Differential pulse eddy current probe for detecting rivet hole edge cracks and system and method thereof

Abstract

The application provides a differential pulse eddy current probe for detecting rivet hole edge cracks, a system and a method thereof. The differential pulse eddy current probe is composed of a rectangular excitation coil, a rectangular magnetic core, a TMR sensor, a PCB board and a probe shell. The rectangular excitation coil is horizontally fixed on the upper side of the PCB board, and the magnetic core is used for enhancing the convergence of the magnetic flux. The bottom of the PCB board and the probe shell is provided with a circular through hole for sleeving the protruding part of the rivet head, and the bottom of the probe shell is provided with a square groove on both sides of the through hole for sleeving the TMR sensor. A pair of TMR sensors sensitive to the change of the horizontal magnetic field are symmetrically welded on both sides of the circular through hole on the lower side of the PCB board to form a differential detection mode. During detection, the probe is rotated in steps with the rivet as the center, and the full-coverage detection of the hole edge cracks is realized by analyzing the sensing signal of the TMR sensor. The application has the advantages of high detection sensitivity, accurate positioning, no need of a reference signal and strong anti-interference capability, and can effectively detect the rivet hole edge crack defects in different directions.

Description

Technical Field

[0001] This invention belongs to the field of pulsed eddy current nondestructive testing technology, specifically relating to a differential pulsed eddy current probe, system, and method for detecting cracks on the edge of rivet holes. Background Technology

[0002] Aerospace aluminum alloys, due to their high strength, low density, and corrosion resistance, are an indispensable key material in aircraft manufacturing. Because of the poor weldability of aluminum alloys and the operational characteristics of aircraft, riveting is commonly used for structural assembly. While multi-layered riveted structures offer high strength and reliability, during long-term service, minor stress concentrations may occur at the riveting points. Vibration and temperature changes can lead to material fatigue, especially when aircraft frequently experience significant acceleration, deceleration, or altitude changes. Fatigue cracks can easily develop on the metal surfaces or joints around the riveting points. If these fatigue cracks are not detected and repaired in time, they can lead to structural failure and seriously affect flight safety.

[0003] Currently, scholars from various countries have conducted extensive research on non-destructive testing of riveted components in aircraft, mainly including visual inspection, ultrasonic testing, and eddy current testing. Among these, pulsed eddy current testing, a branch of eddy current testing, has advantages such as being non-contact, capable of penetrating multiple layers of conductive materials, requiring no coupling agent, and providing rich spectral information, making it a powerful technique for inspecting multi-layered metal riveted structures in aircraft. Pulsed eddy current testing obtains defect information by applying repetitive pulsed rectangular signals to a rectangular excitation coil and utilizing the principle of electromagnetic induction. It is suitable for inspecting multi-layered metal riveted structures in aircraft, where defects exist internally.

[0004] Currently, most eddy current testing probes for multi-layered metal riveted structures in aircraft employ static and sliding detection modes. When the direction and location of crack defects are unknown, it is difficult to obtain the maximum characteristic value of the defect for subsequent analysis, potentially leading to inaccurate defect evaluation. Furthermore, existing technologies typically require comparison with defect-free specimens to determine the presence of defects; without such defect-free specimens, accurate evaluation of defects in the test piece is difficult. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a differential pulsed eddy current probe, system, and method for detecting cracks at the edge of rivet holes, aiming to solve the problems in the background technology.

[0006] To achieve the above objectives, the present invention provides a differential pulsed eddy current probe for detecting cracks on the edge of rivet holes, comprising a rectangular excitation coil, a rectangular magnetic core, a pair of TMR sensors, a PCB board, and a probe housing, characterized in that; The rectangular excitation coil is directly wound on the rectangular magnetic core, and the main plane of the rectangular excitation coil is fixed in the top square area of ​​the PCB board, with the center of the rectangular excitation coil aligned with the center of the top square area of ​​the PCB board. The top square area of ​​the PCB board has a circular through hole with the same maximum diameter as the head of the rivet to be tested, and the circular through hole is centered on the center of the square area of ​​the top square area of ​​the PCB board; on the bottom layer of the PCB board, a pad is provided on each side of the circular through hole along the length of the rectangular magnetic core. The pair of TMR sensors are respectively soldered to two pads on the bottom layer of the PCB board, and the pins of the pair of TMR sensors are connected to the DC power supply through the pads. The probe housing has a square internal space for placing and fixing the rectangular excitation coil, the PCB board, and the pair of TMR sensors.

[0007] Furthermore, the probe housing has a circular through hole at its bottom, the center and diameter of which are consistent with the circular through hole in the PCB board; the inner wall of the bottom of the probe housing has two square grooves, the positions of which are consistent with the positions of two pads in the PCB board, and the shape and size of which are consistent with the shape of the TMR sensor.

[0008] Furthermore, the circular through hole at the bottom of the PCB board and the probe housing is used to accommodate the head of the rivet to be tested.

[0009] Furthermore, when the circular through hole at the bottom of the PCB board and the probe housing is fitted into the head of the rivet to be tested, the center of the rectangular excitation coil coincides with the center of the rivet to be tested, enabling the differential pulse eddy current probe to detect crack defects on the edge of the rivet hole in different orientations by rotation.

[0010] Furthermore, the pair of TMR sensors are of a type sensitive to changes in the horizontal magnetic field, and when the pair of TMR sensors are soldered onto the PCB board pads, the sensitive direction of the pair of TMR sensors is set to be parallel to the length direction of the rectangular excitation coil, so that the strong magnetic flux generated by the rectangular excitation coil can pass through the pair of TMR sensors; the pair of TMR sensors are of the same type and are symmetrically positioned, and the difference between the sensed output signals constitutes a differential detection unit.

[0011] This invention also provides a pulsed eddy current defect detection system based on a differential pulsed eddy current probe for detecting cracks at the edge of rivet holes, comprising a differential pulsed eddy current detection probe, a pulsed eddy current exciter, a DC power supply, a data acquisition card, and a computer, characterized in that: The two ends of the rectangular excitation coil in the differential pulse eddy current probe are electrically connected to the pulse eddy current exciter. The pair of TMR sensor pins in the differential pulse eddy current probe are electrically connected to the DC power supply and the data acquisition card, respectively. The data acquisition card is electrically connected to the computer.

[0012] This invention also provides a pulsed eddy current defect detection method based on a differential pulsed eddy current probe, applied to a pulsed eddy current defect detection system based on a differential pulsed eddy current probe for detecting cracks at the edge of rivet holes, characterized by comprising the following steps: Step 1: Insert the bottom circular through hole of the differential pulse eddy current probe into the head of the rivet to be tested in the riveting structure, set a certain rotation angle step, and prepare to perform unidirectional rotation detection with the rivet to be tested as the center. Step 2: The pulse eddy current exciter generates a rectangular pulse signal with adjustable amplitude, frequency, and duty cycle into the rectangular excitation coil of the differential pulse eddy current probe; Step 3: During the rotation detection of the rivet under test, the differential pulse eddy current probe performs differential processing on the voltage signal obtained at each rotation angle by the voltage signal output by the differential detection unit from the pair of TMR sensors and the voltage signal obtained at the first rotation angle to obtain a differential voltage. When there is no defect on the edge of the rivet hole of the rivet under test, the differential voltage is always zero. When there is a crack defect on the edge of the rivet hole of the rivet under test, there is at least one rotation angle that makes the differential voltage non-zero, and a defect voltage signal appears. The defect voltage signal is acquired by the data acquisition card and transmitted to the computer. Step 4: The computer plots the voltage signals collected by the probe at each rotation angle as voltage-time curves. By analyzing and comparing, the voltage peak value and the time corresponding to the peak value of the curve corresponding to each detection angle are extracted as feature values. Step 5: After the computer extracts the feature values ​​of all rotation angles, it plots the voltage peak value-rotation angle polar coordinate curve. At the same time, the computer corrects the voltage peak value-rotation angle polar coordinate curve. After the correction is completed, the computer analyzes the voltage peak value-rotation angle polar coordinate curve and the time corresponding to the peak value to infer the information of the crack defect on the edge of the rivet hole to be tested.

[0013] Compared with existing technologies, the present invention has the following advantages: The present invention proposes a differential pulsed eddy current probe. This probe uses a horizontally placed rectangular excitation coil instead of the traditional cylindrical excitation coil. After applying a pulse excitation signal, it can generate a unidirectional and uniform eddy current in the specimen at the bottom of the probe, which improves the detection sensitivity of cracks. At the same time, the eddy current has good directionality. Combined with rotation detection, it can better locate the crack position and reflect the crack characteristics.

[0014] This pulsed eddy current probe offers the advantages of comprehensive detection and accurate results even when the crack direction is unknown. The design incorporates a circular through-hole, approximately the same diameter as the rivet head, at the bottom of the probe housing and on the built-in PCB. This reduces interference signals introduced by eccentricity errors when the probe rotates around the rivet, improving the stability and accuracy of the detection signal. Simultaneously, the volume of the through-hole allows the probe to be closer to the surface of the test piece, minimizing the lift-off effect.

[0015] This pulsed eddy current probe uses a small, low-power, and highly sensitive TMR sensor to receive magnetic field signals and constructs them into a differential detection mode. This reduces the possibility of misjudgment caused by geomagnetic field interference and improves the detection sensitivity for abrupt defects. At the same time, the differential probe is used to perform rotation detection on the rivet. After signal correction, there is no need to use a defect-free specimen for comparison, which can achieve the purpose of rapid detection and improve detection efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a differential pulsed eddy current probe according to the present invention; Figure 2 A side view of a rectangular excitation coil and a pair of TMR sensors; Figure 3 Top view of a rectangular excitation coil and a pair of TMR sensors; Figure 4 This is a schematic diagram of the pulsed eddy current defect detection system based on the differential pulsed eddy current probe of the present invention. Figure 5 Defective plates in test specimens of multi-layer riveted structures for aircraft to simulate crack defects at the edge of rivet holes; Figure 6 This is the actual detection signal of cracks on the edge of rivet holes of different lengths according to the present invention; Figure 7 The results of rotational detection of cracks on the edge of rivet holes of different lengths are presented in this invention. Figure 8 This is the actual detection signal of rivet hole edge cracks at different embedment depths according to the present invention; Figure 9 This is the result of rotational detection of cracks at the edge of rivet holes at different embedment depths according to the present invention.

[0017] In the attached diagram: 1. Rectangular excitation coil; 2. Rectangular magnetic core; 3. PCB board; 4. TMR sensor; 5. Probe housing; 6. First lead; 7. Second lead; 8. Excitation terminal; 9. Aviation connector; 10. Differential pulsed eddy current probe; 11. Pulsed eddy current exciter; 12. DC power supply; 13. Data acquisition card; 14. Computer; 15. Workpiece to be tested; 16. Rivet to be tested; 17. Rivet hole edge crack; 18. Pulsed eddy current defect detection system; 19. First crack; 20. Second crack; 21. Third crack; 22. Fourth crack; 23. Fifth crack; 24. Sixth crack; 25. Seventh crack; 26. Original detection signal of the first crack 19; 27. Original detection signal of the second crack 20; 28. Original detection signal of the third crack 21; 29. ​​Original detection signal of the fourth crack 22; 30. Voltage peak value-rotation angle polar coordinate curve of the first crack 19; 31. Voltage peak value-rotation angle polar coordinate curve of the second crack 20; 32. Voltage peak value-rotation angle polar coordinate curve of the third crack 21; 33. Voltage peak value-rotation angle polar coordinate curve of the fourth crack 22; 34. Original detection signal of the fifth crack 23; 35. Original detection signal of the sixth crack 24; 36. Original detection signal of the seventh crack 25; 37. Voltage peak value-rotation angle polar coordinate curve of the fifth crack 23; 38. Voltage peak value-rotation angle polar coordinate curve of the sixth crack 24; 39. Voltage peak value-rotation angle polar coordinate curve of the seventh crack 25. Detailed Implementation

[0018] The specific embodiments of the present invention will now be described in conjunction with the accompanying drawings to enable those skilled in the art to better understand the present invention. It should be noted that in the following description, detailed descriptions of known functions and designs that may obscure the main content of the present invention will be omitted here.

[0019] refer to Figure 1 The present invention provides a differential pulsed eddy current probe 10 for detecting cracks on the edge of rivet holes, which mainly includes a rectangular excitation coil 1, a rectangular magnetic core 2, a PCB board 3, a pair of TMR sensors 4, a probe housing 5, a first lead 6, a second lead 7, an excitation terminal 8, and an aviation plug 9. refer to Figure 2 and Figure 3 Specifically, in this embodiment, the rectangular excitation coil 1 is directly wound on the rectangular magnetic core 2. The rectangular magnetic core 2 has dimensions of 30mm in length, 20mm in width, and 6mm in height. The long × wide side (main plane) of the wound rectangular excitation coil 1 is fixed on the square area on the top layer of the PCB board 3. The center of the rectangular excitation coil 1 is aligned with the center of the square area on the top layer of the PCB board 3. The PCB board 3 has dimensions of 33mm in length, 33mm in width, and 1mm in thickness. The top layer of the PCB board 3 is fixed with a rectangular excitation coil 1, and a circular through hole with the center of the square area as the center is provided, which is equal to the maximum diameter of the 16 heads of the rivet to be tested. The diameter of the circular through hole is 6mm. On the bottom layer of the PCB board 3, a pad is provided on each side of the circular through hole along the length of the rectangular magnetic core 2. The TMR sensor model is TMR2103. A pair of TMR sensors 4 are soldered onto two pads on the bottom layer of PCB board 3 respectively. Two pins of each TMR sensor in the pair of TMR sensors 4 in the differential pulse eddy current probe 10 are electrically connected to the DC power supply 12, and the other two pins of each TMR sensor are electrically connected to the data acquisition card 13. The probe housing 5 is manufactured by 3D printing. The internal space of the probe housing 5 is square. The bottom surface of the probe housing is 35mm long and 35mm wide, and the wall thickness of the probe housing is 2mm. It is used to place and fix the rectangular excitation coil 1, PCB board 3 and a pair of TMR sensors 4. There is a circular through hole at the bottom of the probe housing 5, the center and diameter of which are 6mm. There are two square grooves on the inner wall of the bottom of the probe housing 5. The position of the square grooves is consistent with the position of the two pads in the PCB board 3. The size of the square grooves is 3.5mm long, 3.5mm wide and 0.8mm deep. The first lead 6 connects the rectangular excitation coil 1 to the excitation terminal 8 at the top, realizing the input of the external excitation signal; the second lead 7 connects the TMR sensor 4 on the PCB board 3 to the aviation plug 9, which is used to output the detection signal; the aviation plug 9 and the excitation terminal 8 are both installed on the top of the probe housing 5, serving as the electrical interface between the probe and the external detection equipment, completing the electrical connection and signal transmission function of the entire differential pulse eddy current probe 10.

[0020] Furthermore, the bottom of the PCB board 3 and the probe housing 5 is provided with circular through holes of the same diameter and coincident center to accommodate the head of the rivet 16 to be tested, which facilitates the rotation detection of the head of the rivet 16 to be tested, and at the same time reduces the lift-off effect caused by the increased lifting distance of the probe due to the protrusion of the rivet head; when the circular through hole is fitted into the head of the rivet 16 to be tested, the center of the horizontally fixed rectangular excitation coil 1 coincides with the center of the rivet. After the rectangular excitation coil 1 is excited, the eddy current generated in the multi-layer riveting structure to be tested will gather and be enhanced at the rivet, and as the probe rotates, the direction of the eddy current will also turn synchronously with the direction of probe rotation, so that the probe can detect the rivet hole edge crack 17 defects in different directions.

[0021] Furthermore, the pair of TMR sensors 4 are of a type sensitive to changes in the horizontal magnetic field. When the pair of TMR sensors 4 are soldered onto the pads of the PCB board 3, the sensitive direction of the pair of TMR sensors 4 is set to be parallel to the length direction of the rectangular excitation coil 1, so that the strong magnetic flux generated by the rectangular excitation coil 1 always passes through the pair of TMR sensors 4. The pair of TMR sensors 4 are of the same type and are symmetrically positioned. The difference between the induced output signals constitutes a differential detection unit.

[0022] refer to Figure 4 The pulse eddy current defect detection system 18 based on the differential pulse eddy current probe 10 specifically includes: differential pulse eddy current probe 10, pulse eddy current exciter 11, DC power supply 12, data acquisition card 13, computer 14, and workpiece to be tested 15. The two ends of the rectangular excitation coil 1 in the differential pulsed eddy current probe 10 are electrically connected to the pulsed eddy current exciter 11. Two pins of each pair of TMR sensors 4 in the differential pulse eddy current probe 10 are electrically connected to the DC power supply 12, and the other two pins of the pair of TMR sensors 4 are electrically connected to the data acquisition card 13. Data acquisition card 13 is electrically connected to computer 14.

[0023] The following describes a crack defect detection method using a pulsed eddy current defect detection system, which includes the following steps: Step 1: Insert the bottom circular through hole of the differential pulse eddy current probe 10 into the head of the rivet 16 to be tested in the riveting structure, set a certain rotation angle step, and prepare to perform rotation detection with the rivet 16 to be tested as the center. Step 2: The pulse eddy current exciter 11 excites a rectangular pulse signal with adjustable amplitude, frequency and duty cycle into the rectangular excitation coil 1 of the differential pulse eddy current probe 10; Step 3: During the rotation detection of the rivet 16 under test, the differential pulse eddy current probe 10 performs differential processing on the voltage signal obtained at each rotation angle by the voltage signal output by the differential detection unit from the pair of TMR sensors 4 and the voltage signal obtained at the first rotation angle to obtain a differential voltage. When there is no defect on the edge of the rivet hole of the rivet 16 under test, the differential voltage is always zero. When there is a crack defect on the edge of the rivet hole of the rivet 16 under test, there is at least one rotation angle that makes the differential voltage non-zero, and a defect voltage signal appears. The defect voltage signal is acquired by the data acquisition card 13 and transmitted to the computer 14 for further processing. Step 4: The computer 14 plots the voltage signal collected by the probe at each rotation angle as a voltage-time curve. By analyzing and comparing, the voltage peak value and the time corresponding to the peak value of the curve corresponding to each detection angle are extracted as feature values. Step 5: After extracting the feature values ​​of all rotation angles, computer 14 plots the voltage peak value-rotation angle polar coordinate curve. At the same time, the computer corrects the voltage peak value-rotation angle polar coordinate curve by shifting the entire curve vertically by the difference between the minimum value and 0. This is to prevent inconsistencies in the peak reference of the voltage peak value-rotation angle polar coordinate curve due to different crack angles. After correction, computer 14 analyzes the voltage peak value-rotation angle polar coordinate curve and the time corresponding to the peak value to infer the defect condition, crack location, crack length, and burial depth of the crack 17 at the edge of the rivet hole to be tested.

[0024] In a specific embodiment, a defective plate of an aircraft multi-layer riveted structure test specimen was used as the specimen material. The specimen material consisted of five 2024 aluminum alloy plates, each with dimensions of 550 mm in length, 310 mm in width, and 1 mm in thickness. Cylindrical convex-head rivets made of 6061 aluminum alloy were used, with a head diameter of 6 mm and a height of 1.5 mm, and a shank diameter of 4 mm and a shank height of 11 mm. To fasten the multi-layer aluminum alloy plates to the rivets, each aluminum alloy plate was drilled with a planar hole diameter of 4.2 mm. In the second layer of the aluminum alloy plate, a 0.2 mm wide groove defect penetrating the layer was machined along some of the drilled hole edges. The lengths of the first crack 19, the second crack 20, the third crack 21, and the fourth crack 22 were 3, 4, 5, and 6 mm, respectively. In the third, fourth, and fifth layers of the aluminum alloy plate, a 0.2 mm wide groove defect was machined along some of the drilled hole edges. The fifth crack 23 is a through crack with a length of 6 mm located on the third aluminum alloy plate; the sixth crack 24 is a through crack with a length of 6 mm located on the fourth aluminum alloy plate; and the seventh crack 25 is a through crack with a length of 6 mm located on the fifth aluminum alloy plate. Reference Figure 5 In this embodiment, a differential pulse eddy current probe 10 is used to perform rotational testing on a multi-layer riveted structure test piece of an aircraft. The rotation angle step is set to 5°. A pulse square wave with an amplitude of 1A, a frequency of 50Hz, and a duty cycle of 50% is passed to the differential pulse eddy current probe 10. Insert the circular through hole at the bottom of the differential pulse eddy current probe 10 into the head of the rivet 16 to be tested in the riveting structure, close to the surface of the specimen, turn on the pulse eddy current defect detection system 18 based on the differential pulse eddy current probe 10, so that the differential pulse eddy current probe 10 rotates at a uniform speed step by step according to the rotation detection angle, and at the same time collects and records data. After the differential pulse eddy current probe 10 completes the detection, the collected voltage data is saved and a voltage-time curve is plotted. At the same time, a voltage peak value-rotation angle polar coordinate curve is plotted according to the rotation step, and the voltage change in the voltage-time curve and the voltage peak value-rotation angle polar coordinate curve is observed. Reference Figure 6 A differential pulsed eddy current probe 10 was used to detect voltage-time curves of cracks with a burial depth of 1 mm and lengths of 3, 4, 5, and 6 mm. Figure 6 The curves are marked as follows: curve 26 corresponds to the voltage-time curve of the first crack 19 (3mm in length, 1mm in depth), curve 27 corresponds to the voltage-time curve of the second crack 20 (4mm in length, 1mm in depth), curve 28 corresponds to the voltage-time curve of the third crack 21 (5mm in length, 1mm in depth), and curve 29 corresponds to the voltage-time curve of the fourth crack (6mm in length, 1mm in depth).

[0025] Reference Figure 7 A differential pulsed eddy current probe 10 was used to detect the voltage peak value versus rotation angle polar coordinate curves of cracks with a burial depth of 1 mm and lengths of 3, 4, 5, and 6 mm. Figure 7 The polar coordinate curves are as follows: curve 30 corresponds to the voltage peak value-rotation angle polar coordinate curve of the first crack 19 (3mm in length, 1mm in depth); curve 31 corresponds to the voltage peak value-rotation angle polar coordinate curve of the second crack 20 (4mm in length, 1mm in depth); curve 32 corresponds to the voltage peak value-rotation angle polar coordinate curve of the third crack 21 (5mm in length, 1mm in depth); and curve 33 corresponds to the voltage peak value-rotation angle polar coordinate curve of the fourth crack (6mm in length, 1mm in depth). It can be seen that when the differential pulse eddy current probe 10 rotates to directly above the crack, the voltage peak value reaches its maximum. When the crack depth is consistent, the voltage peak value increases with the crack length, while the time corresponding to the voltage peak value remains almost unchanged.

[0026] Reference Figure 8 A differential pulsed eddy current probe 10 was used to detect voltage-time curves of cracks with a length of 6 mm and burial depths of 1, 2, 3, and 4 mm. Figure 8 The curves are marked as follows: curve 29 corresponds to the voltage-time curve of the fourth crack (6mm in length and 1mm in depth), curve 34 corresponds to the voltage-time curve of the fifth crack (6mm in length and 2mm in depth), curve 35 corresponds to the voltage-time curve of the sixth crack (6mm in length and 3mm in depth), and curve 36 corresponds to the voltage-time curve of the seventh crack (6mm in length and 4mm in depth).

[0027] Reference Figure 9A differential pulsed eddy current probe 10 was used to detect the voltage peak value versus rotation angle polar coordinate curves of cracks with a length of 6 mm and burial depths of 1, 2, 3, and 4 mm. Figure 9 The polar coordinate curves are as follows: curve 33 corresponds to the voltage peak value-rotation angle polar coordinate curve of the fourth crack (6mm length, 1mm burial depth); curve 37 corresponds to the voltage peak value-rotation angle polar coordinate curve of the fifth crack (6mm length, 2mm burial depth); curve 38 corresponds to the voltage peak value-rotation angle polar coordinate curve of the sixth crack (6mm length, 3mm burial depth); and curve 39 corresponds to the voltage peak value-rotation angle polar coordinate curve of the seventh crack (6mm length, 4mm burial depth). It can be seen that when the differential pulse eddy current probe 10 rotates to directly above crack 17, the voltage peak value reaches its maximum. When the crack length is consistent, the voltage peak value decreases as the crack burial depth increases, while the time corresponding to the voltage peak value increases. Therefore, the crack angle position can be deduced from the angle corresponding to the maximum value in the voltage peak value-rotation angle polar coordinate curve, the burial depth position of the crack can be deduced from the time corresponding to the peak value in the voltage-time curve, and finally the crack length can be deduced from the magnitude of the peak value in the voltage-time curve.

[0028] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A differential pulsed eddy current probe for detecting cracks on the edge of rivet holes, comprising a rectangular excitation coil, a rectangular magnetic core, a pair of TMR sensors, a PCB board, and a probe housing, characterized in that, The rectangular excitation coil is directly wound on the rectangular magnetic core, and the main plane of the rectangular excitation coil is fixed in the top square area of ​​the PCB board, with the center of the rectangular excitation coil aligned with the center of the top square area of ​​the PCB board. The top square area of ​​the PCB board has a circular through hole with the same maximum diameter as the head of the rivet to be tested, and the circular through hole is centered on the center of the square area of ​​the top square area of ​​the PCB board; on the bottom layer of the PCB board, a pad is provided on each side of the circular through hole along the length of the rectangular magnetic core. The pair of TMR sensors are soldered onto two pads on the bottom layer of the PCB board. The pair of TMR sensors are of a type that is sensitive to changes in the horizontal magnetic field. The sensitive direction of the pair of TMR sensors is set to be parallel to the length of the rectangular excitation coil so that the strong magnetic flux generated by the rectangular excitation coil can pass through the pair of TMR sensors. The pair of TMR sensors are of the same type and are symmetrically positioned. The difference between the sensed output signals forms a differential detection unit. The probe housing has a square internal space for placing and fixing the rectangular excitation coil, the PCB board, and the pair of TMR sensors; It also includes a differential pulse eddy current probe system for detecting cracks on the edge of rivet holes based on a differential pulse eddy current probe, including a differential pulse eddy current detection probe, a pulse eddy current exciter, a DC power supply, a data acquisition card, and a computer; The two ends of the rectangular excitation coil in the differential pulse eddy current probe are electrically connected to the pulse eddy current exciter. The pair of TMR sensor pins in the differential pulse eddy current probe are electrically connected to the DC power supply and the data acquisition card, respectively. The data acquisition card is electrically connected to the computer.

2. The differential pulsed eddy current probe for detecting cracks on the edge of rivet holes according to claim 1, characterized in that, The probe housing has a circular through hole at the bottom, and the center and diameter of the circular through hole at the bottom of the probe housing are consistent with the circular through hole in the PCB board; the inner wall of the bottom of the probe housing is provided with two square grooves, and the positions of the two square grooves are consistent with the positions of two pads in the PCB board. The shape and size of the square grooves are consistent with the shape of the TMR sensor.

3. A differential pulsed eddy current probe for detecting cracks on the edge of a rivet hole according to claim 2, characterized in that, The circular through hole at the bottom of the PCB board and probe housing is used to accommodate the head of the rivet to be tested.

4. A differential pulsed eddy current probe for detecting cracks on the edge of a rivet hole according to claim 2, characterized in that, When the circular through hole at the bottom of the PCB board and the probe housing is fitted into the head of the rivet to be tested, the center of the rectangular excitation coil coincides with the center of the rivet to be tested, enabling the differential pulse eddy current probe to detect crack defects on the edge of the rivet hole in different directions by rotation.

5. A pulsed eddy current defect detection method based on a differential pulsed eddy current probe, applied to the differential pulsed eddy current probe for detecting cracks at the edge of rivet holes as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Insert the bottom circular through hole of the differential pulse eddy current probe into the head of the rivet to be tested in the riveting structure, set a certain rotation angle step, and prepare to perform unidirectional rotation detection with the rivet to be tested as the center. Step 2: The pulse eddy current exciter generates a rectangular pulse signal with adjustable amplitude, frequency, and duty cycle into the rectangular excitation coil of the differential pulse eddy current probe; Step 3: During the rotation detection of the rivet under test, the differential pulse eddy current probe performs differential processing on the voltage signal obtained at each rotation angle by the voltage signal output by the differential detection unit from the pair of TMR sensors and the voltage signal obtained at the first rotation angle to obtain a differential voltage. When there is no defect on the edge of the rivet hole of the rivet under test, the differential voltage is always zero. When there is a crack defect on the edge of the rivet hole of the rivet under test, there is at least one rotation angle that makes the differential voltage non-zero, and a defect voltage signal appears. The defect voltage signal is acquired by the data acquisition card and transmitted to the computer. Step 4: The computer plots the voltage signals collected by the probe at each rotation angle as voltage-time curves. By analyzing and comparing, the voltage peak value and the time corresponding to the peak value of the curve corresponding to each detection angle are extracted as feature values. Step 5: After the computer extracts the feature values ​​of all rotation angles, it plots the voltage peak value-rotation angle polar coordinate curve. At the same time, the computer corrects the voltage peak value-rotation angle polar coordinate curve. After the correction is completed, the computer analyzes the voltage peak value-rotation angle polar coordinate curve and the time corresponding to the peak value to infer the information of the crack defect on the edge of the rivet hole to be tested.

Images