An eddy current testing probe and method for internal and backside defects of a hole structure

Abstract

The application discloses a kind of eddy current detection probe and method for hole structure inside and back defects, the detection probe and method can realize the high-precision detection of hole structure inside and back defects;The detection probe includes pie type detection coil with middle magnetic core, double-layer orthogonal excitation coil and flexible pad, the middle magnetic core of detection coil increases coil inductance while realizing positioning, and the magnetic field inside and back of hole is strengthened using magnetic collection effect;Double-layer orthogonal excitation coil uses the arrangement mode of two coils orthogonal to avoid the disadvantage that single strike coil is not sensitive to parallel crack, and realizes effective detection to crack in any direction;Flexible structure makes the probe suitable for curved surface structure;Orthogonal differential detection method realizes the identification of hole peripheral defect using the symmetry of hole structure;Compared with the traditional probe for detecting surface and near-surface defects, the present application uses innovative detection and excitation coil configuration and defect identification method, and realizes high-sensitivity detection of back and internal defects around hole structure.

Description

Technical Field

[0001] This invention relates to an eddy current nondestructive testing probe, specifically to an eddy current testing probe and method for defects on the back side and inside of a hole structure. Background Technology

[0002] Hole structures are common in mechanical components and are widely used in engineering fields such as aerospace, automotive manufacturing, and petrochemicals. Hole structures are extensively used in the structural design of aircraft, rockets, and other aircraft. By introducing holes into the structure, hole structures can effectively reduce weight and improve stiffness and strength. Reducing structural weight is crucial in aircraft, as it directly affects fuel consumption and range. Using hole structures reduces material usage, thereby lowering weight and improving aircraft performance. Furthermore, hole structures can enhance structural stiffness and strength. Holes can introduce stress concentration effects, increasing local stiffness and strength, making the structure more resistant to bending and compression. This is significant for aircraft facing complex loads and environmental conditions during flight. Additionally, hole structures are widely used in topology optimization design. Topology optimization refers to achieving optimal structural performance by optimizing the distribution of design variables and the shape of the topology. As a special structural form, hole structures offer significant design freedom and flexibility, playing a vital role in optimization design. By introducing holes, the stiffness and strength distribution of the structure can be adjusted to achieve optimal performance. Furthermore, porous structures can achieve optimal stiffness and strength distributions by optimizing the distribution of design variables. By optimizing the distribution of design variables, the structure can exhibit different stiffness and strength at different locations, thus achieving optimal structural performance. This is significant for improving structural performance and reducing material usage.

[0003] Due to limitations in manufacturing processes and factors such as the materials, dimensions, structure, and surface quality being processed, defects can occur inside and on the back side of the hole structure during the manufacturing process. These defects may adversely affect the performance and service life of the parts. Furthermore, during long-term service, damage can easily occur inside and on the back side of the hole structure. This damage significantly reduces the service life of the components and may lead to safety hazards such as cracking or breakage during subsequent use, or even cause the entire equipment to malfunction. Therefore, it is essential to conduct production inspections of hole structure components and to periodically perform integrity assessments and reliability tests on hole structure components in service.

[0004] Eddy current nondestructive testing (EDT) is a widely used method with advantages such as high sensitivity and non-contact operation. It detects defects in materials by sensing changes in eddy currents. However, applying eddy current testing to the interior of hole structures faces certain challenges. Due to the unique nature of hole structures, it is difficult for the probe coil to directly contact the internal surface. Furthermore, the interior of a hole structure is typically a closed space, preventing the probe coil from directly contacting the internal surface, resulting in low signal strength and sensitivity. In addition, the complex geometry and structure within hole structures further complicate eddy current testing. Secondly, applying eddy current testing to the back side of hole structures also presents technical difficulties. Due to the skin effect, the induced eddy currents are concentrated on the outer and near-surface surfaces of the conductor, resulting in very low eddy current intensity on the back side of the hole structure, leading to low signal strength and sensitivity. Considering the hazards and concealment of defects inside and on the back side of hole structures, the design and development of high-precision eddy current testing probes and identification methods for defects on the back side and inside of hole structures is of great significance in the engineering field. Summary of the Invention

[0005] The purpose of this invention is to design and develop a high-precision eddy current detection probe and defect identification method for defects inside and on the back of hole structures, so as to achieve high-precision and high-sensitivity detection of defects inside and on the back of hole structure components.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] An eddy current detection probe for defects inside and on the back side of a hole structure is disclosed. The probe includes a disc-shaped detection coil 1 with a central magnetic core, a flexible pad 4, and a double-layer orthogonal excitation coil 7. The disc-shaped detection coil 1 with a central magnetic core includes a disc-shaped coil 2 and a central magnetic core 3. The flexible pad 4 has a detection circuit arrangement slot 5 and a detection coil placement slot 6, wherein the detection coil placement slot 6 is used to place the disc-shaped coil 2. The double-layer orthogonal excitation coil 7 is placed above the disc-shaped coil 2 and includes an upper excitation coil 8 and a lower excitation coil 9. The double-layer orthogonal excitation coil 7 is fabricated using FPC flexible circuit board printing technology. The upper excitation coil 8 and the lower excitation coil 9 are separated by an insulating polyester film to avoid mutual interference between the two coils during operation. The upper excitation coil 8 is routed using a horizontally arranged parallel circuit, and the lower excitation coil 9 is routed using a vertically arranged parallel circuit.

[0008] Furthermore, the diameter of the central magnetic core 3 is equal to or smaller than the aperture of the hole structure to be tested. The material of the central magnetic core is sintered magnetic metal oxide, which is a ferromagnetic material. When the probe is in service, the central magnetic core uses the magnetic field collection effect to strengthen the magnetic field inside and on the back of the hole. The setting of the central magnetic core can allow more magnetic field lines to enter the inside and back of the hole structure, so that the disc coil 2 can obtain the magnetic field information inside and on the back of the hole structure, thereby achieving the detection target of defects inside and on the back of the hole structure. The inner diameter of the disc coil 2 is equal to the aperture of the hole structure to be tested. The selection of the outer diameter and thickness of the disc coil 2 is based on a comprehensive consideration of the size of the test piece and the required number of coil turns.

[0009] Furthermore, the flexible pad 4 is made of fluororubber, a high-temperature resistant flexible insulating material. The inner diameter of the detection coil placement slot 6 is the same as the diameter of the disc coil 2, and the thickness of the flexible pad 4 is the same as the thickness of the disc coil 2. This effectively fixes the disc detection coil 1 with a central magnetic core. The detection circuit arrangement slot 5 is used to fix the connection circuit of the disc detection coil 1 with a central magnetic core, making the upper surface of the flexible pad 4 clean and free of protrusions. This effectively avoids uneven lifting caused when the double-layer quadrature excitation coil 7 is attached to the flexible pad 4.

[0010] Furthermore, during probe service, an AC modulated excitation current is first applied to the upper excitation coil 8 to extract the detection signal. Then, the same AC modulated excitation current is applied to the lower excitation coil 9 to extract the detection signal again. The upper excitation coil 8 uses a horizontally arranged parallel circuit for routing, so the first detection is not good at identifying horizontal crack defects. The lower excitation coil 9 uses a vertically arranged parallel circuit for routing, so the second detection is not good at identifying vertical crack defects. Taking into account the results of the two detections, the missed detection of defects caused by cracks parallel to the excitation coils is effectively avoided.

[0011] The method described above is a differential signal detection method for eddy current detection probes targeting defects inside and on the back side of a hole structure. This method uses the differential detection signals from two orthogonally arranged upper excitation coils 8 and lower excitation coils 9 to identify defects inside and on the back side of the hole structure. First, an alternating excitation current is passed through the upper excitation coil 8. This alternating excitation current generates an alternating primary magnetic field in space. The presence of the central magnetic core 3 utilizes the magnetizing effect to allow more of the primary magnetic field to penetrate into the interior and back side of the hole structure, thereby increasing the magnetic induction intensity inside and on the back side of the hole structure. The induced eddy current density will also be greater, which allows the disc coil 2 to acquire more information about the inside and back of the hole structure to be tested, thus improving the signal-to-noise ratio. The alternating primary magnetic field will excite an induced eddy current field in the opposite direction to the excitation current on the surface, inside and back of the hole structure to be tested. The induced eddy current field will generate a secondary magnetic field, which will act on the disc coil 2 to generate a voltage signal. When there are defects such as cracks inside and on the back of the hole structure, the magnitude of the voltage signal induced by the disc coil 2 will be different. The magnitude of the induced voltage signal is collected by the disc coil 2 and recorded as V1 (complex number).

[0012] Secondly, the same AC modulated excitation current as that in the upper excitation coil 8 is passed into the lower excitation coil 9. Since the lower excitation coil 9 adopts a vertical parallel circuit routing method and is orthogonal to the upper excitation coil 8 which adopts a horizontal parallel circuit routing method, an induced eddy current field perpendicular to the direction of the induced eddy current field of the upper excitation coil 8 will be induced on the surface, inside and back of the hole structure to be tested. The induced voltage signal is collected by the disc coil 2 and its magnitude is recorded as V2 (complex number).

[0013] Finally, since the structure of the hole to be tested has a completely symmetrical structure, the induced eddy current field will also be a completely symmetrical field. When there are no defects inside or on the back of the hole structure, the two orthogonal excitation fields will generate induced eddy current fields of equal magnitude on the surface, inside, and back of the hole structure, i.e., V1 = V2. When there are defects inside or on the back of the hole structure, they will disturb the induced eddy current field, thereby interfering with the symmetry of the induced eddy current field. In this case, V1 ≠ V2. By calculating the difference ΔV = |V1 - V2| between the induced voltage signal V1 of the disc coil 2 to the upper excitation coil 8 and the induced voltage signal V2 of the lower excitation coil 9, it can be determined whether there are defects inside or on the back of the hole structure. When there are no defects in the hole structure, ΔV = 0; when there are defects in the hole structure, ΔV ≠ 0. In the actual service of the probe, the experimental conditions are complex and varied. When there are no defects inside or on the back of the hole structure, the values ​​of V1 and V2 cannot be completely equal. Therefore, the average value of V1 and V2 is calculated as V Avg Take the difference ΔV between V1 and V2 and the average value V. AvgThe relative error Δ=(ΔV / V) Avg Δ×100% is the criterion for judging whether there are defects inside and on the back of the hole structure to be tested. When Δ≤5%, the hole structure to be tested is judged to be in good integrity and there are no defects inside or on the back. When Δ>5%, the hole structure to be tested is judged to be in poor integrity and there are defects inside or on the back.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] Traditional eddy current testing probes have low sensitivity to cracks parallel to the eddy current field direction, easily leading to missed detections. 1) The probe and method proposed in this invention, using two orthogonal excitation coils for separate excitation, employs horizontal and vertical parallel circuit routing methods to complement each other, avoiding missed detections of cracks parallel to the eddy current field direction and achieving high-sensitivity detection of cracks in any direction inside and on the back of the hole structure. 2) The central magnetic core of the detection coil in this invention increases coil inductance while achieving positioning, utilizing the magnetic field-collecting effect to strengthen the magnetic field inside and on the back of the hole. 3) The flexible structure allows the probe to be used with curved surfaces. 4) The orthogonal differential detection method utilizes the symmetry of the hole structure to identify defects around the hole; compared to traditional probes that detect surface and near-surface defects, this invention uses innovative detection and excitation coil configurations and defect identification methods to achieve high-sensitivity detection of defects on the back and inside of the hole structure. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the eddy current detection probe for defects inside and on the back side of a hole structure according to the present invention.

[0017] Figure 2 This is a schematic diagram of the disc-shaped detection coil structure with a centrally located magnetic core according to the present invention.

[0018] Figure 3 This is a schematic diagram of the flexible pad structure of the present invention.

[0019] Figure 4 This is a schematic diagram of the double-layer orthogonal excitation coil structure of the present invention.

[0020] Figure 5 This is a schematic diagram of the horizontally arranged parallel circuit routing of the upper excitation coils in this invention.

[0021] Figure 6 This is a schematic diagram of the vertically arranged parallel circuit routing of the lower-level excitation coils in this invention.

[0022] Figure 7 This is a schematic diagram showing the position of the probe of the present invention relative to the structure of the hole to be tested during service. Specific implementation methods

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1 As shown, the present invention provides a high-precision eddy current detection probe for defects inside and on the back side of a hole structure. The probe includes a disc-shaped detection coil 1 with a central magnetic core, a flexible pad 4, and a double-layer orthogonal excitation coil 7.

[0025] like Figure 2 As shown, the disc-shaped detection coil 1 with a central magnetic core includes a disc-shaped coil 2 and a central magnetic core 3. The diameter of the central magnetic core 3 is equal to or slightly smaller than the aperture of the hole structure to be detected. During probe service, the central magnetic core is placed coaxially with the hole structure to be detected. The central magnetic core serves as the positioning element for the detection probe. During probe service, the central magnetic core can enhance the magnetic field inside and on the back of the hole using the magnetic field collection effect. The placement of the central magnetic core allows more magnetic field lines to enter the interior and back of the hole structure, enabling the disc-shaped coil 2 to acquire magnetic field information from the interior and back of the hole structure to be detected, thus achieving the detection of the hole structure. For detecting internal and back defects, when the inner diameter of the disc coil 2 is equal to the aperture of the hole structure to be tested, the disc coil 2 receives the most magnetic field lines entering the hole and back through the hole structure, resulting in the largest magnetic flux. In other words, the disc coil 2 can receive the most magnetic field information about the hole structure's interior and back. At this time, the detection probe has the highest accuracy and sensitivity for detecting internal and back defects of the hole structure to be tested. Therefore, it is necessary to control the inner diameter of the disc coil 2 to be equal to the aperture of the hole structure to be tested. The selection of the outer diameter and thickness of the disc coil 2 needs to be considered comprehensively based on the size of the test piece and the required number of coil turns.

[0026] like Figure 3 As shown, the flexible pad 4 has a detection circuit arrangement slot 5 and a detection coil placement slot 6. The flexible pad is made of fluororubber, which is a high-temperature resistant flexible insulating material. The inner diameter of the detection coil placement slot 6 is the same as the diameter of the disc coil 2, and the thickness of the flexible pad 4 is the same as the thickness of the disc coil 2. This can effectively fix the disc detection coil 1 with a central magnetic core. The detection circuit arrangement slot 5 is used to fix the connection circuit of the disc detection coil 1 with a central magnetic core, making the upper surface of the flexible pad 4 clean and without protrusions, effectively avoiding uneven lifting caused when the double-layer quadrature excitation coil 7 is attached to the flexible pad 4.

[0027] like Figure 4 As shown, the double-layer quadrature excitation coil 7 includes an upper excitation coil 8 and a lower excitation coil 9. The double-layer quadrature excitation coil 7 is manufactured using FPC flexible circuit board printing technology. The upper excitation coil 8 and the lower excitation coil 9 are separated by an insulating polyester film to avoid mutual interference between the two coils during service.

[0028] like Figure 5As shown, the upper excitation coil 8 is routed in a parallel circuit arranged in a horizontal manner. During the service of the probe, an AC modulated excitation current is passed into the upper excitation coil 8. The alternating excitation current will generate an alternating primary magnetic field in the space. The alternating primary magnetic field will cause the test specimen to generate a horizontally oriented eddy current field.

[0029] like Figure 6 As shown, the lower excitation coil 9 is routed in a parallel circuit arranged vertically. During service, the probe passes the same AC modulated excitation current as the upper excitation coil 8 into the lower excitation coil 9. Similarly, the test piece will generate a vertically oriented induced eddy current field.

[0030] like Figure 7 As shown, during probe service, the central magnetic core 3 is placed coaxially with the test specimen 10 of the hole structure to be tested. The central magnetic core 3 is inserted into the test hole structure 11, so that the disc coil 2 and the flexible pad 4 are tightly attached to the test specimen without being lifted. The disc coil 2 is used to sequentially collect the induced voltage signals when the upper excitation coil 8 and the lower excitation coil 9 are excited respectively. After the collection is completed, the detection signals collected twice are differentially processed. Combined with the high-sensitivity identification method for defects inside and on the back of the hole structure, the integrity of the inside and back of the hole structure is evaluated.

[0031] The working principle of this invention is as follows: This invention aims to achieve high-sensitivity detection of defects inside and on the back side of the hole structure to be inspected. The specific implementation steps are as follows:

[0032] Step 1: Place the central magnetic core 3 coaxially with the test specimen of the hole structure to be tested, insert the central magnetic core 3 into the test specimen of the hole structure 11 to be tested, so that the disc coil 2 and the flexible pad 4 are in close contact with the test specimen without being lifted off.

[0033] Step 2: Apply an alternating excitation current to the parallel circuit of the horizontally arranged upper excitation coil 8. The alternating excitation current will generate an alternating primary magnetic field in the space. The alternating primary magnetic field will excite a horizontal induced eddy current field in the opposite direction to the excitation current on the surface of the specimen, inside the hole structure, and on the back side. The induced eddy current field will generate a secondary magnetic field. The secondary magnetic field will act on the disc coil 2 to generate a voltage signal. When there are defects such as cracks inside the hole structure and on the back side, the magnitude of the voltage signal induced by the disc coil 2 will be different. The magnitude of the induced voltage signal is collected by the disc coil 2 and recorded as V1 (complex number).

[0034] Step 3: Pass the same AC modulated excitation current as that in the upper excitation coil 8 into the lower excitation coil 9. Since the lower excitation coil 9 adopts a vertical parallel circuit routing method and is orthogonal to the upper excitation coil 8 which adopts a horizontal parallel circuit routing method, an induced eddy current field perpendicular to the direction of the induced eddy current field of the upper excitation coil 8 will be induced on the surface, inside and back of the hole structure to be tested. The induced voltage signal is collected by the disc coil 2 and its magnitude is recorded as V2 (complex number).

[0035] Step 4: Applying the high-sensitivity identification method for defects inside and on the back of the hole structure proposed in this invention, calculate the difference ΔV = |V1-V2| between the induced voltage signal V1 of the disc coil 2 to the upper excitation coil 8 and the induced voltage signal V2 of the lower excitation coil 9. When there are no defects inside or on the back of the hole structure to be detected, the two orthogonal excitation fields will generate induced eddy current fields of equal magnitude in the hole structure to be detected, i.e., V1 = V2. When there are defects inside or on the back of the hole structure to be detected, they will disturb the induced eddy current field, thereby interfering with the symmetry of the induced eddy current field. At this time, V1 ≠ V2. Therefore, when there are no defects in the hole structure to be detected, ΔV = 0, and when there are defects in the hole structure to be detected, ΔV ≠ 0. In the actual service of the probe, the experimental conditions are complex and varied. When there are no defects inside or on the back of the hole structure to be detected, the values ​​of V1 and V2 cannot be completely equal. Therefore, the average value of V1 and V2 is calculated as V Avg Take the difference ΔV between V1 and V2 and the average value V. Avg The relative error Δ=(ΔV / V) Avg Δ×100% is the criterion for judging whether there are defects inside and on the back of the hole structure to be tested. When Δ≤5%, the hole structure is judged to be in good integrity and there are no defects inside or on the back. When Δ>5%, the hole structure to be tested is judged to be in poor integrity and there are defects inside or on the back.

Claims

1. An eddy current detection probe for defects inside and on the back side of a hole structure, characterized in that: The probe includes a disc-shaped detection coil (1) with a central magnetic core, a flexible pad (4), and a double-layer quadrature excitation coil (7); the disc-shaped detection coil (1) with a central magnetic core includes a disc-shaped coil (2) and a central magnetic core (3); the flexible pad (4) has a detection circuit arrangement slot (5) and a detection coil placement slot (6), wherein the detection coil placement slot (6) is used to place the disc-shaped coil (2); the double-layer quadrature excitation coil (7) is placed above the disc-shaped coil (2), including an upper excitation coil (8) and a lower excitation coil (9). The double-layer quadrature excitation coil (7) is made using FPC flexible circuit board printing technology. The upper excitation coil (8) and the lower excitation coil (9) are separated by an insulating polyester film to avoid mutual interference between the two coils during service; the upper excitation coil (8) is routed using a horizontally arranged parallel circuit, and the lower excitation coil (9) is routed using a vertically arranged parallel circuit. The diameter of the central magnetic core (3) is equal to or smaller than the aperture of the hole structure to be tested. The material of the central magnetic core is sintered magnetic metal oxide, which is a ferromagnetic material. When the probe is in service, the central magnetic core uses the magnetic field collection effect to strengthen the magnetic field inside and on the back of the hole. The setting of the central magnetic core can allow more magnetic field lines to enter the inside and back of the hole structure, so that the disc coil (2) can obtain the magnetic field information inside and on the back of the hole structure, and achieve the detection target of defects inside and on the back of the hole structure. The inner diameter of the disc coil (2) is equal to the aperture of the hole structure to be tested. The outer diameter and thickness of the disc coil (2) are set according to the size of the test piece and the required number of coil turns. The flexible pad (4) is made of fluororubber material. The inner diameter of the detection coil placement groove (6) is the same as the diameter of the disc coil (2). The thickness of the flexible pad (4) is the same as the thickness of the disc coil (2), which effectively fixes the disc detection coil (1) with a central magnetic core. The detection circuit arrangement groove (5) is used to fix the connection circuit of the disc detection coil (1) with a central magnetic core, making the upper surface of the flexible pad (4) clean and without protrusions. When the probe is in service, an AC modulated excitation current is first passed through the upper excitation coil (8) to extract the detection signal, and then the same AC modulated excitation current as that in the upper excitation coil (8) is passed through the lower excitation coil (9).

2. The detection method of the eddy current detection probe for defects inside and on the back side of a hole structure as described in claim 1, characterized in that: This detection method is a differential signal detection method. It uses the detection signals from two orthogonally arranged upper excitation coils (8) and lower excitation coils (9) to differentiate and identify defects inside and on the back of the hole structure to be detected. First, an alternating excitation current is passed through the upper excitation coil (8). The alternating excitation current will generate an alternating primary magnetic field in space. This primary magnetic field will excite an induced eddy current field on the surface, inside, and back of the hole structure to be detected, with a direction opposite to the excitation current. The induced eddy current field will generate a secondary magnetic field, which will act on the disc coil (2) to generate a voltage signal. The disc coil (2) is used to collect the induced voltage signal, and its magnitude is recorded as... , It is a complex number; Next, the same AC modulated excitation current as that in the upper excitation coil (8) is passed into the lower excitation coil (9). Since the lower excitation coil (9) adopts a vertical parallel circuit routing method and is orthogonal to the upper excitation coil (8) which adopts a horizontal parallel circuit routing method, an induced eddy current field perpendicular to the direction of the induced eddy current field of the upper excitation coil (8) will be induced on the surface, inside and back of the hole structure to be tested. The induced voltage signal is collected by the disc coil (2), and its magnitude is recorded as follows: , It is a complex number; Finally, because the hole structure to be tested has a completely symmetrical structural feature, the induced eddy current field will also be a completely symmetrical field. When there are no defects inside and on the back side of the hole structure, the two orthogonal excitation fields will generate induced eddy current fields of consistent magnitude on the surface, inside and on the back side of the hole structure. When there are defects inside or on the back of the hole structure to be inspected, it will disturb the induced eddy current field, thereby interfering with the symmetry of the induced eddy current field. The induced voltage signal of the disc coil (2) to the upper excitation coil (8) is calculated. and the induced voltage signal to the lower excitation coil (9) The difference To determine whether there are defects inside and on the back of the hole structure to be inspected, when there are no defects in the hole structure to be inspected... When the structure of the hole to be tested has defects ,calculate and The average value is ,Pick and The difference and average relative error The criteria for judging whether there are defects inside and on the back side of the hole structure to be inspected are as follows: When it is determined that the structure of the hole to be inspected is intact and there are no defects inside or on the back, When the hole to be tested is found to have poor structural integrity, it is determined that there are defects inside or on the back side.

Images