A method for detecting defects of carbon fiber laminates using electromagnetic probe

Abstract

The present invention relates to a carbon fiber laminate defect detection method using an electromagnetic probe, the electromagnetic probe includes a drive motor, an encoder, a pair of excitation modules, a pair of differential induction coils and an electromagnetic detection circuit; the detection method includes the following steps: probe initialization, starting excitation and reception, extracting signal feature information and calculating signal amplitude, drawing polar coordinate images, induced voltage signal plane images, ply direction angle determination and defect determination. The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention presents the ply direction of the carbon fiber laminate and the direction information indicating the defect in the form of polar coordinates by extracting the induced voltage value signal, and can accurately and effectively realize the judgment of the ply of the carbon fiber laminate and the detection of defects, and the imaging speed is fast, and the imaging results are clear, reliable, intuitive and easy to understand.

Description

Technical Field

[0001] The invention relates to an electromagnetic probe, in particular to a carbon fiber laminate defect detection method using the electromagnetic probe, belonging to the technical field of nondestructive detection of carbon fiber composite materials. Background Art

[0002] The excellent mechanical properties of carbon fiber composites, especially the high specific strength, high specific stiffness, strong designability, corrosion resistance and good fatigue damage resistance, make it one of the increasingly popular materials in the automotive manufacturing industry and aerospace. Carbon fiber composites are made of multiple layers of carbon fiber / epoxy resin sheets stacked together in a certain direction, and the fibers in each layer are arranged in the same direction. In practical applications, in order to improve anisotropy and increase the overall mechanical strength of the composite material, the fiber directions of adjacent layers are laid as required. In order to ensure the quality and normal use of carbon fiber composites, it is very necessary to study the direction of carbon fiber arrangement in the composite structure, that is, the ply direction. In addition, carbon fiber composites will produce various types of defects during the manufacturing and use stages. Among them, fiber breakage defects are a defect that is more likely to occur during manufacturing and use. Fiber breakage defects will significantly reduce the compressive strength and stiffness of the material. In order to ensure the integrity and reliability of carbon fiber composite components, it is necessary to perform non-destructive testing on carbon fiber composites during manufacturing and use.

[0003] Unlike metal parts, the microstructure of carbon fiber composite materials is a complex multiphase system that is inhomogeneous and heterogeneous. The presence of dielectric epoxy resin in the material makes the single-layer board exhibit strong anisotropy in electrical properties. Due to the conductivity of carbon fiber, the eddy current in the board is elongated in the fiber direction and compressed in the other directions. Therefore, the eddy current method can be used to measure the ply direction information and defect information in the composite material, and then evaluate the directionality of the fiber arrangement in the structure.

[0004] The eddy current testing method is a non-destructive testing method based on the principle of electromagnetic induction. It has the advantages of non-contact, no need for coupling medium, high detection speed, easy to realize automated detection, and high detection sensitivity for surface and near-surface defects.

[0005] At present, the main method for detecting the directionality of fiber arrangement is the manual rotating eddy current probe method. This method achieves the detection purpose by manually rotating the probe. However, this method has certain defects and limitations: on the one hand, the probe needs to be rotated and positioned multiple times during use. In actual detection, the distance between the probe and the test piece will inevitably change, thereby introducing measurement errors and having a great impact on the detection sensitivity; on the other hand, for those devices that need to quickly and accurately detect the arrangement direction of carbon fibers, a lot of detection time and error rate of the results are increased.

[0006] The main method for detecting defects in carbon fiber laminates is the high-frequency eddy current probe method, which uses a high-frequency excitation signal to induce a secondary magnetic field to detect defects. Chinese patent CN106546657B discloses a ring array eddy current probe for detecting the direction of carbon fiber composite material plies. The eddy current probes are evenly arranged in a ring manner in the structure, and a one-transmitter and multiple-receiver method is used to judge the direction of the laminate plies according to the polar coordinate diagram. For example, Chinese patent CN111796021A discloses a new type of eddy current probe, which includes a flat excitation coil and an "8"-shaped receiving coil, which can detect the fiber direction and in-plane corrugation defects of CFRP.

[0007] However, the above-mentioned high-frequency eddy current probe method has defects and limitations that cannot be ignored: on the one hand, in a high-frequency environment, a large amount of noise will be introduced, which seriously interferes with the detection signal and has a great negative impact on the accuracy of the detection results; on the other hand, the lift-off effect will also affect the detection method, which will significantly increase the detection error and greatly reduce the reliability of the detection results; in addition, under the influence of the skin effect, the higher the frequency, the smaller the detection depth, which limits the method's ability to detect deep defects inside carbon fiber laminates.

[0008] Therefore, in order to solve the above problems, it is necessary to provide an innovative carbon fiber laminate defect detection method using an electromagnetic probe to overcome the above defects in the prior art. Summary of the invention

[0009] The purpose of the present invention is to provide a carbon fiber laminate defect detection method using an electromagnetic probe, which can accurately and effectively realize the judgment of the carbon fiber laminate ply and the detection of defects, has a fast imaging speed, and the imaging results are clear, reliable, intuitive and easy to understand.

[0010] To achieve the above object, the technical solution adopted by the present invention is: a method for detecting defects of carbon fiber laminates using an electromagnetic probe, wherein the electromagnetic probe includes a drive motor, an encoder, a pair of excitation modules, a pair of differential induction coils and an electromagnetic detection circuit;

[0011] It includes the following process steps:

[0012] 1) Initialize the electromagnetic probe: After the electromagnetic probe is automatically offset, place its lower surface parallel to the carbon fiber laminate to be tested and place it in the center of the laminate;

[0013] 2) The electromagnetic detection circuit simultaneously supplies direct current to one of the excitation modules, the encoder, and the drive motor, and simultaneously receives the angle information of the encoder and the induced voltage signal of the differential induction coil; wherein the direct current is supplied to the excitation module to generate an electromagnetic field, the direct current is supplied to the encoder to record the angle signal, and the direct current is supplied to the drive motor to rotate the drive shaft at a constant speed;

[0014] 3) Extract the characteristic information of the differential induction coil signal and calculate the signal amplitude: Through steps 1) and 2), the signals of the differential induction coil at different angles in the carbon fiber laminate are obtained, and the differential real part of each angle is recorded. and the imaginary part , get the differential induced voltage value ;

[0015] 4) Draw a polar coordinate diagram, where the angle position of the local maximum indicates the ply direction;

[0016] 5) Determine the scanning path according to the ply direction information and start scanning;

[0017] 6) The electromagnetic detection circuit is changed to supply direct current to the two excitation modules at the same time;

[0018] 7) Record the signal at each position on the scanning path, obtain the signal of the electromagnetic probe at different positions on the carbon fiber laminate, and record the differential real part of the signal at each position. and the imaginary part , calculate the differential induced voltage value V= ;

[0019] 8) Based on the scanning path, the differential induced voltage values ​​at each position are integrated to construct a plane image and complete defect detection.

[0020] The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention is further as follows: the excitation module and the differential induction coil are respectively fixed on a rotating seat; the drive motor is arranged on the upper part of the rotating seat and connected to the rotating seat through a drive shaft, so that the drive motor drives the rotating seat to rotate; the differential induction coil is located in the center of the excitation module; the electromagnetic detection circuit is electrically connected to the drive motor, encoder, excitation module and differential induction coil respectively.

[0021] The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention is further as follows: the excitation module is composed of an excitation coil and an iron core; the iron core is symmetrical relative to the center of the drive shaft, and the excitation coil is a spiral coil wound on the iron core, and the spiral coil is wound on the iron core in the same direction.

[0022] The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention is further as follows: the differential induction coil uses a hollow circular ring coil, and the coil normal is radially parallel to the drive shaft; the plane where the differential induction coil is located is the same plane as the plane where the excitation module is located; the winding directions of the two differential induction coils are opposite.

[0023] The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention is further as follows: in the step 1), the lower surface of the electromagnetic probe is at a height of 0.5 mm from the carbon fiber laminate to be tested; the automatic bias adjustment of the electromagnetic probe is achieved by the automatic bias of the phase-locked amplifier, so that the real and imaginary voltages of the differential induction coil are both set to 0.

[0024] The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention is further as follows: in the step 5), the scanning path of the unidirectional carbon fiber composite plate is serpentine, the scanning path of the orthogonal carbon fiber composite plate is spiral, and the scanning mode of the 0° / 45° / 90° carbon fiber composite plate is a composite triangle.

[0025] The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention is further as follows: in the step 7), if the carbon fiber laminate has no defects, the two differential induction coils generate the same voltage signal, and due to the difference, the signal is theoretically 0; when the carbon fiber laminate has defects, the induced current will be disturbed by the defects and change, and then the induced secondary magnetic field will also change, causing the differential induced voltage value V to change.

[0026] The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention is further as follows: in step 8), the integration process is specifically as follows:

[0027] 8-1), move the probe along the determined scanning path, and record the V value and corresponding position coordinate information of each position in turn;

[0028] 8-2), arrange this information in a two-dimensional array or data structure in an orderly manner according to the position relationship. This two-dimensional array is regarded as a data representation form of a plane image;

[0029] 8-3), through image processing software, the gray value of the data in this two-dimensional array is determined according to the set rules to form a plane image that can reflect the internal situation of the carbon fiber laminate. By observing this image, it can be determined whether there are defects and the distribution of defects.

[0030] The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention is also as follows: the grayscale value is determined by: first, finding the minimum and maximum values ​​in the V value; second, applying a normalization formula to calculate the grayscale value: normalizing the data to obtain a proportional value between 0 and 1, and then mapping the proportional value to a grayscale value range of 0-255, thereby obtaining a corresponding grayscale value.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention extracts the induced voltage value signal and presents the ply direction of the carbon fiber laminate and the direction information of the defect in the form of polar coordinates. It can accurately and effectively realize the judgment of the ply direction of the carbon fiber laminate and the detection of defects. The imaging speed is fast, and the imaging results are clear, reliable, intuitive and easy to understand.

[0033] 2. The carbon fiber laminate defect detection method using an electromagnetic probe of the present invention generates a relatively uniform electromagnetic field through an excitation coil, is not affected by the skin effect, and has a deeper detection depth; and the design of the differential induction coil can not only effectively reduce the influence of the lift-off noise and improve the anti-interference ability of the probe, but also its arrangement in which the normal is parallel to the radial direction of the drive shaft also enhances the penetration rate of the secondary magnetic field to the induction coil, significantly enhancing the detection signal and detection sensitivity.

[0034] 3. In the carbon fiber laminate defect detection method using an electromagnetic probe of the present invention, the two differential induction coils are wound in opposite directions, which is conducive to signal analysis and processing. Moreover, since the detection signals of the two differential induction coils contain the same noise, the noise can be reduced after differential processing, and the common mode suppression effect can be exerted, thereby further improving the accuracy and reliability of the detection signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a three-dimensional diagram of the electromagnetic probe of the present invention.

[0036] Figure 2 It is a schematic diagram of the placement of the electromagnetic probe of the present invention and the carbon fiber laminate to be tested.

[0037] Figure 3 It is a principle block diagram of the electromagnetic probe of the present invention.

[0038] Figure 4 It is a flow chart of the carbon fiber laminate defect detection method using an electromagnetic probe of the present invention.

[0039] Figure 5 It is a schematic diagram of the scanning path of the electromagnetic probe of the present invention on the unidirectional carbon fiber composite plate.

[0040] Figure 6 It is a schematic diagram of the scanning path of the electromagnetic probe of the present invention on the orthogonal carbon fiber composite plate.

[0041] Figure 7 It is a schematic diagram of the scanning path of the electromagnetic probe of the present invention for a 0° / 45° / 90° carbon fiber composite plate.

[0042] Figure 8 This is a signal amplitude diagram obtained in step 3) of the carbon fiber laminate defect detection method using an electromagnetic probe of the present invention.

[0043] Fig. 9 This is a polar coordinate diagram drawn in step 4) of the carbon fiber laminate defect detection method using an electromagnetic probe of the present invention.

[0044] Fig.10 It is a plane image constructed in step 8) of the carbon fiber laminate defect detection method using an electromagnetic probe of the present invention. DETAILED DESCRIPTION

[0045] Please refer to the instruction manual Figure 1 To Attachment Fig.10 As shown, the present invention is a method for detecting defects of carbon fiber laminates using an electromagnetic probe, wherein the electromagnetic probe is also called a differential rotating electromagnetic probe, which is composed of a drive motor 2, an encoder 6, a pair of excitation modules 4, a pair of differential induction coils 5, and an electromagnetic detection circuit 7.

[0046] The excitation module 4 and the differential induction coil 5 are respectively fixed on a rotating seat 9. The driving motor 2 is arranged on the upper part of the rotating seat 9 and is connected to the rotating seat 9 through the driving shaft 3, so that the driving motor 2 drives the rotating seat 9 to rotate, thereby enabling the excitation module 4 and the differential induction coil 5 to rotate.

[0047] The excitation module 4 is composed of an excitation coil and an iron core. There are two iron cores, which are symmetrical with respect to the center of the drive shaft 3. The excitation coil is a spiral coil wound on the iron core, and the spiral coils are wound in the same direction on the iron core. When direct current is passed, the electromagnetic fields generated by the excitation coils of the two excitation modules 4 should be in the same direction. The wire bundles of each layer of the excitation coil and the differential induction coil 5 of the excitation module 4 and the wire bundles between layers are tightly and evenly distributed.

[0048] The differential induction coil 5 is located at the bottom of the electromagnetic probe and in the center of the excitation module 4. The differential induction coil 5 uses a hollow ring coil, and the coil normal is radially parallel to the drive shaft 3. The plane where the differential induction coil 5 is located is the same plane as the plane where the excitation module 4 is located. The winding directions of the two differential induction coils 5 are opposite, which, on the one hand, improves the detection sensitivity of the probe to defects, and on the other hand, effectively reduces the influence of the lift-off noise and improves the anti-interference ability of the probe to noise.

[0049] Furthermore, the electromagnetic detection circuit 7 is electrically connected to the drive motor 2, the encoder 6, the excitation module 4 and the differential induction coil 5. Specifically, the electromagnetic detection circuit 7 is used to pass direct current to the excitation module 4, the drive motor 2 and the encoder 6, and to detect the induced voltage signal received by the differential induction coil 5 and the electrical angle signal of the encoder 6.

[0050] The design principle of the electromagnetic probe is as follows: direct current is generated by the signal generating module in the electromagnetic detection circuit 7; the direct current is passed into the power amplifier module to increase the power of the excitation current; the amplified direct current is then connected to the drive motor 2, the encoder 6 and the excitation module 4; the two differential induction coils 5 receive the angle information of the encoder 6 and the voltage signal containing the defect information of the inspected component, and the detected signal is pre-processed and transmitted to the computer 10 for signal analysis and processing.

[0051] The method for detecting defects of carbon fiber laminates using the electromagnetic probe comprises the following process steps:

[0052] 1) Initialize the electromagnetic probe: After the electromagnetic probe is automatically biased, place its lower surface parallel to the carbon fiber laminate 1 to be tested and place it at the center of the carbon fiber laminate 1.

[0053] Specifically, the height between the lower surface of the electromagnetic probe and the carbon fiber laminate 1 to be tested is 0.5 mm. At this height, the lift-off is small, the current field strength is large, and the differential induction coil 5 can pick up more defect signals. The automatic bias adjustment of the electromagnetic probe is achieved through the automatic bias of the lock-in amplifier 8, so that the real and imaginary voltages of the differential induction coil 5 are both set to 0.

[0054] 2), the electromagnetic detection circuit 7 simultaneously supplies direct current to one of the excitation modules 4, the encoder 6, and the drive motor 2, and simultaneously receives the angle information of the encoder 6 and the induced voltage signal of the differential induction coil 5. The direct current is supplied to the excitation module 4 to generate an electromagnetic field, the direct current is supplied to the encoder 6 to record the angle signal, and the direct current is supplied to the drive motor 2 to rotate the drive shaft 3 at a constant speed.

[0055] 3) Extract the signal characteristic information of the differential induction coil 5 and calculate the signal amplitude.

[0056] Since direct current is passed into one of the excitation modules 4, the direct current will generate a constant magnetic field, namely a direct magnetic field, and then the driving shaft 3 drives the excitation module 4 to rotate, and the carbon fiber laminate 1 to be tested placed in the constant magnetic field cuts the magnetic flux lines to generate motional current; the induced current will induce a secondary magnetic field, and the composite magnetic field after the direct magnetic field and the secondary magnetic field are superimposed will cause voltage signals to be generated at both ends of the two differential induction coils 5; due to the influence of different laying directions of the carbon fiber laminate 1, the induced secondary magnetic field will also produce corresponding changes, thereby generating different voltage signals in the two differential induction coils 5.

[0057] Based on this, the signals of the differential induction coil 5 at different angles in the carbon fiber laminate 1 are obtained through steps 1) and 2), and the differential real part of each angle is recorded. and the imaginary part , get the differential induced voltage value Due to the influence of different laying directions of the carbon fiber laminate 1 , the secondary magnetic field induced at different angles will also produce corresponding changes, thereby generating different voltage signals in the two differential induction coils 5 .

[0058] 4) Draw a polar coordinate diagram, and the angular position of the local maximum indicates the ply direction.

[0059] Specifically, when the excitation module 4 cuts the carbon fiber at a vertical speed, the induced motional current is the largest, the secondary magnetic field induced by the current is also the largest, and the differential induced voltage signal is also the largest. Since the coil normals of the two differential induction coils 5 are consistent with the radial direction of the drive shaft 3, the penetration rate of the secondary magnetic field to the differential induction coil 5 is also enhanced, so there is a local maximum at this time. , record the angle information of the encoder 6 and the voltage amplitude at different angles to form a polar coordinate diagram. Since the voltage amplitude in the ply direction is a local maximum, the polar coordinate diagram (as shown in the attached manual) Fig. 9 ) can clearly indicate the laying direction of the carbon fiber laminate.

[0060] The following is a polar coordinate diagram of the differential induced voltage value. This parameter is further explained, the differential induced voltage value It is calculated based on the real voltage and imaginary voltage of the differential induction coil 5 at different angles of the carbon fiber laminate 1. When drawing the polar coordinate diagram, due to the different angles The values ​​will be different, and the angle position corresponding to the local maximum value has special significance. Because carbon fiber is directional, its electromagnetic properties in this direction will make the signal characteristics obtained by the differential induction coil 5 present a relatively large amplitude, that is, There will be a local maximum, so the angle position corresponding to this local maximum indicates the fiber direction. Figure 4 If it is found during the detection process At a certain angle A local maximum value appears at , which means that in this area of ​​the carbon fiber laminate, the fiber direction is roughly along Angular direction.

[0061] 5) Determine the scanning path according to the ply direction information and start scanning. Specifically, the scanning path of the unidirectional carbon fiber composite plate is serpentine (such as Figure 5 As shown in the figure), the scanning path of the orthogonal carbon fiber composite plate is spiral (as shown in the figure), Figure 5 As shown), the 0° / 45° / 90° carbon fiber composite plate scanning mode is a composite triangle (as shown Figure 7 As shown, the left part is scanned from the beginning to the end, and the right part is scanned from the middle to the end point).

[0062] 6), the electromagnetic detection circuit 7 changes to supply direct current to the two excitation modules 4 at the same time.

[0063] 7) Record the signal at each position on the scanning path, obtain the signal of the electromagnetic probe at different positions of the carbon fiber laminate 1, and record the differential real part of the signal at each position and the imaginary part , calculate the differential induced voltage value V= .

[0064] If the carbon fiber laminate has no defects, the two differential induction coils 5 generate the same voltage signal. Due to the difference, the signal is theoretically 0. When there are defects in the carbon fiber laminate 1, the induced current will be disturbed by the defects and change, and then the induced secondary magnetic field will also change, causing the differential induced voltage value V to change.

[0065] Specifically, the parameter V is calculated by the differential real and imaginary parts of the probe at different positions on the carbon fiber laminate 1, which represents the induced voltage intensity information at each position. If the carbon fiber laminate 1 is set as a two-dimensional plane, the corresponding V value can be obtained at different positions (x, y). In order to construct a plane image, we can regard the carbon fiber laminate 1 as consisting of many tiny pixels (similar to the concept of pixels in digital images). The position of each pixel corresponds to the actual position of the probe on the laminate 1, and the brightness or color information of this pixel is determined by the V value of the position. For example, if there is a defect at a certain position, the carbon fiber structure at that position will change, which will cause the electromagnetic properties to change, and then the induced voltage V value obtained by the differential induction coil will be different from the normal position. When constructing a plane image, these points with large differences in V values ​​from the surrounding normal positions will show abnormalities in the image, so that the location of the defect and its approximate shape and other information can be intuitively seen.

[0066] 8) Based on the scanning path, the differential induced voltage values ​​at each position are integrated to construct a plane image and complete defect detection.

[0067] The integration process is specifically as follows:

[0068] 8-1), move the probe along the determined scanning path, and record the V value of each position and the corresponding position coordinate information in turn.

[0069] 8-2), arrange this information in a two-dimensional array or data structure in order according to the position relationship. This two-dimensional array is regarded as a data representation of a plane image.

[0070] 8-3), through image processing software (such as Matlab or origin software), the data in this two-dimensional array is determined according to the set rules to determine the gray value, forming a plane image that can reflect the internal situation of the carbon fiber laminate (such as the attached Fig.10 By observing this image, it is possible to determine whether there are defects and the distribution of defects.

[0071] The grayscale value is determined in the following way: first, find the minimum and maximum values ​​in the V value; second, apply the normalization formula to calculate the grayscale value: normalize the data to obtain a proportional value between 0 and 1, and then map this proportional value to the range of grayscale values, the range of grayscale values ​​is 0 - 255, so as to obtain the corresponding grayscale value.

[0072] The carbon fiber laminate defect detection method of the present invention extracts the induced voltage value signal and presents the carbon fiber laminate ply direction and defect direction information in the form of polar coordinates. It can accurately and effectively realize the judgment of the carbon fiber laminate ply and the detection of defects. The imaging speed is fast, and the imaging results are clear, reliable, intuitive and easy to understand.

[0073] The above specific implementation methods are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting defects in carbon fiber laminates using an electromagnetic probe, characterized in that: The electromagnetic probe comprises a driving motor, an encoder, a pair of excitation modules, a pair of differential induction coils and an electromagnetic detection circuit; the excitation module is composed of an excitation coil and an iron core; the iron core is symmetrical with respect to the center of the driving shaft, the excitation coil is a spiral coil wound on the iron core, and the spiral coils are wound in the same direction on the iron core; the differential induction coil uses a hollow ring coil, and the coil normal is parallel to the radial direction of the driving shaft; the plane where the differential induction coil is located is the same plane as the plane where the excitation module is located; the winding directions of the two differential induction coils are opposite; It includes the following process steps: 1) Initialize the electromagnetic probe: After the electromagnetic probe is automatically offset, place its lower surface parallel to the carbon fiber laminate to be tested and place it in the center of the laminate; The lower surface of the electromagnetic probe is at a height of 0.5 mm from the carbon fiber laminate to be tested; the automatic bias adjustment of the electromagnetic probe is achieved by the automatic bias of the phase-locked amplifier, so that the real and imaginary voltages of the differential induction coil are both set to 0; 2) The electromagnetic detection circuit simultaneously supplies direct current to one of the excitation modules, the encoder, and the drive motor, and simultaneously receives the angle information of the encoder and the induced voltage signal of the differential induction coil; wherein the direct current is supplied to the excitation module to generate an electromagnetic field, the direct current is supplied to the encoder to record the angle signal, and the direct current is supplied to the drive motor to rotate the drive shaft at a constant speed; 3) Extract the characteristic information of the differential induction coil signal and calculate the signal amplitude: Through steps 1) and 2), the signals of the differential induction coil at different angles in the carbon fiber laminate are obtained, and the differential real part of each angle is recorded. and the imaginary part , get the differential induced voltage value ; 4) Draw a polar coordinate diagram, where the angle position of the local maximum indicates the ply direction; 5) Determine the scanning path according to the ply direction information and start scanning; 6) The electromagnetic detection circuit is changed to supply direct current to the two excitation modules at the same time; 7) Record the signal at each position on the scanning path, obtain the signal of the electromagnetic probe at different positions on the carbon fiber laminate, and record the differential real part of the signal at each position. and the imaginary part , calculate the differential induced voltage value V= ; 8) Based on the scanning path, the differential induced voltage values ​​at each position are integrated to construct a plane image and complete defect detection.

2. The carbon fiber laminate defect detection method using an electromagnetic probe as claimed in claim 1, characterized in that: The excitation module and the differential induction coil are respectively fixed on a rotating seat; the drive motor is arranged on the upper part of the rotating seat and connected to the rotating seat through a drive shaft, so that the drive motor drives the rotating seat to rotate; the differential induction coil is located in the center of the excitation module; the electromagnetic detection circuit is electrically connected to the drive motor, encoder, excitation module and differential induction coil respectively.

3. The carbon fiber laminate defect detection method using an electromagnetic probe as claimed in claim 1, characterized in that: In the step 5), the scanning path of the unidirectional carbon fiber composite plate is serpentine, the scanning path of the orthogonal carbon fiber composite plate is spiral, and the scanning mode of the 0° / 45° / 90° carbon fiber composite plate is a composite triangle.

4. The carbon fiber laminate defect detection method using an electromagnetic probe as claimed in claim 1, characterized in that: In the step 7), if the carbon fiber laminate has no defects, the two differential induction coils generate the same voltage signal. Due to the difference, the signal is theoretically 0; when the carbon fiber laminate has defects, the induced current will be disturbed by the defects and change, and then the induced secondary magnetic field will also change, causing the differential induced voltage value V to change.

5. The carbon fiber laminate defect detection method using an electromagnetic probe as claimed in claim 1, characterized in that: In step 8), the integration process is specifically as follows: 8-1), move the probe along the determined scanning path, and record the V value and corresponding position coordinate information of each position in turn; 8-2), arrange this information in a two-dimensional array or data structure in an orderly manner according to the position relationship. This two-dimensional array is regarded as a data representation form of a plane image; 8-3), through image processing software, the gray value of the data in this two-dimensional array is determined according to the set rules to form a plane image that can reflect the internal situation of the carbon fiber laminate. By observing this image, it can be determined whether there are defects and the distribution of defects.

6. The method for detecting defects of carbon fiber laminates using an electromagnetic probe according to claim 5, characterized in that: The grayscale value is determined in the following way: first, find the minimum and maximum values ​​in the V value; second, apply the normalization formula to calculate the grayscale value: normalize the data to obtain a proportional value between 0 and 1, and then map this proportional value to the range of grayscale values, the range of grayscale values ​​is 0 - 255, so as to obtain the corresponding grayscale value.

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