A method for suppressing lift-off jitter based on alternating current electromagnetic field detection

Abstract

The present invention provides a lift-off jitter suppression method based on alternating current electromagnetic field detection, belonging to the technical field of non-destructive testing defect evaluation. The technical solution is as follows: A lift-off jitter suppression method based on alternating current electromagnetic field detection uses an alternating current electromagnetic field detection probe to scan the surface of a test piece to obtain a low-frequency detection signal and a high-frequency detection signal; obtain the X directional magnetic field signal Bx 11 and Bx 21 of the low-frequency detection signal and the high-frequency detection signal corresponding to the background magnetic field-free, convert the high-frequency detection signal through the lift-off relationship fitting formula to eliminate lift-off jitter; calculate the lift-off compensation coefficient S to obtain the compensated X directional magnetic field signal Bx , and make a butterfly diagram with the low-frequency detection signal Z directional magnetic field signal Bz 1 for determination. If a closed circular ring shape appears, it is determined that there is a defect. The beneficial effect of the present invention is: eliminating the influence of lift-off jitter, improving the signal-to-noise ratio of defect signals, and realizing accurate determination of structural defects under lift-off jitter conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of non-destructive testing defect evaluation, and particularly relates to a lift-off jitter suppression method based on alternating current field measurement (ACFM). Background Art

[0002] Aluminum alloys are widely used in the aerospace industry due to their good corrosion resistance, high thermal conductivity, light weight and high strength. Due to long-term service in harsh climate environments during operation, under extreme working conditions such as complex loads, lightning, and high-voltage storms, crack defects such as fatigue cracking are likely to occur on the surface and non-surface areas of aerospace industrial equipment structures. Alternating Current Field Measurement (ACFM) technology is a new electromagnetic non-destructive testing technology mainly used for detecting surface cracks in conductive materials. It uses a detection probe to induce a uniform current on the surface of a conductive specimen, and the current generates perturbations around the defect, causing distortion of the spatial magnetic field. The defect is detected and evaluated by measuring the distorted magnetic field. When there is no defect, the surface current of the conductive specimen is in a uniform state and the spatial magnetic field is not perturbed. Due to its advantages such as non-contact measurement and quantitative evaluation, it is widely used in defect detection of various structures.

[0003] Due to the characteristics of various coatings, skins and multi-layer structures of aerospace equipment, the surface of the structure is mostly rivet connectors, the surface area is uneven, and manual operation is not stable. During the detection process of the probe, lift-off perturbations are likely to occur, resulting in missed detection or misjudgment of defects. Therefore, it is necessary to propose a lift-off jitter suppression method to eliminate the lift-off jitter signal during the detection process, improve the signal-to-noise ratio of the defect signal, and achieve accurate determination of the defects of the structure under the condition of lift-off jitter. Summary of the Invention

[0004] Aiming at the problems in the above-mentioned prior art, the purpose of the present invention is to provide a lift-off jitter suppression method based on alternating current field measurement, which eliminates the influence of lift-off jitter, improves the signal-to-noise ratio of the defect signal, and realizes accurate determination of the defects of the structure under the condition of lift-off jitter.

[0005] The present invention is realized by the following technical solutions: A lift-off jitter suppression method based on alternating current field measurement includes the following steps:

[0006] S1, linearly scanning the same position on the surface of the specimen using an alternating current field measurement probe to obtain a low-frequency detection signal when a low-frequency excitation signal is applied. The low-frequency detection signal includes X direction magnetic field signal Bx 1 and Z direction magnetic field signal Bz 1; Obtain the high-frequency detection signal when loading the high-frequency excitation signal, and the high-frequency detection signal includes X directional magnetic field signal Bx 2 and Z directional magnetic field signal Bz 2 ;

[0007] S2. Respectively use the X directional magnetic field signal Bx 1 and Bx 2 of the low-frequency detection signal and the high-frequency detection signal to subtract the corresponding background magnetic field to obtain the directional magnetic field signal X without background magnetic field Bx 11 and Bx 21；

[0008] S3. Convert the lift-off effect of the high-frequency detection signal into the same lift-off effect as that of the low-frequency detection signal through the lift-off relationship fitting formula to obtain the converted X-directional magnetic field signal Bx 22 , and use the X directional magnetic field signal Bx 11 of the low-frequency detection signal to subtract the converted X directional magnetic field signal Bx 22 to obtain the suppressed X directional magnetic field signal Bx 12 ;

[0009] S4. Calculate the lift-off compensation coefficient S and compensate the suppressed X directional magnetic field signal Bx 12 to obtain the compensated X directional magnetic field signal Bx ;

[0010] S5. Make a butterfly plot of the processed X directional magnetic field signal Bx and the Z directional magnetic field signal Bz 1 of the low-frequency detection signal for determination. If a closed circular ring shape appears, it is determined that there is a defect. If there is no closed circular ring shape, there is no defect.

[0011] Furthermore, the lift-off relationship fitting formula is a linear formula Bx 22 = a* Bx21 + b, where a and b are linear coefficients.

[0012] Furthermore, the frequency of the low-frequency excitation signal is 1 kHz, and the frequency of the high-frequency excitation signal is 10 kHz.

[0013] Further, a=5.76, b=18.07.

[0014] Further, the S4 is specifically: obtaining the low frequency detection signal Z Directional magnetic field signal Bz 1 The peak-to-valley spacing interval range is used to obtain the background-free magnetic field in the corresponding interval range. X Directional magnetic field signal Bx 11 The minimum value of L2 , similarly, the suppressed X Directional magnetic field signal Bx 12 The minimum value of L1 , the lift-off suppression compensation coefficient is recorded as S = L2 / L1 , after suppressing X Directional magnetic field signal Bx 12 Multiply by the lift-off compensation factor S To achieve distortion compensation, add the background magnetic field of the low-frequency detection signal Bx 10 Realize background magnetic field compensation, and obtain the compensation after lifting-off vibration is suppressed X Directional magnetic field signal Bx .

[0015] The beneficial effects of the present invention are as follows: the present invention eliminates the influence of lift-off jitter, improves the signal-to-noise ratio of the defect signal, and realizes accurate determination of structural defects under lift-off jitter conditions; the calculation process is simple, and the determination basis is indirect and clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A flow chart of a lift-off jitter suppression method based on AC electromagnetic field detection provided by the present invention;

[0017] Figure 2 A butterfly diagram drawn at 1 kHz provided by an embodiment of the present invention;

[0018] Figure 3 The 1kHz and 10kHz frequencies provided by the embodiments of the present invention are X Directional magnetic field signal Bx 1 and Bx 2 image;

[0019] Figure 4 The X directional magnetic field signal Bx 12 image provided by the embodiment of the present invention after suppression;

[0020] Figure 5 The Z directional magnetic field signal Bz 1 image of the low-frequency detection signal provided by the embodiment of the present invention;

[0021] Figure 6 The X directional magnetic field signal Bx image provided by the embodiment of the present invention after suppression and compensation;

[0022] Figure 7 The butterfly diagram provided by the embodiment of the present invention after suppression and compensation. Detailed implementation manners

[0023] To clearly illustrate the technical features of this solution, the following elaborates on this solution through specific implementation manners.

[0024] The present invention is implemented through the following technical solutions: As Figure 1 shown, a lift-off jitter suppression method based on alternating current electromagnetic field detection first uses an alternating current electromagnetic field detection probe to linearly scan at the same position on the surface of a test piece to obtain a low-frequency detection signal when a low-frequency excitation signal is applied. The low-frequency detection signal includes X directional magnetic field signal Bx 1 and Z directional magnetic field signal Bz 1 ; obtain a high-frequency detection signal when a high-frequency excitation signal is applied. The high-frequency detection signal includes X directional magnetic field signal Bx 2 and Z directional magnetic field signal Bz 2 ; to eliminate the interference of the background field, respectively use the X directional magnetic field signal Bx 1 and Bx 2 of the low-frequency detection signal and the high-frequency detection signal to subtract the corresponding background magnetic field to obtain the X directional magnetic field signal Bx 11 and Bx 21, the lift-off effect of the high-frequency detection signal is converted to be the same as that of the low-frequency detection signal through the lift-off relationship fitting formula, and the converted high-frequency detection signal is subtracted from the low-frequency detection signal, so that the lift-off jitter can be eliminated. At the same time of eliminating the lift-off jitter, the distortion amount of the defect signal will cause attenuation, and the lift-off compensation coefficient is calculated S , compensate the suppressed signal to obtain the X directional magnetic field signal Bx , and Z directional magnetic field signal Bz 1 make a butterfly diagram for determination. If a closed circular ring shape appears, it is determined that there is a defect. If there is no closed circular ring shape, there is no defect. Finally, the accurate determination of the structure defect is completed under the condition of lift-off jitter.

[0025] The specific application embodiments are as follows:

[0026] Such as Figures 1 - 7 shown, the lift-off jitter suppression method based on alternating current electromagnetic field detection provided by the embodiment of the present invention includes:

[0027] S1, prepare the test piece to be tested, and use a single probe for alternating current electromagnetic field detection to linearly scan the surface of the test piece to obtain the X directional magnetic field signal Bx 1 and Z directional magnetic field signal Bz 1 , as the low-frequency detection signal. According to the same operation, obtain the X directional magnetic field signal Bx 2 and Z directional magnetic field signal Bz 2 , as the high-frequency detection signal.

[0028] S2, use the X directional magnetic field signal Bx 1 and Z directional magnetic field signal Bz 1 to make a butterfly diagram before lift-off suppression. As Figure 2 shown, it can be seen from the figure that there is an obvious straight line tilting to the left. Use the X directional magnetic field signal Bx 1 subtract the background magnetic field Bx 10 to obtain the X directional magnetic field signal without background magnetic fieldBx 11 , using the X directional magnetic field signal Bx 2 to subtract the background magnetic field Bx 20 to obtain a background - free X directional magnetic field signal Bx 21 , as Figure 3 shown.

[0029] S3. Using the lift - off relationship fitting formula Bx 22 = 5.76 * Bx 21 + 18.07, to transform the X directional magnetic field signal Bx 21 and obtain the transformed X directional magnetic field signal Bx 22 . Then subtract the transformed X directional magnetic field signal Bx 11 from the X directional magnetic field signal Bx 22 using the X directional magnetic field signal Bx 12 , as Figure 4 shown.

[0030] S4. First, obtain the Z directional magnetic field signal Bz 1 of the low - frequency detection signal. As Figure 5 shown, it can be seen from the figure that the Z directional magnetic field signal Bz 1 has a peak - valley spacing interval of 62 mm - 85 mm. Within this interval, obtain the minimum value of the background - free X directional magnetic field signal Bx 11 of the low - frequency detection signal, which is - 272.7 mV, denoted as L2 =-272.7 mV. Similarly, obtain the minimum value of the X directional magnetic field signal Bx 12 after suppression, which is - 206.4 mV, denoted as L1 =-206.4 mV. Obtain the lift - off suppression compensation coefficient S = L1 / L2= 1.321, read the background magnetic field of the low-frequency detection signal Bx 10 is 11973.5 mV, and after suppression X direction magnetic field signal Bx 12 Multiply by the lift-off compensation coefficient S Realize distortion compensation, and then add the background magnetic field of the low-frequency detection signal Bx 10 Realize background magnetic field compensation, and obtain the direction magnetic field signal after suppressing lift-off jitter and compensation X direction magnetic field signal Bx , as Figure 6 shown

[0031] S5, the processed X direction magnetic field signal Bx and the low-frequency detection signal Z direction magnetic field signal Bz 1 Make a butterfly diagram, as Figure 7 shown, it can be seen that a closed circular ring shape appears, and there is no diagonal line indicating the lift-off jitter signal, indicating that the lift-off jitter signal is effectively suppressed during the detection process, and it is determined that there are defects during the detection process

[0032] The present invention can eliminate the influence of lift-off jitter during the detection process, improve the signal-to-noise ratio of defect signals, and realize accurate determination of structural defects under the condition of lift-off jitter

[0033] In the description of the present invention, the foregoing detailed description has illustrated various embodiments of the apparatus and / or process by using block diagrams, flowcharts, and / or examples. To the extent that such block diagrams, flowcharts, and / or examples contain one or more functions and / or operations, those skilled in the art will understand that each function and / or operation within such block diagrams, flowcharts, or examples can be individually and / or collectively implemented by many various different hardware, software, firmware, or in fact any combination thereof

[0034] There is little difference between the hardware and software implementations of various aspects of the system; the use of hardware or software is generally (but not always, as the choice between hardware and software may become important in certain scenarios) a design choice representing a cost - efficiency trade - off. There are various means (e.g., hardware, software, and / or firmware) by which the processes and / or systems and / or other technologies described herein can be implemented, and the preferred means will vary depending on the scenario in which the processes and / or systems and / or other technologies are deployed. For example, if the implementer determines that speed and accuracy are of utmost importance, then the implementer may choose means that are primarily hardware and / or firmware; if flexibility is of utmost importance, then the implementer may choose an implementation that is primarily software; or, alternatively, but equally, the implementer may choose a certain combination of hardware, software, and / or firmware.

[0035] The technical features not described in the present invention can be realized by or adopted from the prior art, and will not be elaborated here. Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those of ordinary skill in the art within the scope of the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for suppressing lift-off jitter based on alternating current electromagnetic field detection, characterized in that, It includes the following steps: S1. Use an alternating current electromagnetic field detection probe to linearly scan at the same position on the surface of the test piece to obtain a low-frequency detection signal when a low-frequency excitation signal is applied. The low-frequency detection signal includes X directional magnetic field signal Bx 1 and Z directional magnetic field signal Bz 1; Obtain a high-frequency detection signal when a high-frequency excitation signal is applied. The high-frequency detection signal includes X directional magnetic field signal Bx 2 and Z directional magnetic field signal Bz 2; S2. Respectively use the X directional magnetic field signals Bx 1 and Bx 2 to subtract the corresponding background magnetic fields to obtain the X directional magnetic field signals without background magnetic fields Bx 11 and Bx 21； S3. Convert the lift-off effect of the high-frequency detection signal into the same lift-off effect as that of the low-frequency detection signal through the lift-off relationship fitting formula, and obtain the converted X direction magnetic field signal Bx 22 , and use the X direction magnetic field signal Bx 11 of the low-frequency detection signal to subtract the converted X direction magnetic field signal Bx 22 to obtain the suppressed X direction magnetic field signal Bx 12 ; S4. Calculate the lift-off compensation coefficient S, and compensate the X directional magnetic field signal Bx 12 to obtain the compensated X directional magnetic field signal Bx ; S5. Process the X directional magnetic field signal Bx and the low-frequency detection signal Z directional magnetic field signal Bz to make a butterfly diagram for determination. If a closed circular ring shape appears, it is determined that there is a defect. If there is no closed circular ring shape, there is no defect. The lift-off relationship fitting formula is Bx 22 = a* Bx 21 + b, where both a and b are linear coefficients; The frequency of the low-frequency excitation signal is 1 kHz, and the frequency of the high-frequency excitation signal is 10 kHz; The specific content of S4 is as follows: Obtain the Z directional magnetic field signal of the low-frequency detection signal Bz in the peak-valley spacing interval range of 1, and obtain the X directional magnetic field signal without background magnetic field in the corresponding interval range Bx 11 The minimum value of is denoted as L2 Similarly, the X directional magnetic field signal after suppression Bx 12 The minimum value of is denoted as L1 The lift-off suppression compensation coefficient is denoted as S = L2 / L1 Multiply the X directional magnetic field signal after suppression Bx 12 by the lift-off compensation coefficient S to achieve distortion compensation, and then add the background magnetic field of the low-frequency detection signal Bx 10 to achieve background magnetic field compensation, and obtain the X directional magnetic field signal after suppressing lift-off jitter and compensation Bx .

2. The lift-off jitter suppression method based on alternating current electromagnetic field detection according to claim 1, characterized in that a = 5.76, b = 18.07.

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