Flexible low frequency eddy current probe

Abstract

The utility model provides a flexible low frequency eddy current probe for detecting the crack of fastener hole edge of aircraft curved panel connecting multilayer structure, which comprises a soft bottom provided at the bottom of the flexible low frequency eddy current probe and formed into a semicircular membrane structure with elasticity, and a limiting part fixedly connected with the edge of the soft bottom and used for limiting the position when the flexible low frequency eddy current probe is fixed to the curved panel. The flexible low frequency eddy current probe can effectively solve the problem of poor adaptability of the probe to the curved surface and easy displacement in the detection of the crack of fastener hole edge of the aircraft curved panel, thereby effectively improving the detection precision.

Description

Technical Field

[0001] This utility model relates to a low-frequency eddy current testing device, specifically a flexible low-frequency eddy current probe suitable for multi-layer structures connecting curved panels of aircraft. It can accurately detect fatigue cracks initiating in the fastener hole edge area of ​​such structures. It is particularly suitable for non-destructive testing of fastener hole edges in multi-layer connection parts of curved panels of aircraft, such as spherical frames and slat leading edge ribs, and belongs to the field of non-destructive testing technology for aircraft. Background Technology

[0002] In the aerospace industry, the fatigue reliability of multi-layered connection structures in aircraft (such as the multi-layered connection areas of spherical frames, slat leading edge ribs, etc.) is directly related to flight safety. Among these, the edges of fastener holes in the middle layers of multi-layered connection structures are high-risk areas for fatigue cracks. If cracks in this area are not detected in time, they can easily propagate with cyclic flight loads, potentially leading to structural failure. Therefore, accurate and efficient non-destructive testing of these cracks is of significant engineering importance.

[0003] Currently, the industry typically employs low-frequency eddy current testing technology to detect fatigue cracks at the edges of fastener holes in multi-layered aircraft connection structures. The testing principle is as follows: a ring-shaped probe with low-frequency eddy currents is fitted over the protrusion of the fastener. The probe excites an eddy current field within the metal structure. Then, by utilizing the sensitivity of the eddy current field to structural defects, the differences in eddy current signals in the fastener hole edge region are compared and analyzed to determine whether fatigue cracks or other damage exist at the hole edge.

[0004] However, existing commercially available low-frequency eddy current ring probes are mainly designed for multi-layer flat plate connection structures. If applied to multi-layer curved plate connection structures commonly found on aircraft (such as spherical frames and multi-layer connection parts of slat leading edge ribs), the following two technical problems exist, which can easily lead to a significant decrease in detection sensitivity and make it difficult to meet the requirements of model detection:

[0005] 1. Poor fit between the probe and the curved surface, resulting in insufficient penetration of eddy current energy: The detection surface of the curved panel connection structure is non-planar. When the annular probe is fitted onto the protrusion of the fastener, a large gap is formed between the probe and the curved surface. This gap makes it difficult for the eddy current energy excited by the probe to effectively penetrate into the interior of the structure, especially in the middle layer of multi-layered structures. This results in a weak eddy current signal response from cracks, making it impossible to effectively identify.

[0006] 2. Insufficient probe stability and increased interference signals: Due to the curved detection surface, the ring probe cannot be stably fitted onto the fastener protrusion, and the probe is prone to shaking during the detection process. The instability of the probe will cause random changes in the excitation state of the eddy current field, thereby introducing a large number of interference signals, masking the characteristic signals of the crack, and further reducing the detection sensitivity.

[0007] To address the compatibility issue of eddy current testing on curved structures, existing technologies have proposed improvements. However, these solutions are not directly applicable to the testing of fastener hole edges in the intermediate layers of multi-layered aircraft connection structures. Specific limitations are as follows:

[0008] Chinese utility model patent CN213021423U discloses an eddy current testing fixture that uses an eddy current probe fitted into a flexible adapter to continuously scan and detect the wall thickness of a non-conductive insulation layer pipe. The core design objective of this solution is pipe wall thickness detection. However, the structure of the flexible adapter and the probe arrangement are optimized for continuous scanning of the pipe's outer surface, making it unsuitable for fitting fastener protrusions or focusing on detecting localized cracks in the hole edge area.

[0009] Chinese utility model patent CN211478151U discloses an array probe for eddy current testing of curved workpieces. It places detection coils in an array surrounding the workpiece within a flexible material and embeds them in a contour-fitting base that conforms to the three-dimensional shape of the workpiece. While this solution achieves a close fit to the curved surface, the contour-fitting base needs to be customized according to the workpiece's shape. For aircraft curved panel connection structures with different curvatures, various bases need to be designed, making the fitting process cumbersome. Furthermore, the array probe has a wide signal acquisition range, making it difficult to accurately focus on localized areas such as the edge of fastener holes. Subsequent processing of multi-channel array signals complicates the signal processing flow and hinders rapid identification of crack features.

[0010] Chinese invention patent CN114594156A discloses a metal curved surface eddy current testing device and its testing method. This method fixes an array of eddy current lines to the surface of a flexible testing device panel, utilizing the deformation of the flexible panel to achieve fit with surfaces of different curvatures. While this solution is suitable for testing large-area flat curved surfaces, its flexible panel support structure cannot adapt to scenarios involving fastener protrusions. Furthermore, the testing area is a large area covered by the panel, making it impossible to perform targeted testing on the small, localized area around the fastener hole, thus failing to meet the precise detection requirements for fatigue cracks at the hole edge.

[0011] In summary, existing low-frequency eddy current testing technologies and related improvement schemes cannot effectively solve the problem of detecting fatigue cracks at the edges of fastener holes in multi-layer structures with curved panel connections in aircraft. There is an urgent need to propose an eddy current testing scheme that is adapted to curved surface structures, can stably mount fastener protrusions, and can accurately focus on the hole edge area, so as to improve the detection sensitivity of fatigue cracks in such key parts and meet the testing requirements of aerospace models. Utility Model Content

[0012] This disclosure is made to solve the above-mentioned technical problems, and its purpose is to provide a flexible low-frequency eddy current probe that can effectively detect fatigue cracks at the edges of fastener holes in multi-layer structures of curved panel connections in aircraft.

[0013] To achieve the purpose of this disclosure, a flexible low-frequency eddy current probe is provided. The flexible low-frequency eddy current probe is used to detect cracks at the edges of fastener holes in a multi-layer structure connecting a curved panel of an aircraft. The flexible low-frequency eddy current probe includes: a soft bottom disposed at the bottom of the flexible low-frequency eddy current probe and formed as an elastic semi-circular membrane structure; and a limiting portion fixedly connected to the edge of the soft bottom and used to limit the position of the flexible low-frequency eddy current probe when it is fixed to the curved panel.

[0014] Based on the above-described configuration, the "soft bottom with a flexible semi-circular membrane structure" can adapt to the curved surface of the aircraft panel, thereby solving the problem that traditional probes cannot fit the curved surface. At the same time, the position of the probe is limited by the limiting part to avoid probe displacement during detection, which can effectively solve the problem of "poor probe compatibility with the curved surface and easy displacement" in the detection of cracks at the edge of fastener holes on aircraft curved panels.

[0015] Preferably, the flexible low-frequency eddy current probe further includes a flexible coil, which is formed into an arc-shaped structure adapted to the soft bottom and fixed to the side of the soft bottom facing the curved panel.

[0016] As described above, the flexible coil and the soft bottom are designed with an arc shape that can fit the curved panel surface synchronously with the soft bottom, ensuring that the distance between the coil and the curved panel surface is uniform. This can effectively avoid the problem of disordered eddy current field distribution caused by uneven gaps between the traditional planar coil and the curved surface, and improve the uniformity of eddy current field coverage of the curved panel and fastener area.

[0017] Preferably, the lead end of the flexible coil extends from the edge of the soft bottom and is connected to the signal output terminal of the eddy current detector via a power line to receive the low-frequency excitation electrical signal emitted by the eddy current detector, so as to generate a low-frequency eddy current field around the fasteners of the curved panel.

[0018] Based on the above-described configuration, the signal connection design between the flexible coil and the eddy current detector can accurately receive low-frequency excitation electrical signals and generate a low-frequency eddy current field around the fastener. The low-frequency characteristics enable the eddy current field energy to effectively penetrate into the multi-layer connection structure of the aircraft curved panel, solving the problem that traditional high-frequency eddy current fields cannot penetrate multi-layer structures and are difficult to detect deep cracks.

[0019] Preferably, the flexible low-frequency eddy current probe further includes a receiving coil, which is composed of multiple small coils connected in parallel. The multiple small coils are evenly distributed circumferentially inside the flexible coil, and their centers all point to the axial direction of the flexible coil.

[0020] As described above, the design of multiple small coils connected in parallel and evenly distributed circumferentially with the center pointing towards the axis enables "surround" signal acquisition of the fastener hole edge area. Compared with the traditional single receiving coil, it can more comprehensively cover the area of ​​the hole edge that is prone to cracking, thereby avoiding the problem of missed crack detection due to the limited acquisition range.

[0021] Preferably, the flexible low-frequency eddy current probe further includes a signal processor, which is fixedly installed on the inner wall of the flexible low-frequency eddy current probe. Its output end is connected to the signal input end of the eddy current detector through a communication line, and it can process the signal collected by the receiving coil and transmit it to the eddy current detector.

[0022] As described above, integrating the signal processor into the inner wall of the probe can shorten the signal transmission path between the receiving coil and the processor, reducing signal attenuation and interference during transmission. At the same time, by preprocessing the signal through the processor, the problem of "high signal noise and low recognition" caused by directly transmitting the original weak signal to the detector can be avoided, which can effectively improve the accuracy of subsequent crack signal analysis.

[0023] Preferably, the receiving coil is connected to the input terminal of the signal processor to acquire abnormal eddy current field signals caused by cracks in the inspected area and transmit the abnormal signals to the signal processor.

[0024] Based on the above configuration, the receiving coil specifically collects "abnormal signals of eddy current fields caused by cracks," which can directly capture the interference characteristics of cracks on eddy current fields. Then, through direct connection with the signal processor, it can realize the rapid transmission and processing of abnormal signals, avoiding the problems of difficult signal screening and low crack identification efficiency caused by irrelevant signals mixing in, thereby effectively improving the response speed of crack detection.

[0025] Preferably, the limiting part includes a limiting collar, a limiting foot, and a limiting switch. The limiting collar is sleeved on the outer side of the soft bottom and fixedly connected to the edge of the soft bottom. Multiple limiting feet are formed and are evenly distributed along the circumference of the limiting collar and can extend and retract along the axial direction of the limiting collar. The limiting switch is embedded in the outer wall of the limiting collar and electrically connected to the limiting feet, and can control the extension and retraction state of the limiting feet.

[0026] As described above, the fixed connection between the limiting collar and the soft bottom can effectively ensure the synchronous movement of the limiting part and the soft bottom, avoiding relative displacement between the two and affecting the fitting accuracy; multiple sets of circumferentially evenly distributed telescopic limiting feet can support and position the probe from multiple directions. With the limit switch controlling the telescopic state, it can effectively solve the problem of "easy shaking and unstable positioning" of traditional probes when detecting curved surfaces, thereby ensuring the consistency of the probe position during the detection process.

[0027] Preferably, the aforementioned limiting foot uses a spring telescopic structure to achieve axial extension and retraction.

[0028] As described above, the limiting feet of the spring telescopic structure have the ability to automatically adapt to the height difference of the curved panel surface. When the probe is pressed against the curved surface, the spring can automatically adjust the telescopic length according to the local curvature of the curved surface, ensuring that all limiting feet can reliably contact the curved panel surface. This effectively avoids the problem of some limiting feet being suspended and unstable due to the undulation of the curved surface, and further improves the reliability of probe positioning.

[0029] Preferably, the semi-circular membrane structure of the soft bottom is capable of bending and deforming synchronously with the curvature of the curved panel to be tested under the action of external force.

[0030] As described above, the characteristic of the soft bottom bending synchronously with the curvature of the curved panel can effectively ensure that the soft bottom and the coil fixed on it are always in close contact with the curved surface, minimizing the gap between the coil and the curved surface. Compared with traditional rigid bottom probes, it can avoid the problem of "more energy loss of eddy current field and weak crack signal" caused by excessive gap, thereby improving the penetration efficiency of eddy current field into multi-layer structures and the intensity of crack signal.

[0031] Preferably, after the soft bottom of the flexible low-frequency eddy current probe is pressed against the curved surface of the curved panel, the flexible low-frequency eddy current probe is fixed in place by the limiting part.

[0032] As described above, the tight fit between the soft bottom and the curved surface ensures the compatibility between the coil and the curved surface. Then, the position of the probe is fixed by the limiting part, forming a double guarantee of "fitting-fixing". This can avoid the problem of probe slippage caused by fixing by the bonding force alone, and also prevent the problem of loose fit caused by fixing first and then fitting. Ultimately, it can effectively ensure that the gap between the coil and the curved surface is always kept within a small and stable range during the detection process, thereby effectively ensuring the accuracy of crack detection. Attached Figure Description

[0033] With reference to the above objectives, the technical features of this utility model are clearly described in the following technical solutions, and its advantages are apparent from the following detailed description with reference to the accompanying drawings, which illustrate preferred embodiments of this utility model by way of example, without limiting the scope of the inventive concept.

[0034] Figure 1 This is a schematic diagram showing the overall structure of the flexible low-frequency eddy current probe of this utility model.

[0035] Figure 2 This is a schematic diagram showing the improved structure of the flexible low-frequency eddy current probe of this invention compared to previous low-frequency eddy current probes.

[0036] Figure 3A This is a schematic diagram showing the structure of the curved panel. Figure 3B This is a schematic diagram showing the state of the flexible low-frequency eddy current probe of this utility model when it is installed on a curved panel, compared to the conventional low-frequency eddy current probe. Symbol Explanation

[0037] 1. Flexible low-frequency eddy current probe; 11. Soft bottom; 12. Limiting part; 121 Limit foot; 122 Limiting collar; 123 Limit switches; 13. Flexible coil; 14. Receiving coil; 15 Signal Processors 2. Eddy current detector; QMB curved panel; FSJ Fasteners; TXC communication line; 1' Existing low-frequency eddy current probe. Detailed Implementation

[0038] Various embodiments of the present invention will now be described in detail, examples of which are shown in the accompanying drawings.

[0039] Although this invention has been described in conjunction with exemplary embodiments, it should be understood that this specification is not intended to limit the invention to the exemplary embodiments described below. Rather, the invention is intended to cover not only these exemplary embodiments, but also various alternatives, modifications, equivalents, and other embodiments that may be included within the spirit and scope of the invention as defined by the appended claims.

[0040] The core of this invention is to provide a flexible low-frequency eddy current probe 1 to solve the problem of difficulty in detecting fatigue cracks in the fasteners FSJ in the multi-layer structure of the QMB curved panel of an aircraft.

[0041] The following is for reference Figure 1 The overall structure of the flexible low-frequency eddy current probe 1 of this utility model will be described.

[0042] like Figure 1 As shown, the flexible low-frequency eddy current probe 1 of this utility model mainly includes a soft bottom 11, a limiting part 12, a flexible coil 13, a receiving coil 14 and a signal processor 15, and is also equipped with an eddy current detector 2. The flexible low-frequency eddy current probe 1 and the eddy current detector 2 are connected by a communication line TXC to achieve signal transmission.

[0043] The aforementioned soft bottom 11 is made of an insulating material (such as silicone rubber composite material) that is resistant to bending and has a certain degree of elasticity. Its overall shape is a semi-circular membrane structure. This structure design can adapt to the curved surface of the aircraft curved panel QMB and can bend and deform synchronously with the curvature of the curved panel QMB under the action of external force, thereby ensuring the degree of fit between the flexible coil 13 described later and the surface of the curved panel QMB.

[0044] The aforementioned limiting part 12 includes a limiting foot 121, a limiting collar 122, and a limiting switch 123.

[0045] The aforementioned limiting collar 122 is sleeved on the outer side of the aforementioned soft bottom 11 and is fixedly connected to the edge of the semi-circular membrane of the soft bottom 11. The aforementioned limiting feet 121 are evenly distributed along the circumference of the limiting collar 122 (preferably 3-4 feet are provided), and each limiting foot 121 is provided in a manner that can extend and retract along the axial direction of the limiting collar 122 (for example, using a spring telescopic structure). The aforementioned limiting switch 123 is embedded in the outer wall of the limiting collar 122 and is electrically connected to the limiting feet 121, and can control the extension and retraction state of the limiting feet 121 and the relative fixed position of the limiting feet 121 and the limiting collar 122.

[0046] The aforementioned flexible coil 13 is a flexible excitation coil formed by winding enameled copper wire. Its overall shape is an arc structure that adapts to the semi-circular film of the soft bottom 11, and it is fixedly installed on the inner side of the soft bottom 11 (towards the curved panel QMB) by high-temperature resistant insulating glue.

[0047] In addition, the input end of the aforementioned flexible coil 13 is connected to the signal output end of the eddy current detector 2 via a power line (not shown), and can receive the excitation electrical signal emitted by the eddy current detector 2, thereby generating a low-frequency eddy current field around the curved panel QMB and the fastener FSJ.

[0048] The receiving coil 14 is composed of multiple small enameled copper wire coils (preferably 4-6) connected in parallel. Each small coil has a circular or square structure and is evenly distributed circumferentially on the inner side of the flexible coil 13. The center of each small coil points to the axis of the fastener FSJ (focusing on the hole edge area of ​​the fastener FSJ).

[0049] Furthermore, the output terminal of the aforementioned receiving coil 14 is connected to the input terminal of the signal processor 15 via a communication line (not shown), enabling the acquisition of abnormal signals of the eddy current field caused by cracks in the inspected area.

[0050] The signal processor 15 is an embedded microprocessor that integrates signal filtering, amplification and coil positioning modules. The signal processor 15 is fixedly installed on the inner wall of the limiting collar 122. Its output end is connected to the signal input end of the eddy current detector 2 through the communication line TXC. It can process the signal collected by the receiving coil 14 and transmit it to the eddy current detector 2.

[0051] The following is for reference Figure 2 The advantages of the flexible low-frequency eddy current probe 1 of this utility model compared with the existing low-frequency eddy current probe 1' are explained.

[0052] like Figure 2 As shown, compared with the existing low-frequency eddy current probe 1', the improved flexible low-frequency eddy current probe 1 has a soft bottom 11 and a limiting part 12 added to the bottom. By promoting the semi-circular flexible structure of the soft bottom 11 and the supporting and positioning function of the limiting part 12, the separation between the flexible coil 13 and the curved surface can be effectively reduced, and more eddy current field energy can be penetrated into the multi-layer structure, thereby effectively solving the problem of weak crack signal due to large gaps in the existing probe.

[0053] Next, continue to refer to Figures 3A to 3B The assembly method of the flexible low-frequency eddy current probe 1 of this utility model will be described.

[0054] like Figure 3A As shown, an arc-shaped curved surface is formed on the curved panel QMB, and multiple fasteners FSJ are provided through the curved panel QMB. These fasteners FSJ are distributed in an array inside the curved panel.

[0055] When it is necessary to detect cracks near the fastener FSJ of the curved panel QMB using the flexible low-frequency eddy current probe 1 of this utility model, the first step is to complete the system assembly of the flexible low-frequency eddy current probe 1. The specific assembly steps are as follows:

[0056] The flexible coil 13 is bonded and fixed to the inside of the soft bottom 11 with insulating adhesive, ensuring that the arc-shaped contour of the flexible coil 13 is completely in contact with the semi-circular film of the soft bottom 11, and the lead end of the flexible coil 13 passes through the edge of the soft bottom 11 and is connected to one end of the power cord.

[0057] Multiple small coils are connected in parallel to form a receiving coil 14. The receiving coil 14 is fixed to the inside of the soft bottom 11 with insulating glue, and each small coil is located in the inner area of ​​the flexible coil 13. After the lead ends of each small coil are combined, they are connected to the input end of the signal processor 15.

[0058] The signal processor 15 is fixed to the inner wall of the limiting collar 122 with screws, and the limit switch 123 is embedded into the preset mounting hole of the limiting collar 122, and the circuit connection between the limit switch 123 and the limit foot 121 is completed.

[0059] The limiting collar 122 is fixedly connected to the semi-circular membrane edge of the soft bottom 11 by welding, so as to ensure a firm connection between the two without affecting the bending performance of the soft bottom 11.

[0060] Finally, connect the other end of the communication line TXC to the corresponding interface of the eddy current detector 2 to complete the assembly of the entire detection system.

[0061] like Figure 3B As shown, the existing low-frequency eddy current probe 1' is prone to wobbling when fitted onto the fasteners of the curved panel because it lacks a limiting and flexible structure adapted to the curved surface. The flexible low-frequency eddy current probe 1 of this utility model can stably fit with the curved panel and fasteners by means of a limiting collar and limiting feet.

[0062] Next, after assembling the flexible low-frequency eddy current probe 1, it needs to be installed and fixed in the area to be tested on the curved panel QMB. The specific operation method is as follows:

[0063] Probe placement: The operator holds the limiting collar 122 and aligns the semi-circular membrane opening end of the soft bottom 11 of the flexible low-frequency eddy current probe 1 with the protrusion of the fastener FSJ of the curved panel QMB, and slowly places the probe on the protrusion of the fastener FSJ, so that the inner side of the soft bottom 11 faces the surface of the area to be tested on the curved panel QMB.

[0064] Curved surface fitting and limiting fixation: Next, press down on the limiting collar 122. At this time, the semi-circular membrane of the soft bottom 11 bends with the curvature of the curved panel QMB under pressure, and drives the inner flexible coil 13 to deform synchronously until the inner side of the soft bottom 11 is completely fitted with the surface of the curved panel QMB. During this process, the limiting foot 121 extends along the axial direction until its end contacts the surface of the curved panel QMB and forms a support. After the operator observes that the extension length of the limiting foot 121 is stable, press the limiting switch 123 on the limiting collar 122. The limiting foot 121 immediately stops extending and retracting, and the relative position of the limiting foot 121 and the limiting collar 122 is fixed. At this time, the distance between the flexible coil 13 and the surface of the curved panel QMB can be controlled within a small distance range.

[0065] After the flexible low-frequency eddy current probe 1 is installed and fixed in the area to be inspected on the curved panel QMB, the operator can begin crack detection. The specific operation method is as follows:

[0066] Eddy current excitation and signal acquisition: The eddy current detector 2 is started. The eddy current detector 2 sends a low-frequency excitation electrical signal of a preset frequency to the flexible coil 13 through the communication line TXC. Under the action of the excitation signal, the flexible coil 13 generates a uniform eddy current field in the aircraft curved panel QMB, fastener FSJ and multi-layer structure. If there is a fatigue crack at the edge of the hole of the fastener FSJ being tested, the crack will cut the eddy current field, resulting in an abnormal distribution of the eddy current field. Since each small coil is focused at a different position at the edge of the hole, only the small coil corresponding to the area where the crack is located will collect an obvious abnormal signal. Therefore, this abnormal signal is easily captured by the surrounding receiving coil 14 (multiple parallel small coils).

[0067] Signal processing and crack location: Next, the receiving coil 14 transmits the collected abnormal signal to the signal processor 15 through the communication line TXC. Then, the signal processor 15 transmits the processed crack information to the eddy current detector 2 through the communication line TXC. The display screen of the eddy current detector 2 will simultaneously display the crack location mark and signal amplitude, thereby completing the detection and location of the crack at the edge of the hole of the fastener FSJ in the curved multi-layer structure. (Technical effect)

[0068] Compared with existing low-frequency eddy current probes, the flexible low-frequency eddy current probe of this invention has the following significant advantages:

[0069] The flexible low-frequency eddy current probe of this invention uses a flexible semi-circular membrane structure with a soft bottom and a limiting part for support and positioning. This allows the distance between the flexible coil and the surface of the aircraft curved panel to be much smaller than that of existing probes. The eddy current field energy can be more effectively delivered to the middle layer of the multi-layer structure, thereby solving the problem of weak crack signals caused by large gaps in existing probes.

[0070] Furthermore, the flexible low-frequency eddy current probe of this invention has higher detection stability. Through the support of the limiting foot and the fixing effect of the limiting switch, the shaking caused by the sliding of the curved surface during the detection process can be avoided, thereby effectively reducing interference signals. In contrast, existing probes have no limiting structure and are prone to introducing noise due to shaking.

[0071] Moreover, the flexible low-frequency eddy current probe of this invention provides more accurate crack location. Because the receiving coil adopts a multi-small coil parallel design, it can identify the source coil of the abnormal signal through the signal processor, thereby achieving accurate location of the crack. In contrast, existing probes can only determine whether a crack exists, but cannot determine the specific location of the crack, and the detection accuracy is significantly lower than that of the flexible low-frequency eddy current probe disclosed in this invention.

[0072] Although the structure and working principle of this utility model have been described above in conjunction with preferred embodiments, those skilled in the art should recognize that the above examples are merely illustrative and do not constitute a limitation on this utility model. Modifications and variations can be made to this utility model within the spirit and scope of the claims, and all such modifications and variations will fall within the protection scope of this utility model.

[0073] For example, this invention shows an example of a flexible low-frequency eddy current probe with four limiting feet and eight flexible coils. However, this invention is not limited to this, and the number of the limiting feet and flexible coils can be optimized and adjusted according to the curvature of the surface and actual needs.

Claims

1. A flexible low-frequency eddy current probe (1), said flexible low-frequency eddy current probe (1) is used to detect cracks at the edges of fastener holes (FSJ) in a multi-layer structure connecting a curved panel (QMB) of an aircraft, characterized in that, The flexible low-frequency eddy current probe (1) includes: A soft bottom (11) is disposed at the bottom of the flexible low-frequency eddy current probe (1) and is formed as an elastic semi-circular membrane structure; and The limiting part (12) is fixedly connected to the edge of the soft bottom (11) and is used to limit the position when the flexible low-frequency eddy current probe (1) is fixed to the curved panel (QMB).

2. The flexible low-frequency eddy current probe (1) as described in claim 1, characterized in that, The flexible low-frequency eddy current probe (1) also includes a flexible coil (13). The flexible coil (13) is formed into an arc-shaped structure that fits the soft bottom (11) and is fixed to the soft bottom (11) on the side facing the curved panel (QMB).

3. The flexible low-frequency eddy current probe (1) as described in claim 2, characterized in that, The lead end of the flexible coil (13) extends from the edge of the soft bottom (11) and is connected to the signal output end of the eddy current detector (2) via a power line to receive the low-frequency excitation electrical signal emitted by the eddy current detector (2) to generate a low-frequency eddy current field around the fastener (FSJ) of the curved panel (QMB).

4. The flexible low-frequency eddy current probe (1) as described in claim 3, characterized in that, The flexible low-frequency eddy current probe (1) also includes a receiving coil (14). The receiving coil (14) is composed of multiple small coils connected in parallel. The multiple small coils are evenly distributed circumferentially inside the flexible coil (13), and their centers all point to the axial direction of the flexible coil (13).

5. The flexible low-frequency eddy current probe (1) as described in claim 4, characterized in that, The flexible low-frequency eddy current probe (1) also includes a signal processor (15). The signal processor (15) is fixedly installed on the inner wall of the flexible low-frequency eddy current probe (1), and its output end is connected to the signal input end of the eddy current detector (2) through a communication line (TXC). It can process the signal collected by the receiving coil (14) and transmit it to the eddy current detector (2).

6. The flexible low-frequency eddy current probe (1) as described in claim 5, characterized in that, The receiving coil (14) is connected to the input terminal of the signal processor (15) to collect abnormal signals of the eddy current field caused by cracks in the inspected area and transmit the abnormal signals to the signal processor (15).

7. The flexible low-frequency eddy current probe (1) as described in claim 1, characterized in that, The limiting part (12) includes a limiting collar (122), a limiting foot (121), and a limiting switch (123). The limiting collar (122) is sleeved on the outside of the soft bottom (11) and is fixedly connected to the edge of the soft bottom (11). Multiple limiting feet (121) are formed and are evenly distributed along the circumference of the limiting collar (122) and can extend and retract along the axial direction of the limiting collar (122). The limit switch (123) is embedded in the outer wall of the limit collar (122) and electrically connected to the limit foot (121), and can control the extension and retraction state of the limit foot (121).

8. The flexible low-frequency eddy current probe (1) as described in claim 7, characterized in that, The limiting foot (121) adopts a spring telescopic structure to achieve axial extension and retraction.

9. The flexible low-frequency eddy current probe (1) as described in any one of claims 1 to 8, characterized in that, The semi-circular membrane structure of the soft bottom (11) can bend and deform synchronously with the curvature of the curved panel (QMB) to be tested under the action of external force.

10. The flexible low-frequency eddy current probe (1) as described in claim 9, characterized in that, After the soft bottom (11) of the flexible low-frequency eddy current probe (1) is pressed against the curved surface of the curved panel (QMB), the flexible low-frequency eddy current probe (1) is fixed in place by the limiting part (12).

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