direction (Z-axis direction) from the inspection object P to the surface CF of the concrete structure C to be inspected is approximately 100 to 200 mm, then the spacing between the magnetic sensors 6 in the y-axis direction is preferably approximately 50 to 100 mm, and the width W of the area in which the magnetic sensors 6 are provided is preferably approximately 300 to 1000 mm.

[0032] Although eight magnetic sensors 6 are provided in FIG. 1(B), the number of magnetic sensors 6 is not particularly limited as long as it is three or more.

[0033] Furthermore, it is desirable that the multiple magnetic sensors 6 are arranged so that one of the magnetic sensors 6 is located on the center line B of the mobile body 2. For example, in FIG. 1(B), the magnetic sensor 6 Y03 is arranged on the center line B of the mobile body 2, and the other seven magnetic sensors 6 are arranged three on one side of the center line B of the mobile body 2 and four on the other side. In particular, if the number of magnetic sensors 6 is odd, it is desirable that one magnetic sensor 6 is arranged on the center line B of the mobile body 2 and the other magnetic sensors 6 are arranged symmetrically with respect to the center line B of the mobile body 2. In other words, it is desirable to arrange the multiple magnetic sensors 6 so that the same number of magnetic sensors 6 are arranged on both sides of the center line B of the mobile body 2. For example, if a plane that includes the center line B of the mobile body 2 and is perpendicular to the y-axis direction is defined as a reference plane SA, it is desirable that the multiple magnetic sensors 6 are arranged symmetrically with respect to this reference plane SA.

[0034] Furthermore, the multiple magnetic sensors 6 do not necessarily have to be arranged symmetrically with respect to the center line B of the moving body 2. It is sufficient that at least one magnetic sensor 6, preferably two or more magnetic sensors 6 are provided on both sides of the center line B of the moving body 2.

[0035] Furthermore, the multiple magnetic sensors 6 may be arranged so that none of the magnetic sensors 6 is located on the center line B of the moving body 2. In this case, at least one, preferably two or more magnetic sensors 6 should be provided on both sides of the center line B of the moving body 2. In particular, it is desirable to arrange the multiple magnetic sensors 6 symmetrically with respect to the center line B of the moving body 2.

[0036] <Control unit 4> 3, the control unit 4 has a position calculation function that calculates the positions of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5, and an operation control function that controls the operation of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5. The control unit 4 also has a storage function that associates data on the measurement values ​​of magnetic flux density measured by the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 with the positions of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 calculated by the position calculation function, and stores these data in a storage unit such as a memory.

[0037] Furthermore, the control unit 4 has an analysis function that uses the data stored in the storage unit to create graphs and maps that show fluctuations in the measured values ​​of magnetic flux density.

[0038] Furthermore, if the control unit 4 is provided with a data communication function to send and receive measurement data, etc., between an external personal computer or cloud computer, it is possible to have the storage function, analysis function, etc. of the control unit 4 cooperate with an external personal computer, etc.

[0039] <Position calculation function> The control unit 4 has a position calculation function that calculates the amount of movement of the mobile object 2, in other words, the amount of movement of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5. This position calculation function calculates the movement distance of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 from the initial position (the position where the mobile object 2 is placed on the surface CF of the concrete structure C to be inspected) to the current position, in other words, the current positions of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 based on the initial position. For example, if the relative positions of the multiple magnetic sensors 6 with respect to a reference position of the mobile object 2 (e.g., the position of the wheel 2r) are stored in the storage unit, the position calculation function can calculate the movement distance of the multiple magnetic sensors 6 in the X-axis direction and the positions of the multiple magnetic sensors 6 after the movement (positions in the X-axis direction) based on the amount of movement of the mobile object 2 from the initial position in the x-axis direction and the relative positions of the multiple magnetic sensors 6 with respect to the reference position at the initial position.

[0040] The method for calculating the movement distance of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 from the initial position in the X-axis direction to the current position is not particularly limited. As shown in FIG. 3, the mobile object 2 may be provided with a detector 4c that detects the movement distance from the initial position of the mobile object 2. For example, an encoder that can detect the amount of rotation (rotation angle) of the wheel 2r may be provided as the detector 4c. In this case, the position calculation function can calculate the movement distance of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 in the X-axis direction from the initial position and the positions (positions in the X-axis direction) of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 from the initial position after the movement, based on the rotation angle of the wheel 2r detected by the detector 4c and the diameter of the wheel 2r.

[0041] Furthermore, the detector 4c that detects the movement distance from the initial position of the moving object 2 is not limited to the above-mentioned encoder that detects the movement distance in the X-axis direction based on the number of rotations of the wheel 2r. An optical mouse, an accelerometer, or the like may also be used as the detector 4c that detects the movement distance in the X-axis direction.

[0042] Furthermore, the method for determining the current positions of the plurality of magnetic sensors 6 (in other words, the positions where the plurality of magnetic sensors 6 are measuring the magnetic flux density) is not limited to the above-mentioned method. For example, a position marker may be provided on or near the concrete structure C, and the position of the magnetic flux measuring unit 5 relative to this position marker at the timing when the magnetic flux density is measured may be measured to determine the position where the magnetic flux measuring unit 5 measured the magnetic flux density (position in the X-axis direction).

[0043] <Operation control function> The control unit 4 has an operation control function that controls the operation of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5. This operation control function has the functions of determining the timing at which the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 measure the magnetic flux density and causing the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 to measure the magnetic flux density at that timing, and transmitting the measured values ​​to the storage function. For example, when a measurement start signal is input using an operation button or the like, the operation control function then causes the multiple magnetic sensors 6 to measure the magnetic flux density at predetermined time intervals (e.g., every 10 milliseconds) and transmit the measured values ​​to the storage function (hereinafter, the term "causing the multiple magnetic sensors 6 to measure the magnetic flux density and transmitting the measured values ​​to the storage function" may be used). Alternatively, the operation control function may cause the multiple magnetic sensors 6 to measure the magnetic flux density at predetermined distances based on the amount of movement of the mobile object 2 in the x-axis direction calculated by the position calculation function. Of course, the control unit 4 may also be configured to cause the multiple magnetic sensors 6 to continuously measure the magnetic flux density and continuously transmit the measured values ​​to the storage function when a measurement start signal is input using an operation button or the like. The control unit 4 may control all of the magnetic sensors 6 to measure the magnetic flux density at the same timing, or may control each magnetic sensor 6 to measure at an appropriate timing. For example, the control unit 4 may control each magnetic sensor 6 to measure at the timing when the movement amount of each magnetic sensor reaches a predetermined movement amount.

[0044] If the position calculation function has the detector 4c as described above, the signal transmitted by the detector 4c may be directly supplied to the operation control function, and the operation control function may cause the plurality of magnetic sensors 6 to measure the magnetic flux density based on the signal transmitted by the detector 4c. For example, if the detector 4c is an encoder, the operation control function may cause the plurality of magnetic sensors 6 to measure the magnetic flux density in accordance with the rotation angle of the wheel 2r detected by the detector 4c (i.e., when the wheel 2r rotates by a predetermined angle). Furthermore, the timing at which the plurality of magnetic sensors 6 start measuring the magnetic flux density may also be determined based on the signal transmitted by the detector 4c. For example, when the detector 4c detects that the wheel 2r has started to rotate from a non-rotating state and transmits a signal, the plurality of magnetic sensors 6 may start measuring the magnetic flux density based on the signal.

[0045] Furthermore, the multiple magnetic sensors 6 of the magnetic flux measuring unit 5 may be in a state where they are constantly measuring the magnetic flux density regardless of a command from the operation control function. In this case, the operation control function only needs to have a function of transmitting signals from the multiple magnetic sensors 6 to the storage function at the above-mentioned time intervals or after a predetermined moving distance after a measurement start signal is input.

[0046] <Memory function> The storage function is a function that associates and stores the movement distance of the magnetic flux measurement unit 5 calculated by the position calculation function (i.e., the movement distance of the multiple magnetic sensors 6) with the measurement values ​​of magnetic flux density measured by the multiple magnetic sensors 6 of the magnetic flux measurement unit 5. Specifically, the storage function has a function that associates and stores in the storage unit the measurement values ​​of magnetic flux density measured by the multiple magnetic sensors 6 of the magnetic flux measurement unit 5, the time when the multiple magnetic sensors 6 measured the magnetic flux density, and the positions of the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 at that time (the movement amount of the mobile object 2 in the x-axis direction, the signal of the detector 4c, etc.).

[0047] The storage unit also stores information relating to the position (for example, initial position) at which each magnetic sensor 6 starts measurement and the start time thereof, in association with each magnetic sensor 6.

[0048] Therefore, by acquiring the information stored in the storage unit, it is possible to identify the position at which the magnetic flux density measured by each magnetic sensor 6 was measured.

[0049] <Analysis function> The control unit 4 also has an analysis function for analyzing the data stored in the storage unit. This analysis function uses the data stored in the storage unit to determine whether or not the test object P is broken, and to estimate the break length (Gap) of the test object P. Details of the analysis function will be described later.

[0050] The control unit 4 does not have to have the above-mentioned analysis function, and may have only the above-mentioned position calculation function, operation control function, and storage function. In this case, a function for supplying the data stored in the control unit 4 to an external device may be provided so that the data can be analyzed by an analysis device provided separately from the nondestructive testing device 1. In this case, the data may be supplied from the control unit to the analysis device via a wired or wireless connection, or the data may be stored in a storage device such as a USB and supplied from the control unit to the analysis device.

[0051] Furthermore, the analysis function may perform preprocessing such as smoothing or flattening of data as needed to improve the accuracy of the analysis. In other words, when forming a variation curve of magnetic flux density as described below, the analysis function may have a function for performing preprocessing such as smoothing or flattening of data to improve the accuracy of analysis based on the variation curve of magnetic flux density. The method for smoothing or flattening data is not particularly limited, and well-known methods (for example, moving average method, filtering, slope correction using an approximate straight line, etc.) can be used.

[0052] <Non-destructive inspection method of this embodiment> A method for inspecting for fractures in an inspection object P embedded in a concrete structure C to be inspected using the non-destructive inspection device 1 of this embodiment described above will be described. Note that the following description will be given on the assumption that the surface CF of the concrete structure C to be inspected is a horizontal plane. Of course, even if the surface CF of the concrete structure C to be inspected is a vertical plane or an inclined plane, inspection can be performed in a similar manner using the non-destructive inspection device 1 of this embodiment.

[0053] First, a magnet is moved along the surface of the concrete structure C to be inspected to magnetize the inspection object P embedded in the concrete structure C to be inspected. Note that the method for magnetizing the inspection object P is not particularly limited. In the following explanation, a case will be described in which the magnet is moved along the first direction of the inspection object P with the north and south poles of the magnet aligned in the first direction of the inspection object P (the X-axis direction in FIG. 1). It is also preferable to demagnetize the inspection object P after it has been magnetized. The method for demagnetizing the inspection object P is also not particularly limited.

[0054] After the inspection object P is magnetized, the movable body 2 of the non-destructive inspection device 1 is placed on the surface CF of the concrete structure C to be inspected (see FIG. 1(A)). At this time, the movable body 2 is placed so that the central axis of the inspection object P is included in the reference plane SA. Then, when the movable body 2 is moved along the surface CF of the concrete structure C to be inspected and the first direction of the inspection object P, one magnetic sensor 6 (magnetic sensor 6 Y03 in FIG. 1(B)) is placed vertically above the inspection object P, and the movable body 2 can be moved while maintaining a constant relative position between the multiple magnetic sensors 6 (Y00 to Y07) and the inspection object P (see FIG. 1(B)).

[0055] The movable body 2 may be disposed with the central axis of the inspection object P slightly offset from the reference plane SA. For example, in the Y-axis direction, the reference plane SA of the movable body 2 and the central axis of the inspection object P may be offset by approximately 0 to 10 mm.

[0056] Furthermore, the mobile object 2 does not necessarily have to be positioned so that the central axis of the inspection object P is included in the reference plane SA, as long as it is positioned so that the central axis of the inspection object P is parallel to the reference plane SA. In this case, it is desirable that one of the multiple magnetic sensors 6 is located on a plane that includes the central axis of the inspection object P and is perpendicular to the surface CF of the concrete structure C, and that at least one magnetic sensor 6 is positioned on both sides of this plane.

[0057] Once the moving body 2 is placed, a measurement start signal is input using an operation button or the like, and the moving body 2 is moved along the first direction (X-axis direction) of the inspection object P. Then, the magnetic sensors 6 of the magnetic flux measurement unit 5 measure the magnetic flux density along the movement path of the magnetic sensors 6. In other words, the magnetic flux density along the first direction of the inspection object P at the positions of the magnetic sensors 6 is measured. The measured values ​​of the magnetic flux density measured by the magnetic sensors 6 are stored in the memory function in association with the measurement position, measurement time, and the magnetic sensor 6 that performed the measurement.

[0058] When the movable body 2 has been moved to the area where the inspection object P is to be inspected, that is, the distance where the inspection object P is to be inspected, the inspection is completed.

[0059] Once the measurement is completed, the presence or absence of a break in the test object P is determined by the analysis function of the control unit 4. In addition, the break length Gap can be estimated as necessary.

[0060] <About magnetic sensor 6> In the above example, the multiple magnetic sensors 6 are capable of measuring magnetic flux density in three axis directions, but when measuring magnetic flux density in three axis directions, multiple magnetic sensors capable of measuring magnetic flux density in one axis direction may be used to measure the magnetic flux density in three axis directions. For example, three magnetic sensors that measure magnetic flux density in one axis direction may be arranged adjacent to each other at each measurement position (Y00 to Y07 in FIG. 1(B)) to measure the magnetic flux density in three axis directions. Furthermore, the magnetic flux density in three axial directions may be measured by the magnetic sensor 6, but it may also be measured in only one axial direction or only two axial directions. When measuring the magnetic flux density in two axial directions, two magnetic sensors that measure the magnetic flux density in one axial direction may be arranged side by side at each measurement position (Y00 to Y07 in FIG. 1(B)) to measure the magnetic flux density in the two axial directions.

[0061] <Detailed explanation of analysis functions> As described above, the non-destructive inspection device 1 of this embodiment can determine whether or not there is a fracture in the inspection object P by utilizing the magnetic flux densities measured by the multiple magnetic sensors 6 of the magnetic flux measurement unit 5. In addition, the magnetic flux densities measured by the multiple magnetic sensors 6 of the magnetic flux measurement unit 5 may also be utilized to estimate the fracture length Gap.

[0062] Hereinafter, a method for determining whether or not the inspection object P has been broken and a method for estimating the break length Gap using the analysis function of the control unit 4 will be described.

[0063] <Method for determining whether or not the inspection object P is broken> The analysis function has a function of estimating that a break has occurred in the inspection object P by analyzing the fluctuation of the magnetic flux density along a first direction (the X-axis direction in FIG. 1 ) measured by the multiple magnetic sensors 6. The break in the inspection object P can be estimated based on the fluctuation of the magnetic flux density in the x-axis direction along the first direction of the magnetic flux density, the fluctuation of the magnetic flux density in the y-axis direction along the first direction of the magnetic flux density, and the fluctuation of the magnetic flux density in the z-axis direction along the first direction of the magnetic flux density.

[0064] The data used in the following explanation is data obtained by measuring the magnetic flux density in a concrete structure C in which vertical and horizontal reinforcement bars are embedded in addition to the inspection object P, using eight three-axis magnetic sensors 6 (Y00 to Y07, see Figure 1(B)), with the magnetic sensor 6 of Y03 (the magnetic sensor 6 disposed on the center line B of the moving body 2) located on a plane (orthogonal plane) that includes the central axis of the inspection object P and is orthogonal to the surface CF of the concrete structure C. In this state, the reference plane SA and the orthogonal plane are the same plane.

[0065] <X-axis direction> The breakage of the inspection target P can be estimated by the following method based on the variation of the magnetic flux density in the x-axis direction along the first direction of the magnetic flux density.

[0066] First, when measuring the magnetic flux density in the x-axis direction along the first direction (X-axis direction) of the inspection target P of the concrete structure C, a first-direction variation curve showing the relationship between the measured value of each of the plurality of magnetic sensors 6 and the measurement position in the first direction is formed (see Fig. 5(A)).

[0067] When forming the first-direction variation curves for each of the plurality of magnetic sensors 6, the first-direction variation curves are differentiated by the first order. Then, a first-direction differential curve showing the relationship between the first-order differential value of each of the plurality of magnetic sensors 6 and the measurement position in the first direction corresponding to the first-order differential value is formed (see Fig. 5(B)).

[0068] When forming the first-direction differential curves for each of the plurality of magnetic sensors 6, the difference ΔdBx between the maximum value and the minimum value and the difference ΔdXx between the position of the maximum value and the position of the minimum value are calculated (see Fig. 5(B)). Specifically, for each first-direction differential curve, the maximum value and the minimum value sandwiching the position where the first-direction differential curve becomes 0 are calculated, and the difference ΔdBx between the maximum value and the minimum value is calculated. Also, for each first-direction differential curve, the difference ΔdXx between the position where the maximum value is obtained and the position where the minimum value is obtained is calculated.

[0069] When the difference ΔdBx between the maximum value and the minimum value and the difference ΔdXx between the position of the maximum value and the position of the minimum value are calculated, the presence or absence of breakage is estimated by the following method.

[0070] <Example of using the difference ΔdBx> First, R -3 which is the inverse cube of the distance R (see Fig. 2) from the plurality of magnetic sensors 6 to the inspection target P is calculated. Then, the difference ΔdBx calculated from the first-direction differential curve of each magnetic sensor 6 and the calculated R -3After calculating the linear approximation formula, it is determined whether the difference ΔdBx calculated from the first direction differential curve of each magnetic sensor 6 satisfies the linear approximation formula. For example, if the difference ΔdBx is set as the first axis and R -3 The difference ΔdBx calculated from the first direction differential curve of each magnetic sensor 6 is plotted on a graph with a second axis as the second axis, and it is determined whether the plotted points are distributed near the first-order approximation formula (see FIG. 6(A)).

[0071] If the plotted points are distributed near the first-order approximation, that is, if the difference ΔdBx and R -3 If the relationship satisfies a linear approximation, it is determined that a fracture has occurred in the inspection object P.

[0072] The difference ΔdBx and R -3 The relationship between R and R satisfies the first-order approximation. -3 When the same, the R -3 This means that the relative error between the value of the linear approximation formula and the difference ΔdBx is within ±30%. Relative error = [{(actual measurement value) / (value of linear approximation formula)}-1] x 100%

[0073] <Example of using the difference ΔdXx> In the above example, the case where the difference ΔdBx is used to determine whether the inspection object P has been broken or not has been explained, but the difference ΔdXx may also be used to determine whether the inspection object P has been broken or not.

[0074] In this case, first, R is calculated as the 1 / 2 power of the distance R (see FIG. 2) from the plurality of magnetic sensors 6 to the inspection object P. 1 / 2 Then, the difference ΔdXx calculated from the first direction differential curve of each magnetic sensor 6 and the calculated R 1 / 2 After calculating the linear approximation formula, it is determined whether the difference ΔdXx calculated from the first direction differential curve of each magnetic sensor 6 satisfies the linear approximation formula. For example, if the difference ΔdXx is set as the first axis and R 1 / 2The difference ΔdXx calculated from the first direction differential curve of each magnetic sensor 6 is plotted on a graph with the second axis as the second axis, and it is determined whether the plotted points are distributed near the first-order approximation formula (see FIG. 6(B)).

[0075] If the plotted points are distributed near the first-order approximation, that is, if the difference ΔdXx and R 1 / 2 If the relationship satisfies a linear approximation, it is determined that a fracture has occurred in the inspection object P.

[0076] The difference ΔdXx and R 1 / 2 The relationship between R and R satisfies the first-order approximation. 1 / 2 When the same, the R 1 / 2 This means that the relative error between the value of the linear approximation formula and the difference ΔdXx is within ±30%. Relative error = [{(actual measurement value) / (value of linear approximation formula)}-1] x 100%

[0077] <Example of using a first-order approximation equation for the test structure TM> In the above-described method, when the magnetic flux density of the concrete structure C to be inspected is measured by the multiple magnetic sensors 6 provided in the nondestructive inspection device 1 of this embodiment, the measured magnetic flux density is used to calculate a linear approximation formula. However, the magnetic flux density of a test structure TM simulating the concrete structure C to be inspected by the nondestructive inspection device 1 of this embodiment may be measured, and a linear approximation formula (a judgment linear approximation formula) may be calculated in advance based on this magnetic flux density. Then, a fracture may be determined based on whether the difference ΔdBx or the difference ΔdXx calculated from the first direction differential curves of the magnetic sensors 6 measured by each magnetic sensor 6 at the inspection target P of the concrete structure C satisfies the judgment linear approximation formula.

[0078] In this case, the test structure TM used is one in which a test object Q (preferably made of the same material as the test object P) that is a component equivalent to the test object is embedded in concrete. In other words, the test object Q is embedded in concrete so that the depth of coverage (the distance from the surface of the test structure TM to the test object Q) is the same as the depth of coverage (the distance from the surface of the concrete structure C to the test object P) of the test structure TM, and after magnetizing and magnetizing the test object Q using the same method as in the inspection, the magnetic sensor 6 of the nondestructive inspection device 1 measures the test structure TM, and the magnetic flux density obtained is used to calculate the first-order approximation formula for judgment.

[0079] Since the magnetic permeability of dry concrete is generally similar to that of air, the test structure TM does not necessarily have to be a structure in which the test object TM is embedded in concrete; a pseudo-concrete-embedded structure can also be used. Examples of pseudo-concrete-embedded structures include structures in which the test object Q and other structures (e.g., crossed rebars CR) are simply installed to form a predetermined structure or shape. These structures include those in which the test object Q and other structures are installed in an exposed state, and structures in which the test object Q and other structures are installed to form a predetermined structure or shape and are provided with a covering (e.g., a plate-like member). In the case of a structure in which a covering member is provided, the surface of the covering member corresponds to the concrete surface of the test structure TM, which has a structure in which the test object Q is embedded in concrete. Hereinafter, the concrete surface of the test structure TM and the surface of the covering member of the test structure are sometimes referred to as the surface CF of the test structure TM.

[0080] In the following, when we refer to a test structure TM, it includes both a structure in which the test object Q or other structures (e.g., crossed rebars CR, etc.) are embedded in concrete, and a pseudo-concrete-embedded structure in which the test object Q or other structures are embedded.

[0081] The method for creating a judgment linear approximation equation from the test structure TM is carried out in the same manner as the method for creating a linear approximation equation for the concrete structure C described above.

[0082] That is, a test structure TM having crossed rebars CR with vertical rebars R2 and horizontal rebars R1 as shown in Fig. 4 is formed, and the nondestructive inspection device 1 of this embodiment is moved on the surface CF of the test structure TM along a first direction (left-right direction in Fig. 4, X-axis direction) of the test object Q to measure the magnetic flux density in the x-axis direction. Then, a first-direction variation curve is formed that shows the relationship between the measurement values ​​of each of the multiple magnetic sensors 6 and the measurement position in the first direction of the test object Q (see Fig. 5(A)).

[0083] After forming the first direction variation curves for each of the plurality of magnetic sensors 6, the first direction variation curves are first differentiated, and a first direction differential curve is formed that indicates the relationship between the first differential value of each of the plurality of magnetic sensors 6 and the measurement position in the first direction corresponding to the first differential value (see FIG. 5(B)).

[0084] Once the first direction differential curves are formed for each of the multiple magnetic sensors 6, the difference ΔdBx between the maximum and minimum values ​​and the difference ΔdXx between the positions of the maximum and minimum values ​​are calculated (see FIG. 5(B)). Specifically, for each first direction differential curve, the maximum and minimum values ​​that sandwich the position where the first direction differential curve becomes 0 are calculated, and the difference ΔdBx between these maximum and minimum values ​​is calculated. Furthermore, the difference ΔdXx between the positions of the maximum and minimum values ​​is calculated for each first direction differential curve.

[0085] Then, R is the inverse cube of the distance R (see FIG. 2) from the magnetic sensors 6 to the test object Q. -3 Then, the difference ΔdBx calculated from the first direction differential curve of each magnetic sensor 6 and the calculated R -3 A linear approximation formula is calculated to represent the relationship between the above (see FIG. 6(A)).

[0086] In addition, R is a square root of the distance R (see FIG. 2) from the magnetic sensors 6 to the inspection object P. 1 / 2Then, the difference ΔdXx calculated from the first direction differential curve of each magnetic sensor 6 and the calculated R 1 / 2 A linear approximation formula is calculated to represent the relationship between the

[0087] If the difference ΔdBx or difference ΔdXx obtained from the magnetic flux density measurement values ​​of the non-destructive inspection device 1 of this embodiment is distributed near the judgment linear approximation formula calculated in this manner, it can be determined that a fracture has occurred in the inspection object P.

[0088] <How to use the Diagnostic Map MP> When a first-order approximation formula for judgment is created using the test structure TM, it is desirable to form a diagnostic map MP using the test structure TM (see FIG. 14(A)). If an area (fracture area BA) where the difference ΔdBx or difference ΔdXx is distributed when a fracture occurs in the test object Q is set in this diagnostic map MP, it is possible to determine whether a fracture occurs in the test object P depending on whether the difference ΔdBx or difference ΔdXx obtained from the measured values ​​of the magnetic flux density of the actual concrete structure C is located in the fracture area BA.

[0089] The diagnostic map MP is created for each distance Ya (see FIG. 2) from the test object Q to the magnetic sensor 6 in the Y-axis direction, with the difference ΔdBx obtained using the test structure TM as the first axis and the difference ΔdXx as the second axis. On this diagnostic map MP, results obtained using test structures TM with different distances Za (see FIG. 2) from the magnetic sensor 6 to the test object Q in the Z-axis direction and other structures are plotted. That is, the differences ΔdBx and ΔdXx when a fracture occurs in the test object Q are plotted on the diagnostic map MP to set a fracture region BA (see FIG. 14(A)). That is, for the distance Ya, a fracture region BA corresponding to the distance Za is set. Then, by plotting a combination of the difference ΔdBx and the difference ΔdXx obtained based on the magnetic flux density measured by the magnetic sensor 6 at the distance Ya of the nondestructive testing device 1 of this embodiment at the concrete structure C at the distance Za on the diagnostic map MP for the distance Ya, it is possible to determine whether a fracture occurs in the test object P. In other words, if the combination of the difference ΔdBx and the difference ΔdXx is located in the fracture area BA of the diagnostic map MP, it can be determined that a fracture has occurred in the object of inspection P, and if the combination of the difference ΔdBx and the difference ΔdXx is outside the fracture area BA, it can be determined that no fracture has occurred in the object of inspection P.

[0090] For example, as shown in FIG. 14(A), if the object to be inspected P is a PC twisted wire, the distance Ya is 100 mm, and the distance Za is 100 or 150 mm, then in the diagnostic map MP, the fracture region BA1 when the distance Za is 100 mm will be as shown in FIG. 14(A), and the fracture region BA2 when the distance Za is 150 mm will be as shown in FIG. 14(A). Therefore, when measuring the magnetic flux density of a concrete structure C using the nondestructive inspection device 1 of this embodiment, if the distance Ya is 100 mm and the distance Za is 100 mm, it can be determined that a fracture has occurred if the combination of the difference ΔdBx and the difference ΔdXx falls within the fracture region BA1. Furthermore, if the distance Ya is 100 mm and the distance Za is 150 mm, it can be determined that a fracture has occurred if the combination of the difference ΔdBx and the difference ΔdXx falls within the fracture region BA2.

[0091] <Method using the measurement value of a specific magnetic sensor 6> When determining whether or not the inspection object P has a break, if a difference ΔdXx equal to or greater than a certain value satisfies a linear approximation equation among the differences ΔdXx obtained from the magnetic flux densities measured by the multiple magnetic sensors 6, it may be determined that the inspection object P has a break. For example, whether or not the inspection object P has a break may be determined using only the difference ΔdXx obtained from the measurement values ​​of the magnetic sensors 6 that are in a specific positional relationship with the inspection object P.

[0092] This is preferable in that it allows the fracture region of the diagnostic map MP to be narrowed down. In particular, when a judgment linear approximation formula is created using the test structure TM, fracture can be judged simply by providing a magnetic sensor 6 that is in a specific positional relationship with the inspection object P. This allows the number of magnetic sensors 6 provided in the nondestructive inspection device 1 of this embodiment to be reduced, which simplifies the configuration of the nondestructive inspection device 1 of this embodiment and also speeds up data processing after measurement.

[0093] The reason why this is possible is as follows.

[0094] When crossing rebars such as horizontal and vertical rebars exist in the concrete structure C, or when there are no crossing rebars, the slope of the linear approximation formula differs depending on the condition, and R 1 / 2 Even if the same value, the difference ΔdXx will be a different value (see Figure 7). Also, if the type of inspection object P is different, the slope of the linear approximation formula will be different, and R 1 / 2 Even if the magnetic flux densities are the same, the difference ΔdXx will have a different value (see FIG. 7). Therefore, in order to improve the accuracy of detecting a fracture in the inspection object P, it is desirable to use multiple differences ΔdXx obtained using the magnetic flux densities measured by multiple magnetic sensors 6 to determine whether the multiple differences ΔdXx satisfy the linear approximation formula.

[0095] However, the difference ΔdXx obtained from the fluctuation of the magnetic flux density measured by the magnetic sensor 6 where Ya / Za, which indicates the relationship between the distance Ya from the inspection object P to the magnetic sensor 6 in the Y-axis direction (see FIG. 2) and the distance Za to the inspection object P in the Z-axis direction (see FIG. 2), is 0.5 to 1.0, will be approximately the same value, regardless of the presence or type of intersecting rebars, provided that the type of inspection object P is the same. Therefore, by creating a judgment linear approximation formula for each type of inspection object P, providing a magnetic sensor 6 where Ya / Za is 0.5 to 1.0, and measuring the magnetic flux density at that position, the configuration of the nondestructive inspection device 1 of this embodiment can be simplified while maintaining the accuracy of detecting fractures in the inspection object P.

[0096] For example, as shown in Figure 7(A), if the object to be inspected P is a PC twisted wire, and the distance Za is 100 mm, if the difference ΔdXx obtained from the fluctuation in magnetic flux density measured by the magnetic sensor 6 at a position where the distance Ya is 100 mm satisfies the first-order approximation equation obtained using the test structure TM, it can be determined that the object to be inspected P is broken.

[0097] Similarly, as shown in Figure 7(B), even if the inspection object P is a PC steel bar, if the distance Za is 100 mm, and the difference ΔdXx obtained from the fluctuation in magnetic flux density measured by the magnetic sensor 6 at a position where the distance Ya is 100 mm satisfies the first-order approximation equation obtained using the test structure TM, it can be determined that the inspection object P is fractured.

[0098] The same determination can be made when a linear approximation formula for determination has not been created, that is, when a linear approximation formula is created by measuring the magnetic flux density of the concrete structure C using multiple magnetic sensors 6. In other words, for the linear approximation formula created by measuring the magnetic flux density of the concrete structure C, only the difference ΔdXx obtained from the magnetic flux densities measured by the magnetic sensors 6 with Ya / Za between 0.5 and 1.0 may be used, and whether or not the inspection object P is fractured may be determined based on whether or not this difference ΔdXx satisfies the linear approximation formula.

[0099] <Method for estimating the gap of the fractured GA of the inspection object P> If there are no buried rebars other than the inspection target P, it is also possible to estimate the gap Gap of the fracture GA of the inspection target P.

[0100] First, when the magnetic flux density in the x-axis direction is measured along the first direction of the inspection object P of the concrete structure C, a first direction variation curve is formed showing the relationship between the measurement values ​​of each of the multiple magnetic sensors 6 and the measurement position in the first direction (see Figure 5(A)).

[0101] Once the first direction variation curves are formed for each of the multiple magnetic sensors 6, the first direction variation curves are first differentiated. Then, first direction differential curves are formed that indicate the relationship between the first differential values ​​of each of the multiple magnetic sensors 6 and the measurement positions in the first direction corresponding to the first differential values, and the difference ΔdXx between the positions of the maximum and minimum values ​​is calculated. Specifically, for each first direction differential curve, the maximum and minimum values ​​that sandwich the position where each first direction differential curve becomes 0 are calculated, and the difference ΔdXx between the positions of the maximum and minimum values ​​is calculated.

[0102] Then, the distance from the magnetic sensor 6 at the position of the position difference Y to the inspection object P is defined as distance R(Y), and R is the 1 / 2 power of distance R. 1 / 2 The value estimated by a linear approximation formula expressing the relationship between the difference ΔdXx calculated from the first direction differential curve at each measurement position and the value ΔdXx(Y) is taken as the value ΔdXx(Y). Then, ΔdXx(Y) / ΔdXx(0) and (R(Y) / R(0)) 1 / 2 Then, when the distance Za from the magnetic sensor 6 to the inspection object P in the Z-axis direction is Gap≧Za, the fracture gap Gap of the fracture GA of the inspection object P can be estimated based on the slope of the linear approximation equation (see FIG. 15).

[0103] The position difference Y is the distance from the test object P to each magnetic sensor 6 in the Y-axis direction, and is a value that may be positive or negative in the Y-axis direction. Hereinafter, the position difference Y in this specification means this value.

[0104] Also, R(0) means the distance from the magnetic sensor 6 (magnetic sensor of Y03 in Fig. 1(B)) provided on the center line B of the moving body 2, that is, at a position intersecting the reference plane SA, to the inspection target P in the Z-axis direction. That is, for a plurality of magnetic sensors 6, if the distance Za from the magnetic sensor 6 to the inspection target P in the Z-axis direction is the same, substantially, R(0) becomes the same as the distance Za. Hereinafter, R(0) in this specification means this value.

[0105] Also, the relationship between the slope of the primary approximation formula and the fracture gap Gap of the fracture GA of the inspection target P may be obtained in advance by changing the distance Za from the magnetic sensor 6 to the inspection target P and the fracture gap Gap in the Z-axis direction in the test structure TM.

[0106] <Y-axis direction> In the above example, the case where the fracture of the inspection target P is determined based on the variation of the magnetic flux density in the x-axis direction along the first direction of the magnetic flux density has been described. However, the fracture of the inspection target P may be determined by the following method based on the variation of the magnetic flux density in the y-axis direction along the first direction of the magnetic flux density.

[0107] First, when measuring the magnetic flux density in the y-axis direction along the first direction (X-axis direction) of the inspection target P of the concrete structure C, a second-direction variation curve showing the relationship between the measured values of each of the plurality of magnetic sensors 6 and the measurement position in the first direction is formed (see Fig. 8(A)).

[0108] When second-direction variation curves are formed for each of the plurality of magnetic sensors 6, the second-direction variation curves are second-order differentiated. Then, a second-direction differential curve showing the relationship between the second-order differential values of each of the plurality of magnetic sensors 6 and the measurement position in the first direction corresponding to the second-order differential values is formed (see Fig. 8(B)).

[0109] Once the second direction differential curves are formed for each of the multiple magnetic sensors 6, the difference Δd2By between the maximum and minimum values ​​and the difference Δd2Xy between the positions of the maximum and minimum values ​​are calculated for the second direction differential curve of each magnetic sensor 6 (see FIG. 8(B)). Specifically, for each second direction differential curve, the maximum and minimum values ​​that sandwich the position where the second direction differential curve becomes 0 are calculated, and the difference Δd2By between these maximum and minimum values ​​is calculated. In addition, the difference Δd2Xy between the positions of the maximum and minimum values ​​is calculated.

[0110] After calculating the difference Δd2By between the maximum value and the minimum value and the difference Δd2Xy between the positions of the maximum value and the minimum value, the presence or absence of a fracture is estimated by the following method.

[0111] <Example of using the difference Δd2By> First, R is the inverse cube of the distance R (see FIG. 2) from the magnetic sensors 6 to the inspection target P. -3 Furthermore, a correction coefficient β=(Y / Za)·SIGN(Δd2Xy) is calculated from the difference Y in the position from the inspection object P to each magnetic sensor 6 in the Y-axis direction and the distance Za from the magnetic sensor 6 to the inspection object P in the Z-axis direction. Then, the difference Δd2By calculated from the second direction differential curve of each magnetic sensor 6 is divided by the correction coefficient β, and the calculated R -3 A linear approximation formula expressing the relationship between the above is calculated (see FIG. 9(A)).

[0112] Note that SIGN(A) takes the value "+1" when A is a positive number or 0, and "-1" when A is a negative number, depending on the positive or negative sign of A. For example, in Fig. 8(B), when the magnetic sensor 6 is Y00 to Y02, the difference Δd2Xy is a negative number, so SIGN(Δd2Xy) is "-1", and when the magnetic sensor 6 is Y03 to Y07, the difference Δd2Xy is a positive number or 0, so SIGN(Δd2Xy) is "+1".

[0113] The position difference Y is the distance from the inspection object P to each magnetic sensor 6 in the Y-axis direction, and is a value that can be positive or negative in the Y-axis direction. For example, in FIG. 1, when the magnetic sensors 6 are Y00 to Y02, Y is a negative value, and when the magnetic sensors 6 are Y04 to Y07, Y is a positive value. Furthermore, when the magnetic sensor 6 is Y03, Y=0. Therefore, the value Δd2By / β cannot be calculated from the magnetic flux density measured by the magnetic sensor 6 of Y03, and is therefore excluded from the data.

[0114] After calculating the linear approximation formula, it is determined whether the value Δd2By / β calculated from the second direction differential curve of each magnetic sensor 6 satisfies the linear approximation formula. For example, if the value Δd2By / β is set to the first axis, -3 The value Δd2By / β calculated from the second direction differential curve of each magnetic sensor 6 is plotted on a graph with Δd2By / β as the second axis, and it is determined whether the plotted points satisfy the linear approximation equation (see FIG. 9(A)).

[0115] If the plotted points are distributed near the first-order approximation, that is, if the values ​​Δd2By / β and R -3 If the relationship satisfies a linear approximation, it is determined that a fracture has occurred in the inspection object P.

[0116] Note that the values ​​Δd2By / β and R -3 The relationship between R and R satisfies the first-order approximation. -3 When the same, the R -3 This means that the relative error between the value of the linear approximation formula and the value Δd2By / β is within ±30%. Relative error = [{(actual measurement value) / (value of linear approximation formula)}-1] x 100%

[0117] The reason for using the value Δd2By / β instead of the difference Δd2By is that although the difference Δd2By changes discontinuously directly above the fracture location (position Y03, Y=0), if the difference is corrected using the geometric relationship between the difference Δd2By and the difference Δd2Bz caused by the fracture of the inspection object P, that is, Δd2By / Δd2Bz=(Y / Za)·SIGN(Δd2Xy)=β, it can be treated in the same way as the difference Δd2Bz obtained from the fluctuation of the magnetic flux density in the z-axis direction, which will be described later.

[0118] <Example of using the difference Δd2Xy> In the above example, the case where the value Δd2By / β is used to determine whether the inspection object P has been broken or not has been explained, but the difference Δd2Xy may also be used to determine whether the inspection object P has been broken or not.

[0119] In this case, first, R is calculated as the 1 / 2 power of the distance R (see FIG. 2) from the plurality of magnetic sensors 6 to the inspection object P. 1 / 2 Then, the positive / negative sign of the difference Δd2Xy calculated from the second direction differential curve of each magnetic sensor 6 is corrected by the positive / negative sign of the difference Y in the Y-axis direction from the inspection object P to each magnetic sensor 6, and the calculated R 1 / 2 After calculating the linear approximation equation, it is determined whether the value Δd2Xy·α calculated from the second direction differential curve of each magnetic sensor 6 satisfies the linear approximation equation. For example, if the value Δd2Xy·α is set as the first axis and R 1 / 2 The value Δd2Xy·α calculated from the second direction differential curve of each magnetic sensor 6 is plotted on a graph with a second axis as the second axis, and it is determined whether the plotted points satisfy the linear approximation equation (see FIG. 9(B)).

[0120] Note that α is set to α=SIGN(Y). SIGN(A) is the value of "+1" when A is a positive number or 0, depending on the positive or negative sign of A, and "-1" when A is a negative number. For example, in Fig. 1, when the magnetic sensor 6 is Y00 to Y02, Y is a negative number, so α = SIGN(Y) is "-1", and when the magnetic sensor 6 is Y03 to Y07, Y is a positive number or 0, so α = SIGN(Y) is "+1".

[0121] Then, if the plotted points satisfy the first-order approximation equation, that is, the values ​​Δd2Xy α and R 1 / 2 If the relationship satisfies a linear approximation, it is determined that a fracture has occurred in the inspection object P.

[0122] In addition, the values ​​Δd2Xy α and R 1 / 2 The relationship between R and R satisfies the first-order approximation.1 / 2 When the same, the R 1 / 2 This means that the relative error between the value of the linear approximation formula and the value Δd2Xy·α is within ±30%. Relative error = [{(actual measurement value) / (value of linear approximation formula)}-1] x 100%

[0123] <Example of using a first-order approximation equation for the test structure TM> In the above-described method, when the magnetic flux density of the concrete structure C to be inspected is measured by the multiple magnetic sensors 6 included in the nondestructive inspection device 1 of this embodiment, the measured magnetic flux density is used to calculate a linear approximation equation. However, similar to the method of determining whether a fracture of the inspection object P is present based on the variation of the magnetic flux density in the y-axis direction along the first direction of the magnetic flux density, the magnetic flux density of a test structure TM simulating the concrete structure C to be inspected by the nondestructive inspection device 1 of this embodiment may be measured, and a linear approximation equation (a judgment linear approximation equation) may be calculated in advance based on this magnetic flux density. Then, whether a fracture is present may be determined based on whether the value Δd2By / β or the value Δd2Xy·α calculated from the second direction differential curves of the magnetic sensors 6 measured by each magnetic sensor 6 at the inspection object P of the concrete structure C satisfies the judgment linear approximation equation.

[0124] The method for creating a judgment linear approximation equation from the test structure TM is carried out in the same manner as the method for creating a linear approximation equation for the concrete structure C described above.

[0125] That is, a test structure TM having crossed rebars CR with vertical rebars R2 and horizontal rebars R1 as shown in Fig. 4 is formed, and the nondestructive inspection device 1 of this embodiment is moved on the surface CF of the test structure TM along a first direction (left-right direction in Fig. 4, X-axis direction) of the test object Q to measure the magnetic flux density in the y-axis direction. Then, a second direction variation curve is formed that shows the relationship between the measurement values ​​of each of the multiple magnetic sensors 6 and the measurement position in the first direction of the test object Q (see Fig. 8(A)).

[0126] After forming the second direction variation curves for each of the plurality of magnetic sensors 6, the second direction variation curves are second-order differentiated, and second direction differential curves are formed that indicate the relationship between the second-order differential values ​​of each of the plurality of magnetic sensors 6 and the measurement positions in the first direction corresponding to the second-order differential values ​​(see FIG. 8(B)).

[0127] Once second direction differential curves are formed for each of the multiple magnetic sensors 6, the difference Δd2By between the maximum and minimum values ​​and the difference Δd2Xy between the positions of the maximum and minimum values ​​are calculated (see FIG. 8(B)). Specifically, for each second direction differential curve, the maximum and minimum values ​​that sandwich the position where the second direction differential curve becomes 0 are calculated, and the difference Δd2By between the maximum and minimum values ​​is divided by a correction coefficient β1 to calculate Δd2By / β1. In addition, the difference Δd2Xy between the positions of the maximum and minimum values ​​is calculated, and the sign of the difference Δd2Xy is corrected to calculate Δd2Xy·α1.

[0128] Then, R is the inverse cube of the distance R (see FIG. 2) from the magnetic sensors 6 to the test object Q. -3 Then, the value Δd2By / β1 calculated from the second direction differential curve of each magnetic sensor 6 and the calculated R -3 A linear approximation formula is calculated to represent the relationship between the above (see FIG. 9(A)).

[0129] In addition, R is a square root of the distance R (see FIG. 2) from the magnetic sensors 6 to the inspection object P. 1 / 2 Then, the value Δd2Xy·α1 calculated from the second direction differential curve of each magnetic sensor 6 and the calculated R 1 / 2 A linear approximation formula is calculated to represent the relationship between the above (see FIG. 9(B)).

[0130] If the value Δd2By / β or the value Δd2Xy·α obtained from the magnetic flux density measurement values ​​of the nondestructive inspection device 1 of this embodiment is distributed near the judgment linear approximation formula calculated in this manner, it can be determined that a fracture has occurred in the inspection object P.

[0131] In the test structure TM, the correction coefficient β1=(Y1 / Za)·SIGN(Δd2Xy) and α1=SIGN(Y1). The position difference Y1 is the distance from the test object Q to each magnetic sensor 6 in the Y-axis direction of the test structure TM, and is a value that can be positive or negative in the Y-axis direction.

[0132] <How to use the Diagnostic Map MP> When creating a judgment linear approximation equation using the test structure TM, it is desirable to form a diagnostic map MP using the test structure TM (see Figure 14(B)). If a region (fracture region BA) where the values ​​Δd2By / β1 and Δd2Xy·α1 are distributed when a fracture occurs in the test object Q is set in this diagnostic map MP, it is possible to determine whether a fracture has occurred in the test object P by determining whether the values ​​Δd2By / β and Δd2Xy·α obtained from the measured values ​​of the magnetic flux density of the actual concrete structure C are located in the fracture region BA.

[0133] The diagnostic map MP is created for each distance Ya from the test object Q to the magnetic sensor 6 in the Y-axis direction (see FIG. 2), with the value Δd2By / β1 obtained using the test structure TM as the first axis and the value Δd2Xy·α1 as the second axis. On this diagnostic map MP, results obtained using test structures TM with different distances Za from the magnetic sensor 6 to the test object Q in the Z-axis direction (see FIG. 2) and other structures are plotted. That is, the values ​​Δd2By / β1 and Δd2Xy·α1 when a fracture occurs in the test object Q are plotted on the diagnostic map MP to set a fracture region BA (see FIG. 14(B)). That is, a fracture region BA is set for the distance Ya and corresponding to the distance Za. Then, by plotting a combination of the value Δd2By / β and the value Δd2Xy·α obtained based on the magnetic flux density measured by the nondestructive testing device 1 of this embodiment at the concrete structure C at the distance Za on the diagnostic map MP for the distance Ya, it is possible to determine whether a fracture occurs in the test object P. In other words, if the combination of the values ​​Δd2By / β and Δd2Xy·α is located in the fracture area BA of the diagnostic map MP, it can be determined that a fracture has occurred in the inspection object P, and if the combination of the values ​​Δd2By / β and Δd2Xy·α is outside the fracture area BA, it can be determined that no fracture has occurred in the inspection object P.

[0134] For example, as shown in FIG. 14(B), if the object of inspection P is a PC strand, the distance Ya is 100 mm, and the distance Za is 100 or 150 mm, then in the diagnostic map MP, the fracture region BA1 when the distance Za is 100 mm will be as shown in FIG. 14(B), and the fracture region BA2 when the distance Za is 150 mm will be as shown in FIG. 14(B). Therefore, when measuring the magnetic flux density of a concrete structure C using the nondestructive inspection device 1 of this embodiment, if the distance Ya is 100 mm and the distance Za is 100 mm, it can be determined that a fracture has occurred if the combination of the value Δd2By / β and the value Δd2Xy·α falls within the fracture region BA1. Furthermore, if the distance Ya is 100 mm and the distance Za is 150 mm, it can be determined that a fracture has occurred if the combination of the value Δd2By / β and the value Δd2Xy·α falls within the fracture region BA2.

[0135] <Method using the measurement value of a specific magnetic sensor 6> When determining whether or not the inspection object P has a fracture, it may be determined that the inspection object P has a fracture if a certain value or more of the values ​​Δd2Xy·α obtained from the magnetic flux densities measured by the multiple magnetic sensors 6 satisfies a linear approximation equation. For example, it may be determined whether or not the inspection object P has a fracture using only the value Δd2Xy·α obtained from the measurement values ​​of the magnetic sensors 6 that are in a specific positional relationship with the inspection object P.

[0136] This is preferable in that it allows the fracture region of the diagnostic map MP to be narrowed down. In particular, when a judgment linear approximation formula is created using the test structure TM, fracture can be judged simply by providing a magnetic sensor 6 that is in a specific positional relationship with the inspection object P. This allows the number of magnetic sensors 6 provided in the nondestructive inspection device 1 of this embodiment to be reduced, which simplifies the configuration of the nondestructive inspection device 1 of this embodiment and also speeds up data processing after measurement.

[0137] The reason why this is possible is as follows.

[0138] When crossing rebars such as horizontal and vertical rebars exist in the concrete structure C, or when there are no crossing rebars, the slope of the linear approximation formula differs depending on the condition, and R 1 / 2 Even if the value of Δd2Xy·α is the same, the value of Δd2Xy·α will be different (see Figure 10). Also, if the type of inspection object P is different, the slope of the linear approximation formula will be different, and R 1 / 2 Even if the magnetic flux densities are the same, the value Δd2Xy·α will be different (see FIG. 10). Therefore, in order to improve the accuracy of detecting fractures in the inspection object P, it is desirable to use multiple values ​​Δd2Xy·α obtained from the magnetic flux densities measured by multiple magnetic sensors 6 to determine whether the multiple values ​​Δd2Xy·α satisfy the linear approximation equation.

[0139] However, the value Δd2Xy·α obtained from the fluctuation of the magnetic flux density measured by the magnetic sensor 6 where Ya / Za, which indicates the relationship between the distance Ya from the inspection object P to the magnetic sensor 6 in the Y-axis direction (see FIG. 2) and the distance Za from the magnetic sensor 6 to the inspection object P in the Z-axis direction (see FIG. 2), is 0.5 to 1.0, will be approximately the same value regardless of the presence or type of crossing rebars, provided that the type of inspection object P is the same. Therefore, by creating a judgment linear approximation formula for each type of inspection object P, installing a magnetic sensor 6 where Ya / Za is 0.5 to 1.0, and measuring the magnetic flux density at that position, the configuration of the nondestructive inspection device 1 of this embodiment can be simplified while maintaining the accuracy of detecting fractures in the inspection object P.

[0140] For example, as shown in Figure 10(A), if the inspection object P is a PC twisted wire and the distance Za is 100 mm, it can be determined that the inspection object P is broken if the value Δd2Xy·α obtained from the fluctuation in magnetic flux density measured by the magnetic sensor 6 at a position where the distance Ya is 100 mm satisfies the first-order approximation equation obtained using the test structure TM.

[0141] Similarly, as shown in Figure 10(B), even if the inspection object P is a PC steel bar, if the distance Za is 100 mm, and the value Δd2Xy·α obtained from the fluctuation in magnetic flux density measured by the magnetic sensor 6 at a position where the distance Ya is 100 mm satisfies the first-order approximation equation obtained using the test structure TM, it can be determined that the inspection object P is fractured.

[0142] The same determination can be made even when a first-order approximation formula for judgment has not been created, that is, when a first-order approximation formula is created by measuring the magnetic flux density of the concrete structure C using multiple magnetic sensors 6. In other words, for the first-order approximation formula created by measuring the magnetic flux density of the concrete structure C, only the value Δd2Xy·α obtained from the magnetic flux density measured by the magnetic sensors 6 where Ya / Za is 0.5 to 1.0 may be used, and whether or not the inspection object P is fractured may be determined based on whether or not this value Δd2Xy·α satisfies the first-order approximation formula.

[0143] <Method for estimating the gap of the fractured GA of the inspection object P> If there are no buried rebars other than the inspection target P, it is also possible to estimate the gap Gap of the fracture GA of the inspection target P.

[0144] First, when the magnetic flux density in the y-axis direction is measured along the first direction of the inspection object P of the concrete structure C, a second direction variation curve is formed showing the relationship between the measurement values ​​of each of the multiple magnetic sensors 6 and the measurement position in the first direction (see Figure 8(A)).

[0145] Once the second direction variation curves are formed for each of the multiple magnetic sensors 6, these second direction variation curves are second-order differentiated. Then, second direction differential curves are formed that show the relationship between the second differential values ​​of each of the multiple magnetic sensors 6 and the measurement positions in the first direction corresponding to the second differential values, and the difference Δd2Xy between the positions of the maximum and minimum values ​​is calculated. Specifically, for each second direction differential curve, the maximum and minimum values ​​that sandwich the position where each second direction differential curve becomes 0 are calculated, and the values ​​Δd2Xy·α of the positions of the maximum and minimum values ​​are calculated.

[0146] Then, the distance from the magnetic sensor 6 at the position of the position difference Y to the inspection object P is defined as distance R(Y), and R is the 1 / 2 power of distance R. 1 / 2 The value estimated by the linear approximation that expresses the relationship between the value Δd2Xy·α calculated from the second direction differential curve at each measurement position and the value Δd2Xy(Y)·α(Y) is taken as the value. Then, (Δd2Xy(Y)·α(Y)) / (Δd2Xy(0)·α(0)) and (R(Y) / R(0)) 1 / 2 Then, when the distance Za from the magnetic sensor 6 to the inspection object P in the Z-axis direction is Gap≧Za, the fracture gap Gap of the fracture GA of the inspection object P can be estimated based on the slope of the relative linear approximation equation (see FIG. 15).

[0147] Note that the relationship between the slope of the first-order approximation formula and the fracture gap Gap of the fracture GA of the inspection target P can be obtained in advance by changing the distance Za from the magnetic sensor 6 to the inspection target P and the fracture gap Gap in the Z-axis direction in the test structure TM.

[0148] <Z-axis direction> In the above example, the case where the fracture of the inspection target P is determined based on the fluctuations of the magnetic flux density in the x-axis direction and the y-axis direction along the first direction of the magnetic flux density has been described. However, the fracture of the inspection target P may also be determined by the following method based on the fluctuation of the magnetic flux density in the z-axis direction along the first direction of the magnetic flux density.

[0149] First, when measuring the magnetic flux density in the z-axis direction along the first direction (X-axis direction) of the inspection target P of the concrete structure C, a third-direction variation curve showing the relationship between the measured values of each of the plurality of magnetic sensors 6 and the measurement position in the first direction is formed (see Fig. 11(A)).

[0150] When third-direction variation curves are formed for each of the plurality of magnetic sensors 6, the third-direction variation curves are second-order differentiated. Then, a third-direction differential curve showing the relationship between the second-order differential values of each of the plurality of magnetic sensors 6 and the measurement position in the first direction corresponding to the second-order differential values is formed (see Fig. 11(B)).

[0151] When third-direction differential curves are formed for each of the plurality of magnetic sensors 6, for the third-direction differential curve of each magnetic sensor 6, the difference Δd2Bz between the maximum value and the minimum value and the difference Δd2Xz between the position of the maximum value and the position of the minimum value are calculated (see Fig. 11(B)). Specifically, for each third-direction differential curve, the maximum value and the minimum value sandwiching the position where the third-direction differential curve becomes 0 are calculated, and the difference Δd2Bz between this maximum value and the minimum value is calculated. Also, the difference Δd2Xz between the position where the maximum value is obtained and the position where the minimum value is obtained is calculated.

[0152] When the difference Δd2Bz between the maximum value and the minimum value and the difference Δd2Xz between the position of the maximum value and the position of the minimum value are calculated, the presence or absence of fracture is estimated by the following method.

[0153] <Example of using the difference Δd2Bz> First, R is the inverse cube of the distance R (see FIG. 2) from the magnetic sensors 6 to the inspection target P. -3 Then, the difference Δd2Bz calculated from the third direction differential curve of each magnetic sensor 6 and the calculated R -3 After calculating the linear approximation formula, it is determined whether the difference Δd2Bz calculated from the third direction differential curve of each magnetic sensor 6 satisfies the linear approximation formula. For example, if the difference Δd2Bz is set as the first axis and R -3 The difference Δd2Bz calculated from the third direction differential curve of each magnetic sensor 6 is plotted on a graph with a second axis as the second axis, and it is determined whether the plotted points satisfy the linear approximation formula (see FIG. 12(A)).

[0154] If the plotted points satisfy the linear approximation, that is, the difference Δd2Bz and R -3 If the relationship satisfies a linear approximation, it is determined that a fracture has occurred in the inspection object P.

[0155] The difference Δd2Bz and R -3 The relationship between R and R satisfies the first-order approximation. -3 When the same, the R -3 This means that the relative error between the value of the linear approximation formula and the difference Δd2Bz is within ±30%. Relative error = [{(actual measurement value) / (value of linear approximation formula)}-1] x 100%

[0156] <Example of using the difference Δd2Xz> In the above example, the case where the difference Δd2Bz is used to determine whether the inspection object P has been broken or not has been explained, but the difference Δd2Xz may also be used to determine whether the inspection object P has been broken or not.

[0157] In this case, first, R is calculated as the 1 / 2 power of the distance R (see FIG. 2) from the plurality of magnetic sensors 6 to the inspection object P. 1 / 2 Then, the difference Δd2Xz calculated from the third direction differential curve of each magnetic sensor 6 and the calculated R 1 / 2After calculating the linear approximation formula, it is determined whether the difference Δd2Xz calculated from the third direction differential curve of each magnetic sensor 6 satisfies the linear approximation formula. For example, if the difference Δd2Xz is set as the first axis and R 1 / 2 The difference Δd2Xz calculated from the third direction differential curve of each magnetic sensor 6 is plotted on a graph with a second axis as the second axis, and it is determined whether the plotted points satisfy the linear approximation equation (see FIG. 12(B)).

[0158] If the plotted points are distributed near the first-order approximation, that is, if the difference Δd2Xz and R 1 / 2 If the relationship satisfies a linear approximation, it is determined that a fracture has occurred in the inspection object P.

[0159] The difference Δd2Xz and R 1 / 2 The relationship between R and R satisfies the first-order approximation. 1 / 2 When the same, the R 1 / 2 This means that the relative error between the value of the linear approximation formula and the difference Δd2Xz is within ±30%. Relative error = [{(actual measurement value) / (value of linear approximation formula)}-1] x 100%

[0160] <Example of using a first-order approximation equation for the test structure TM> In the above-described method, when the magnetic flux density of the concrete structure C to be inspected is measured by the multiple magnetic sensors 6 provided in the nondestructive inspection device 1 of this embodiment, the measured magnetic flux density is used to calculate a linear approximation formula. However, similar to the method of determining whether or not a fracture of the inspection object P is occurring based on the variation in magnetic flux density in the z-axis direction along the first direction of the magnetic flux density, the magnetic flux density of a test structure TM simulating the concrete structure C to be inspected by the nondestructive inspection device 1 of this embodiment may be measured, and a linear approximation formula (determination linear approximation formula) may be calculated in advance based on this magnetic flux density. Then, whether or not a fracture is occurring may be determined based on whether or not the difference Δd2Bz or the difference Δd2Xz calculated from the third direction differential curves of each magnetic sensor 6 measured by each magnetic sensor 6 satisfies the determination linear approximation formula.

[0161] The method for creating a judgment linear approximation equation from the test structure TM is carried out in the same manner as the method for creating a linear approximation equation for the concrete structure C described above.

[0162] That is, a test structure TM is formed having crossed rebars CR with vertical rebars R2 and horizontal rebars R1 as shown in Fig. 4, and the nondestructive inspection device 1 of this embodiment is moved on the surface CF of the test structure TM along the first direction of the test object Q to measure the magnetic flux density in the z-axis direction. Then, a third direction variation curve is formed that shows the relationship between the measurement values ​​of each of the multiple magnetic sensors 6 and the measurement position in the first direction of the test object Q (see Fig. 11(A)).

[0163] After forming the third direction variation curves for each of the plurality of magnetic sensors 6, the third direction variation curves are second-order differentiated, and a third direction differential curve is formed that indicates the relationship between the second-order differential value of each of the plurality of magnetic sensors 6 and the measurement position in the first direction corresponding to the second-order differential value (see FIG. 11(B)).

[0164] Once the third direction differential curves are formed for each of the multiple magnetic sensors 6, the difference Δd2Bz between the maximum and minimum values ​​and the difference Δd2Xz between the positions of the maximum and minimum values ​​are calculated (see FIG. 11(B)). Specifically, for each third direction differential curve, the maximum and minimum values ​​that sandwich the position where the third direction differential curve becomes 0 are calculated, and the difference Δd2Bz between these maximum and minimum values ​​is calculated. In addition, the difference Δd2Xz between the positions of the maximum and minimum values ​​is calculated for each third direction differential curve.

[0165] Then, R is the inverse cube of the distance R (see FIG. 2) from the magnetic sensors 6 to the test object Q. -3 Then, the difference Δd2Bz calculated from the third direction differential curve of each magnetic sensor 6 and the calculated R -3 A linear approximation formula is calculated to represent the relationship between the above (see FIG. 12(A)).

[0166] In addition, R is a square root of the distance R (see FIG. 2) from the magnetic sensors 6 to the inspection object P. 1 / 2Then, the difference Δd2Xz calculated from the third direction differential curve of each magnetic sensor 6 and the calculated R 1 / 2 A linear approximation formula is calculated to represent the relationship between the above (see FIG. 12(B)).

[0167] If the difference Δd2Bz or difference Δd2Xz obtained from the magnetic flux density measurement values ​​of the non-destructive inspection device 1 of this embodiment is distributed on the judgment linear approximation formula calculated in this manner, it can be determined that a fracture has occurred in the inspection object P.

[0168] <How to use the Diagnostic Map MP> When creating a judgment linear approximation formula using the test structure TM, it is desirable to form a diagnostic map MP using the test structure TM (see FIG. 14(C)). If an area (fracture area BA) where the difference Δd2Bz or the difference Δd2Xz is distributed when a fracture occurs in the test object Q is set in this diagnostic map MP, it is possible to determine whether a fracture occurs in the test object P depending on whether the difference Δd2Bz or the difference Δd2Xz obtained from the measured values ​​of the magnetic flux density of the actual concrete structure C is located in the fracture area BA.

[0169] The diagnostic map MP is created for each distance Ya from the test object Q to the magnetic sensor 6 in the Y-axis direction (see FIG. 2), with the difference Δd2Bz obtained using the test structure TM as the first axis and the difference Δd2Xz as the second axis. On this diagnostic map MP, results obtained using test structures TM with different distances Za (see FIG. 2) from the magnetic sensor 6 to the test object Q in the Z-axis direction and other structures are plotted. That is, the differences Δd2Bz and Δd2Xz when a fracture occurs in the test object Q are plotted on the diagnostic map MP to set a fracture region BA (see FIG. 14(C)). That is, for the distance Ya, a fracture region BA corresponding to the distance Za is set. Then, by plotting a combination of the difference Δd2Bz and the difference Δd2Xz obtained based on the magnetic flux density measured by the magnetic sensor 6 at the distance Ya of the nondestructive testing device 1 of this embodiment at the concrete structure C at the distance Za on the diagnostic map MP for the distance Ya, it is possible to determine whether a fracture occurs in the test object P. In other words, if the combination of difference Δd2Bz and difference Δd2Xz is located in the fracture area BA of the diagnostic map MP, it can be determined that a fracture has occurred in the object of inspection P, and if the combination of difference Δd2Bz and difference Δd2Xz is outside the fracture area BA, it can be determined that no fracture has occurred in the object of inspection P.

[0170] For example, as shown in FIG. 14(C), if the object of inspection P is a PC strand, the distance Ya = 100 mm, and the distance Za = 100 and 150 mm, then in the diagnostic map MP, the fracture region BA1 when the distance Za = 100 mm is as shown in FIG. 14(C), and the fracture region BA2 when the distance Za = 150 mm is as shown in FIG. 14(C). Therefore, when measuring the magnetic flux density of a concrete structure C using the nondestructive inspection device 1 of this embodiment, if the distance Ya = 100 mm and the distance Za = 100 mm, and the combination of the difference Δd2Bz and the difference Δd2Xz falls within the fracture region BA1, it can be determined that a fracture has occurred. Also, if the distance Ya = 100 mm and the distance Za = 150 mm, and the combination of the difference Δd2Bz and the difference Δd2Xz falls within the fracture region BA2, it can be determined that a fracture has occurred.

[0171] <Method using the measurement value of a specific magnetic sensor 6> When determining whether or not the inspection object P has a break, if a difference Δd2Xz equal to or greater than a certain value satisfies a linear approximation equation among the differences Δd2Xz obtained from the magnetic flux densities measured by the multiple magnetic sensors 6, it may be determined that the inspection object P has a break. For example, whether or not the inspection object P has a break may be determined using only the difference Δd2Xz obtained from the measurement values ​​of the magnetic sensors 6 that are in a specific positional relationship with the inspection object P.

[0172] This is preferable in that it allows the fracture region of the diagnostic map MP to be narrowed down. In particular, when a judgment linear approximation formula is created using the test structure TM, fracture can be judged simply by providing a magnetic sensor 6 that is in a specific positional relationship with the inspection object P. This allows the number of magnetic sensors 6 provided in the nondestructive inspection device 1 of this embodiment to be reduced, which simplifies the configuration of the nondestructive inspection device 1 of this embodiment and also speeds up data processing after measurement.

[0173] The reason why this is possible is as follows.

[0174] When crossing rebars such as horizontal and vertical rebars exist in the concrete structure C, or when there are no crossing rebars, the slope of the linear approximation formula differs depending on the condition, and R 1 / 2 Even if the same value, the difference Δd2Xz will be a different value (see Figure 13). Also, if the type of inspection object P is different, the slope of the linear approximation formula will be different, and R 1 / 2 Even if the magnetic flux densities are the same, the difference Δd2Xz will have a different value (see FIG. 13). Therefore, in order to improve the accuracy of detecting a fracture in the inspection object P, it is desirable to use multiple differences Δd2Xz obtained using the magnetic flux densities measured by multiple magnetic sensors 6 to determine whether the multiple differences Δd2Xz satisfy the linear approximation formula.

[0175] However, the difference Δd2Xz obtained from the fluctuation of the magnetic flux density measured by the magnetic sensor 6 where Ya / Za, which indicates the relationship between the distance Ya from the inspection object P to the magnetic sensor 6 in the Y-axis direction (see FIG. 2) and the distance Za from the magnetic sensor 6 to the inspection object P in the Z-axis direction (see FIG. 2), is 0.5 to 1.0, will be approximately the same value, regardless of the presence or type of intersecting rebars, provided that the type of inspection object P is the same. Therefore, by creating a judgment linear approximation formula for each type of inspection object P, installing a magnetic sensor 6 where Ya / Za is 0.5 to 1.0, and measuring the magnetic flux density at that position, the configuration of the nondestructive inspection device 1 of this embodiment can be simplified while maintaining the accuracy of detecting fractures in the inspection object P.

[0176] For example, as shown in Figure 13(A), if the object to be inspected P is a PC twisted wire, and the distance Za is 100 mm, if the difference Δd2Xz obtained from the fluctuation in magnetic flux density measured by the magnetic sensor 6 at a position where the distance Ya is 100 mm satisfies the first-order approximation equation obtained using the test structure TM, it can be determined that the object to be inspected P is broken.

[0177] Similarly, as shown in Figure 13(B), even if the inspection object P is a PC steel bar, if the distance Za is 100 mm, and the difference Δd2Xz obtained from the fluctuation in magnetic flux density measured by the magnetic sensor 6 at a position where the distance Ya is 50 mm satisfies the judgment first-order approximation formula obtained using the test structure TM, it can be determined that the inspection object P is fractured.

[0178] The same determination can be made when a linear approximation formula for determination has not been created, that is, when a linear approximation formula is created by measuring the magnetic flux density of the concrete structure C using multiple magnetic sensors 6. In other words, for the linear approximation formula created by measuring the magnetic flux density of the concrete structure C, only the difference Δd2Xz obtained from the magnetic flux densities measured by the magnetic sensors 6 where Ya / Za is 0.5 to 1.0 may be used, and whether or not the inspection object P is fractured may be determined based on whether or not this difference Δd2Xz satisfies the linear approximation formula.

[0179] <Method for estimating the gap of the fractured GA of the inspection object P> If there are no buried rebars other than the inspection target P, it is also possible to estimate the gap Gap of the fracture GA of the inspection target P.

[0180] First, when the magnetic flux density in the z-axis direction is measured along the first direction of the inspection object P of the concrete structure C, a third direction variation curve is formed that shows the relationship between the measurement values ​​of each of the multiple magnetic sensors 6 and the measurement position in the first direction (see Figure 11(A)).

[0181] Once the third direction variation curves are formed for each of the multiple magnetic sensors 6, these third direction variation curves are second-order differentiated. Then, third direction differential curves are formed that indicate the relationship between the second-order differential values ​​of each of the multiple magnetic sensors 6 and the measurement positions in the first direction corresponding to the second-order differential values, and the difference Δd2Xz between the positions of the maximum and minimum values ​​is calculated. Specifically, for each third direction differential curve, the maximum and minimum values ​​that sandwich the position where each third direction differential curve becomes 0 are calculated, and the difference Δd2Xz between the positions of the maximum and minimum values ​​is calculated.

[0182] Then, the distance from the magnetic sensor 6 at the position of the position difference Y to the inspection object P is defined as distance R(Y), and R is the 1 / 2 power of distance R. 1 / 2 The difference estimated by the linear approximation formula expressing the relationship between the difference Δd2Xz calculated from the third direction differential curve at each measurement position and the difference Δd2Xz(Y) is defined as the difference Δd2Xz(Y). Then, Δd2Xz(Y) / Δd2Xz(0) and (R(Y) / R(0)) 1 / 2 When the distance Za from the magnetic sensor 6 to the inspection object P in the Z-axis direction is Gap≧Za, the fracture gap Gap of the fracture GA of the inspection object P can be estimated based on the slope of the linear approximation equation (see FIG. 15).

[0183] The relationship between the slope of the linear approximation equation and the fracture gap Gap of the fracture GA of the test object P can be determined in advance by changing the distance Za from the magnetic sensor to the test object P in the Z-axis direction in the test structure TM and the fracture gap Gap. [Industrial Applicability]

[0184] The non-destructive inspection method of the present invention is suitable as a method for detecting fractures in reinforcing bars, steel rods, steel wires, etc. installed within concrete structures. [Explanation of symbols]

[0185] 1. Non-destructive testing equipment 2. Mobile 5 Magnetic flux measurement section 6 Magnetic Sensors A Second measurement direction B Central axis of moving body 2 SA reference plane C. Concrete structures CF Surface of concrete structure C CR cross bars P Inspection subject TM Test Structure Q Test Subjects R1 Crossed rebars (horizontal bars) R2 Crossed rebars (vertical rebars) GA fracture Gap Breaking gap

Claims

1. A method for estimating the presence or absence of a fracture in an inspection object embedded in a concrete structure, the method comprising: measuring a magnetic flux density of the inspection object extending in a first direction outside the concrete structure along the first direction of the inspection object; and estimating the presence or absence of a fracture in the inspection object based on a variation in the measured magnetic flux density, measuring the magnetic flux density in a first direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming a first direction variation curve for each of the measurement positions, the first direction variation curve indicating the variation along the first direction of the magnetic flux density measured at the plurality of measurement positions; forming first-direction differential curves by first-order differentiation of the first-direction fluctuation curves at each measurement position; For the first directional differential curve at each measurement position, a difference ΔdBx between the maximum value and the minimum value on either side of the position where the first directional differential curve becomes zero, and / or a difference ΔdXx between the position of the maximum value and the position of the minimum value on either side of the position where the first directional differential curve becomes zero are calculated; creating a linear approximation formula expressing the relationship between R −3 , which is the inverse cube of the distance R from each measurement position to the inspection object, and the difference ΔdBx calculated from the first direction differential curve at each measurement position, and / or creating a linear approximation formula expressing the relationship between R 1 / 2 , which is the ½ power of the distance R from each measurement position to the inspection object, and the difference ΔdXx calculated from the first direction differential curve at each measurement position; When the difference ΔdBx calculated from the first direction differential curve at each measurement position and / or the difference ΔdXx calculated from the first direction differential curve at each measurement position satisfies a linear approximation formula, it is determined that a fracture has occurred in the test object. A non-destructive inspection method characterized by:

2. A method for estimating whether or not the test object has a fracture, comprising measuring a magnetic flux density of a test object embedded in a concrete structure and extending in a first direction outside the concrete structure along the first direction of the test object, and estimating whether or not the test object has a fracture based on fluctuations in the measured magnetic flux density, measuring the magnetic flux density in a first direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming a first direction variation curve for each of the measurement positions, the first direction variation curve indicating the variation along the first direction of the magnetic flux density measured at the plurality of measurement positions; forming first-direction differential curves by first-order differentiation of the first-direction fluctuation curves at each measurement position; For the first directional differential curve at each measurement position, a difference ΔdBx between the maximum value and the minimum value on either side of the position where the first directional differential curve becomes zero, and / or a difference ΔdXx between the position of the maximum value and the position of the minimum value on either side of the position where the first directional differential curve becomes zero are calculated; A test structure simulating a concrete structure having a test object having a fracture that is a member equivalent to the inspection object, measuring a magnetic flux density in a first direction along the first direction of the test object at a plurality of measurement positions aligned along a second direction parallel to a surface of the test structure and perpendicular to the first direction of the test object; forming a first direction variation curve for each of the measurement positions, the first direction variation curve indicating the variation along the first direction of the magnetic flux density measured at the plurality of measurement positions; forming first-direction differential curves by first-order differentiation of the first-direction fluctuation curves at each measurement position; For the first directional differential curve at each measurement position, a difference ΔdBx between the maximum value and the minimum value on either side of the position where the first directional differential curve becomes zero, and / or a difference ΔdXx between the position of the maximum value and the position of the minimum value on either side of the position where the first directional differential curve becomes zero are calculated; R, which is the inverse cube of the distance R from each measurement position to the test object －３ and a first-order approximation formula representing the relationship between the difference ΔdBx calculated from the first-directional differential curve at each measurement position, and / or R, which is the ½ power of the distance R from each measurement position to the test object. １／２ and a first-order approximation formula representing the relationship between the difference ΔdXx calculated from the first direction differential curve at each measurement position, When the difference ΔdBx and / or the difference ΔdXx calculated from the magnetic flux density measured in the concrete structure satisfies the first-order approximation formula, it is determined that a fracture has occurred in the inspection object. A non-destructive inspection method characterized by:

3. A method for estimating whether or not the test object has a fracture, comprising measuring a magnetic flux density of a test object embedded in a concrete structure and extending in a first direction outside the concrete structure along the first direction of the test object, and estimating whether or not the test object has a fracture based on fluctuations in the measured magnetic flux density, measuring the magnetic flux density in a first direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming a first direction variation curve for each of the measurement positions, the first direction variation curve indicating the variation along the first direction of the magnetic flux density measured at the plurality of measurement positions; forming first-direction differential curves by first-order differentiation of the first-direction fluctuation curves at each measurement position; For the first directional differential curve at each measurement position, a difference ΔdBx between the maximum value and the minimum value on either side of the position where the first directional differential curve becomes zero, and / or a difference ΔdXx between the position of the maximum value and the position of the minimum value on either side of the position where the first directional differential curve becomes zero are calculated; A test structure simulating a concrete structure having a test object having a fracture that is a member equivalent to the inspection object, measuring a magnetic flux density in a first direction along the first direction of the test object at a plurality of measurement positions aligned along a second direction parallel to a surface of the test structure and perpendicular to the first direction of the test object; forming a first direction variation curve for each of the measurement positions, the first direction variation curve indicating the variation along the first direction of the magnetic flux density measured at the plurality of measurement positions; forming first-direction differential curves by first-order differentiation of the first-direction fluctuation curves at each measurement position; For the first directional differential curve at each measurement position, a difference ΔdBx between the maximum value and the minimum value on either side of the position where the first directional differential curve becomes zero, and / or a difference ΔdXx between the position of the maximum value and the position of the minimum value on either side of the position where the first directional differential curve becomes zero are calculated; forming a diagnostic map having a fracture region for estimating a fracture of the inspection object, the difference ΔdBx being a first axis and the difference ΔdXx being a second axis; The presence or absence of a fracture in the inspection object is estimated based on whether or not the difference ΔdBx and the difference ΔdXx calculated from the magnetic flux density measured in the concrete structure are located in a fracture region of the diagnostic map. A non-destructive inspection method characterized by:

4. A method for estimating whether or not the test object has a fracture, comprising measuring a magnetic flux density of a test object embedded in a concrete structure and extending in a first direction outside the concrete structure along the first direction of the test object, and estimating whether or not the test object has a fracture based on fluctuations in the measured magnetic flux density, measuring the magnetic flux density in a first direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming a first direction variation curve for each of the measurement positions, the first direction variation curve indicating the variation along the first direction of the magnetic flux density measured at the plurality of measurement positions; forming first-direction differential curves by first-order differentiation of the first-direction fluctuation curves at each measurement position; For the first directional differential curve at each measurement position, a difference ΔdBx between the maximum value and the minimum value on either side of the position where the first directional differential curve becomes zero, and / or a difference ΔdXx between the position of the maximum value and the position of the minimum value on either side of the position where the first directional differential curve becomes zero are calculated; In cases where there are no buried rebars other than those subject to inspection in the concrete structure, R, which is the 1 / 2 power of the distance R from each measurement position to the inspection object １／２ and a first-order approximation formula expressing the relationship between the difference ΔdXx calculated from the first direction differential curve at each measurement position, The position difference from the inspection object to the measurement position in the second direction is defined as position difference Y, the distance from the inspection object to the measurement position of position difference Y is defined as distance R(Y), and the difference ΔdXx in the case of position difference Y is defined as a value ΔdXx(Y) estimated by the linear approximation formula, ΔdXx(Y) / ΔdXx(0) and (R(Y) / R(0)) １／２ Create a relative linear approximation that expresses the relationship between The fracture gap of the inspection object is estimated based on the slope of the relative value linear approximation formula. A non-destructive inspection method characterized by: R(0): The distance from the measurement position to the test object on a third direction line perpendicular to the first and second directions is the same as the distance from the test object to the measurement position, and the measurement position is on the third direction line of the test object.

5. A method for estimating the presence or absence of a fracture in an inspection object embedded in a concrete structure, the method comprising: measuring a magnetic flux density of the inspection object extending in a first direction outside the concrete structure along the first direction of the inspection object; and estimating the presence or absence of a fracture in the inspection object based on a variation in the measured magnetic flux density, measuring the magnetic flux density in a second direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming second direction variation curves each showing a variation along the first direction of the magnetic flux density in the second direction measured at a plurality of measurement positions; forming second-direction differential curves by second-order differentiating the second-direction fluctuation curves at each measurement position; For the second directional differential curve at each measurement position, a difference Δd2By between the maximum value and the minimum value on either side of the position where the second directional differential curve becomes zero and / or a difference Δd2Xy between the position of the maximum value and the position of the minimum value on either side of the position where the second directional differential curve becomes zero are calculated; a linear approximation formula expressing the relationship between R −3 , which is the inverse cube of the distance R from each measurement position to the inspection object, and Δd2By / β, which is the value obtained by dividing the difference Δd2By calculated from the second directional differential curve at each measurement position by a correction coefficient β, and / or a linear approximation formula expressing the relationship between R 1 / 2 , which is the ½ power of the distance R from each measurement position to the inspection object, and Δd2Xy·α, which is the value obtained by correcting the positive or negative sign of the difference Δd2Xy calculated from the second directional differential curve at each measurement position; When the value Δd2By / β calculated from the second direction differential curve at each measurement position and / or the value Δd2Xy·α calculated from the second direction differential curve at each measurement position satisfies a linear approximation formula, it is determined that a fracture has occurred in the inspection object. A non-destructive inspection method characterized by: α: SIGN(Y) β:Y / Za・SIGN(Δd2Xy) Y: Difference in position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, if A is a positive number or 0, the value is "+1", and if A is a negative number, the value is "-1". Za: distance from each measurement position to the inspection object in a third direction perpendicular to the first and second directions

6. A method for estimating whether or not the test object has a fracture, comprising measuring a magnetic flux density of a test object embedded in a concrete structure and extending in a first direction outside the concrete structure along the first direction of the test object, and estimating whether or not the test object has a fracture based on fluctuations in the measured magnetic flux density, measuring the magnetic flux density in a second direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming second direction variation curves each showing a variation along the first direction of the magnetic flux density in the second direction measured at a plurality of measurement positions; forming second-direction differential curves by second-order differentiating the second-direction fluctuation curves at each measurement position; For the second directional differential curve at each measurement position, a difference Δd2By between the maximum value and the minimum value on either side of the position where the second directional differential curve becomes zero and / or a difference Δd2Xy between the position of the maximum value and the position of the minimum value on either side of the position where the second directional differential curve becomes zero are calculated; A test structure simulating a concrete structure having a test object having a fracture that is a member equivalent to the inspection object, measuring magnetic flux density in a second direction along the first direction of the test object at a plurality of measurement positions arranged along a second direction parallel to a surface of the test structure and perpendicular to the first direction of the test object; forming a second direction variation curve for each of the measurement positions, the second direction variation curve indicating the variation along the first direction of the magnetic flux density measured in the second direction at each of the measurement positions; forming second-direction differential curves by second-order differentiating the second-direction fluctuation curves at each measurement position; For the second directional differential curve at each measurement position, a difference Δd2By between the maximum value and the minimum value on either side of the position where the second directional differential curve becomes zero and / or a difference Δd2Xy between the position of the maximum value and the position of the minimum value on either side of the position where the second directional differential curve becomes zero are calculated; R, which is the inverse cube of the distance R from each measurement position to the inspection object －３ and a value Δd2By / β1 obtained by dividing the difference Δd2By calculated from the second directional differential curve at each measurement position by a correction coefficient β1, and / or R, which is the ½ power of the distance R from each measurement position to the test object. １／２ and a value Δd2Xy·α1 obtained by correcting the positive or negative sign of the difference Δd2Xy calculated from the second directional differential curve at each measurement position, If the value Δd2By / β and / or the value Δd2Xy·α calculated from the magnetic flux density measured in the concrete structure satisfies the first-order approximation formula, it is determined that a fracture has occurred in the inspection object. A non-destructive inspection method characterized by: α: SIGN(Y) β:Y / Za・SIGN(Δd2Xy) Y: Difference in position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, if A is a positive number or 0, the value is "+1", and if A is a negative number, the value is "-1". Za: distance from each measurement position to the inspection object in a third direction perpendicular to the first and second directions α1: SIGN (Y1) β1:Y1 / Za1・SIGN(Δd2Xy) Y1: Difference in position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, if A is a positive number or 0, the value is "+1", and if A is a negative number, the value is "-1". Za1: Distance from each measurement position to the test object in a third direction perpendicular to the first and second directions

7. A method for estimating whether or not the test object has a fracture, comprising measuring a magnetic flux density of a test object embedded in a concrete structure and extending in a first direction outside the concrete structure along the first direction of the test object, and estimating whether or not the test object has a fracture based on fluctuations in the measured magnetic flux density, measuring the magnetic flux density in a second direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming second direction variation curves each showing a variation along the first direction of the magnetic flux density in the second direction measured at a plurality of measurement positions; forming second-direction differential curves by second-order differentiating the second-direction fluctuation curves at each measurement position; For the second directional differential curve at each measurement position, a difference Δd2By between the maximum value and the minimum value on either side of the position where the second directional differential curve becomes zero and / or a difference Δd2Xy between the position of the maximum value and the position of the minimum value on either side of the position where the second directional differential curve becomes zero are calculated; A test structure simulating a concrete structure having a test object having a fracture that is a member equivalent to the inspection object, measuring magnetic flux density in a second direction along the first direction of the test object at a plurality of measurement positions arranged along a second direction parallel to a surface of the test structure and perpendicular to the first direction of the test object; forming a second direction variation curve for each of the measurement positions, the second direction variation curve indicating the variation along the first direction of the magnetic flux density measured in the second direction at each of the measurement positions; forming second-direction differential curves by second-order differentiating the second-direction fluctuation curves at each measurement position; For the second directional differential curve at each measurement position, a value Δd2By / β1 is calculated by dividing the difference Δd2By between the maximum value and the minimum value on either side of the position where the second directional differential curve is zero by a correction coefficient β1, and / or a value Δd2Xy·α1 is calculated by correcting the positive or negative sign of the difference Δd2Xy between the position where the second directional differential curve is zero and the position where the maximum value is zero on either side of the position where the second directional differential curve is zero, forming a diagnostic map having a fracture region for estimating a fracture of the object to be inspected, the diagnostic map having a first axis representing the value Δd2By / β1 and a second axis representing the value Δd2Xy·α1; The presence or absence of a fracture in the inspection object is estimated based on whether or not the value Δd2By / β and the value Δd2Xy·α calculated from the magnetic flux density measured in the concrete structure are located in a fracture region of the diagnostic map. A non-destructive inspection method characterized by: α: SIGN(Y) β:Y / Za・SIGN(Δd2Xy) Y: Difference in position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, if A is a positive number or 0, the value is "+1", and if A is a negative number, the value is "-1". Za: distance from each measurement position to the inspection object in a third direction perpendicular to the first and second directions α1: SIGN (Y1) β1:Y1 / Za1・SIGN(Δd2Xy) Y1: Difference in position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, if A is a positive number or 0, the value is "+1", and if A is a negative number, the value is "-1". Za1: Distance from each measurement position to the test object in a third direction perpendicular to the first and second directions

8. A method for estimating whether or not the test object has a fracture, comprising measuring a magnetic flux density of a test object embedded in a concrete structure and extending in a first direction outside the concrete structure along the first direction of the test object, and estimating whether or not the test object has a fracture based on fluctuations in the measured magnetic flux density, measuring the magnetic flux density in a second direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming second direction variation curves each showing a variation along the first direction of the magnetic flux density in the second direction measured at a plurality of measurement positions; forming second-direction differential curves by second-order differentiating the second-direction fluctuation curves at each measurement position; For the second directional differential curve at each measurement position, a difference Δd2By between the maximum value and the minimum value on either side of the position where the second directional differential curve becomes zero and / or a difference Δd2Xy between the position of the maximum value and the position of the minimum value on either side of the position where the second directional differential curve becomes zero are calculated; In cases where there are no buried rebars other than those subject to inspection in the concrete structure, R, which is the 1 / 2 power of the distance R from each measurement position to the inspection object １／２ and a value Δd2Xy α calculated from the second directional differential curve at each measurement position, The position difference from the inspection object to the measurement position in the second direction is defined as position difference Y, the distance from the inspection object to the measurement position is defined as distance R(Y), and the value Δd2Xy·α in the case of position difference Y is defined as a value Δd2Xy(Y)·α(Y) estimated by the linear approximation equation, (Δd2Xy(Y)・α(Y)) / (Δd2Xy(0)・α(0)) and (R(Y) / R(0)) １／２ Create a relative linear approximation that expresses the relationship between The fracture gap of the inspection object is estimated based on the slope of the relative value linear approximation formula. A non-destructive inspection method characterized by: α: SIGN(Y) β:Y / Za・SIGN(Δd2Xy) Y: Difference in position in the second direction from the test object to each measurement position SIGN(A): Depending on the sign of A, if A is a positive number or 0, the value is "+1", and if A is a negative number, the value is "-1". Za: distance from each measurement position to the inspection object in a third direction perpendicular to the first and second directions R(0): The distance from the measurement position to the test object on a third direction line perpendicular to the first and second directions is the same as the distance from the test object to the measurement position, and the measurement position is on the third direction line of the test object.

9. A method for estimating the presence or absence of a fracture in an inspection object embedded in a concrete structure, the method comprising: measuring a magnetic flux density of the inspection object extending in a first direction outside the concrete structure along the first direction of the inspection object; and estimating the presence or absence of a fracture in the inspection object based on a variation in the measured magnetic flux density, measuring the magnetic flux density in a third direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming third direction variation curves each showing a variation along the first direction of the magnetic flux density in the third direction measured at a plurality of measurement positions; forming third-direction differential curves by second-order differentiation of the third-direction fluctuation curves at each measurement position; For the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value on either side of the position where the third direction differential curve is zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value on either side of the position where the third direction differential curve is zero, are calculated; creating a linear approximation formula expressing the relationship between R −3 , which is the inverse cube of the distance R from each measurement position to the inspection object, and the difference Δd2Bz calculated from the third direction differential curve at each measurement position, and / or a linear approximation formula expressing the relationship between R 1 / 2 , which is the ½ power of the distance R from each measurement position to the inspection object, and the difference Δd2Xz calculated from the third direction differential curve at each measurement position; When the difference Δd2Bz calculated from the third direction differential curve at each measurement position and / or the difference Δd2Xz calculated from the third direction differential curve at each measurement position satisfies a linear approximation formula, it is determined that a fracture has occurred in the test object. A non-destructive inspection method characterized by:

10. A method for estimating whether or not the test object has a fracture, comprising measuring a magnetic flux density of a test object embedded in a concrete structure and extending in a first direction outside the concrete structure along the first direction of the test object, and estimating whether or not the test object has a fracture based on fluctuations in the measured magnetic flux density, measuring the magnetic flux density in a third direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming third direction variation curves each showing a variation along the first direction of the magnetic flux density in the third direction measured at a plurality of measurement positions; forming third-direction differential curves by second-order differentiation of the third-direction fluctuation curves at each measurement position; For the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value on either side of the position where the third direction differential curve is zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value on either side of the position where the third direction differential curve is zero, are calculated; A test structure simulating a concrete structure having a test object having a fracture that is a member equivalent to the inspection object, measuring a magnetic flux density in a third direction along the first direction of the test object at a plurality of measurement positions aligned along a second direction parallel to a surface of the test structure and perpendicular to the first direction of the test object; forming a third direction variation curve for each measurement position, the third direction variation curve indicating the variation along the first direction of the magnetic flux density in the third direction measured at each measurement position; forming third-direction differential curves by second-order differentiation of the third-direction fluctuation curves at each measurement position; For the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value on either side of the position where the third direction differential curve is zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value on either side of the position where the third direction differential curve is zero, are calculated; R, which is the inverse cube of the distance R from each measurement position to the inspection object －３ and a first-order approximation formula representing the relationship between the difference Δd2Bz calculated from the third direction differential curve at each measurement position, and / or R, which is the ½ power of the distance R from each measurement position to the test object. １／２ and a first-order approximation formula representing the relationship between the difference Δd2Xz calculated from the third direction differential curve at each measurement position, If the difference Δd2Bz and / or the difference Δd2Xz calculated from the magnetic flux density measured in the concrete structure satisfies the first-order approximation formula, it is determined that a fracture has occurred in the inspection object. A non-destructive inspection method characterized by:

11. A method for estimating whether or not the test object has a fracture, comprising measuring a magnetic flux density of a test object embedded in a concrete structure and extending in a first direction outside the concrete structure along the first direction of the test object, and estimating whether or not the test object has a fracture based on fluctuations in the measured magnetic flux density, measuring the magnetic flux density in a third direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming third direction variation curves each showing a variation along the first direction of the magnetic flux density in the third direction measured at a plurality of measurement positions; forming third-direction differential curves by second-order differentiation of the third-direction fluctuation curves at each measurement position; For the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value on either side of the position where the third direction differential curve is zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value on either side of the position where the third direction differential curve is zero, are calculated; A test structure simulating a concrete structure having a test object having a fracture that is a member equivalent to the inspection object, measuring a magnetic flux density in a third direction along the first direction of the test object at a plurality of measurement positions aligned along a second direction parallel to a surface of the test structure and perpendicular to the first direction of the test object; forming a third direction variation curve for each measurement position, the third direction variation curve indicating the variation along the first direction of the magnetic flux density in the third direction measured at each measurement position; forming third-direction differential curves by second-order differentiation of the third-direction fluctuation curves at each measurement position; For the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value on either side of the position where the third direction differential curve is zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value on either side of the position where the third direction differential curve is zero, are calculated; forming a diagnostic map having a fracture region for estimating a fracture of the inspection object, the diagnostic map having the difference Δd2Bz as a first axis and the difference Δd2Xz as a second axis; The presence or absence of a fracture in the inspection object is estimated based on whether or not the difference Δd2Bz and the difference Δd2Xz calculated from the magnetic flux density measured in the concrete structure are located in a fracture region of the diagnostic map. A non-destructive inspection method characterized by:

12. A method for estimating whether or not the test object has a fracture, comprising measuring a magnetic flux density of a test object embedded in a concrete structure and extending in a first direction outside the concrete structure along the first direction of the test object, and estimating whether or not the test object has a fracture based on fluctuations in the measured magnetic flux density, measuring the magnetic flux density in a third direction at a plurality of measurement positions arranged along a second direction parallel to the surface of the concrete structure and perpendicular to the first direction of the inspection object; forming third direction variation curves each showing a variation along the first direction of the magnetic flux density in the third direction measured at a plurality of measurement positions; forming third-direction differential curves by second-order differentiation of the third-direction fluctuation curves at each measurement position; For the third direction differential curve at each measurement position, a difference Δd2Bz between the maximum value and the minimum value on either side of the position where the third direction differential curve is zero, and / or a difference Δd2Xz between the position of the maximum value and the position of the minimum value on either side of the position where the third direction differential curve is zero, are calculated; In cases where there are no buried rebars other than those subject to inspection in the concrete structure, R, which is the 1 / 2 power of the distance R from each measurement position to the inspection object １／２ and a value Δd2Xz calculated from the third direction differential curve at each measurement position, The position difference from the inspection object to the measurement position in the second direction is defined as position difference Y, the distance from the inspection object to the measurement position is defined as distance R(Y), and the difference Δd2Xz in the case of position difference Y is defined as a value Δd2Xz(Y) estimated by the linear approximation formula, A relative linear approximation formula expressing the relationship between Δd2Xz(Y) / Δd2Xz(0) and (R(Y) / R(0)) is created, The fracture gap of the inspection object is estimated based on the slope of the relative value linear approximation formula. A non-destructive inspection method characterized by: R(0): The distance from the measurement position to the test object on a third direction line perpendicular to the first and second directions is the same as the measurement position, and the measurement position on the third direction line of the test object is the distance from the measurement position to the test object.

13. The presence or absence of a fracture in the inspection object is estimated using the difference between the maximum value and the minimum value of a differential curve obtained from fluctuations in magnetic flux density measured at a measurement position where Ya / Za, which indicates the relationship between the distance Ya from the inspection object to the measurement position in the second direction and the distance Za from the surface of the concrete structure to the inspection object, is 0 to 1.5, and / or the difference between the position of the maximum value and the position of the minimum value of the differential curve.

13. The non-destructive inspection method according to claim 1.

14. When the distance Za is 100 mm, the distance Ya is 0 to 150 mm.

14. The non-destructive inspection method according to claim 13.

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