A method for detecting corrosion of steel bars inside cement covers based on a TMR array

Abstract

The present invention relates to a method for detecting the corrosion of steel bars in a cement cover plate based on a TMR array, belonging to the field of electromagnetic measurement. In this method, the electromagnetic characteristics of the steel bars in the cement cover plate are simulated and analyzed by COMSOL software. The basic method selects the finite element analysis method, and the magnetic field solver is selected in the solver. According to the literature and simulation results, the influence of steel bar corrosion on its electromagnetic characteristics is analyzed, and a typical value of steel bar corrosion is proposed. The present invention designs a system for detecting the corrosion of steel bars in a cement cover plate based on a TMR array, measures the magnitude of the magnetic induction intensity in the measurement space, and constructs a magnetic induction intensity surface by interpolation. On this basis, the surface is integrated, and the corrosion degree of the steel bar is judged by the magnitude of the integral value.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic measurement and relates to a method for detecting steel bar corrosion in a cement cover plate based on a TMR array. Background Art

[0002] Cement cover is a common reinforced concrete structure in our daily life. The quality of its internal steel bars (rust condition) directly determines its ability to resist compression and impact. However, after long-term operation, it is affected by environmental changes or human damage, resulting in corrosion of internal steel bars, which poses a huge safety hazard. At present, the policy of regular replacement is adopted for cement cover, resulting in the replacement of some cement cover that are still in service, causing unnecessary waste. Therefore, timely detection of the degree of steel corrosion in cement cover is an important issue that needs to be solved in engineering at this stage.

[0003] At present, there are many methods for detecting steel corrosion. According to whether the protective layer of the cement cover is damaged during the detection process, it can be divided into two categories: destructive testing and non-destructive testing. Destructive testing requires peeling off the protective layer of the cement cover, observing the corrosion of the internal steel bars with the naked eye, or measuring the diameter of the internal steel bars after rust removal to judge the corrosion, which causes irreversible damage and is generally not used. Non-destructive testing is widely used due to its non-destructive nature. According to the detection principle, non-destructive testing is divided into three categories: analytical method, electrochemical method and physical method. The analytical method is to conduct a comprehensive analysis of various factors in the environment where the steel bars are located, and the reliability is relatively low; the electrochemical method is to judge the corrosion of the internal steel bars by the change of a certain parameter in the electrolyte solution system of the cement cover, which can be used to estimate the probability of steel bar corrosion, but cannot accurately judge whether the steel bars have already rusted; in the physical method, electromagnetic non-destructive testing has become the focus of research in recent years because it does not require coupling agents and the measurement device is lower in cost than other methods.

[0004] At present, the magnetic sensors used in electromagnetic nondestructive testing mainly include induction coils, Hall elements, anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), etc. Induction coil measurement cannot detect static and slowly changing magnetic fields, and has low sensitivity to low-frequency alternation; Hall sensors have high power consumption and poor linearity; AMR elements have a narrow linear range and complex manufacturing process; GMR elements have a small linear range.

[0005] The methods using magnetic field detection have emerged in an endless stream, but the research objects are mostly RC structures in roads and bridges, which are different from the steel bars in cement covers. Therefore, the present invention proposes a method for detecting the corrosion of steel bars in cement covers based on a TMR (Tunnel Magnetoresistive) array. The TMR element has high sensitivity, low power consumption, good linearity, and a simple structure; its working range is 0.001 - 200 Gs, the resolution can reach 0.1 mGs, the power consumption is small, the signal-to-noise ratio is high, and it has better temperature stability, higher sensitivity, and lower power consumption compared with other elements. And because the TMR sensor is small in size, only 0.5 * 0.5 mm. The number of arrangements in the same volume is much larger than that of other sensors. Composing the TMR elements into a sensor array to measure the magnetic induction intensity in space can effectively improve the resolution of later imaging.

[0006] In summary, the TMR sensor has high sensitivity and high resolution, can accurately measure magnetic parameters, greatly improves the detection accuracy, and can replace traditional sensors to detect the corrosion of steel bars in cement covers. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a method for detecting the corrosion of steel bars in cement covers based on a TMR array.

[0008] To achieve the above purpose, the present invention provides the following technical solutions:

[0009] A method for detecting the corrosion of steel bars in cement covers based on a Tunnel Magnetoresistive (TMR) array, the method comprising the following steps:

[0010] S1: Establish a simulation model of the cement cover;

[0011] S2: Analyze the electromagnetic characteristics of steel bar corrosion;

[0012] S3: Calculate and judge the corrosion degree of steel bars in the cement cover.

[0013] Optionally, the specific content of S1 is:

[0014] Build a simulation for a unit grid of the cement cover; the thickness of the simulated model of the cement cover is 30 mm, the diameter of the main steel bar is 12 mm, the length is 200 mm, the distance between every two main steel bars is 60 mm, the diameter of the stirrup is 3 mm, the length is 80 mm, and it is arranged perpendicular to the main steel bar; the cuboid outside the steel bar is concrete, and the relative magnetic permeability of the steel bar is selected as 4000;

[0015] Select a circular multi-turn coil as the magnetic field excitation source to generate a constant magnetic field; the number of turns of the coil is 1000, and an excitation signal with a current of 1 A is applied; the measurement point is selected on the surface of the cement cover, 15 mm away from the center of the steel bar; the coil applies the excitation at a height of 20 mm from the measurement plane; a three-dimensional simulation physical model established by COMSOL.

[0016] Optionally, the S2 is specifically as follows:

[0017] The weight loss rate is manifested as the loss of the average cross-sectional area. The electromagnetic characteristics exhibited by a steel bar with a corrosion cross-sectional area of 0.9 times the original cross-sectional area of the steel bar and a corrosion length of a are used as the electromagnetic characteristics that need to be replaced. When the integral value I measured at a certain location is less than the integral value of the corroded steel bar and the weight loss rate within the range exceeds 10%, it is considered that the steel bar needs to be replaced.

[0018] Optionally, the S3 is specifically as follows:

[0019] The surface is fitted by the interpolation method based on the detection values of the TMR array, and the corrosion degree of the steel bar is judged by the integral value of the surface. The TMR array measures the magnetic induction intensity at 25 points, and the surface is constructed by the interpolation method. The bicubic interpolation algorithm uses the values of 16 nearby known data points to estimate the value of the point to be measured. Due to the corrosion of the steel bar, the magnetic induction intensity at the measurement point shows different degrees of decrease. And a method for judging the corrosion situation based on the surface integral value is proposed.

[0020] Let the interpolation point coordinates be (x i , y j ), 1 ≤ i, j ≤ n, and the function value obtained by interpolation is f(x i , y j ); Δs is the area of the corresponding area element, and the integral value is:

[0021]

[0022] It is the sum of the volumes of the curved-top cylinders corresponding to each small area element;

[0023] Under the conditions of this simulation model, the integral value of the non-corroded steel bar is 143.4015, and the integral value of the corroded steel bar is 141.3025. If the integral value measured in actual detection is lower than this, it is considered that the steel bar needs to be replaced.

[0024] The beneficial effects of the present invention are as follows: An array composed of high-sensitivity and high-resolution TMR sensors is used to measure magnetic parameters, greatly improving the detection accuracy. The use of the function integral value for judgment is proposed, which can more comprehensively reflect the influence of steel bar corrosion on the space magnetic field. The present invention can conveniently and accurately detect the corrosion situation of the steel bars in the cement cover plate.

[0025] Other advantages, objectives, and features of the present invention will be described to some extent in the subsequent description, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. Description of the Drawings

[0026] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail and preferably below in conjunction with the drawings, where:

[0027] Figure 1 is the three-dimensional physical model of the steel bars and the detection device inside the cement cover plate;

[0028] Figure 2 is the magnetic field distribution diagram of the corroded steel bar under the excitation of the coil;

[0029] Figure 3 is the schematic diagram of the steel bar corrosion detection system inside the TMR cement cover plate;

[0030] Figure 4 is the schematic diagram of the TMR array;

[0031] Figure 5 is the fitting surface diagram of the presence or absence of steel bar corrosion. Detailed Embodiments

[0032] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0033] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as a limitation to the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which does not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0034] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and cannot be understood as a limitation of the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0035] The object of the present invention is to propose a method for detecting the corrosion of steel bars in cement covers based on a TMR array. First, the electromagnetic characteristics of the steel bars in the cement cover are simulated and analyzed by COMSOL software. The basic method selects the finite element analysis method, and the magnetic field solver is selected in the solver. According to the literature and simulation results, the influence of steel bar corrosion on its electromagnetic characteristics is summarized. The present invention designs a TMR array to measure the magnitude of the magnetic induction intensity in space, constructs a magnetic induction intensity surface by interpolation, and integrates the surface to judge the corrosion degree of the steel bar according to the magnitude of the integral value I.

[0036] (1) Establishment of the cement cover simulation model

[0037] The present invention conducts modeling and simulation on a unit grid of the cement cover. This simulation model is a unit possessed by general cement covers and can be extended to the mesh structure in actual projects. After preliminary research, some typical values commonly used in the project are selected. The thickness of the simulated model cement cover is 30 mm, the main bar diameter is 12 mm, the length is 200 mm, the distance between every two main bars is 60 mm, the stirrup diameter is 3 mm, the length is 80 mm, and it is arranged perpendicular to the main bars. The cuboid outside the steel bar is concrete, and the relative magnetic permeability of the steel bar is selected as 4000.

[0038] The present invention selects a circular multi-turn coil as the magnetic field excitation source to generate a constant magnetic field. The number of turns of the coil is 1000, and an excitation signal with a current of 1 A is applied. The measurement point is selected on the surface of the cement cover, 15 mm away from the center of the steel bar. Since the different degrees of steel bar corrosion are considered, the distance of the coil should not be too close to the measurement point, otherwise the influence degree of the steel bar on the magnetic field at the space measurement point will be reduced. The coil applies excitation at a height of 20 mm from the measurement plane. The three-dimensional simulation physical model established by COMSOL is as Figure 1 shown.

[0039] In the physical device, a TMR sensor is used to convert the value of the magnetic induction intensity into a voltage value for measurement. In the simulation, the magnetic induction intensity values of the point array in space can be directly calculated, and the corrosion is judged based on this result.

[0040] (2) Electromagnetic Characteristics Analysis of Reinforcement Corrosion

[0041] Magnetization refers to the phenomenon that under the action of a magnetic field, due to the alignment of magnetic moments in the material tending to be consistent, a certain magnetism is presented. The main component of the reinforcement in the cement cover plate is iron, so it also has this property. When the reinforcement is placed in a magnetic field, the molecular current in the iron material will be affected by the Lorentz force of the magnetic field, and its magnetic moment will deflect towards the external magnetic field direction, tending to be more orderly arranged, presenting magnetism externally, and showing a macroscopic magnetic moment to enhance the original magnetic field. The magnetization intensity M characterizes the magnetization strength of the medium at each point in the medium.

[0042] The parameters of the excitation coil, the iron content in the reinforcement (affected by the corrosion degree of the reinforcement), and the relative position of the reinforcement and the excitation coil will all affect the magnitude of the magnetization intensity, and thus affect the magnetic field distribution in space.

[0043] Due to reinforcement corrosion, its properties will also be very different. Reinforcement corrosion is manifested as a reduction in the effective cross-sectional area, thus bringing about a reduction in the ultimate bearing capacity and ductility of the reinforcement. The loss rate of the weakest cross-section reflects the maximum degree of corrosion on the reinforcement cross-sectional area, and this point is the weakest point of the reinforcement under stress. According to the literature, there is a linear relationship between the loss rate of the weakest cross-section of the reinforcement and the weight loss rate. When the weight loss rate of the corroded reinforcement exceeds 10%, the tensile strength at the weakest cross-section will not reach the minimum limit specified by the code. The requirements for the replacement strength of the reinforcement are different, and the corresponding corrosion degree of the reinforcement is also different. The present invention takes this index as the basis for judging the corrosion degree of the reinforcement. Reinforcement corrosion is actually a reduction in the iron content, and under the excitation of the coil magnetic field, the magnetization effect in space is different. As the corrosion degree increases, the magnetization effect gradually weakens. Figure 2 It is a simulation diagram of the influence on the magnetic induction intensity in space under the condition of reinforcement corrosion.

[0044] The weight loss rate is manifested as the loss of the average cross-sectional area. The electromagnetic characteristics shown by the reinforcement with a corroded cross-sectional area of 0.9 times the original reinforcement cross-sectional area and a corroded length of a are taken as a typical electromagnetic characteristic that needs to be replaced. When the integral value I measured by the detection device of the present invention at a certain place is less than the integral value of this typical corroded reinforcement, and the weight loss rate within this range exceeds 10%, it is considered that the reinforcement needs to be replaced.

[0045] Since the measurement plane is 15 mm away from the center of the reinforcement in the cover plate, it is not very far. Therefore, as the corrosion length a of the reinforcement surface increases, the influence on the TMR detection array will gradually weaken until it levels off. Through parametric scanning of the COMSOL software, when a ≥ 30 mm, the influence of the increase in the corrosion length on the integral value can be ignored. Therefore, the present invention selects a as 30 mm.

[0046] (3) TMR-based Reinforcement Corrosion Detection System for Cement Covers

[0047] As shown in Figure 3 , Figure 4, the hardware is based on a TMR array and an STM32 single-chip microcomputer, and consists of an excitation source, a power drive module, an excitation coil, a signal acquisition and conditioning amplification module, an LCD display, and an STM32 processor. When the system is powered on and working, the excitation source generates a current signal, and the amplified signal is input into the excitation coil through the power drive device, generating a constant magnetic field acting on the steel bar. Due to the magnetization effect, the steel bar will generate a secondary magnetic field, which is superimposed on the original magnetic field. A 5*5 equidistant array composed of TMR sensors is used to collect the magnitude of the magnetic induction intensity in space and convert it into a corresponding voltage signal, which is collected by the STM32 single-chip microcomputer through the signal amplification device after passing through the signal amplification device. Through preliminary analysis, the collected data is calculated to judge the position, corrosion degree, etc. of the steel bar.

[0048] This device selects the TMR2503 type sensor as the array detection element. The TMR2503 sensor contains 4 non-shielded high-sensitivity TMR sensor elements, and is designed with a push-pull type Wheatstone full-bridge structure, measuring the differential voltage signal as the sensor output. In the probe structure, the sensitive axis direction of the chip is placed in the same direction as the magnetic field generated by the coil to obtain the best detection effect. When in use, the TMR sensors are welded on the PCB board to form a sensor array. The spacing of the TMR sensors in this device is preset to 3mm. If you want to improve the measurement accuracy, you can increase the number of sensors and appropriately reduce the spacing of the sensor array. However, to avoid interference and capacitance generation, the minimum safe distance between chips in the design shall not be less than 0.3mm.

[0049] (4) Calculation and Judgment of the Corrosion Degree of Reinforcement in Cement Covers

[0050] This invention uses the TMR array to measure the magnetic induction intensity at 25 points and constructs a magnetic induction intensity distribution map at the spatial measurement plane, and judges the corrosion situation of the steel bar by calculating the integral I of the curved surface. Compared with measuring the magnetic induction intensity at one point, calculating the surface integral can more comprehensively reflect the influence of steel bar corrosion on the spatial magnetic field.

[0051] In this design, since the equation form of the magnetic induction intensity curved surface is unknown and the measurement accuracy of the TMR array is relatively high, using the interpolation method is more suitable for constructing the curved surface than the fitting function. Using the bicubic interpolation algorithm in MATLAB, the function value of the point to be measured is estimated through the data of the 25 measured points. The following is the formula derivation.

[0052] Suppose the coordinates of the point to be calculated on the known function are f(i+u, j+v), and the bicubic interpolation method obtains the function value of this point through the following formula

[0053] f(l + u, j + v) = A·B·C

[0054] Wherein,

[0055] A = [S(u + 1) S(u + 0) S(u - 1) S(u - 2)],

[0056]

[0057]

[0058]

[0059] Where S(x) is the co - function of the bicubic interpolation method. According to the calculation formula and the basis function S(x), we can obtain:

[0060] S(1 + x) = -(|x| - 2|x| 2 -|x| 3 ),

[0061] S(x) = (1 - |x|) + (|x| - 2|x| 2 +|x| 3 ),

[0062] If we let k = |x| - 2|x| 2 +|x| 3 , then we can get

[0063] S(1 + x) = -k, S(x) = (1 - |x|) + k

[0064] Where the role of k is the constraint effect on the interpolation point caused by the change rate of the function values of the points around the point to be interpolated. Due to using the information of a larger range of functions and adding the change rate constraint, the bicubic interpolation method has a higher interpolation quality.

[0065] The three - dimensional surface after interpolation is as shown in the appendix Figure 5 . As can be seen in the figure, due to the corrosion of the steel bars, the magnetic induction intensity at the measurement points shows different degrees of decrease. And as the corrosion degree increases, the height of the surface is also continuously decreasing. Thus, a method for judging the corrosion situation based on the surface integral value is proposed.

[0066] Since the surface is constructed by the interpolation method and the specific expression of the function is not obtained. When integrating, the most basic micro - element idea is adopted, that is, using the sum of the volumes of the curved - top cylinders to approximate the surface integral. Let the coordinates of the interpolation points be (x i , y j ), (1 < i, j ≤ n). The function value corresponding to this point is f(x i , y j ).

[0067] Then the integral value

[0068]

[0069] Since the purpose of this design is not to accurately calculate the integral, but to judge the relative magnitude of the integral values corresponding to corroded and uncorroded steel bars, and when the division of the area element is small enough, it is reasonable to approximate the integral using this method. When calculating, the coordinates of x and y can be calculated according to the unit coordinates.

[0070] Under the conditions of the present invention, the integral value of the uncorroded steel bar is 143.4015, and the integral value of the typical corroded steel bar mentioned above is 141.3025. If the measured integral value is lower than this in actual detection, it can be considered that the steel bar needs to be replaced.

[0071] Example:

[0072] (1) Refer to Figure 1 : Construction of the simulation model

[0073] Use COMSOL software for modeling and simulation. Use a circular multi-turn coil as the magnetic field excitation source to generate a constant magnetic field. The number of turns of the coil is 1000, and an excitation signal with a current of 1 A is applied. The measurement point is selected on the surface of the cement cover, 15 mm away from the center of the steel bar. The parameters of the cement cover are selected as some typical values commonly used in engineering. The thickness of the cement cover in the simulation model is 30 mm, the diameter of the main steel bar is 12 mm, the length is 200 mm, the distance between every two main steel bars is 60 mm, the diameter of the stirrup is 3 mm, the length is 80 mm, and it is arranged perpendicular to the main steel bar. The cuboid outside the steel bar is concrete, and the relative magnetic permeability of the steel bar is selected as 4000.

[0074] Based on this model, physical field simulation studies can be carried out by changing parameters such as the diameter, position, and coil excitation of the steel bar.

[0075] (2) Refer to Figure 2 : Analysis of the electromagnetic characteristics of steel bar corrosion

[0076] Under the excitation of an external magnetic field, the steel bar has a magnetization effect and will enhance the original magnetic field. Among them, the parameters of the excitation coil, the iron content in the steel bar (affected by the degree of steel bar corrosion), and the relative position of the steel bar and the excitation coil will all affect the magnitude of the magnetization intensity, and thus affect the magnetic field distribution in space. As Figure 2 shown, the presence of the steel bar and the degree of corrosion will have different effects on the magnetic field.

[0077] Due to steel corrosion, its properties will also vary greatly. Steel corrosion is manifested as a reduction in the effective cross-sectional area, resulting in a reduction in the ultimate bearing capacity and ductility of the steel bar. The loss rate of the weakest section reflects the maximum degree of corrosion on the cross-sectional area of the steel bar, and this point is the weakest point of the steel bar under stress. By analyzing the relationship between the weight loss rate of the steel bar and the loss rate of the weakest section, the present invention proposes a characteristic of typical steel bar corrosion. In practical applications, if the calculated integral value is less than the integral value corresponding to this typical corrosion, it is considered that the steel bar corrosion is relatively serious.

[0078] (3) See Figure 3 and Figure 4 : Reinforcement corrosion detection system based on TMR cement cover plate

[0079] The schematic diagram of the whole system is shown in Appendix Figure 3 、 4 as shown. This device uses the excellent-performance TMR2503 type sensor as the array detection element to detect the magnetic induction intensity. The spacing of the TMR sensors in the device is preset to 3 mm. If the measurement accuracy is improved, the number of sensors can be increased, and the spacing of each sensor can be appropriately reduced. In this way, the constructed curved surface will be more delicate.

[0080] A circular multi-turn coil is used to apply a magnetic field excitation to the steel bar. When the system works, the excitation source generates a current signal, and the amplified signal is input into the excitation coil through the power driving device, generating a constant magnetic field acting on the steel bar. Due to the magnetization effect, the steel bar will generate a secondary magnetic field, which is superimposed on the original magnetic field. The STM32 single-chip microcomputer then collects the amplified voltage signal, judges the position, corrosion degree, etc. of the steel bar after calculation and processing, and displays the results on the LCD screen.

[0081] (4) See Figure 5 : Calculation and judgment of the corrosion degree of the steel bar in the cement cover plate

[0082] The present invention uses the TMR array to measure the magnetic induction intensity at 25 points, and uses the interpolation method to construct the magnetic induction intensity value curved surface of the spatial measurement plane. By calculating the integral of the curved surface, the corrosion situation of the steel bar is judged. Compared with measuring the magnetic induction intensity at one point, calculating the surface integral can more comprehensively reflect the influence of steel bar corrosion on the spatial magnetic field.

[0083] The bicubic interpolation method is selected as the interpolation method used. This is a more complex interpolation method, which can create smoother image edges than bilinear interpolation. After constructing the magnetic field curved surface, the integral value of the curved surface is replaced by the volume sum of the curved-top cylinder using the calculus idea, making the calculation more convenient. And finally, the corrosion degree of the steel bar is judged using the calculated integral value.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for detecting the corrosion of steel bars in a cement cover plate based on a tunnel magnetoresistive (TMR) array, characterized in that: the method comprises the following steps: S1: Establish a simulation model of the cement cover plate; Perform modeling and simulation on a unit grid of the cement cover plate; the thickness of the simulated cement cover plate is 30 mm, the diameter of the main steel bars is 12 mm, the length is 200 mm, the distance between every two main steel bars is 60 mm, the diameter of the stirrups is 3 mm, the length is 80 mm, and they are arranged perpendicular to the main steel bars; the cuboid outside the steel bars is concrete, and the relative magnetic permeability of the steel bars is selected as 4000; Select a circular multi-turn coil as the magnetic field excitation source to generate a constant magnetic field; the number of turns of the coil is 1000, and an excitation signal with a current of 1 A is applied; the measurement point is selected on the surface of the cement cover plate, 15 mm away from the center of the steel bar; the coil applies the excitation at a height of 20 mm from the measurement plane; a three-dimensional simulation physical model established by COMSOL; S2: Electromagnetic characteristic analysis of steel bar corrosion; The weight loss rate is manifested as the loss of the average cross-sectional area. The electromagnetic characteristics exhibited by a steel bar with a corroded cross-sectional area of 0.9 times the original cross-sectional area of the steel bar and a corroded length of a are taken as the electromagnetic characteristics that need to be replaced; when the integral value I measured at a certain place during detection is less than the integral value of the corroded steel bar, and the weight loss rate within the range exceeds 10%, it is considered that the steel bar needs to be replaced; S3: Calculate and judge the corrosion degree of the steel bars in the cement cover plate; Use the interpolation method to fit a surface according to the detection values of the TMR array, and use the integral value of the surface to judge the corrosion degree of the steel bars; the TMR array measures the magnetic induction intensity at 25 points, and constructs a surface by interpolation; the bicubic interpolation algorithm uses the values of 16 known data points nearby to estimate the value of the point to be measured; due to the corrosion of the steel bars, the magnetic induction intensity at the measurement point shows different degrees of decrease; and a method for judging the corrosion situation according to the surface integral value is proposed accordingly; Let the coordinates of the interpolation points be (x i , y j ), where 1 ≤ i, j ≤ n, and the function value obtained by interpolation is f(x i , y j ); Δs is the area of the corresponding area element, and the integral value is: is the sum of the volumes of the curved-top cylinders corresponding to each small area element. Among them, let the interpolation point coordinates be (x i , y j )(1 ≤ i, j ≤ n), and the function values obtained by interpolation are f(x i , y j ); Δs is the area of the corresponding area element; Under the conditions of this simulation model, the integral value of the non-corroded steel bar is 143.4015, and the integral value of the corroded steel bar is 141.3025. If the integral value measured in actual detection is lower than this, it is considered that the steel bar needs to be replaced.

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