Edge defect identification method and measurement device based on Lamb wave mode separation

Abstract

The present invention discloses a method and a measuring device for edge defect identification based on Lamb wave modal separation. The measuring device uses a signal generator, a high-voltage amplifier, an excitation probe, a receiving probe, a voltage amplifier, and an oscilloscope to build a measurement system, and establishes a bilinear sensor array to record the reflection of the Lamb wave on the structure to be measured. By separating the direct wave and the boundary reflection wave of the received signal, the damage reflection wave is extracted. The Hilbert transform of the damage reflection wave is associated with the pixel value of a given point on the structure to be measured to generate a damage image. The position with a higher pixel value in the damage image shows the specific position of the edge defect. It can be seen that the present invention provides a new method and a measuring device suitable for identifying structural edge defects.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-destructive testing, and in particular to an edge defect identification method and a measurement device based on Lamb wave modal separation. Background Art

[0002] Lamb waves hold broad application prospects in structural health monitoring and nondestructive testing. Lamb wave characteristics, such as propagation velocity, dispersion, frequency shift, attenuation, modal conversion, transmission, and reflection, enable damage detection, location, and quantification. However, identifying structural edge defects is often challenging, yet they can have a significant impact on structural failure. Therefore, developing new methods and measurement devices for this purpose is crucial. Summary of the Invention

[0003] In view of the deficiencies in the prior art, the present invention provides an edge defect identification method and a measurement device based on Lamb wave modal separation.

[0004] In order to achieve the above technical objectives, the present invention will adopt the following technical solutions:

[0005] An edge defect measurement device based on Lamb wave modal separation includes: a signal generator, a high-voltage amplifier, an excitation probe, an oscilloscope, a voltage amplifier, and a receiving probe, wherein: the signal generator is used to generate an incident wave, and the output end of the signal generator is connected to the input end of the high-voltage amplifier; the high-voltage amplifier is used to amplify the energy of the incident wave generated by the signal generator, and the output end of the high-voltage amplifier is connected to the excitation probe; the incident wave amplified by the high-voltage amplifier is recorded as an amplified incident wave; the excitation probe is used to transmit the amplified vibration wave to the surface of the structure to be measured , which is installed on the surface of the structure to be measured when in use; the receiving probe is used to receive the vibration wave of the amplified incident wave after it is transmitted through the structure to be measured, is installed on the surface of the structure to be measured and is connected to the input end of the voltage amplifier, and the receiving probe is located between the test area of ​​the structure to be measured and the excitation probe; the vibration wave received by the receiving probe is the receiving wave; the receiving wave after amplification by the voltage amplifier is recorded as the amplified receiving wave; the output end of the signal generator, the monitoring end of the high-voltage amplifier and the output end of the voltage amplifier are all connected to the oscilloscope; the oscilloscope is used to display the incident wave, the amplified incident wave and the amplified receiving wave.

[0006] Preferably, there are several receiving probes; each receiving probe is arranged in a bilinear array on the surface of the structure to be measured, and the excitation probe is arranged on the axis of the bilinear array of receiving probes.

[0007] Preferably, the number of the receiving probes is 14.

[0008] Another technical object of the present invention is to provide an edge defect identification method based on Lamb wave mode separation, comprising the following steps:

[0009] Step 1: Draw the Lamb wave phase velocity and group velocity dispersion curves based on the material properties and thickness of the structure to be measured to obtain wave velocity information;

[0010] Step 2: Equipment preparation: signal generator, high-voltage amplifier, excitation probe, receiving probe, voltage amplifier, oscilloscope and the structure to be tested. There are several receiving probes.

[0011] Step 3: Based on the equipment prepared in step 2, build an edge defect measurement device based on Lamb wave mode separation;

[0012] Step 4: Apply coupling agent on the excitation probe and the receiving probe respectively;

[0013] Step 5: Arrange the receiving probes in a dual linear array on the surface of the structure to be measured, and arrange the excitation probes on the axis of the linear array of the receiving probes, with the receiving probes located between the test area of ​​the structure to be measured and the excitation probes;

[0014] Step 6: Input an incident wave generated by a signal generator and amplified by a high-voltage amplifier to the surface of the structure to be measured through an excitation probe, and collect a received signal through each receiving probe according to the position of the excitation probe, the receiving probe, and the boundary of the structure to be measured; the received signal is a numerical simulation signal of the single-mode Lamb wave propagation corresponding to the position of each receiving probe;

[0015] Step 7: Separate the direct wave and the boundary reflected wave from the received signal received in step 6 to reconstruct the reflected wave caused by the damage;

[0016] Step 8. Determine the corresponding damage location based on the reflected wave generated by the damage obtained in step 7: Based on the coordinates corresponding to the excitation probe, the receiving probe, and the imaging point, first calculate the propagation time Δt of each imaging point. By referring to the pixel value corresponding to the propagation time Δt, assign a pixel value to the imaging point. Then, add the pixel values ​​generated by each received signal to determine the final pixel value of the imaging point, thereby completing the image reconstruction of the damage location and identifying the damage location.

[0017] Preferably, in step 1, the phase velocity c p , group velocity c g The calculation formulas are:

[0018]

[0019] Where: k is the wave number of the Lamb wave, ω is the circular frequency of the Lamb wave; f is the frequency of the Lamb wave, λ is the wavelength of the Lamb wave, and h is half the thickness of the structure to be measured.

[0020] Preferably, in step five, the number of receiving probes is 14; the distance between the receiving probes arranged in a bilinear array is 2 cm, and the distance between adjacent receiving probes is also 2 cm.

[0021] Preferably, in step 6, the received signal g(x, t) is a one-dimensional wave of the propagation waveform g(t) of the excitation signal propagating in the positive direction, and the specific calculation formula is:

[0022]

[0023] Where x is the propagation position of a single wave mode, k is the wave number, and ω is the frequency; i is a complex number; k0, k1, and k2 are the first three terms of the Taylor expansion for wave number k; m(t) is the modulation envelope function, and ω0 is the center frequency of the signal.

[0024] Preferably, in step seven, the specific steps of reconstructing the reflected wave generated by the damage include:

[0025] Step 7.1. Based on the numerical simulation signal of single-mode Lamb wave propagation in the structure to be measured, select a rectangular truncation window for the received signal and define the truncation signal h0(x0,t) as follows:

[0026]

[0027] Where h0(x0,t) is the truncated signal, x0 is the specific position of the rectangular truncation window, h(x0,t) is the numerical simulation signal of the single-mode Lamb wave when time t is between t1 and t2, and when time t is between t1 and t2, the truncated signal h0(x0,t) only contains the signal mode to be separated;

[0028] Step 7.2: Based on the expression of the truncated signal h0(x0,t), obtain the propagation expression g of the Lamb wave of any β mode β (x0,t), construct the signal g0(x0,t,Δn):

[0029]

[0030] T is the sampling period of the basic signal, Δn is the number of periods of the sampling period T, an integer variable set according to the received waveform range, and its value is an integer between 50 and 100;

[0031] Step 7.3: Find the optimal integer ΔN so that the truncated signal h0 and the constructed signal g0 are most similar, so as to complete the separation of the specific modal signal. The value of the optimal integer ΔN is calculated by the following formula:

[0032]

[0033] Where: is the mean of the constructed signal g0(x0,t,Δn), is the mean of the truncated signal h0(x0,t);

[0034] Step 7.4: Calculate the ratio ΔC between the amplitude of the analog signal and the amplitude of the signal to be separated. The calculation formula is as follows:

[0035]

[0036] Step 7.5. Calculate the residual signal R(x0,t) after removing the separation signal:

[0037] R(x0,t)=h(x0,t)-ΔC·g0(x0,t,ΔN);

[0038] The residual signal R(x0,t) after removing the separated signal is the reflected wave generated by the reconstruction damage.

[0039] In step eight, the specific steps of determining the corresponding damage location according to the damage reflection wave include: first establishing Cartesian coordinates on the surface of the structure to be measured, and then using the position coordinates (x, y) of the imaging point and the position coordinates (x T ,y T ) and the position coordinates of the receiving probe (x R ,y R ) Calculate the time difference between the Lamb wave emission and reception, and finally select the amplitude of the damage reflection wave in the received signal as the pixel value of the imaging point based on the time difference;

[0040] The calculation formula for the time difference Δt between the Lamb wave emission and reception is:

[0041]

[0042] Where: v1 represents the propagation velocity of the Lamb wave from the excitation probe to the imaging point, and v2 represents the propagation velocity of the damage reflection wave from the imaging point to the receiving probe.

[0043] Based on the above technical objectives, the present invention has the following advantages over the prior art:

[0044] In response to the shortcomings of the existing technology, the present invention provides an edge defect identification method and measurement device based on Lamb wave modal separation. By separating the edge reflection waves generated by the influence of the boundary position, the identification method of the present invention is suitable for identifying edge defects of the structure to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the structure of the edge defect measurement device based on Lamb wave mode separation.

[0046] In the figure: 1-signal generator; 2-high-voltage amplifier; 3-oscilloscope; 4-voltage amplifier; 5-excitation probe; 6-receiving probe; 7-structure to be measured; 8-edge defect.

[0047] Figure 2 for Figure 1 The incident wave waveform generated by the signal generator.

[0048] Figure 3 Schematic diagram of the structure of the edge defect measurement device in an embodiment of the present invention when performing aluminum plate inspection.

[0049] Figure 4 is the antisymmetric A0 mode of the Lamb wave phase velocity in the aluminum plate;

[0050] Figure 5 is the antisymmetric A0 mode of the Lamb wave group velocity in the aluminum plate;

[0051] Figure 6 The received signal recorded by the #2 receiving probe is shown;

[0052] Figure 7 yes Figure 6 The displayed received signal is a numerical simulation signal of the direct wave obtained after processing;

[0053] Figure 8 It is the signal after the direct wave is removed from the received signal;

[0054] Figure 9 It is the numerical simulation signal of the boundary reflection wave obtained after the direct wave is removed from the received signal;

[0055] Figure 10 It is the signal after removing the boundary reflected wave from the received signal after removing the direct wave;

[0056] Figure 11 This is a schematic diagram of the imaging of edge defects and damage on aluminum plates. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention. Unless otherwise specified, the relative arrangement of components and steps, expressions and numerical values ​​described in these embodiments do not limit the scope of the present invention. Technologies, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the technologies, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of the exemplary embodiments may have different values.

[0058] The edge defect identification method based on Lamb wave mode separation of the present invention comprises the following steps:

[0059] Step 1: According to the material properties and thickness of the structure to be tested, draw the phase velocity and group velocity dispersion curves of the Lamb wave to obtain the wave velocity information; when the structure to be tested is an isotropic plate, the characteristic equation followed by the Lamb wave propagation is

[0060]

[0061] in, h is half the thickness of the structure to be measured, k is the wave number, ω is the circular frequency, c L is the velocity of the longitudinal wave, c T is the velocity of the shear wave, +1 and -1 in formula (1) represent the symmetric and antisymmetric modes respectively;

[0062] Phase velocity c p It refers to the speed at which the phase of the wave propagates in space, and its formula is:

[0063]

[0064] In formula (2), f is the frequency and λ is the wavelength.

[0065] Group velocity c g It refers to the envelope propagation velocity of the wave, and its formula is:

[0066]

[0067] Step 2: Equipment preparation: signal generator, high-voltage amplifier, excitation probe, receiving probe, voltage amplifier, oscilloscope, and structure to be tested.

[0068] Step 3: Build a test platform

[0069] Based on the equipment prepared in the second step, build Figure 1 The measuring device shown, wherein:

[0070] (1) The signal generator is connected to the input terminal of the high voltage amplifier. The signal generator is used to generate the incident wave (composed of an 8-cycle Hanning window sine wave, as shown in formula (4), and the waveform is shown in Figure 2 shown).

[0071] The amplitude of the incident wave x(t) is set to 6 vpp and the center frequency ω0 is set to 200 kHz.

[0072]

[0073] 2) The output end of the high-voltage amplifier is connected to the excitation probe. The high-voltage amplifier is used to amplify the energy of the incident wave, and the excitation probe is used to transmit the incident wave to the surface of the structure to be measured.

[0074] (3) The receiving probe is connected to the input end of the voltage amplifier. The receiving probe is used to receive the vibration wave after being transmitted from the structure to be tested, and the voltage amplifier is used to amplify the energy of the received wave.

[0075] (4) The output end of the signal generator, the monitoring end of the high-voltage amplifier, and the output end of the voltage amplifier are all connected to an oscilloscope; the oscilloscope is used to display the vibration wave generated by the signal generator, the vibration wave amplified by the high-voltage amplifier, and the received vibration wave amplified by the voltage amplifier.

[0076] Step 4: Apply coupling agent to the excitation probe and the receiving probe respectively to remove the air between the probe and the structure to be measured during measurement.

[0077] Step 5: There are 14 receiving probes arranged in a dual linear array. The excitation probe is on the axis of the linear array and between the test area and the excitation probe. The distance between adjacent receiving probes is 2 cm. The receiving probes are placed in a dual linear array with a distance of 2 cm between the arrays.

[0078] Step 6: Based on the excitation probe, receiving probe and boundary position, the corresponding numerical simulation signal of the single-mode Lamb wave propagation at the receiving position can be obtained. The method for obtaining the simulation signal is as follows:

[0079] Step 1: Based on the propagation waveform of Lamb waves in the thin plate (structure to be tested) under the excitation signal:

[0080]

[0081] Where g(t) is the propagation waveform of the excitation signal, m(t) is the modulation envelope function, and ω0 is the center frequency of the signal.

[0082] Step ②: Based on the expression of a one-dimensional wave propagating in the positive direction according to any modal waveform:

[0083]

[0084] Where x is the propagation position of a single wave mode, k is the wave number, ω is the frequency, and G(ω) is the frequency spectrum of g(t).

[0085] Step 3: Substitute equation (5) into equation (6) to obtain:

[0086]

[0087] in:

[0088] k=k(ω)=k0+k1(ω-ω0)+k2(ω-ω0) 2 +…,

[0089] Here we take the first three terms of the Taylor expansion: k0=ω0 / c p ,

[0090] Step ④: Substitute the k expansion into equation (7) and rearrange the exponential terms to obtain:

[0091]

[0092] Step 5: According to the excitation probe, receiving probe and boundary position, substitute k0, k1, k2, x into formula (8) in step 4 to obtain the numerical simulation signal of the corresponding single-mode Lamb wave propagation at the receiving position.

[0093] Step 7: Separate the direct wave and boundary reflection wave from the received signal and reconstruct the reflection wave caused by the damage. The specific separation method is as follows:

[0094] Step 1: Based on the numerical simulation signal of single-mode Lamb wave propagation in a thin plate, a rectangular truncation window is selected for the received signal, which is defined as follows:

[0095]

[0096] Where h0(x0,t) is the truncated signal, x0 is the specific position of the rectangular truncation window, h(x0,t) is the numerical simulation signal of the single-mode Lamb wave, and t1 and t2 are determined based on the received signal to be processed, ensuring that only the signal mode to be separated is contained between t1 and t2.

[0097] Step ②: According to formula (8), the propagation expression g of Lamb wave of any β mode can be obtained: β (x0,t), construct signal The separation of specific modal signals is achieved by finding the optimal integer ΔN so that h0 and g0 are most similar, where T is the sampling period of the basic signal.

[0098] Step 3: Obtain the value of ΔN using the following formula:

[0099]

[0100] Wherein, Δn is an integer variable set according to the received waveform range and can be an integer between 50 and 100. are the means of g0(x0,t,Δn) and h0(x0,t) respectively.

[0101] Step ④: According to the following formula:

[0102]

[0103] The ratio ΔC of the amplitude of the analog signal and the signal to be separated can be obtained.

[0104] Step ⑤: The residual signal after removing the separation signal can be obtained by the following formula:

[0105] R(x0,t)=h(x0,t)-ΔC·g0(x0,t,ΔN) (12)

[0106] Step 8: Determine the corresponding damage location based on the damage reflection wave

[0107] Step 1: According to the separated damage reflection wave, Cartesian coordinates are established on the surface of the structure to be tested. The time difference between the emission and reception of the Lamb wave is calculated by the positions of the imaging point, the excitation probe, and the receiving probe in the Cartesian coordinates. According to the time difference, the amplitude of the damage reflection wave in the received signal is selected as the pixel value of the imaging point; wherein, the linear Lamb wave moves at a speed of c g (v) The damage reflection wave propagates from the excitation probe to the imaging point at a speed of c g (v) Propagation from the imaging point to the receiving probe.

[0108] Specifically, in Cartesian coordinates, the imaging point coordinates are (x, y), and the excitation probe coordinates are (x T ,y T ), the receiving probe coordinates are (x R ,y R ), assuming the distance from the imaging point to the excitation probe is d1, and the distance from the imaging point to the receiving probe is d2, the Lamb wave vibration propagation time calculation formula is

[0109]

[0110] Among them, the excitation probe is located at (0.1, 0), and the fourteen receiving probes are marked as #1, #2, #3, #4, #5, #6, #7, #8, #9, #10, #11, #12, #13, and #14, and their positions in Cartesian coordinates are (0.04, 0.15), (0.06, 0.15), (0.08, 0.15), (0.1, 0.15), (0.12, 0.15), (0.14, 0.15), (0.16, 0.15), (0.0 4,0.13), (0.06,0.13), (0.08,0.13), (0.1,0.13), (0.12,0.13), (0.14,0.13), (0.16,0.13) cm, the Lamb wave propagates from the excitation probe to the imaging point at a speed of v(v1), and the damage reflection wave propagates from the imaging point to the receiving probes #1, #2, #3, #4, #5, #6, #7, #8, #9, #10, #11, #12, #13, #14 at a speed of v(v2);

[0111] Calculate the Lamb wave vibration propagation time Δt obtained by each receiving probe. The amplitude of the damage reflection wave at Δt represents the reflection intensity of the imaging point. This is because when the imaging point coincides with an edge defect, a strong reflection occurs, resulting in a peak in the damage reflection wave. When the imaging point is not on an edge defect, no significant reflection occurs, and the amplitude of the damage reflection wave approaches 0. Therefore, the amplitude of the damage reflection wave can be used as the pixel value to represent the reflection intensity of the imaging point.

[0112] Step 9: The coordinates of the excitation probe and the receiving probe are known. The propagation time Δt of the imaging point can be calculated according to formula (13). By referring to the pixel value corresponding to Δt, a pixel value is assigned to the imaging point. One transmitting-receiving vibration wave produces one pixel value. By adding the 14 pixel values ​​generated by 14 pairs of transmitting-receiving vibration waves, the final pixel value of the imaging point can be determined. Based on this principle, the damage image is reconstructed. The damage image is normalized, and the area with higher pixel values ​​is the damage site.

[0113] Example:

[0114] The accuracy of the proposed method is verified by numerical simulation experiments on an aluminum plate with a size of 500×600×2mm. The material properties of the plate are shown in Table 1. There is a hole with a radius of 10mm and a height of 2mm on the edge of the aluminum plate, with coordinates of (0.1, 0.235)m. The defect location and instrument layout are shown in Figure 3 shown.

[0115] Table 1

[0116] Young's modulus Poisson's ratio density 70GPa 0.33 <![CDATA[2700kg / m 3 ]]>

[0117] According to the first step, the dispersion curve of the phase velocity, group velocity and frequency-thickness product of the linear Lamb wave of the glass plate is drawn to obtain information about the wave velocity. Figure 4 The antisymmetric A0 mode of the Lamb wave phase velocity in the aluminum plate is shown as Figure 5 The antisymmetric A0 mode of the Lamb wave group velocity in the aluminum plate is shown.

[0118] According to the fourth and fifth steps, the signal waves of the receiving probes at positions #1, #2, #3, #4, #5, #6, #7, #8, #9, #10, #11, #12, #13, and #14 are obtained. Figure 6 The figure shows the received signal recorded by the receiving probe at #2. The first part of the received signal is the direct wave, and the second part is a mixture of edge reflection waves and damage reflection waves.

[0119] Through the sixth step, the direct wave numerical simulation signal is obtained as Figure 7 shown.

[0120] Through the seventh step, the signal after removing the direct wave from the received signal is as follows Figure 8 shown.

[0121] Through the sixth step, the numerical simulation signal of the boundary reflection wave is obtained as follows Figure 9 shown.

[0122] Through the seventh step, the received signal after removing the direct wave and the boundary reflection wave is as follows Figure 10 As shown, it is the damage reflection wave signal.

[0123] According to step 8, the excitation probe is located at (0.1, 0), and the fourteen receiving probes are marked as #1, #2, #3, #4, #5, #6, #7, #8, #9, #10, #11, #12, #13, and #14, and their positions in Cartesian coordinates are (0.04, 0.15), (0.06, 0.15), (0.08, 0.15), (0.1, 0.15), (0.12, 0.15), (0.14, 0.15), (0.16, 0.15), (0.0 The Lamb wave propagates from the excitation probe to the imaging point at a speed of 3060 m / s, and the damage reflection wave propagates from the imaging point to the receiving probes #1, #2, #3, #4, #5, #6, #7, #8, #9, #10, #11, #12, #13, and #14 at a speed of 3060 m / s.

[0124] According to the ninth step, since the coordinates of the transmitter and receiver are known, the propagation time Δt of the vibration wave to a given imaging point can be calculated according to formula (6), and a pixel value is assigned to the focus by referring to the pixel value corresponding to Δt. One transmitting and receiving pair generates one pixel value. By adding the 14 pixel values ​​generated by 14 pairs of transmitting and receiving pairs, the final pixel value of the focus can be determined. Based on this principle, the damage image is reconstructed. The final image is as follows Figure 11 Show.

Claims

1. A method for edge hole identification based on Lamb wave mode separation, characterized in that: The steps include: Step 1: Draw the Lamb wave phase velocity and group velocity dispersion curves based on the material properties and thickness of the structure to be measured to obtain wave velocity information; Step 2: Equipment preparation: signal generator, high-voltage amplifier, excitation probe, receiving probe, voltage amplifier, oscilloscope and the structure to be tested. There are several receiving probes. Step 3: Using the equipment prepared in step 2, build an edge hole measurement device based on Lamb wave mode separation; Step 4: Apply coupling agent on the excitation probe and the receiving probe respectively; Step 5: Arrange the receiving probes in a dual linear array on the surface of the structure to be measured, and arrange the excitation probes on the axis of the linear array of the receiving probes, with the receiving probes located between the test area of ​​the structure to be measured and the excitation probes; Step 6: Input an incident wave generated by a signal generator and amplified by a high-voltage amplifier to the surface of the structure to be measured through an excitation probe, and collect a received signal through each receiving probe according to the position of the excitation probe, the receiving probe, and the boundary of the structure to be measured; the received signal is a numerical simulation signal of the single-mode Lamb wave propagation corresponding to the position of each receiving probe; The received signal g(x,t) is a one-dimensional wave propagating in the positive direction of the propagation waveform g(t) of the excitation signal. The specific calculation formula is: Where: x is the propagation position of a single wave mode, k is the wave number, ω is the frequency; i is a complex number; k0, k1, k2 are the first three terms of the Taylor expansion of wave number k; m(t) is the modulation envelope function, ω0 is the center frequency of the signal; Step 7: Separate the direct wave and the boundary reflected wave from the received signal received in step 6 to reconstruct the reflected wave caused by the damage; Step 8. Determine the corresponding damage location based on the reflected wave generated by the damage obtained in step 7: Based on the coordinates corresponding to the excitation probe, the receiving probe, and the imaging point, first calculate the propagation time Δt of each imaging point. By referring to the pixel value corresponding to the propagation time Δt, assign a pixel value to the imaging point. Then, add the pixel values ​​generated by each received signal to determine the final pixel value of the imaging point, thereby completing the image reconstruction of the damage location and identifying the damage location.

2. The edge hole identification method based on Lamb wave mode separation according to claim 1 is characterized in that: In step 1, the phase velocity c p , group velocity c g The calculation formulas are: Where: k is the wave number of the Lamb wave, ω is the circular frequency of the Lamb wave; f is the frequency of the Lamb wave, λ is the wavelength of the Lamb wave, and h is half the thickness of the structure to be measured.

3. The edge hole identification method based on Lamb wave mode separation according to claim 1 is characterized in that: In step 5, the number of receiving probes is 14; the distance between the receiving probes arranged in a dual linear array is 2 cm, and the distance between adjacent receiving probes is also 2 cm.

4. The edge hole identification method based on Lamb wave mode separation according to claim 1 is characterized in that: In step 7, the specific steps of reconstructing the reflected wave generated by the damage include: Step 7.

1. Based on the numerical simulation signal of single-mode Lamb wave propagation in the structure to be measured, select a rectangular truncation window for the received signal and define the truncation signal h0(x0,t) as follows: Where h0(x0,t) is the truncated signal, x0 is the specific position of the rectangular truncation window, h(x0,t) is the numerical simulation signal of the single-mode Lamb wave when time t is between t1 and t2, and when time t is between t1 and t2, the truncated signal h0(x0,t) only contains the signal mode to be separated; Step 7.2: Based on the expression of the truncated signal h0(x0,t), obtain the propagation expression g of the Lamb wave of any β mode β (x0,t), construct the signal g0(x0,t,Δn): T is the sampling period of the basic signal, Δn is the number of periods of the sampling period T, an integer variable set according to the received waveform range, and its value is an integer between 50 and 100; Step 7.3: Find the optimal integer ΔN so that the truncated signal h0 and the constructed signal g0 are most similar, so as to complete the separation of the modal signals. The value of the optimal integer ΔN is calculated by the following formula: Where: is the mean of the constructed signal g0(x0,t,Δn), is the mean of the truncated signal h0(x0,t); Step 7.4: Calculate the ratio ΔC between the amplitude of the analog signal and the amplitude of the signal to be separated. The calculation formula is as follows: Step 7.

5. Calculate the residual signal R(x0,t) after removing the separation signal: R(x0,t)=h(x0,t)-ΔC·g0(x0,t,ΔN); The residual signal R(x0,t) after removing the separated signal is the reflected wave generated by the reconstruction damage.

5. The edge hole identification method based on Lamb wave mode separation according to claim 1 is characterized in that: In step eight, the specific steps of determining the corresponding damage location according to the damage reflection wave include: first establishing Cartesian coordinates on the surface of the structure to be measured, and then using the position coordinates (x, y) of the imaging point and the position coordinates (x T ,y T ) and the position coordinates of the receiving probe (x R ,y R ) Calculate the time difference between the Lamb wave emission and reception, and finally select the amplitude of the damage reflection wave in the received signal as the pixel value of the imaging point based on the time difference; The calculation formula for the time difference Δt between the Lamb wave emission and reception is: Where: v1 represents the propagation velocity of the Lamb wave from the excitation probe to the imaging point, and v2 represents the propagation velocity of the damage reflection wave from the imaging point to the receiving probe.

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