Array eddy current detection method and device for rivet hole edge cracks

Abstract

The invention provides an array eddy current testing method and device for rivet hole edge cracks, and belongs to the technical field of nondestructive testing. An array eddy current detection method for rivet hole edge cracks comprises the following steps: S1, probe fitting: inserting a flexible eddy current array probe into a to-be-detected rivet hole, and controlling a miniature air pressure bag to inflate, so that the probe is adaptively fitted with a hole wall; s2, a signal acquisition step: applying a multi-frequency mixed excitation signal to the probe, moving the probe in a spiral progressive scanning mode, and acquiring an eddy current response signal of the hole wall; s3, signal compensation: according to the radial distance and azimuth angle of the current position of the probe; according to the device, the flexible eddy current array probe is matched with the air pressure attaching mechanism, so that the device can adapt to rivet holes with different hole diameters, the lift-off effect is eliminated, the signal consistency is improved, a hole edge false signal is effectively inhibited by establishing an accurate electromagnetic distortion function model and performing real-time compensation, and the false alarm rate is greatly reduced.

Description

Technical Field

[0001] This application belongs to the field of nondestructive testing technology, specifically relating to an array eddy current testing method and apparatus for rivet hole edge cracks. Background Technology

[0002] In the field of aerospace manufacturing and maintenance, riveting is the primary connection method for aircraft structures, and its quality directly affects flight safety. Rivet hole edges are prone to fatigue crack initiation under alternating loads; therefore, regular and effective non-destructive testing of rivet holes is crucial. Eddy current testing technology is widely used due to its high sensitivity to surface cracks.

[0003] However, traditional eddy current testing technology faces three major technical bottlenecks in rivet hole defect detection: First, conventional rigid probes are difficult to adapt to complex curved surfaces with different hole diameters, resulting in an air gap (lift-off effect) between the probe and the hole wall, causing inconsistent signal attenuation and even blind spots. Second, a single-frequency excitation signal cannot simultaneously meet the detection requirements of surface microcracks and deeper subsurface defects, creating a contradiction between detection depth and resolution. Finally, the magnetic field distortion effect at the edge of the rivet hole generates strong spurious signals, severely interfering with the identification and judgment of true defect signals. Currently, although some studies have attempted to improve detection results through multi-frequency excitation or simple signal compensation algorithms, most remain at the theoretical or laboratory stage, failing to form a systematic engineering solution. Especially in array-based detection, existing technologies mostly use rigid array probes with fixed spacing, which not only have poor adaptability but also cannot effectively solve the problem of accurate extraction of edge interference and complex defect features.

[0004] Therefore, developing an array eddy current testing technology that can adapt to different apertures, effectively suppress aperture edge interference, and achieve accurate quantification and identification of defects has become a key problem that urgently needs to be solved in the field of aerospace nondestructive testing. Summary of the Invention

[0005] This application aims to address at least one of the technical problems existing in the prior art or related technologies.

[0006] To address this, this application presents an array eddy current detection method and apparatus for rivet hole edge cracks. This approach effectively solves problems such as probe fit, depth detection, and edge interference suppression by combining innovative flexible eddy current array probe design, multi-frequency excitation, and intelligent signal processing technology, significantly improving the accuracy, reliability, and efficiency of detection.

[0007] This application provides an array eddy current detection method for cracks at the edge of rivet holes, comprising the following steps: S1, Probe bonding step: Insert the flexible eddy current array probe into the rivet hole to be tested, control the micro air pressure bag to inflate, so that the probe self-adapts to the hole wall; S2, Signal acquisition steps: Apply a multi-frequency mixed excitation signal to the probe, and move the probe in a spiral progressive scanning manner to acquire the eddy current response signal of the borehole wall; S3, Signal compensation step: Based on the radial distance and azimuth of the current probe position, query the pre-established electromagnetic distortion function library to perform real-time compensation on the acquired raw signal; S4, Signal fusion step: Perform dynamic weighted fusion of signal-to-noise ratio on the compensated multi-band signals to generate a fused feature map; S5, Defect Judgment Steps: Calculate the local contrast and local region energy of each point in the fused feature map, and identify defects based on the dual-feature joint judgment criterion.

[0008] Furthermore, the method for establishing the electromagnetic distortion function library includes: A reference signal was obtained by measuring on a non-porous flat plate using the flexible eddy current array probe. The probe was used to scan standard rivet hole test blocks of different diameters and to collect signals at different radial distances and azimuth angles at the edge of the hole. By comparing the signal with the aperture with the reference signal, the amplitude distortion function and the phase distortion function are established respectively. By fusing the amplitude distortion function and the phase distortion function in the complex domain, a comprehensive electromagnetic distortion function model is constructed.

[0009] Furthermore, the signal compensation step specifically includes: calculating the corresponding amplitude compensation coefficient and phase compensation amount from the distortion function model based on the radial distance and azimuth angle of the detection point, performing gain compensation on the amplitude of the original signal, and performing phase offset correction.

[0010] Furthermore, the signal-to-noise ratio dynamic weighting strategy in the signal fusion step is as follows: based on the signal-to-noise ratio of each frequency band signal in the defect area and the background area, its weight in the fusion process is dynamically allocated, and the frequency band with the higher signal-to-noise ratio has a greater weight.

[0011] Furthermore, when the local contrast of a point is greater than 2.5, and the energy of the local window where the point is located is greater than three times the median energy of all windows in the entire region of interest, the point is determined to be a defect.

[0012] This application provides an array eddy current detection device for cracks at the edge of rivet holes, comprising: A flexible eddy current array probe is used to adaptively fit with the curved surface of the inner wall of a rivet hole for signal sensing. A multi-frequency excitation signal generation module is used to generate mixed excitation signals of low, medium and high frequencies and apply them to the flexible eddy current array probe. The signal acquisition and processing module is used to acquire and process the response signals from the flexible eddy current array probe; The defect determination module is used to determine whether there are cracks on the edge of the rivet hole based on the processed signal. The flexible eddy current array probe includes: The flexible substrate with a U-shaped structure can be inserted into rivet holes; The core layer is a flexible PCB substrate disposed on the flexible substrate, on which multiple micro eddy current coils are etched in a two-dimensional array. The functional layer integrates a miniature airbag and a pressure sensor. The miniature airbag is controlled to inflate and deflate to push the probe to expand or contract, so that the probe is in close contact with or away from the hole wall. The pressure sensor is used to monitor the contact force in real time and perform closed-loop control. A protective layer, a wear-resistant coating covering the outside of the probe.

[0013] Furthermore, the arrangement of the micro eddy current coil array is as follows: all coils are divided into several parallel rows in the horizontal direction, and the coils in the same row are arranged in a straight line at equal intervals, with a center-to-center distance of d between adjacent coils; the projection position of each coil in the (n+1)th row in the vertical direction is located at the midpoint between two adjacent coils in the nth row.

[0014] Furthermore, the signal acquisition and processing module includes: The electromagnetic distortion compensation unit has a pre-stored electromagnetic distortion function library based on different apertures and azimuth angles, which is used to compensate the acquired raw signals in real time to suppress the pseudo signals generated by the magnetic field distortion at the aperture edge. The multi-frequency signal fusion unit is used to perform dynamic signal-to-noise ratio weighted fusion of compensated low, medium and high frequency signals to generate fused characteristic signals.

[0015] Furthermore, the defect determination module performs a dual-feature joint determination by extracting the local contrast features and regional energy features of the fused feature signal. A defect is determined only when the local contrast is greater than a first threshold and the regional energy is greater than a second threshold.

[0016] Compared with the prior art, the technical solution provided in this application has at least the following beneficial effects: This application provides an array eddy current detection method and device for rivet hole edge cracks. By using a flexible eddy current array probe in conjunction with a pneumatic attachment mechanism, it can adapt to rivet holes of different diameters, eliminate the lift-off effect, and improve signal consistency, thus exhibiting strong adaptability. By establishing an accurate electromagnetic distortion function model and performing real-time compensation, the pseudo signal at the hole edge was effectively suppressed, the false alarm rate was greatly reduced, and the anti-interference capability was outstanding. By using multi-frequency hybrid excitation and SNR weighted fusion technology, it can detect both surface micro-cracks and deeper subsurface defects, achieving layered defect depth detection and facilitating a balance between detection depth and resolution. By employing a dual feature of local contrast and regional energy for joint determination, the system effectively distinguishes between genuine defects and pseudo-signals caused by random noise or uneven background, thereby improving the reliability of identification and achieving high accuracy. The integrated design automates the entire process from signal acquisition to defect determination, reducing reliance on operator experience, improving detection efficiency, and achieving a high degree of automation.

[0017] Additional aspects and advantages of this application will become apparent in the following description or may be learned by practice of this application. Attached Figure Description

[0018] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic flowchart of an array eddy current detection method for rivet hole edge cracks according to some embodiments of this application; Figure 2 This is a flowchart of an array eddy current detection device for rivet hole edge cracks according to some embodiments of this application; Figure 3 This is a schematic diagram of a flexible eddy current array probe structure of an array eddy current detection device for rivet hole edge cracks according to some embodiments of this application; Figure 4 This is a cross-sectional view of a flexible eddy current array probe of an array eddy current detection device for rivet hole edge cracks according to some embodiments of this application. Figure 5 This is a cross-sectional structural schematic diagram of a flexible PCB substrate for an array eddy current detection device for rivet hole edge cracks according to some embodiments of this application.

[0019] Figure label: Flexible PCB substrate 1, coil 2, protective layer 3, airbag 4, core layer 5, functional layer 6. Detailed Implementation

[0020] To better understand the above-mentioned objectives, features, and advantages of this application, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0022] The following reference Figures 1 to 2 This application describes an array eddy current detection method and apparatus for rivet hole edge cracks according to some embodiments.

[0023] Example 1 The specific steps of the detection method are as follows: S1, Probe Fitting Steps: Insert the flexible eddy current array probe into the rivet hole to be tested, control the micro airbag to inflate, so that the probe fits adaptively with the hole wall, as follows.

[0024] Establish an electromagnetic distortion function library (conducted offline to prepare for real-time compensation). To address the problem of magnetic field distortion interference in the detection of edge defects in aviation rivet holes, a multi-band electromagnetic field coupling modeling and adaptive weighted fusion technology is used to achieve real-time compensation of the edge distortion field and accurate extraction of real defects.

[0025] The generation of multi-frequency hybrid excitation uses the AD9959 chip to generate low, medium, and high frequency synchronization signals. A three-channel direct digital frequency synthesis is employed to output the excitation signal. These are the weighting coefficients for low, medium, and high frequency signals, respectively.

[0026] S2, Signal Acquisition Steps: Using the flexible eddy current array probe as described in claim 1, signal acquisition is performed on standard aviation rivet holes with diameters ranging from 3 to 15 mm. Artificial defects are introduced for rivet holes of different diameters for comparative verification. A radial scan is performed along the edge of the hole, with each scan sector representing 10°, resulting in a total of 36 data sets.

[0027] Using the flexible eddy current array probe described in this invention, eddy current signals are measured on a holeless flat plate. The specimen with holes was scanned, and the signal at the edge of the holes was recorded. , The radial distance from the detection point to the edge of the hole. The azimuth angle of the detection point is measured three times and averaged to suppress random noise. A moving average filter is used for data preprocessing. Simultaneously, normalization is performed to normalize the signal amplitude and phase to a reference.

[0028] After completing edge signal acquisition and preprocessing, to accurately quantify the electromagnetic distortion characteristics of the aperture edge, a distortion function model covering different radial distances r and azimuth angles θ needs to be established. This model is constructed by separating the amplitude and phase distortion characteristics of the signal and combining them with spatial distribution features. The specific steps are as follows: Amplitude distortion function The attenuation effect of the aperture edge on the magnetic field amplitude is characterized by calculating the amplitude ratio of the signal in the aperture region to that in the reference region without aperture: Because the electromagnetic distortion at the aperture edge exhibits a decreasing trend radially and fluctuates periodically due to the influence of the azimuth angle, for each To quantify this phenomenon, an exponential decay curve is fitted along the radial direction r. In the formula The distortion amplitude related to the azimuth angle. Attenuation coefficient, Spatial period, R is the radial distance from the detection point to the edge of the hole, and R is the radius of the rivet hole.

[0029] Phase distortion function The phase difference between the signal from the region with the aperture and the reference signal from the region without the aperture is calculated to characterize the phase shift effect of the magnetic field at the aperture edge: In the formula This indicates the phase of the eddy current signal at the detection point on the specimen with holes. This indicates the phase of the eddy current signal in the corresponding region on the non-porous flat plate.

[0030] Since the phase distortion exhibits a nonlinear decay characteristic with respect to radial distance, a rational polynomial is used for each... Fitting along the radial direction r: This is the amplitude coefficient related to the azimuth angle, which controls the distortion intensity. The attenuation scale parameter related to the azimuth angle determines the range of distortion influence. R is the rivet hole radius.

[0031] Synthetic distortion function By fusing the amplitude distortion function and the phase distortion function in the complex domain, a complete electromagnetic distortion model is constructed to comprehensively describe any position at the edge of the aperture. The magnetic field distortion pattern: S3, Signal compensation steps: Based on the radial distance and azimuth of the probe's current position, query the pre-established electromagnetic distortion function library to perform real-time compensation on the acquired raw signal, as follows.

[0032] Probe application and scanning: Insert the probe into the hole to be inspected, and inflate the air bladder to 0.08 MPa. The control mechanism drives the probe in a spiral, progressive motion within the hole for scanning. Input includes amplitude. phase Real-time detection signal The current detection point is obtained through sensor position feedback. These are the radial distance and azimuth angle. The radial distance and azimuth angle data of the detection points are input into the distortion function to perform real-time compensation for each frequency band signal. In the formula, K=(L,M,H) represents the low, medium and high frequency bands.

[0033] Amplitude compensation eliminates edge amplitude attenuation: Phase compensation corrects phase shift: S4, Signal fusion step: Perform dynamic weighted fusion of signal-to-noise ratio on the compensated multi-band signals to generate a fusion feature map, as shown below.

[0034] To fully utilize the advantages of each frequency band and mitigate its disadvantages, multi-frequency signal fusion technology is needed to achieve information complementarity and improve the identification of defect characteristics. The specific process is as follows: First, the compensated signals for each frequency band are subjected to Fourier transform to convert them to the frequency domain, so as to more intuitively reflect the distribution characteristics of different frequency components: Secondly, to further eliminate background interference in defect-free areas and highlight signal differences in potential defects, differential calculation is performed on the frequency domain signal (where...). (The compensated signal with a defect-free background) Finally, a dynamic SNR weighting strategy is employed for signal fusion. Considering the differences in signal-to-noise ratio across different frequency bands, dynamic weight allocation prioritizes the retention of high-quality signals. It is a linear rectified function. The dynamic weight of the k-th frequency band is determined by the signal-to-noise ratio (SNR): This represents the average signal value of the k-th frequency band in the defect area. This represents the standard deviation of the k-th frequency band in the background region (characterizing the noise level). This is the adaptive threshold for the k-th frequency band, used to suppress background noise. The value is adaptively adjusted based on the background noise level of each frequency band. The specific value can be determined through experimental calibration or by setting a preset empirical range. This fusion process can aggregate effective information from multiple frequency bands into a single feature map. This provides a more robust input for subsequent defect assessment.

[0035] S5, Defect Judgment Steps: To accurately distinguish between genuine defects and pseudo-signals, this invention extracts local anomaly features and regional energy features of the signal to construct a dual-feature joint judgment criterion, achieving reliable defect identification. The specific steps are as follows: (1) Local contrast LC Signal diagram after multi-frequency fusion Local statistical analysis is performed to quantify the degree of defect anomaly. By calculating the deviation of the current point signal value from the mean signal value in a 3×3 local neighborhood, the characteristics of local abrupt changes are highlighted. (2) Regional energy E By accumulating signal energy within a window, defect regions and noise are distinguished. Defects, as continuous regions of a certain size, exhibit significant signal energy aggregation within the local window, while noise energy is more dispersed. The energy aggregation within the local window Ω is extracted. In the formula This represents the position parameter within a local window, used to traverse various points within the window; (3) Joint judgment A single feature is insufficient to completely eliminate spurious signal interference. For example, high local contrast may be caused by impulse noise, and high regional energy may be caused by background unevenness. Therefore, a dual-feature joint determination is adopted. If and only if LC is greater than 2.5 and E is greater than 3 times the median ( When ), it is judged as a defect. Among them, median ( ) is the median of the energy of all windows within the region of interest (ROI), used to adaptively adapt to the background energy level under different detection scenarios.

[0036] Example 2 An array eddy current detection device for cracks on the edge of a rivet hole, characterized in that it comprises: a flexible eddy current array probe for adaptively fitting with the curved surface of the inner wall of the rivet hole and for signal sensing; a multi-frequency excitation signal generation module for generating mixed excitation signals of low, medium, and high frequencies and applying them to the flexible eddy current array probe; a signal acquisition and processing module for acquiring and processing the response signals from the flexible eddy current array probe; and a defect determination module for determining whether a crack exists on the edge of the rivet hole based on the processed signals; wherein the flexible eddy current array probe comprises: a U-shaped flexible substrate capable of being inserted into the rivet hole; a core layer, which is a flexible PCB substrate disposed on the flexible substrate, on which multiple micro eddy current coils are etched in a two-dimensional array; a functional layer integrating a micro air bladder and a pressure sensor, wherein the micro air bladder is controlled to inflate or deflate to push the probe to expand or contract, causing the probe to fit tightly or detach from the hole wall, and the pressure sensor is used to monitor the fitting force in real time and perform closed-loop control; and a protective layer, a wear-resistant coating covering the outside of the probe. The arrangement of the micro eddy current coil array is as follows: all coils are divided into several parallel rows in the horizontal direction, with coils in the same row arranged in a straight line at equal intervals, and the center-to-center distance between adjacent coils is d; the vertical projection position of each coil in the (n+1)th row is located at the midpoint between two adjacent coils in the nth row. The signal acquisition and processing module includes: an electromagnetic distortion compensation unit, which has a pre-stored electromagnetic distortion function library based on different apertures and azimuth angles, used to compensate the acquired raw signal in real time to suppress pseudo-signals generated by magnetic field distortion at the aperture edge; and a multi-frequency signal fusion unit, used to dynamically weight and fuse the compensated low, medium, and high frequency signals to generate a fused feature signal. The defect determination module performs dual-feature joint determination by extracting the local contrast features and regional energy features of the fused feature signal. A defect is determined only when the local contrast is greater than a first threshold and the regional energy is greater than a second threshold.

[0037] Furthermore, such as Figure 1 As shown, the detection device of this invention mainly consists of a flexible eddy current array probe, a multi-frequency excitation signal generation module, a signal acquisition and processing module (including amplification, filtering, analog-to-digital conversion circuits, etc.), a main control computer (running signal processing and defect judgment algorithms), and a mechanical scanning mechanism. The substrate material uses a flexible PCB substrate as the carrier, with a thickness controlled at 0.15-0.25 mm and a bending radius of 1-1.5 mm to accommodate rivet hole diameters of 3-15 mm. Multiple sets of rectangular eddy current coils are etched or printed on the substrate. Each set of coils is independently excited and received, with an axial spacing controlled at 0.8-1.2 mm and a circumferential spacing of 1-1.5 mm. The coils are connected to an external high-frequency connector via embedded microstrip lines, with impedance matched to 50Ω to reduce signal attenuation.

[0038] Furthermore, such as Figure 3As shown, this probe adopts a "sandwich" layered structure, which includes a functional layer, a core layer and a protective layer from the inside out: the functional layer contains a miniature air bladder and a pressure sensor, wherein the surface of the miniature air bladder is provided with micro-grooves to make the pressure distribution uniform and avoid local overpressure; the core layer is a flexible PCB coil array, which serves as the core component to realize the detection function; the protective layer is a wear-resistant coating to provide protection.

[0039] Furthermore, the inflatable micro-bladder expands the probe upon inflation, ensuring it adheres tightly to the orifice wall. Closed-loop control via an internal pressure sensor maintains the probe's contact force within the optimal range of 0.05-0.1 MPa. This design eliminates the air gap between the orifice wall and the probe, significantly reducing the lift-off effect. Moreover, the same probe can be adapted to different orifice diameters without requiring tooling changes.

[0040] Furthermore, the flexible eddy current array probe comprises a flexible PCB substrate, a miniature airbag, and an outer protective layer (specific structure as follows). Figure 4 (As shown). The flexible PCB substrate integrates multiple precision-etched eddy current detection coils, arranged in a regular pattern: all probes are divided into several parallel rows in the horizontal direction, with probes within the same row arranged equidistantly in a straight line, and the center-to-center distance between adjacent probes is d; specifically, the vertical projection position of each probe in the (n+1)th row is precisely located at the midpoint between two adjacent probes in the nth row (the specific arrangement is as follows). Figure 5 (As shown). Based on this U-shaped structure and flexible array design, the probe adopts a spiral progressive scanning method, combined with the contact force control of the airbag, to ensure that each coil maintains stable coupling with the borehole wall during the scanning process, providing highly reliable raw data for multi-frequency signal acquisition and processing.

[0041] Furthermore, the multi-frequency excitation signal generation module uses the AD9959 chip as its core, setting the low frequency f_L=50kHz for detecting deeper defects, the medium frequency f_M=200kHz for detecting medium-depth defects, and the high frequency f_H=1MHz for detecting surface cracks. The weighting coefficients are set to α_L=0.4, α_M=0.35, and α_H=0.25.

[0042] In summary, the array eddy current detection method and apparatus for rivet hole edge cracks provided in this application have the following advantages: Strong adaptability: The flexible eddy current array probe, combined with a pneumatic attachment mechanism, can adapt to rivet holes of different diameters, eliminating the lift-off effect and improving signal consistency; Outstanding anti-interference capability: By establishing an accurate electromagnetic distortion function model and performing real-time compensation, pseudo-signals at the hole edge are effectively suppressed, greatly reducing the false alarm rate; Balanced detection depth and resolution: Multi-frequency hybrid excitation and SNR weighted fusion technology can detect both surface micro-cracks and deeper subsurface defects, achieving layered defect depth detection; High judgment accuracy: The joint judgment using local contrast and regional energy dual features effectively distinguishes between real defects and pseudo-signals caused by random noise or background inhomogeneity, improving the reliability of identification; High degree of automation: The integrated design realizes full automation from signal acquisition to defect judgment, reducing reliance on operator experience and improving detection efficiency.

[0043] In this application, it should be noted that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0045] In this application, unless otherwise expressly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. The term "multiple" refers to two or more, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0046] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0047] In this application, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0048] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for detecting cracks at the edge of rivet holes using an array of eddy currents, characterized in that, Includes the following steps: S1, Probe bonding step: Insert the flexible eddy current array probe into the rivet hole to be tested, control the micro air pressure bag to inflate, so that the probe self-adapts to the hole wall; S2, Signal acquisition steps: Apply a multi-frequency mixed excitation signal to the probe, and move the probe in a spiral progressive scanning manner to acquire the eddy current response signal of the borehole wall; S3, Signal compensation step: Based on the radial distance and azimuth of the current probe position, query the pre-established electromagnetic distortion function library to perform real-time compensation on the acquired raw signal; S4, Signal fusion step: Perform dynamic weighted fusion of signal-to-noise ratio on the compensated multi-band signals to generate a fused feature map; S5, Defect Judgment Steps: Calculate the local contrast and local region energy of each point in the fused feature map, and identify defects based on the dual-feature joint judgment criterion.

2. The array eddy current detection method for rivet hole edge cracks according to claim 1, characterized in that, The method for establishing the electromagnetic distortion function library includes: A reference signal was obtained by measuring on a non-porous flat plate using the flexible eddy current array probe. The probe was used to scan standard rivet hole test blocks of different diameters and to collect signals at different radial distances and azimuth angles at the edge of the hole. By comparing the signal with the aperture with the reference signal, the amplitude distortion function and the phase distortion function are established respectively. By fusing the amplitude distortion function and the phase distortion function in the complex domain, a comprehensive electromagnetic distortion function model is constructed.

3. The array eddy current detection method for rivet hole edge cracks according to claim 1, characterized in that, The signal compensation step specifically includes: calculating the corresponding amplitude compensation coefficient and phase compensation amount from the distortion function model based on the radial distance and azimuth angle of the detection point, performing gain compensation on the amplitude of the original signal, and performing phase offset correction.

4. The array eddy current detection method for rivet hole edge cracks according to claim 1, wherein the signal-to-noise ratio dynamic weighting strategy in the signal fusion step is as follows: based on the signal-to-noise ratio of each frequency band signal in the defect area and the background area, the weight of each frequency band in the fusion process is dynamically allocated, and the frequency band with the higher signal-to-noise ratio has a greater weight.

5. The array eddy current detection method for rivet hole edge cracks according to claim 1, characterized in that, When the local contrast of a point is greater than 2.5, and the energy of the local window containing that point is greater than three times the median energy of all windows in the entire region of interest, that point is determined to be a defect.

6. An array eddy current detection device for cracks at the edge of rivet holes, characterized in that, include: A flexible eddy current array probe is used to adaptively fit with the curved surface of the inner wall of a rivet hole for signal sensing. A multi-frequency excitation signal generation module is used to generate mixed excitation signals of low, medium and high frequencies and apply them to the flexible eddy current array probe. The signal acquisition and processing module is used to acquire and process the response signals from the flexible eddy current array probe; The defect determination module is used to determine whether there are cracks on the edge of the rivet hole based on the processed signal. The flexible eddy current array probe includes: The flexible substrate with a U-shaped structure can be inserted into rivet holes; The core layer is a flexible PCB substrate disposed on the flexible substrate, on which multiple micro eddy current coils are etched in a two-dimensional array. The functional layer integrates a miniature airbag and a pressure sensor. The miniature airbag is controlled to inflate and deflate to push the probe to expand or contract, so that the probe is in close contact with or away from the hole wall. The pressure sensor is used to monitor the contact force in real time and perform closed-loop control. A protective layer, a wear-resistant coating covering the outside of the probe.

7. The array eddy current detection device for rivet hole edge cracks according to claim 6, characterized in that, The arrangement of the micro eddy current coil array is as follows: all coils are divided into several parallel rows in the horizontal direction, and the coils in the same row are arranged in a straight line at equal intervals, with the center distance between adjacent coils being d; the projection position of each coil in the (n+1)th row in the vertical direction is located at the middle position of the two adjacent coils in the nth row.

8. The array eddy current detection device for rivet hole edge cracks according to claim 6, characterized in that, The signal acquisition and processing module includes: The electromagnetic distortion compensation unit has a pre-stored electromagnetic distortion function library based on different apertures and azimuth angles, which is used to compensate the acquired raw signals in real time to suppress the pseudo signals generated by the magnetic field distortion at the aperture edge. The multi-frequency signal fusion unit is used to perform dynamic signal-to-noise ratio weighted fusion of compensated low, medium and high frequency signals to generate fused characteristic signals.

9. The array eddy current detection device for rivet hole edge cracks according to claim 8, characterized in that, The defect determination module performs a dual-feature joint determination by extracting the local contrast features and regional energy features of the fused feature signal. It determines a defect only when the local contrast is greater than the first threshold and the regional energy is greater than the second threshold.

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