Non-destructive testing methods

Abstract

A non-destructive inspection method is provided that can estimate the state of thinning of reinforcing bars and the like installed in a concrete structure. [Solution] A method for measuring the magnetic flux density of an object to be inspected P embedded in a concrete structure C and extending in a first direction outside the concrete structure C, and estimating damage to the object to be inspected P based on fluctuations in the measured magnetic flux density. The method comprises moving a magnetizer in a first movement direction along the first direction of the object to be inspected P and in a second movement direction opposite to the first movement direction to magnetize the object to be inspected P, then moving a magnetic flux density measuring unit 5 that measures the magnetic flux density in the first movement direction to measure the magnetic flux density, creating a fluctuation curve along the first direction of the object to be inspected P based on the measured magnetic flux density, creating a polynomial approximation curve of the fluctuation curve, subtracting the polynomial approximation curve from the fluctuation curve to create a corrected fluctuation curve, squaring the corrected fluctuation curve to create a corrected fluctuation squared curve, and estimating the state of metal thinning CR of the object to be inspected P based on the corrected fluctuation squared curve.

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 damage to 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 of the magnetic flux 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 measurement results of the magnetic flux density. 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 technologies disclosed in Patent Documents 1 to 6, it is possible to detect damaged areas where reinforcing bars, etc. have broken, but it is difficult to detect thinning before it leads to breakage, and in particular, it is difficult to grasp the state of thinning, such as the amount of thinning.

[0005] In view of the above circumstances, an object of the present invention is to provide a non-destructive inspection method capable of estimating the state of thinning of reinforcing bars or the like installed in a concrete structure. [Means for solving the problem]

[0006] A non-destructive testing method of a first invention is a method for measuring, outside the concrete structure, the magnetic flux density of an object to be tested that is embedded in the concrete structure and extends in a first direction, and estimating damage to the object to be tested based on fluctuations in the measured magnetic flux density, the method comprising: moving a magnetizer in a first movement direction along the first direction of the object to be tested and a second movement direction that is opposite to the first movement direction to magnetize the object to be tested; then moving a magnetic flux density measuring unit that measures the magnetic flux density in the first movement direction to measure the magnetic flux density; creating a variation curve of the magnetic flux density along the first direction of the object to be tested based on the measured magnetic flux density; creating a polynomial approximation curve of the variation curve; subtracting the polynomial approximation curve from the variation curve to create a corrected variation curve; squaring the corrected variation curve to create a corrected variation squared curve; and estimating a state of wall thinning of the object to be tested based on the corrected variation squared curve. The non-destructive testing method of the second invention is characterized in that, in the first invention, an integral value of a predetermined section in the corrected variation square curve is calculated, and the amount of thinning of the test object is estimated based on the corrected variation mean square value, which is a value obtained by dividing the integral value by the length of the section in which the integral value was calculated. The non-destructive testing method of the third invention is characterized in that, in the first invention, the fluctuation curve is a fluctuation curve formed based on a first direction magnetic flux density, which is a magnetic flux density along a first direction of the object to be tested. A non-destructive inspection method according to a fourth aspect of the present invention is characterized in that, in the third aspect of the present invention, the polynomial approximation curve is a curve formed based on any one of fourth- to seventh-order approximation equations of the fluctuation curve. The non-destructive testing method of the fifth invention is characterized in that, in the first invention, a third direction differential curve is used as the variation curve of magnetic flux density along the first direction of the test object, which is obtained by first-order differentiation of the variation curve of magnetic flux density formed along the first direction of the test object based on a third direction magnetic flux density, which is the magnetic flux density in the normal direction to the surface of the concrete structure. A non-destructive testing method according to a sixth aspect of the present invention is characterized in that, in the fifth aspect of the present invention, the polynomial approximation curve is a curve formed based on any one of fourth- to seventh-order approximation equations of the third directional differential curve. [Effects of the Invention]

[0007] According to the first aspect of the present invention, if a test object embedded in a concrete structure has wall thinning that does not lead to fracture, the state of wall thinning can be estimated. According to the second aspect of the present invention, it is possible to improve the accuracy of estimating the state of wall thinning. According to the third to sixth aspects of the present invention, the state of wall thinning can be appropriately estimated. [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] 1A and 1B are schematic explanatory diagrams of a magnetizer 10 used in the nondestructive testing method of this embodiment, in which (A) is a side view of the magnetizer 10 moving in a first moving direction D1, and (B) is a side view of the magnetizer 10 moving in a second moving direction D2. [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] Schematic diagrams of test objects installed in the test structure, where (A) is a schematic diagram of a wall-thinning state where the wall-thinning length is 0 mm (wedge-shaped), (B) is a schematic diagram of a wall-thinning state where the wall-thinning length is 100 mm, and (C) is a schematic diagram of a wall-thinning state where the wall-thinning length is 200 mm. [Figure 5]Graphs of magnetic flux density measured on a test object with a wall-thinning length of 100 mm installed on a test structure, where (A) is a graph of the X-axis direction variation curve, (B) is a graph of a sixth-order polynomial approximation curve of the X-axis direction variation curve, and (C) is a graph of the X-axis direction corrected variation curve. [Figure 6] These are graphs of the X-axis direction corrected variation curves (hereinafter simply referred to as "fxn(x) (n is the degree of the polynomial approximation curve)") calculated for the test object installed in the test structure, where (A) is a graph of fx6(x) when the wall-thinning length is 0 mm (wedge-shaped), (B) is a graph of fx6(x) when the wall-thinning length is 100 mm, and (C) is a graph of fx6(x) when the wall-thinning length is 200 mm. [Figure 7] 7 is a graph of the X-axis direction corrected fluctuation squared curve (hereinafter simply referred to as "fxn(x)2 (n is the degree of the polynomial approximation curve)") calculated from the corrected fluctuation curve in FIG. 6, where (A) is a graph of fx6(x)2 when the wall-thinning length is 0 mm (wedge-shaped), (B) is a graph of fx6(x)2 when the wall-thinning length is 100 mm, and (C) is a graph of fx6(x)2 when the wall-thinning length is 200 mm. [Figure 8] Graphs of magnetic flux density measured on a test object with a wall thinning length of 100 mm installed on a test structure, where (A) is a graph of the Z-axis direction fluctuation curve, (B) is a graph of the Z-axis direction first-order differential curve, (C) is a graph of a sixth-order polynomial approximation curve of the Z-axis direction first-order differential curve, and (D) is a graph of the Z-axis direction corrected fluctuation curve. [Figure 9] These are graphs of the Z-axis direction corrected variation curves (hereinafter simply referred to as "fzn(x) (n is the degree of the polynomial approximation curve)") calculated for a test object installed in a test structure, where (A) is a graph of fz6(x) when the wall-thinning length is 0 mm (wedge-shaped), (B) is a graph of fz6(x) when the wall-thinning length is 100 mm, and (C) is a graph of fz6(x) when the wall-thinning length is 200 mm. [Figure 10]These are graphs of the Z-axis direction corrected variation square curve (hereinafter simply referred to as "fzn(x)2 (n is the degree of the polynomial approximation curve)") calculated for a test object installed in a test structure, where (A) is a graph of fz6(x)2 when the wall-thinning length is 0 mm (wedge-shaped), (B) is a graph of fz6(x)2 when the wall-thinning length is 100 mm, and (C) is a graph of fz6(x)2 when the wall-thinning length is 200 mm. [Figure 11] Graph (A) shows the relationship between the corrected mean square value of fluctuation (hereinafter simply referred to as “fxn(x)2 mean (n is the degree of the polynomial approximation curve)”) calculated for a test object installed on a test structure and the average cross-sectional loss rate S, and graph (B) shows the relationship between the corrected mean square value of fluctuation (hereinafter simply referred to as “fzn(x)2 mean (n is the degree of the polynomial approximation curve)”) calculated for a test object installed on a test structure and the average cross-sectional loss rate S. [Figure 12] Graph (A) shows the relationship between the average fx3(x)2 and the average cross-sectional loss rate S when a third-order polynomial approximation curve is used to create the X-axis direction corrected variation curve, and graph (B) shows the relationship between the average fx4(x)2 and the average cross-sectional loss rate S when a fourth-order polynomial approximation curve is used to create the X-axis direction corrected variation curve. [Figure 13] (C) is a graph showing the relationship between the average fx5(x)2 and the average cross-sectional loss rate S when a fifth-order polynomial approximation curve is used to create the X-axis direction corrected variation curve, and (D) is a graph showing the relationship between the average fx6(x)2 and the average cross-sectional loss rate S when a sixth-order polynomial approximation curve is used to create the X-axis direction corrected variation curve. [Figure 14] (E) is a graph showing the relationship between the average fx7(x)2 and the average cross-sectional loss rate S when a 7th-order polynomial approximation curve is used to create the X-axis direction corrected variation curve, and (F) is a graph showing the relationship between the average fx8(x)2 and the average cross-sectional loss rate S when an 8th-order polynomial approximation curve is used to create the X-axis direction corrected variation curve. [Figure 15](G) is a graph showing the relationship between the average fx9(x)2 and the average cross-sectional loss rate S when a 9th-order polynomial approximation curve is used to create the X-axis direction corrected variation curve, and (H) is a graph showing the relationship between the average fx10(x)2 and the average cross-sectional loss rate S when a 10th-order polynomial approximation curve is used to create the X-axis direction corrected variation curve. [Figure 16] Graph (A) shows the relationship between the average fz3(x)2 and the average cross-sectional loss rate S when a third-order polynomial approximation curve is used to create the Z-axis direction corrected fluctuation curve, and graph (B) shows the relationship between the average fz4(x)2 and the average cross-sectional loss rate S when a fourth-order polynomial approximation curve is used to create the Z-axis direction corrected fluctuation curve. [Figure 17] (C) is a graph showing the relationship between the average fz5(x)2 and the average cross-sectional loss rate S when a fifth-order polynomial approximation curve is used to create the Z-axis direction corrected fluctuation curve, and (D) is a graph showing the relationship between the average fz6(x)2 and the average cross-sectional loss rate S when a sixth-order polynomial approximation curve is used to create the Z-axis direction corrected fluctuation curve. [Figure 18] (E) is a graph showing the relationship between the average fz7(x)2 and the average cross-sectional loss rate S when a 7th-order polynomial approximation curve is used to create the Z-axis direction corrected fluctuation curve, and (F) is a graph showing the relationship between the average fz8(x)2 and the average cross-sectional loss rate S when an 8th-order polynomial approximation curve is used to create the Z-axis direction corrected fluctuation curve. [Figure 19] (G) is a graph showing the relationship between the average fz9(x)2 and the average cross-sectional loss rate S when a 9th-order polynomial approximation curve is used to create the Z-axis direction corrected fluctuation curve, and (H) is a graph showing the relationship between the average fz10(x)2 and the average cross-sectional loss rate S when a 10th-order polynomial approximation curve is used to create the Z-axis direction corrected fluctuation curve. DETAILED DESCRIPTION OF THE INVENTION

[0009] The non-destructive testing method of this embodiment is a method for estimating damage to an object to be tested that is buried inside a concrete structure using the leakage magnetic flux method, and is capable of detecting the state of thinning that has occurred in an object to be tested 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 nondestructive 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 nondestructive inspection method of this embodiment. In particular, the nondestructive inspection method of this embodiment is suitable as a method for inspecting thinning of rebars, etc., buried in concrete structures where no intersecting rebars exist between the inspection target and the surface of the concrete structure. For example, the nondestructive inspection method of this embodiment is suitable as a method for inspecting thinning of rebars, etc., buried in utility poles, etc.

[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, pillar-shaped structures such as utility poles with cylindrical surfaces can also be listed as concrete structures 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 thinning. 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 remaining 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 the tangent plane of the surface of the concrete structure is used as the reference for a curved concrete structure.

[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 parallel to this surface CF in one direction (the left-right direction in Figure 1). 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 below as the first direction of the inspection object P.

[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 Z-axis direction referred to here is the third direction referred to in the claims.

[0018] In addition, the concept of the surface CF of the concrete structure C and the inspection object P being 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 a part of the inspection object P has a slight inclination relative to the surface CF of the concrete structure C being inspected.

[0019] <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.

[0020] <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 density 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).

[0021] Specifically, the moving body 2 has a main body 2a and a wheel 2r rotatably attached to the main body 2a (see FIG. 1(A)). The wheel 2r is provided so that its rotation axis is perpendicular to the central axis B of the moving body 2. Furthermore, the wheel 2r is provided so that its rotation axis is 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 axis of the wheel 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).

[0022] Furthermore, the 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 density 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 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 density 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.

[0023] 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 density measuring unit 5 and the surface CF of the concrete structure C to be inspected, the number of wheels 2r may be one, or multiple, such as two, three, or four or more.

[0024] 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 density 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 density measurement unit 5 and the surface CF of the concrete structure C to be inspected also includes a case where the distance H between them varies by about 5 mm when the mobile body 2 moves along the surface CF of the concrete structure C.

[0025] <Magnetic flux density measurement unit 5> The magnetic flux density 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 density measuring unit 5. Specifically, the magnetic sensor 6 is disposed so that the magnetic flux density of the inspection object P in the X-axis, Y-axis, and Z-axis directions can be measured when the moving object 2 is placed on the surface CF of the concrete structure C to be inspected.

[0026] The magnetic sensor 6 is not limited to one that can measure magnetic flux density in three axial directions, but may be any one that can measure magnetic flux density in at least two axes (the X-axis direction and the Z-axis direction of the inspection object P), and various known magnetic sensors may be used. For example, a Hall element sensor, an MR sensor, an MI sensor, a TMR sensor, or the like may be used as the magnetic sensor 6. Furthermore, the magnetic sensor 6 may be configured to measure magnetic flux density in at least two axial directions by using a plurality of magnetic sensors that can measure magnetic flux density in one axial direction. For example, two magnetic sensors that measure magnetic flux density in one axial direction may be arranged adjacent to each other to measure magnetic flux density in two axial directions.

[0027] <Control unit 4> 3, the control unit 4 has a position calculation function that calculates the position of the magnetic sensor 6 of the magnetic flux density measurement unit 5, and an operation control function that controls the operation of the magnetic sensor 6 of the magnetic flux density measurement unit 5. The control unit 4 also has a storage function that associates the data of the measured value of the magnetic flux density measured by the magnetic sensor 6 of the magnetic flux density measurement unit 5 with the position of the magnetic sensor 6 of the magnetic flux density measurement unit 5 calculated by the position calculation function, and stores these data in a storage unit such as a memory.

[0028] Furthermore, the control unit 4 has an analysis function that uses the data stored in the storage unit to create graphs showing fluctuations in measured values ​​of magnetic flux density, etc.

[0029] 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.

[0030] <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 magnetic sensor 6 of the magnetic flux density measurement unit 5. This position calculation function calculates the distance that the magnetic sensor 6 of the magnetic flux density measurement unit 5 has moved from its initial position (the position where the mobile object 2 is placed on the surface CF of the concrete structure C being inspected) to its current position, in other words, the current position of the magnetic sensor 6 of the magnetic flux density measurement unit 5 with respect to the initial position. For example, if the position of the magnetic sensor 6 relative to a reference position of the mobile object 2 (e.g., the position of the wheel 2r) is stored in the storage unit, the position calculation function can calculate the distance that the magnetic sensor 6 has moved in the X-axis direction and the position of the magnetic sensor 6 after the movement (position in the X-axis direction) based on the amount of movement of the mobile object 2 from its initial position in the x-axis direction and the position of the magnetic sensor 6 relative to the reference position, using the reference position at the initial position as the basis.

[0031] The method for calculating the movement distance of the magnetic sensor 6 of the magnetic flux density measuring 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 moving object 2 may be provided with a detector 4c that detects the movement distance from the initial position of the moving 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 magnetic sensor 6 of the magnetic flux density measuring unit 5 in the X-axis direction relative to the initial position and the position (position in the X-axis direction) of the magnetic sensor 6 of the magnetic flux density measuring unit 5 relative to 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.

[0032] 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.

[0033] Furthermore, the method for determining the current position of the magnetic sensor 6 (in other words, the position where the magnetic sensor 6 is 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 density measuring unit 5 relative to the position marker at the timing when the magnetic flux density is measured may be measured to determine the position where the magnetic flux density measuring unit 5 measured the magnetic flux density (position in the X-axis direction).

[0034] <Operation control function> The control unit 4 has an operation control function that controls the operation of the magnetic sensor 6 of the magnetic flux density measurement unit 5. This operation control function has the functions of determining the timing at which the magnetic sensor 6 of the magnetic flux density measurement unit 5 measures the magnetic flux density and causing the magnetic sensor 6 of the magnetic flux density measurement unit 5 to measure the magnetic flux density at that timing, and transmitting the measured value 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 magnetic sensor 6 to measure the magnetic flux density at predetermined time intervals (e.g., every 10 milliseconds) and transmit the measured value to the storage function (hereinafter, causing the magnetic sensor 6 to measure the magnetic flux density and transmit the measured value to the storage function may be referred to as "measurement, etc."), or causes the magnetic sensor 6 to measure the magnetic flux density at predetermined distances based on the movement amount 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 magnetic sensor 6 to continuously measure the magnetic flux density and continuously transmit the measured value to the storage function when a measurement start signal is input using an operation button or the like.

[0035] If the position calculation function has the detector 4c as described above, the signal transmitted by the detector 4c may be supplied to the operation control function, and the operation control function may cause the magnetic sensor 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 magnetic sensor 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). The timing at which the magnetic sensor 6 starts 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 magnetic sensor 6 may start measuring the magnetic flux density based on the signal.

[0036] Furthermore, the magnetic sensor 6 of the magnetic flux density measuring unit 5 may be in a state where it constantly measures 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 a signal from the magnetic sensor 6 to the storage function at the above-mentioned time intervals or after a predetermined moving distance after a measurement start signal is input.

[0037] <Memory function> The storage function is a function for storing, in association with each other, the movement distance of the magnetic flux density measurement unit 5 (i.e., the movement distance of the magnetic sensor 6) calculated by the position calculation function and the measurement value of the magnetic flux density measured by the magnetic sensor 6 of the magnetic flux density measurement unit 5. Specifically, the storage function has a function for storing, in association with each other, the measurement value of the magnetic flux density measured by the magnetic sensor 6 of the magnetic flux density measurement unit 5, the time when the magnetic sensor 6 measured the magnetic flux density, the position of the magnetic sensor 6 of the magnetic flux density measurement unit 5 at that time (the movement amount in the x-axis direction of the mobile object 2, the signal of the detector 4c, etc.), and the movement direction of the magnetic sensor 6.

[0038] <Analysis function> The control unit 4 also has an analysis function for analyzing the data stored in the storage unit. This analysis function has a function for determining the state of thinning CR of the inspection object P using the data stored in the storage unit. The analysis function will be described in detail later.

[0039] The control unit 4 does not necessarily 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, and the data may 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 4 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.

[0040] 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.

[0041] <Magnetizer 10> In the nondestructive inspection method of this embodiment, the inspection object P is magnetized before measuring the magnetic flux density using the nondestructive inspection device 1. Specifically, as will be described later, in the nondestructive inspection method of this embodiment, the nondestructive inspection device 1 is moved in a first movement direction D1 (see FIG. 1(A)) to measure the magnetic flux density. At this time, the inspection object P is magnetized before measuring the magnetic flux density. This magnetization of the inspection object P is performed using a magnetizer, and therefore, hereinafter, an example of a magnetizer used for magnetization (hereinafter referred to as magnetizer 10) will be shown.

[0042] As shown in Fig. 2, the magnetizer 10 has a moving body 11. This moving body 11 has a structure that allows it to move smoothly in one direction along the surface CF of the concrete structure C to be inspected. Moreover, the moving body 11 has a function that allows it to move while maintaining a constant distance HM between the surface CF of the concrete structure C to be inspected and a magnetic force generator 12, which will be described later.

[0043] Specifically, the mobile body 11 includes a main body 11a and a wheel 11r rotatably attached to the main body 11a (see FIG. 2). The wheel 11r is arranged so that its rotation axis is parallel to the surface CF of the concrete structure C to be inspected when the mobile body 11 is placed on the surface CF of the concrete structure C to be inspected. The wheel 11r is arranged so that the mobile body 11 can move while maintaining a constant distance HM (distance in the Z-axis direction) between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected. In other words, by rolling the wheel 11r while it is in contact with the surface CF of the concrete structure C to be inspected, the mobile body 11 can move along the X-axis direction on the surface CF of the concrete structure C to be inspected while maintaining a constant distance HM between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected. The following description will be given assuming that the direction of movement of the mobile body 11 is along the X-axis direction.

[0044] There is no particular limitation on the number of wheels 11r provided on the moving body 11. As described above, as long as the moving body 11 can be moved in the X-axis direction while maintaining a constant distance in the Z-axis direction between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected, the number of wheels 11r may be one, or multiple, such as two, three, or four or more.

[0045] Furthermore, the structure of the mobile body 11 is not particularly limited as long as it can maintain a constant distance HM in the Z-axis direction between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected and can smoothly move along the X-axis direction on the surface CF of the concrete structure C to be inspected. In the above example, the mobile body 11 has wheels 11r, 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 11 along this guide rail or the like. Note that maintaining a constant distance HM in the Z-axis direction between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected also includes a case where the distance HM between them varies by about 5 mm when the mobile body 11 moves along the surface CF of the concrete structure C.

[0046] <Magnetic generator 12> The magnetic force generator 12 has a function of magnetizing the inspection object P buried in the concrete structure C. Specifically, the magnetic force generator 12 has a function of magnetizing the inspection object P to such an extent that the magnetic flux leaking from the magnetized inspection object P (i.e., the magnetic flux leaking from the surface CF of the concrete structure C) can be measured by the magnetic sensor 6 of the magnetic flux density measuring unit 5 of the nondestructive inspection device 1 after a certain period of time (e.g., within 30 minutes) has elapsed since the inspection object P was magnetized by the magnetic force generator 12. In other words, the magnetic force generator 12 has a function of magnetizing the inspection object P so that the intensity of the magnetic flux density measured by the magnetic sensor 6 of the magnetic flux density measuring unit 5 of the nondestructive inspection device 1 after a certain period of time has elapsed since the inspection object P was magnetized by the magnetic force generator 12 is strong enough to enable the analysis described below. For example, an electromagnet or a permanent magnet can be used as the magnetic force generator 12. In particular, by using an electromagnet, the test object P, etc. can be magnetized only when necessary, which makes it easier to prevent errors in analysis using the measured magnetic flux density due to the effects of unnecessary magnetization, etc.

[0047] The magnetic force generator 12 is provided on the movable body 11 so that both magnetic poles (N pole and S pole) are aligned along the direction of movement of the movable body 11. Moreover, the magnetic force generator 12 is provided on the movable body 11 so that the distances from both magnetic poles to the surface CF of the concrete structure C to be inspected are both distances HM.

[0048] The magnetizer that magnetizes the inspection object P is not limited to the magnetizer 10 described above, and various magnetizers can be used. For example, a general permanent magnet may be moved manually in the first movement direction and the second movement direction. Furthermore, the inspection object P may be magnetized by an autonomous mobile robot or the like that has a permanent magnet or an electromagnet.

[0049] <Non-destructive inspection method of this embodiment> A method for inspecting the wall-reduced state CR of 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 surface. Of course, even if the surface CF of the concrete structure C to be inspected is a vertical surface or an inclined surface, the wall-reduced state CR of the inspection object P can be inspected in a similar manner using the non-destructive inspection device 1 of this embodiment.

[0050] <Measurement> First, the magnetizer 10 magnetizes the inspection object P embedded in the concrete structure C to be inspected. This magnetization is performed by moving the magnetizer 10 along a first movement direction D1 (see FIG. 2A) to magnetize the inspection object P, and then moving the magnetizer 10 along a second movement direction D2 (see FIG. 2B) that is opposite to the first movement direction to magnetize the inspection object P. Specifically, with the wheels 11r in contact with the surface CF of the concrete structure C, the magnetizer 10 is positioned so that the movement direction of the moving body 11 and the first direction of the inspection object P are parallel (in other words, so that the direction in which the north and south poles of the magnetic force generator 12 are aligned is parallel to the first direction of the inspection object P). Furthermore, the magnetizer 10 is positioned so that the north pole of the magnetic force generator 12 is positioned forward of the movement direction of the first movement direction D1. In this state, the wheels 11r of the magnetizer 10 are rolled to move the magnetizer 10 in the first movement direction D1 and the second movement direction D2. That is, the magnetizer 10 is moved back and forth along the first direction of the inspection object P with the N pole of the magnetic force generator 12 facing in the same direction (facing right in FIG. 2). Then, the inspection object P can be magnetized by the magnetic force generator 12 while maintaining a constant distance HM in the Z-axis direction between the magnetic force generator 12 and the surface CF of the concrete structure C to be inspected.

[0051] Note that there is no particular limitation on the number of times magnetization is performed by magnetizer 10, that is, the number of times magnetizer 10 is moved back and forth along the first direction of inspection object P. At least one reciprocating movement is sufficient. Furthermore, magnetization may be performed with either the north pole or south pole of the magnetic force generator 12 positioned ahead of the magnetizer 10 in the movement direction, but as mentioned above, the magnetizer 10 must be moved with each pole of the magnetic force generator 12 facing the same direction. In other words, when moving the magnetizer 10 in the first movement direction D1 and when moving the magnetizer 10 in the second movement direction D2, the magnetizer 10 must be moved so that the magnetic pole positioned ahead of the magnetizer 10 in the movement direction is opposite.

[0052] After magnetizing the inspection target P by the magnetizer 10, the moving body 2 of the nondestructive 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 moving body 2 is placed so that the moving direction of the moving body 2 is parallel to the first direction of the inspection target P.

[0053] When the moving body 2 is placed, a measurement start signal is input by an operation button or the like, and the moving body 2 is moved in the first moving direction D1 (the positive direction of the X-axis direction) along the first direction of the inspection target P. Then, the magnetic flux density along the moving path of the magnetic sensor 6 is measured by the magnetic sensor 6 of the magnetic flux density measurement unit 5. That is, the magnetic flux density along the first direction of the inspection target P at the position of the magnetic sensor 6 is measured. And the measured value of the magnetic flux density measured by the magnetic sensor 6 is stored in the storage function in association with the measurement position and the measurement time.

[0054] Then, when the moving body 2 is moved by the distance for inspecting the inspection target P, that is, the area for inspecting the inspection target P, the measurement ends.

[0055] <Analysis> When the measurement by the magnetic sensor 6 of the magnetic flux density measurement unit 5 ends, the thinning situation of the inspection target P is analyzed using the measured magnetic flux density.

[0056] The analysis function has a function of estimating the thinning situation of the inspection target P by analyzing the variation along the first direction (the X-axis direction in Fig. 1) of the magnetic flux density measured by the magnetic sensor 6. Specifically, it has a function of estimating the amount of thinning of the inspection target P. The thinning of the inspection target P can be estimated respectively based on the variation of the magnetic flux density in the X-axis direction along the first direction of the magnetic flux density and the variation of the magnetic flux density in the Z-axis direction (the third direction) along the first direction of the magnetic flux density.

[0057] <Estimation by variation of magnetic flux density in X-axis direction> The thinning state 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.

[0058] First, based on the magnetic flux density in the X-axis direction obtained by measurement, a variation curve Bx(X) of the magnetic flux density in the X-axis direction is created, which shows the relationship between the measured value of the magnetic flux density in the X-axis direction at each position and the measurement position in the first direction (see Figure 5(A)).

[0059] Note that, since the measured value of the magnetic flux density in the X-axis direction may contain disturbances such as noise, processing may be performed to remove the effects of noise and mitigate fluctuations in the magnetic flux density in the X-axis direction depending on the position. For example, the magnetic flux density in the X-axis direction at each position may be corrected using a moving average, filtering, or other methods for the fluctuation curve Bx(X) of the magnetic flux density in the X-axis direction.

[0060] Once the magnetic flux density variation curve Bx(X) in the X-axis direction (hereinafter sometimes referred to simply as the "X-axis variation curve Bx(X)") is created, a polynomial approximation curve Pxn(x) (where n is the degree of the polynomial approximation curve) of this X-axis variation curve Bx(X) is created. Figure 5(B) is an example of a sixth-order polynomial approximation curve Px6(x). Once the polynomial approximation curve Pxn(x) is created, the value of this polynomial approximation curve Pxn(x) is subtracted from the X-axis variation curve Bx(X) to create the X-axis modified variation curve fxn(x). In other words, the value of the polynomial approximation curve Pxn(x) at the corresponding position is subtracted from the value of the X-axis variation curve Bx(X) to create the X-axis modified variation curve fxn(x). 5(C) and 6 are examples of the corrected X-axis fluctuation curve fx6(x) obtained by subtracting the sixth-order polynomial approximation curve Px6(x) from the X-axis fluctuation curve Bx(X).

[0061] When the X-axis direction correction fluctuation curve fxn(x) is created, the square value is calculated at each position of the X-axis direction correction fluctuation curve fxn(x), and the X-axis direction correction fluctuation squared curve fxn(x) is calculated based on the square value at each position. 2 (Hereafter, simply "fxn(x) 2 ) is created. Note that Figure 7 shows the X-axis direction corrected fluctuation square curve fx6(x) created from the 6th-order X-axis direction corrected fluctuation curve fx6(x). 2 This is an example.

[0062] fxn(x) 2Once created, the given interval fxn(x) 2 The integral value of the x-axis direction is calculated (hereinafter simply referred to as "fxn(x) 2 (Integral) This fxn(x) 2 The integral is, for example, fx6(x) in a predetermined section in the graph of FIG. 2 and the X axis. And, fxn(x) in a given interval 2 fxn(x) is the integral divided by the length of the given interval L 2 Calculate the average and use this fxn(x) 2 The amount of thinning of the inspection object P is estimated using the average. Specifically, the previously calculated fxn(x) 2 The average cross-sectional loss rate S of the inspection object P is calculated using the thinning estimation formula (2) obtained from the regression line (1) showing the correlation between the average and the thinning amount of the inspection object P (see Figure 11(A)). Regression line (1) fxn(x) 2 Average=a×S+b Thickness reduction estimation formula (2) S=(fxn(x) 2 Average-b) / a a, b: constants determined by experiment, etc. n: Degree of polynomial approximation curve

[0063] As described above, according to the non-destructive testing method of this embodiment, even if thinning that does not lead to fracture occurs in the test object P embedded in the concrete structure C, it is possible to estimate the state of the thinning. In other words, it is possible to estimate the average cross-sectional loss rate S that represents the amount of thinning in the test object P.

[0064] In this specification, the cross-sectional loss ratio refers to the ratio (D / A) of the cross-sectional area D of the thinned portion to the cross-sectional area A of the inspection object P where no loss has occurred, in a cross section that intersects with the axial direction (first direction) of the inspection object P. In other words, it is a value that indicates the amount of thinning (thickness reduction ratio) of the inspection object P. The average cross-sectional loss ratio S refers to the average value of the cross-sectional loss ratios in a predetermined section in the axial direction of the inspection object P, and is a value that indicates the degree of thinning that has occurred in the predetermined section.

[0065] The predetermined section is a portion of the inspection object P that is considered to be free of factors (abnormal factors) that affect the magnetic flux density other than thinning. For example, if the inspection object P is a rebar, the predetermined section can be an area that is a certain distance from its end. Also, if there is a magnetic body around the inspection object P or if the inspection object P itself has protrusions or attachments, the area where these exist becomes a section where an abnormal factor exists, and the predetermined section can be an area that is a certain distance from this section.

[0066] <Calculation of regression line (1)> The regression line (1) described above can be formed based on experimental results obtained using a test structure. The experiment using the test structure can be carried out as follows.

[0067] For example, a test object is created by simulating thinning of the wall of an inspection object equivalent to the inspection object P that is actually embedded in the concrete structure C that will be inspected.The test object is then installed in the test structure so that it is in a substantially similar embedded state to the concrete structure that will be inspected.In other words, the test object is installed in the test structure so that the cover depth and arrangement are the same as those of the concrete structure C that will be inspected.

[0068] For this test structure, fxn(x) is calculated using the same procedure as in the non-destructive inspection method of this embodiment described above. 2 A test is conducted to calculate the average. This test is conducted by changing the test object installed in the test structure. In other words, the state of simulated thinning formed in the test object is changed, and fxn(x) 2 A test to calculate the average is performed on the test structure. If this test is performed on multiple test structures, that is, multiple test structures with different wall thinning conditions, the fxn(x) obtained from the tests on these multiple test structures can be calculated. 2 Based on the average and the average cross-sectional loss rate S of the test object, fxn(x) 2A regression line (1) showing the correlation between the average and the average cross-sectional loss rate S can be obtained, and the metal loss estimation formula (2) can be obtained.

[0069] For example, a plurality of test objects, each made of steel with a thickness of 9.0 mm and a length of 500 mm, are prepared with different states of thinning. For example, test objects with thinning lengths of 0 mm (wedge-shaped), 100 mm, and 200 mm and cross-sectional loss rates of 0%, 25%, 50%, and 75% are prepared (see FIG. 4). These test objects are then placed on the test structure so that the distance HX from their central axes to the surface of the test structure is 20 mm. For this test structure, fxn(x) is calculated using the same procedure as in the non-destructive inspection method of this embodiment described above. 2 A test is carried out to calculate the average. The test structure with the test object installed is arranged as shown in Figure 1 to measure the magnetic flux density. Once the magnetic flux density is measured, the modified variation squared curve fxn(x) 2 is calculated (see Figure 7). At this time, fxn(x) is calculated by measuring the magnetic flux density leaking from the end of the test object. 2 Since averaging can cause problems in determining wall thinning, when testing a test structure, a certain section from the end of the test object is used as the specified section, and in the case of the above-mentioned test object, a 300 mm section excluding a 100 mm section from each end is used. fxn(x) 2 Once the average is calculated, fxn(x) 2 The correlation between the average and the average cross-sectional loss rate S is confirmed. For example, fx6(x) obtained by using a sixth-order polynomial approximation curve Px6(x) is 2 Since the relationship shown in FIG. 11(A) can be obtained between the average and the average cross-sectional loss rate S, a regression line (1) can be calculated based on this relationship, and the wall thinning estimation formula (2) can be obtained from this regression line (1). 2 By applying the average to the wall thinning estimation formula (2), the average cross-sectional loss rate S of the inspection object P embedded in the concrete structure C that is actually being inspected, i.e., the wall thinning state, can be obtained.

[0070] When conducting a test to calculate the regression line (1) as described above, it is desirable to conduct the test multiple times on test objects with the same wall thinning length and cross-sectional loss rate. 2 By using the average of the averages, it is possible to reduce variations due to measurement, and therefore to improve the estimation accuracy of the average cross-sectional defect rate S of the test object P calculated from the obtained regression line (1). Note that Figure 11(A) shows the fx6(x) calculated using the sixth-order polynomial approximation curve Px6(x) obtained by performing tests under each condition, that is, two tests on the same test object. 2 The graph is generated using the averages, and the regression line (1) is calculated based on this graph.

[0071] In general, the magnetic permeability of dry concrete is nearly the same as that of air, so the test structure does not necessarily have to be a structure in which the test object is embedded in concrete; a pseudo-concrete-embedded structure can also be used as the test structure. Examples of pseudo-concrete-embedded structures include test structures in which the test object is simply installed to have a predetermined structure and shape, i.e., a structure in which the test object is installed in an exposed state, or a structure in which the test object is installed to have a predetermined structure and shape and a member (e.g., a plate-shaped member) is provided to cover the test object. In the case of a structure in which a member is provided to cover the test object, the surface of the member covering the test object corresponds to the surface of the concrete in a test structure in which the test object is embedded in concrete.

[0072] <About polynomial approximation> As described above, a fourth to ninth degree polynomial approximation curve can be used as the polynomial approximation curve to be subtracted from the X-axis direction variation curve to create the X-axis direction correction variation curve. As shown in FIGS. 12 to 15, when a third to tenth degree polynomial approximation curve is used as the polynomial approximation curve to create the X-axis direction correction variation curve, fxn(x) 2 When checking the correlation between the average and the average cross-sectional loss rate S, when using a 4th to 9th degree polynomial approximation curve, fxn(x) 2The correlation coefficient between the average and the average cross-sectional loss rate S is 0.8 or more. When using a polynomial approximation curve of the 4th to 7th order, fxn(x) 2 The correlation coefficient between the average and the average cross-sectional loss rate S is 0.9 or more. When using a polynomial approximation curve of the 6th and 7th order, fxn(x) 2 The correlation coefficient between the average and the average cross-sectional loss rate S is 0.95 or more. Therefore, for the polynomial approximation curve for creating the corrected variation curve, a polynomial approximation curve of the 4th to 9th order can be adopted, preferably a polynomial approximation curve of the 4th to 7th order, and more preferably a polynomial approximation curve of the 6th or 7th order.

[0073] <Estimation based on the variation of the magnetic flux density in the Z-axis direction> Based on the variation of the magnetic flux density in the Z-axis direction along the first direction of the magnetic flux density, the amount of material removal of the inspection target P can also be estimated by the following method.

[0074] First, based on the measured magnetic flux density in the Z-axis direction, a variation curve Bz(X) of the magnetic flux density in the Z-axis direction showing the relationship between the measured value of the magnetic flux density in the Z-axis direction at each position and the measurement position in the first direction is created (see Fig. 8(A)). Then, the Z-axis direction variation curve Bz(X) is differentiated once to create a Z-axis direction differential curve dBz(X) / dx (see Fig. 8(B)).

[0075] Note that since the measured value of the magnetic flux density may include disturbances such as noise, a process of removing the influence of noise and the like and relaxing the variation depending on the position of the magnetic flux density in the Z-axis direction may be performed. For example, the magnetic flux density at each position may be corrected for the Z-axis direction variation curve Bz(X) by methods such as moving average or filtering. This process is preferably performed before differentiating the Z-axis direction variation curve Bz(X) once, but a process of relaxing the variation may also be performed on this Z-axis direction differential curve dBz(X) / dx after creating the Z-axis direction differential curve dBz(X) / dx.

[0076] Once the Z-axis direction differential curve dBz(X) / dx is created, a polynomial approximation curve Pzn(x) (n is the degree of the polynomial approximation curve) of this Z-axis direction differential curve dBz(X) / dx is created. Figure 8(C) shows an example of a sixth-order polynomial approximation curve Pz6(x). Once the polynomial approximation curve Pz6(x) is created, the value of this polynomial approximation curve Pz6(x) is subtracted from the Z-axis direction differential curve dBz(X) / dx to create the Z-axis direction corrected fluctuation curve fzn(x). In other words, the value of the polynomial approximation curve Pz6(x) at the corresponding position is subtracted from the value of the Z-axis direction differential curve dBz(X) / dx to create the Z-axis direction corrected fluctuation curve fzn(x). 8(D) and 9 are examples of the Z-axis direction corrected fluctuation curve fz6(x) obtained by subtracting the sixth-order polynomial approximation curve Pz6(x) from the Z-axis direction differential curve dBz(X) / dx.

[0077] When the Z-axis direction correction fluctuation curve fzn(x) is created, a square value is calculated at each position of the Z-axis direction correction fluctuation curve fzn(x), and the Z-axis direction correction fluctuation square curve (hereinafter simply referred to as "fzn(x)") is calculated based on the square value at each position. 2 ) is created. Note that Figure 10 shows the Z-axis direction corrected fluctuation squared curve fz6(x) created from the sixth-order Z-axis direction corrected fluctuation curve fz6(x). 2 This is an example.

[0078] fzn(x) 2 Once created, fzn(x) in the given interval 2 The integral value is calculated (hereinafter simply referred to as "fzn(x) 2 (Integral) This fzn(x) 2 The integral is, for example, fz6(x) in a predetermined section in the graph of FIG. 2 and the X axis. And, fzn(x) in a given interval 2 fzn(x) is the integral divided by the length of the given interval L 2 Calculate the average and use this fzn(x) 2 The average is used to estimate the amount of thinning of the inspection object P. Specifically, the previously calculated fzn(x) 2The average cross-sectional loss rate S of the inspection object P is calculated using the thinning estimation formula (4) obtained from the regression line (3) showing the correlation between the average and the thinning amount of the inspection object P (see Figure 11(B)). Regression line (3) fzn(x) 2 Average=a×S+b Thickness reduction estimation formula (4) S=(fzn(x) 2 Average-b) / a a, b: constants determined by experiment, etc. n: Degree of polynomial approximation curve

[0079] As described above, according to the non-destructive inspection method of this embodiment, even if the inspection object P embedded in the concrete structure C has experienced thinning that does not lead to fracture, the state of thinning can be estimated using the magnetic flux density in the Z-axis direction. In other words, the average cross-sectional loss rate S, which represents the amount of thinning of the inspection object P, can be estimated.

[0080] <Calculation of regression line (3)> The regression line (3) described above can be formed based on experimental results obtained using a test structure. The experiment obtained using the test structure can be carried out as follows.

[0081] For example, a test object is created by simulating thinning of the wall of an inspection object equivalent to the inspection object P that is actually embedded in the concrete structure C that will be inspected.The test object is then installed in the test structure so that it is in a substantially similar embedded state to the concrete structure that will be inspected.In other words, the test object is installed in the test structure so that the cover depth and arrangement are the same as those of the concrete structure C that will be inspected.

[0082] For this test structure, fzn(x) is calculated using the same procedure as in the non-destructive inspection method of this embodiment described above. 2 A test is conducted to calculate the average. This test is conducted by changing the test object installed in the test structure. In other words, the state of simulated thinning formed in the test object is changed, and fzn(x) 2A test to calculate the average is performed on the test structure. If this test is performed on multiple test structures, that is, multiple test structures with different wall thinning conditions, the fzn(x) obtained from the tests on these multiple test structures can be calculated. 2 Based on the average and average cross-sectional defect rate S, fzn(x) 2 A regression line (3) showing the correlation between the average and the average cross-sectional loss rate S can be obtained, and the metal loss estimation formula (4) can be obtained.

[0083] For example, a plurality of test objects, each made of steel with a thickness of 9.0 mm and a length of 500 mm, are prepared with different states of thinning. For example, test objects with thinning lengths of 0 mm (wedge-shaped), 100 mm, and 200 mm and cross-sectional loss rates of 0%, 25%, 50%, and 75% are prepared (see FIG. 4). These test objects are then placed on the test structure so that the distance HX from their top surfaces to the surface of the test structure is 20 mm. For this test structure, fzn(x) is calculated using the same procedure as in the nondestructive inspection method of this embodiment described above. 2 A test is carried out to calculate the average. The test structure with the test object installed is arranged as shown in Figure 1 to measure the magnetic flux density. Once the magnetic flux density is measured, the modified fluctuation squared curve fzn(x) 2 is calculated (see Figure 10). At this time, fzn(x) is calculated by measuring the magnetic flux density leaking from the end of the test object. 2 Since averaging can cause problems in determining wall thinning, when testing a test structure, a certain section from the end of the test object is used as the specified section, and in the case of the above-mentioned test object, a 300 mm section excluding a 100 mm section from each end is used. fzn(x) 2 Once the average is calculated, fzn(x) 2 The correlation between the average and the average cross-sectional loss rate S is confirmed. For example, fz6(x) obtained by using the sixth-order polynomial approximation curve Pz6(x) is 2Since the relationship shown in FIG. 11(B) can be obtained between the average and the average cross-sectional loss rate S, a regression line (3) can be calculated based on this relationship, and the wall thinning estimation formula (4) can be obtained from this regression line (3). fzn(x) obtained by carrying out the non-destructive inspection method of this embodiment described above on the concrete structure C to be actually inspected is 2 By applying the average to the wall thinning estimation formula (4), the average cross-sectional loss rate S of the inspection object P embedded in the concrete structure C that is actually being inspected, i.e., the wall thinning state, can be obtained.

[0084] When conducting a test to calculate the regression line (3) as described above, it is desirable to conduct the test multiple times for the same test object with the same wall thinning length and cross-sectional loss rate. 2 By using the average of the averages, it is possible to reduce the variation due to the measurement, and therefore it is possible to improve the estimation accuracy of the average cross-sectional defect rate S of the test object P calculated from the obtained regression line (3). Note that in Figure 11(B), fz6(x) calculated using the sixth-order polynomial approximation curve Pz6(x) obtained by performing tests under each condition, that is, two tests on the same test object, is used. 2 The graph is formed using the average of the means, and the regression line (3) is calculated based on this graph.

[0085] In general, the magnetic permeability of dry concrete is nearly the same as that of air, so the test structure does not necessarily have to be a structure in which the test object is embedded in concrete; a pseudo-concrete-embedded structure can also be used as the test structure. Examples of pseudo-concrete-embedded structures include structures in which the test object is simply installed to have a predetermined structure and shape, i.e., a structure in which the test object is installed in an exposed state, or a structure in which the test object is installed to have a predetermined structure and shape and a member (e.g., a plate-shaped member) is provided to cover the test object. In the case of a structure in which a member is provided to cover the test object, the surface of the member covering the test object corresponds to the surface of the concrete in a test structure in which the test object is embedded in concrete.

[0086] <About polynomial approximation> As described above, a fourth to ninth degree polynomial approximation curve can be used as the polynomial approximation curve to be subtracted from the Z-axis direction differential curve to create the Z-axis direction correction fluctuation curve. As shown in FIGS. 16 to 19, when a third to tenth degree polynomial approximation curve is used as the polynomial approximation curve to create the Z-axis direction correction fluctuation curve, fzn(x) 2 When checking the correlation between the average and the average cross-sectional loss rate S, when using a 4th to 9th degree polynomial approximation curve, fzn(x) 2 The correlation coefficient between the average and the average cross-sectional loss rate S is 0.8 or more. When a polynomial approximation curve of degree 4 to 7 is used, fzn(x) 2 The correlation coefficient between the average and the average cross-sectional loss rate S is 0.95 or more. Therefore, a polynomial approximation curve of the fourth to ninth degree can be used as the polynomial approximation curve for creating the corrected variation curve, a polynomial approximation curve of the fourth to seventh degree is preferably used, and a polynomial approximation curve of the fourth or fifth degree is more preferably used. [Industrial Applicability]

[0087] The non-destructive inspection method of the present invention is suitable as a method for estimating the state of thinning of reinforcing bars, steel rods, steel wires, etc. installed within a concrete structure. [Explanation of symbols]

[0088] 1. Non-destructive testing equipment 2. Mobile 5 Magnetic flux density measurement section 6 Magnetic Sensors 10 Magnetizer 11 Mobile 12 Magnetic generator B Central axis of moving body 2 C. Concrete structures CF Surface of concrete structure C P Inspection subject CR thinning

Claims

1. A method for estimating damage to an inspection object embedded in a concrete structure, the inspection object extending in a first direction, by measuring a magnetic flux density outside the concrete structure and estimating damage to the inspection object based on fluctuations in the measured magnetic flux density, the method comprising: a magnetizer is moved in a first movement direction along a first direction of the object to be inspected and in a second movement direction opposite to the first movement direction to magnetize the object to be inspected, and then a magnetic flux density measuring unit that measures a magnetic flux density is moved in the first movement direction to measure the magnetic flux density; creating a variation curve of the magnetic flux density along the first direction of the test object based on the measured magnetic flux density; A polynomial approximation curve of the fluctuation curve is created; A corrected fluctuation curve is created by subtracting the polynomial approximation curve from the fluctuation curve; A modified variation squared curve is created by squaring the modified variation curve, and a state of thinning of the inspection object is estimated based on the modified variation squared curve. A non-destructive inspection method characterized by:

2. An integral value of a predetermined section of the corrected fluctuation square curve is calculated, and the amount of thinning of the inspection object is estimated based on the corrected fluctuation mean square value, which is a value obtained by dividing the integral value by the length of the section in which the integral value was calculated.

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

3. The variation curve is a variation curve formed based on a first direction magnetic flux density, which is a magnetic flux density along a first direction of the test object; 2. The non-destructive inspection method according to claim 1.

4. The polynomial approximation curve is The curve is formed based on any of the 4th to 7th order approximations of the fluctuation curve.

4. The non-destructive inspection method according to claim 3.

5. A variation curve of magnetic flux density along a first direction of the object to be inspected, A third direction differential curve is used, which is a first-order differential of a variation curve of the magnetic flux density formed along the first direction of the inspection object based on a third direction magnetic flux density, which is a magnetic flux density in a normal direction of the surface of the concrete structure.

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

6. The polynomial approximation curve is The third directional differential curve is a curve formed based on any one of the fourth to seventh order approximations.

6. The non-destructive inspection method according to claim 5.

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