Electromagnetic ultrasonic / motion-induced eddy current composite detection system and detection method for high-speed train tracks

Abstract

The present invention discloses an electromagnetic ultrasonic / motion-induced eddy current composite detection system and detection method for high-speed train tracks, the system includes a detection probe, an electromagnetic ultrasonic signal generator receiver, a signal separation module, a drive module, a signal conditioning module and a signal acquisition and processing module; the method adopts an electromagnetic ultrasonic excitation mode, and considering the characteristics of the high-speed relative motion between the probe and the train track to excite the motion-induced eddy current, the detection coil signal is separated into an electromagnetic ultrasonic signal and a motion-induced eddy current signal, thereby obtaining a depth-signal characteristic quantity calibration curve of the track buried cracks and surface cracks, and finally based on the calibration curve, the buried / surface properties and depth values ​​of the track cracks to be detected are evaluated. The present invention can detect both buried and surface cracks in the track, is suitable for the detection of high-speed moving train tracks, and has great application prospects in the fields of rail transportation.

Description

Technical Field

[0001] The present invention relates to a track defect nondestructive detection system and method, and in particular to an electromagnetic ultrasonic / motion-induced eddy current composite detection system and method for high-speed train tracks. Background Art

[0002] my country has become the country with the largest scale of high-speed railway construction in the world. As a key component for carrying freight and passenger traffic, the strength and operating status of rails will affect the safety of railways. With the increase of running time, the operation of trains will inevitably cause surface defects such as rolling contact fatigue and rail head crushing on the rails. These hidden dangers will lead to accidents such as derailment during train operation, which will cause significant economic losses. In addition, since the track is affected by the locomotive load for a long time, the bending stress on the bottom of the rail is much greater than the stress on the rail head. Therefore, damage to the bottom of the rail is also an important factor in causing the rail to break and cause accidents. Therefore, efficient and real-time flaw detection of surface / buried cracks in rails is expected to achieve early prediction of potential accidents and prevent them before they happen.

[0003] At present, there are many methods for rail inspection, such as eddy current inspection, magnetic particle inspection, radiographic inspection, and ultrasonic inspection. However, each of these methods has its own advantages and disadvantages. Eddy current inspection is suitable for rail surface / near-surface crack detection. The detection depth is low, and the detection speed is limited to less than 70km / h, and high-speed detection is not possible. Magnetic particle inspection can only detect surface cracks, and magnetization and demagnetization are required during the inspection. The process is cumbersome and the detection efficiency is extremely low. Radiographic inspection only has a good detection effect on volume defects (pores, etc.), and has a poor detection effect on area defects (cracks, etc.). In addition, because it uses highly penetrating X-rays and other inspections, the equipment is generally large and has radiation. Piezoelectric ultrasound needs to carry a large amount of coupling agent, which seriously affects the detection speed. Electromagnetic ultrasound can avoid the use of coupling agent and has a faster detection speed, but the transduction efficiency is low, and it is more difficult to detect surface cracks. Overall, these methods cannot quickly and effectively achieve comprehensive detection of buried / surface cracks in rails. Summary of the invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide an electromagnetic ultrasonic / motion-induced eddy current composite detection system and detection method for high-speed train tracks, which has the advantages of fast detection speed and the ability to simultaneously detect buried / surface cracks, and can be widely used in non-destructive testing of high-speed train tracks.

[0005] In order to achieve the above purpose, the present invention adopts the following technical scheme:

[0006] An electromagnetic ultrasonic / motion-induced eddy current composite detection system for high-speed train tracks, comprising a detection probe 1 and a detection auxiliary device, wherein the detection probe 1 is composed of a permanent magnet 14 and a coil 15 connected to each other; the detection auxiliary device comprises a track to be inspected 2, a track inspection vehicle 3, a drive module 4 for driving the track inspection vehicle 3 forward, a track inspection mounting connector 10, a RAM-5000 instrument 5, a duplexer 6, a signal separation module 7, a signal conditioning module 8 and a signal acquisition and processing module 9; the track to be inspected 2 is laid flat on the ground, and the track inspection vehicle 3 is located directly above the track to be inspected 2 to ensure that the detection probe 1 will not deviate from the track to be inspected 2 during later detection; the roller 12 of the wheeled clamp is placed on the surface of the track to be inspected 2, and the detection probe 1 is placed in the clamp 13 in the middle of the wheeled clamp, and the wheeled clamp is fixed to one end of the track inspection mounting connector 10 through a shaft rod at its top, and a spring 11 is sleeved on the shaft rod, and the original length and rigidity of the spring 11 are selected The degree coefficient is used to ensure that the wheel 12 of the wheel fixture is always in contact with the surface of the track 2 to be inspected during the inspection process, and the other end of the track inspection mounting connector 10 is fixed on the track inspection vehicle 3; the detection probe 1 is adjusted to the specified lift-off to ensure that the lift-off of the detection probe remains unchanged during the inspection process; the driving module 4 is connected to the track inspection vehicle 3, and the pulse excitation signal output by the RAM-500 instrument 5 enters the coil 15 of the detection probe through the duplexer 6. The detection voltage signal of the coil 15 is divided into two parts through the signal separation module 7. One part enters the duplexer 6 to separate the motional eddy current signal and then enters the RAM-500 instrument 5. After passing through the signal conditioning module 8, the electromagnetic ultrasonic signal is obtained through the signal acquisition and processing module 9, and the other part enters the signal conditioning module 8 and then obtains the motional eddy current signal through the signal acquisition and processing module 9. By sorting and analyzing the electromagnetic ultrasonic signal and the motional eddy current signal, the purpose of inspecting the track 2 to be inspected is achieved.

[0007] The permanent magnet 14 of the detection probe 1 is an axially magnetized cylindrical permanent magnet, and is placed with its axis perpendicular to the surface of the track 2 .

[0008] The coil 15 of the detection probe 1 is spiral, so as to excite vertically incident body waves and efficiently detect signals.

[0009] The detection method of the electromagnetic ultrasonic / motion-induced eddy current composite detection system for high-speed train tracks,

[0010] 1) Establishing a calibration curve of buried / surface crack depth-signal characteristic quantity: Processing a calibration track for establishing a calibration curve of buried / surface crack depth-signal characteristic quantity, and processing longitudinal cracks of different depths at the bottom and surface of the calibration track respectively; Fixing the calibration track on the ground, adjusting the position of the track inspection vehicle 3 so that it is located directly above the calibration track, and lifting the detection probe 1 from the clamp 13 fixed in the middle of the wheeled clamp, and finally starting the drive module 4 to drive the track inspection vehicle 3 to move forward. At the same time, the detection probe 1 moves at a high speed relative to the calibration track. According to Faraday's law of electromagnetic induction, due to the high-speed movement of the permanent magnet 14, motional eddy currents will be generated inside the calibration track. Since the coil 15 is passed with a time-varying current, the calibration track will generate induced eddy currents. The induced eddy currents will be subjected to the time-varying Lorentz force under the magnetic field of the permanent magnet 14. At the same time, due to the magnetization, there are magnetized body force and magnetostrictive force in the calibration track. Under the action of the three forces, the calibration track Ultrasonic waves are excited inside, so the conductor cuts the magnetic flux lines to generate motional eddy currents. The coil 15 generates an induced voltage due to the magnetic field excited by the motional eddy currents, which is an electromagnetic ultrasonic signal. The coil voltage signal containing the motional eddy current signal and the electromagnetic ultrasonic signal is divided into two parts by the signal separation module 7. One part enters the duplexer 6 to separate the motional eddy current signal and then enters the RAM-500 instrument 5. After passing through the signal conditioning module 8, the electromagnetic ultrasonic signal is obtained by the signal acquisition and processing module 9. The other part enters the signal conditioning module 8 and then obtains the motional eddy current signal by the signal acquisition and processing module 9. By sorting and analyzing the electromagnetic ultrasonic signal and the motional eddy current signal, the time interval between the primary echo and the secondary echo of the electromagnetic ultrasonic signal is used as the characteristic quantity to calibrate the buried crack depth of the track, and obtain the buried crack depth-signal characteristic quantity calibration curve; the voltage amplitude of the motional eddy current signal is used as the characteristic quantity to calibrate the surface crack depth of the track, and obtain the surface crack depth-signal characteristic quantity calibration curve;

[0011] 2) Obtain crack detection characteristic quantities of the track to be tested through experiments: fix the track to be tested 2 at the position of the calibration track in step 1), start the driving module 4 according to the process of step 1), make the track inspection vehicle 3 move forward at exactly the same speed as in step 1), obtain the voltage signal of the coil 15 and separate it into an electromagnetic ultrasonic signal and a motional eddy current signal, and extract the corresponding time interval and voltage amplitude as characteristic quantities respectively;

[0012] 3) Calculate the crack depth of the track to be tested: In the calibration curve obtained in step 1), obtain the crack depth value corresponding to the characteristic value obtained in step 2), which is the crack depth of the track to be tested. In addition, since the time interval between the first and second echoes of the electromagnetic ultrasonic wave of the surface crack is short, the depth information cannot be obtained, and the motional eddy current signal has a very high sensitivity to the surface crack. Therefore, the buried / surface properties of the crack at the corresponding position can be judged according to the response time of each signal.

[0013] The expression of the buried crack depth-signal characteristic calibration curve established in step 1) is as follows:

[0014] t=0.625x-0.09

[0015] Wherein, t is the time interval between two echoes of the coil voltage signal of the detection probe 1 output by the signal acquisition and processing module 9 of the electromagnetic ultrasonic signal, and x is the depth of the buried longitudinal crack of the calibration track.

[0016] The expression of the surface crack depth-signal characteristic calibration curve established in step 1) is as follows:

[0017] V=-0.0475x 2 +0.839x+0.84

[0018] Wherein, V is the coil voltage amplitude of the detection probe 1 output by the signal acquisition and processing module 9 of the motional eddy current signal, and x is the surface longitudinal crack depth of the calibration track.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] 1) The detection system and detection method of the present invention adopts an electromagnetic ultrasonic / motion-induced eddy current composite detection method, which can simultaneously detect buried cracks and surface cracks of the track.

[0021] 2) Since the detection system and detection method of the invention detect track surface defects through the motion-induced eddy currents generated by the permanent magnet relative to the track to be inspected, and the electromagnetic ultrasonic signal will not be distorted during high-speed detection, the detection system and detection method of the invention of the present invention are suitable for high-speed detection, and the motion-induced eddy current signal has a great advantage that the higher the detection speed, the greater the output signal amplitude and the higher the detection sensitivity, and is particularly suitable for non-destructive detection of high-speed relative metal moving parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the electromagnetic ultrasonic / motion-induced eddy current composite detection system for high-speed train tracks.

[0023] Figure 2 Schematic diagram of the detection probe.

[0024] Figure 3 Schematic diagram of buried / surface crack distribution in phenotypic tracks.

[0025] Figure 4 This is a flow chart of the electromagnetic ultrasonic / motion-induced eddy current composite detection method for high-speed train tracks.

[0026] Figure 5 Calibration curve for buried crack.

[0027] Figure 6Surface crack calibration curve. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0029] like Figure 1 and Figure 2 As shown, the electromagnetic ultrasonic / motion-induced eddy current composite detection system for high-speed train tracks of the present invention includes a detection probe 1 and a detection auxiliary device, wherein the detection probe 1 is composed of a permanent magnet 14 and a coil 15 connected to each other; the detection auxiliary device includes a track to be inspected 2, a track inspection vehicle 3, a driving module 4 for driving the track inspection vehicle 3 forward, a track inspection mounting connector 10, a RAM-5000 instrument 5, a duplexer 6, a signal separation module 7, a signal conditioning module 8 and a signal acquisition and processing module 9; the track to be inspected 2 is laid flat on the ground, and the track inspection vehicle 3 is located directly above the track to be inspected 2 to ensure that the detection probe 1 will not deviate from the track to be inspected 2 during later detection; the roller 12 of the wheeled clamp is placed on the surface of the track to be inspected 2, and the detection probe 1 is placed in the clamp 13 in the middle of the wheeled clamp, and the wheeled clamp is fixed to one end of the track inspection mounting connector 10 through a shaft rod at its top, and a spring 11 is sleeved on the shaft rod, and the original length of the spring 11 is selected and stiffness coefficient to ensure that the roller 12 of the wheel fixture is always in contact with the surface of the track 2 to be inspected during the detection process, and the other end of the track inspection mounting connector 10 is fixed on the track inspection vehicle 3; the detection probe 1 is adjusted to the specified lift-off to ensure that the lift-off of the detection probe remains unchanged during the detection process; the driving module 4 is connected to the track inspection vehicle 3, and the pulse excitation signal output by the RAM-500 instrument 5 enters the coil 15 of the detection probe through the duplexer 6, and the detection voltage signal of the coil 15 is divided into two parts through the signal separation module 7. One part enters the duplexer 6 to separate the motional eddy current signal and then enters the RAM-500 instrument 5. After passing through the signal conditioning module 8, the electromagnetic ultrasonic signal is obtained through the signal acquisition and processing module 9, and the other part enters the signal conditioning module 8 and then obtains the motional eddy current signal through the signal acquisition and processing module 9. By sorting and analyzing the electromagnetic ultrasonic signal and the motional eddy current signal, the purpose of detecting the track 2 to be inspected is achieved.

[0030] like Figure 4 As shown, the detection method of the electromagnetic ultrasonic / motion-induced eddy current composite detection system for high-speed train tracks proposed in the present invention mainly includes the following steps:

[0031] 1) Establishing the buried / surface crack depth-signal characteristic calibration curve: Processing a calibration track for establishing the buried / surface crack depth-signal characteristic calibration curve, at the bottom of the calibration track and processing longitudinal cracks of different depths (the bottom crack depths are 12mm, 14mm, 16mm, and 18mm respectively; the surface crack depths are 2mm, 4mm, 6mm, and 8mm respectively, such as Figure 3 As shown); fix the calibration track on the ground, adjust the position of the track inspection vehicle 3 so that it is located directly above the calibration track, and lift the detection probe 1 (the permanent magnet 14 in the detection probe 1 is a cylindrical permanent magnet with a diameter of 30mm and a height of 50mm, with a residual magnetism of 1.2T, and the coil 15 is a spiral coil with a diameter of 20mm and a total of 100 turns) from the clamp 13 fixed in the middle of the wheel clamp, and finally start the drive module 4 to drive the track inspection vehicle 3 to move forward at a speed of 120km / h. At the same time, the detection probe 1 moves at a high speed relative to the calibration track. According to Faraday's law of electromagnetic induction, due to the high-speed movement of the permanent magnet 14, motional eddy currents will be generated inside the calibration track. Since the coil 15 is passed through a time-varying current, the calibration track will generate induced eddy currents, and the induced eddy currents will be subjected to the time-varying Lorentz force under the magnetic field of the permanent magnet 14. At the same time, due to the magnetization of the magnetized body force and magnetic field in the calibration track The three forces cause the expansion and contraction force to excite ultrasonic waves in the calibration track, so the conductor cuts the magnetic flux lines to generate motional eddy currents. The coil 15 generates an induced voltage due to the magnetic field excited by the motional eddy currents, which is an electromagnetic ultrasonic signal. The coil voltage signal containing the motional eddy current signal and the electromagnetic ultrasonic signal is divided into two parts by the signal separation module 7. One part enters the duplexer 6 to separate the motional eddy current signal and then enters the RAM-500 instrument 5. After passing through the signal conditioning module 8, the electromagnetic ultrasonic signal is obtained by the signal acquisition and processing module 9. The other part enters the signal conditioning module 8 and then obtains the motional eddy current signal by the signal acquisition and processing module 9. The electromagnetic ultrasonic signal and the motional eddy current signal are sorted and analyzed, and the time interval between the primary echo and the secondary echo of the electromagnetic ultrasonic signal is used as the characteristic quantity to calibrate the buried crack depth of the track, and the voltage amplitude of the motional eddy current signal is used as the characteristic quantity to calibrate the surface crack depth of the track. The buried crack depth of the calibrated track and the corresponding characteristic quantity are shown in Table 1. The established buried crack depth-signal characteristic quantity calibration curve is shown in Figure 5 As shown, the expression is as follows:

[0032] t=0.625x-0.09

[0033] Wherein, t is the time interval between two echoes of the coil voltage signal of the detection probe 1 output by the signal acquisition and processing module 9 of the electromagnetic ultrasonic signal, and x is the depth of the buried longitudinal crack of the calibration track.

[0034] Table 1 Calibration of buried cracks in track

[0035]

[0036] The surface crack depth and corresponding characteristic quantity of the calibration track are shown in Table 2. The established surface crack depth-signal characteristic quantity calibration curve is shown in Figure 6 As shown, the expression is as follows:

[0037] V=-0.0475x 2 +0.839x+0.84

[0038] Wherein, V is the coil voltage amplitude of the detection probe 1 output by the signal acquisition and processing module 9 of the motional eddy current signal, and x is the surface longitudinal crack depth of the calibration track.

[0039] Table 2 Crack parameters of calibration parts

[0040]

[0041] 2) Obtain crack detection characteristic quantities of the track to be tested through experiments: fix the track to be tested 2 at the position of the calibration track in step 1), start the driving module 4 according to the process of step 1), make the track inspection vehicle 3 move forward at the same speed (120 km / h) as in step 1), obtain the voltage signal of the coil 15 and separate it into electromagnetic ultrasonic signal and motional eddy current signal, and extract the corresponding time interval and voltage amplitude as characteristic quantities respectively;

[0042] 3) Calculate the crack depth of the track to be tested: In the calibration curve obtained in step 1), obtain the crack depth value corresponding to the characteristic value obtained in step 2), which is the crack depth of the track to be tested. The detection values, true values ​​and relative errors of the depths of the three buried cracks and three surface cracks of the track to be tested are shown in Table 3.

[0043] Table 3 Detection results of crack depth to be tested

[0044]

[0045] It can be seen from the test results in Table 3 that the detection error is within the allowable range, thereby proving the feasibility of the detection system and detection method of the present invention.

Claims

1. An electromagnetic ultrasonic / motion-induced eddy current composite detection system for high-speed train tracks, characterized in that: The invention comprises a detection probe (1) and a detection auxiliary device, wherein the detection probe (1) is composed of a permanent magnet (14) and a coil (15) connected to each other; the detection auxiliary device comprises a track to be inspected (2), a track inspection vehicle (3), a drive module (4) for driving the track inspection vehicle (3) forward, a track inspection mounting connector (10), a RAM-5000 instrument (5), a duplexer (6), a signal separation module (7), a signal conditioning module (8) and a signal acquisition and processing module (9); the track to be inspected (2 ) is laid flat on the ground, the track inspection vehicle (3) is located directly above the track to be inspected (2) to ensure that the detection probe (1) will not deviate from the track to be inspected (2) during the later detection; the roller (12) of the wheeled clamp is placed on the surface of the track to be inspected (2), the detection probe (1) is placed in the clamp (13) in the middle of the wheeled clamp, and the wheeled clamp is fixed to one end of the track inspection mounting connector (10) through the shaft rod at its top, and a spring (11) is sleeved on the shaft rod. The original length and stiffness coefficient of the spring (11) are selected to ensure the inspection During the test, the roller (12) of the wheeled fixture is always in contact with the surface of the track (2) to be tested, and the other end of the track test mounting connector (10) is fixed on the track test vehicle (3); the detection probe (1) is adjusted to a specified lift-off to ensure that the lift-off of the detection probe remains unchanged during the test; the drive module (4) is connected to the track test vehicle (3), and the pulse excitation signal output by the RAM-500 instrument (5) enters the coil (15) of the detection probe through a duplexer (6), and the detection voltage signal of the coil (15) is divided into two parts through a signal separation module (7), one part enters the duplexer (6) to separate the motional eddy current signal and then enters the RAM-500 instrument (5), and after passing through the signal conditioning module (8), an electromagnetic ultrasonic signal is obtained through the signal acquisition and processing module (9), and the other part enters the signal conditioning module (8) and then a motional eddy current signal is obtained through the signal acquisition and processing module (9), and the purpose of testing the track (2) to be tested is achieved by sorting and analyzing the electromagnetic ultrasonic signal and the motional eddy current signal.

2. The electromagnetic ultrasonic / motion-induced eddy current composite detection system for high-speed train tracks according to claim 1 is characterized in that: The permanent magnet (14) of the detection probe (1) is an axially magnetized cylindrical permanent magnet, and is placed with its axis perpendicular to the surface of the track (2).

3. The electromagnetic ultrasonic / motion-induced eddy current composite detection system for high-speed train tracks according to claim 1 is characterized in that: The coil (15) of the detection probe (1) is of a spiral type, which is used to excite vertically incident body waves and efficiently detect signals.

4. The detection method of the electromagnetic ultrasonic / motion-induced eddy current composite detection system for high-speed train tracks according to claim 1, 2 or 3, characterized in that: 1) Establishing a calibration curve of buried / surface crack depth-signal characteristic quantity: processing a calibration track for establishing a calibration curve of buried / surface crack depth-signal characteristic quantity, and processing longitudinal cracks of different depths at the bottom and surface of the calibration track respectively; fixing the calibration track on the ground, adjusting the position of the track inspection vehicle (3) so that it is located directly above the calibration track, lifting the detection probe (1) from the clamp (13) fixed in the middle of the wheel clamp, and finally starting the drive module (4) to drive the track inspection vehicle (3 ... The vehicle (3) moves forward, and at the same time, the detection probe (1) moves at a high speed relative to the calibration track. According to Faraday's law of electromagnetic induction, due to the high-speed movement of the permanent magnet (14), motional eddy currents will be generated inside the calibration track. Since the coil (15) is passed with a time-varying current, the calibration track will generate induced eddy currents. The induced eddy currents will be subjected to a time-varying Lorentz force under the action of the magnetic field of the permanent magnet (14). At the same time, due to the magnetization, there are magnetized body force and magnetostrictive force in the calibration track. Under the action of these three forces, the calibration track Ultrasonic waves are excited in the track, so the conductor cuts the magnetic flux lines to generate motional eddy currents. The coil (15) generates an induced voltage due to the magnetic field excited by the motional eddy currents, which is an electromagnetic ultrasonic signal. The coil voltage signal containing the motional eddy current signal and the electromagnetic ultrasonic signal is divided into two parts through the signal separation module (7). One part enters the duplexer (6) to separate the motional eddy current signal and then enters the RAM-500 (5). After passing through the signal conditioning module (8), the electromagnetic ultrasonic signal is obtained through the signal acquisition and processing module (9). The other part enters the signal conditioning module (8) and then obtains the motional eddy current signal through the signal acquisition and processing module (9). By sorting and analyzing the electromagnetic ultrasonic signal and the motional eddy current signal, the time interval between the primary echo and the secondary echo of the electromagnetic ultrasonic signal is used as a characteristic quantity to calibrate the buried crack depth of the track, and obtain a buried crack depth-signal characteristic quantity calibration curve; the voltage amplitude of the motional eddy current signal is used as a characteristic quantity to calibrate the surface crack depth of the track, and obtain a surface crack depth-signal characteristic quantity calibration curve; 2) Obtain crack detection characteristic quantities of the track to be tested through experiments: fix the track to be tested (2) at the position of the calibration track in step 1), start the driving module (4) according to the process of step 1), make the track inspection vehicle (3) move forward at the same speed as in step 1), obtain the voltage signal of the coil (15) and separate it into electromagnetic ultrasonic signal and motional eddy current signal, and extract the corresponding time interval and voltage amplitude as characteristic quantities respectively; 3) Calculate the crack depth of the track to be tested: In the calibration curve obtained in step 1), obtain the crack depth value corresponding to the characteristic value obtained in step 2), which is the crack depth of the track to be tested; in addition, since the time interval between the first echo and the second echo of the electromagnetic ultrasonic wave of the surface crack is short, the depth information cannot be obtained, and the motional eddy current signal has a very high sensitivity to the surface crack. Therefore, the buried / surface properties of the crack at the corresponding position can be judged according to the response time of each signal.

5. The detection method according to claim 4, characterized in that: The expression of the buried crack depth-signal characteristic calibration curve established in step 1) is as follows: t=0.625x-0.09 Wherein, t is the time interval between two echoes of the coil voltage signal of the detection probe 1 output by the signal acquisition and processing module 9 of the electromagnetic ultrasonic signal, and x is the depth of the buried longitudinal crack of the calibration track; The expression of the surface crack depth-signal characteristic calibration curve established in step 1) is as follows: V=-0.0475x 2 +0.839x+0.84 Wherein, V is the detection coil voltage of the detection probe (1) output by the signal acquisition and processing module (9), and x is the depth of the longitudinal crack on the surface of the calibration track.

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