Micro-crack nonlinear ultrasonic lamb wave detection method and system based on acoustic filtering metamaterial

Abstract

The invention relates to a microcrack nonlinear ultrasonic lamb wave detection method and system based on an acoustic filtering metamaterial. According to the method, an acoustic filtering metamaterial is fused into a detection model so as to filter out system nonlinearity. The method comprises the following steps: firstly, constructing an acoustic filtering metamaterial structure containing an acoustic black hole structure; constructing a micro-crack nonlinear ultrasonic Lamb wave detection finite element model, and integrating the acoustic filtering metamaterial structure into the micro-crack nonlinear ultrasonic Lamb wave detection finite element model to obtain an acoustic filtering metamaterial-based nonlinear ultrasonic Lamb wave detection finite element model; and finally, detecting the micro-crack by using the constructed micro-crack nonlinear ultrasonic Lamb wave detection finite element model. Compared with the prior art, the method has the advantages of improving the sensitivity and accuracy of microcrack detection and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of microcrack detection, and in particular to a microcrack nonlinear ultrasonic Lamb wave detection method and system based on acoustic filtering metamaterial. Background Art

[0002] Early detection of microcracks is extremely important in the health monitoring of engineering structures. Microcracks usually do not cause obvious physical changes, but they will gradually expand and eventually lead to component fracture and failure. At present, common non-destructive testing methods mainly include radiographic testing, eddy current testing, magnetic particle testing, ultrasonic testing, etc. Among them, ultrasonic testing is widely used in the industrial field due to its advantages of fast detection speed and high detection accuracy.

[0003] In ultrasonic testing, traditional linear detection methods can detect macroscopic defects in structures, but are insensitive to microscopic damage such as microcracks. Among them, the propagation characteristics of Lamb waves are highly sensitive to the identification of internal defects in materials, such as microcracks. In particular, the nonlinear response stimulated by microcracks can be detected by high-order nonlinear signals, and the nonlinear response will change significantly with the degree of crack extension, which is conducive to the detection and characterization of microcracks. However, the nonlinear signals caused by microcracks are often weak and easily interfered by the nonlinearity of the system, thus affecting the sensitivity and accuracy of the detection.

[0004] For example, the invention patent with publication number CN116448891A discloses a method for measuring the directivity of microcracks in metal pipes based on nonlinear Lamb waves. The method selects a calibration sample with the same material and diameter as the microcrack pipe to be measured; draws a curved circle; determines a test angle; determines the ultrasonic nonlinear coefficient of the microcrack pipe to be measured at different measurement angles; and brings the ultrasonic nonlinear coefficient at different measurement angles into a microcrack directivity angle evaluation function to obtain the microcrack directivity angle of the pipe to be measured. However, the method does not take into account the interference of system nonlinearity, and the accuracy of the detection result is not high. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a nonlinear ultrasonic Lamb wave detection method and system for microcracks based on acoustic filtering metamaterials.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] According to one aspect of the present invention, a nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials is provided, and the method comprises the following steps:

[0008] S1. Combining acoustic black hole structure and phononic crystal to build acoustic filtering metamaterial structure;

[0009] S2. Construct a finite element model for nonlinear ultrasonic Lamb wave detection of microcracks, and integrate the acoustic filter metamaterial structure into it to obtain a finite element model for nonlinear ultrasonic Lamb wave detection based on acoustic filter metamaterial;

[0010] S3. Use the constructed nonlinear ultrasonic Lamb wave detection finite element model for microcrack detection to perform microcrack detection.

[0011] As a preferred technical solution, the acoustic filtering metamaterial structure in S1 is composed of a unit cell structure, wherein the unit cell structure includes a substrate and an acoustic black hole structure, and the acoustic black hole structure is attached to the middle position of the substrate.

[0012] As a preferred technical solution, the process of S1 building an acoustic filtering metamaterial structure includes: combining an acoustic black hole structure with a phononic crystal, and adjusting the structural parameters and material properties of the acoustic filtering metamaterial so that the fundamental frequency is located in the passband and the double frequency is located in the band gap; the structural parameters are the dimensions of the acoustic filtering metamaterial structure, and the dimensions include the lattice constant, the substrate thickness, the minimum thickness and the maximum thickness of the acoustic black hole structure, and the length of the connection between the acoustic black hole structure and the substrate; the material properties are the types of materials corresponding to the substrate and the acoustic black hole structure in the acoustic filtering metamaterial structure.

[0013] As a preferred technical solution, the thickness of the acoustic black hole structure changes gradually according to the parabolic law, and its expression is:

[0014]

[0015] Where h(x) is the thickness of the acoustic black hole structure contour, h0 and h1 represent the minimum thickness and maximum thickness of the acoustic black hole structure, respectively, l represents the length of the connection between the acoustic black hole structure and the substrate, and x represents the distance to the minimum thickness position, i.e., the origin O.

[0016] As a preferred technical solution, the substrate material in the acoustic filtering metamaterial structure is aluminum, and the acoustic black hole structure material is steel.

[0017] As a preferred technical solution, the base frequency is 220kHz, and the corresponding double frequency is 440kHz.

[0018] As a preferred technical solution, S2 integrates the acoustic filtering metamaterial structure into the finite element model of microcrack nonlinear ultrasonic Lamb wave detection by means of attachment.

[0019] As a preferred technical solution, the specific process of microcrack detection in S3 is: first, the excitation signal is input into the microcrack nonlinear ultrasonic Lamb wave detection finite element model, the system nonlinearity and the contact nonlinearity caused by the microcracks are analyzed, and the displacement time domain signal is output. Based on the displacement time domain signal, the fundamental frequency Lamb wave component and the double frequency Lamb wave component can be obtained, and then the nonlinear acoustic parameters are calculated. The nonlinear acoustic parameters are the microcrack detection results.

[0020] As a preferred technical solution, the fundamental frequency Lamb wave component and the double frequency Lamb wave component are extracted from the displacement time domain signal using the reverse pulse technology.

[0021] According to another aspect of the present invention, there is provided a microcrack nonlinear ultrasonic Lamb wave detection system based on acoustic filtering metamaterials, the system being operated by a microcrack nonlinear ultrasonic Lamb wave detection method based on acoustic filtering metamaterials as described above, the system comprising an acoustic filtering metamaterial structure building module, a model building and optimization module and a microcrack detection module;

[0022] The acoustic filtering metamaterial structure building module is used to combine the acoustic black hole structure and the phononic crystal to build an acoustic filtering metamaterial structure;

[0023] The model building and optimization module is used to build a finite element model for nonlinear ultrasonic Lamb wave detection of microcracks, and integrate the acoustic filter metamaterial structure into it to obtain a nonlinear ultrasonic Lamb wave detection finite element model based on acoustic filter metamaterial;

[0024] The microcrack detection module is used to perform microcrack detection using the constructed microcrack nonlinear ultrasonic Lamb wave detection finite element model based on acoustic filtering metamaterials.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. In a nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filter metamaterials of the present invention, the acoustic filter metamaterial is integrated into the detection model to filter out the nonlinearity of the system; the method first combines the acoustic black hole structure and the phononic crystal to build an acoustic filter metamaterial structure; then a finite element model for nonlinear ultrasonic Lamb wave detection of microcracks is constructed, and the acoustic filter metamaterial structure is integrated therein to obtain a nonlinear ultrasonic Lamb wave detection finite element model based on the acoustic filter metamaterial; finally, the constructed nonlinear ultrasonic Lamb wave detection finite element model for microcracks is used to perform microcrack detection. The method effectively filters out the system nonlinearity in nonlinear ultrasonic Lamb wave detection, thereby improving the sensitivity and accuracy of microcrack detection.

[0027] 2. In the present invention, the acoustic filtering metamaterial structure is composed of a unit cell structure, and the unit cell structure includes a substrate and an acoustic black hole structure, and the acoustic black hole structure is attached to the middle of the substrate. This method integrates the acoustic black hole structure into the design of the acoustic filtering metamaterial structure, and combines the characteristics of the acoustic black hole structure and the phononic crystal to achieve the regulation of elastic waves.

[0028] 3. In the present invention, when constructing an acoustic filtering metamaterial structure, the structural parameters and material properties of the acoustic filtering metamaterial are adjusted so that the fundamental frequency is located in the passband and the double frequency is located in the band gap; wherein the structural parameter is the size of the acoustic filtering metamaterial structure, and the material property is the type of material of the acoustic filtering metamaterial structure. This method can optimize the band gap range by adjusting the structural parameters and material properties of the acoustic filtering metamaterial to meet different application requirements, thereby expanding the scope of application of the detection model.

[0029] 4. In the present invention, the acoustic filtering metamaterial structure is integrated into the finite element model of microcrack nonlinear ultrasonic Lamb wave detection by means of attachment, so as to achieve the effect of convenient installation while avoiding damage to the structure to be detected, and has high application potential in the field of nondestructive testing.

[0030] 5. In the present invention, the substrate material in the acoustic filtering metamaterial structure is aluminum, and the acoustic black hole structure material is steel. Both materials are easy to obtain and convenient to process and manufacture. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a method flow chart of a nonlinear ultrasonic Lamb wave detection method for micro-cracks based on acoustic filtering metamaterials in the present invention;

[0032] Figure 2 It is a schematic diagram of the principle of a nonlinear ultrasonic Lamb wave detection method for micro-cracks based on acoustic filtering metamaterials in the present invention;

[0033] Figure 3 A schematic diagram of a unit cell structure of an acoustic filtering metamaterial in an embodiment;

[0034] Figure 4a Schematic diagram of the energy band structure of the acoustic filtering metamaterial in the embodiment;

[0035] Figure 4b is a frequency response curve diagram of the filtering metamaterial in the embodiment;

[0036] Figure 5a It is a displacement field distribution diagram of the fundamental frequency Lamb wave when propagating in the acoustic filtering metamaterial in the embodiment;

[0037] Figure 5b This is a displacement field distribution diagram of a double frequency Lamb wave when propagating in an acoustic filtering metamaterial in an embodiment;

[0038] Figure 6a Figure 2 is a diagram of the fundamental frequency Lamb wave signal received respectively when there is / is not an acoustic filtering metamaterial in the case of considering the nonlinearity of the system in the embodiment;

[0039] Figure 6b Figure 2 is a diagram of the double frequency Lamb wave signal received with and without the acoustic filtering metamaterial when the system nonlinearity is considered in the embodiment;

[0040] Figure 7 Schematic diagram of comparison of second harmonic components generated by system nonlinearity and contact nonlinearity when there is / is no acoustic filtering metamaterial in the embodiment;

[0041] Figure 8 Schematic diagram of the curve of the change of the normalized nonlinear acoustic parameter β with the microcrack length L in the embodiment. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0043] Early detection of microcracks is extremely important in the health monitoring of engineering structures. Microcracks usually do not cause obvious physical changes, but they will gradually expand and eventually lead to component fracture and failure. Therefore, the ability to detect microcracks at an early stage is of great value in improving component safety, extending service life, and reducing maintenance costs. At present, common non-destructive testing methods mainly include X-ray testing, eddy current testing, magnetic particle testing, ultrasonic testing, etc. Among them, ultrasonic testing is widely used in the industrial field due to its advantages of fast detection speed and high detection accuracy.

[0044] In ultrasonic testing, traditional linear detection methods can detect macroscopic defects in structures, but are insensitive to microscopic damage such as microcracks. Nonlinear ultrasonic detection methods can effectively overcome this shortcoming and are widely used for early damage detection and characterization. Moreover, Lamb waves have become an important detection wave type because they can propagate in thin plate materials, and have the advantages of fast and efficient detection. The propagation characteristics of Lamb waves have high sensitivity for the identification of internal defects in materials, such as microcracks. In particular, the nonlinear response excited by microcracks can be detected by high-order nonlinear signals, and the nonlinear response will change significantly with the degree of crack extension, which is conducive to the detection and characterization of microcracks. However, the nonlinear signals caused by microcracks are often weak and easily interfered by the nonlinearity of the system, thus affecting the sensitivity and accuracy of detection.

[0045] In order to solve this problem, the application of acoustic metamaterials in the field of sound wave control has become a research hotspot in recent years. As an artificial composite structure with extraordinary physical properties, acoustic metamaterials can freely control sound waves through their special structure, which has attracted widespread attention from researchers at home and abroad. The bandgap characteristics of acoustic filtering metamaterials can prevent the propagation of elastic waves within the bandgap range, while waves in other frequency ranges can pass smoothly. Therefore, introducing acoustic filtering metamaterials into nonlinear ultrasonic Lamb wave detection can effectively filter out irrelevant nonlinear components, thereby improving the signal-to-noise ratio of the detection signal and enhancing the sensitivity and accuracy of nonlinear ultrasonic Lamb wave detection of microcracks.

[0046] Example

[0047] In this embodiment, a nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filter metamaterials is applied. The method integrates the acoustic filter metamaterial into the detection model to filter out the nonlinearity of the system. The method flow is as follows: Figure 1 As shown, the following steps are included:

[0048] S1. Combining acoustic black hole structure and phononic crystal to build acoustic filtering metamaterial structure;

[0049] S2. Construct a finite element model for nonlinear ultrasonic Lamb wave detection of microcracks, and integrate the acoustic filter metamaterial structure into it to obtain a finite element model for nonlinear ultrasonic Lamb wave detection based on acoustic filter metamaterial;

[0050] S3. Use the constructed nonlinear ultrasonic Lamb wave detection finite element model for microcrack detection to perform microcrack detection.

[0051] In this embodiment, an acoustic filtering metamaterial is first designed, and its structural parameters and material properties are determined to establish a finite element model, wherein the structural parameters are the dimensions of the acoustic filtering metamaterial structure, and the material properties are the types of materials of the acoustic filtering metamaterial structure.

[0052] The principle of a nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials used in this embodiment is shown as follows: Figure 2 As shown in the figure. The basic principle is that the excitation process includes the fundamental frequency Lamb wave and the second harmonic Lamb wave related to the system nonlinearity (SN). When passing through the acoustic filtering metamaterials (MF), the second harmonic Lamb wave is prohibited from propagating, while the fundamental frequency Lamb wave can pass smoothly and interact with the microcracks to generate the second harmonic caused by the contact nonlinearity (CN). The acoustic filtering metamaterial effectively filters out the irrelevant system nonlinearity, which is conducive to accurately distinguishing the nonlinear response caused by the microcracks themselves, thereby improving the sensitivity and accuracy of nonlinear ultrasonic Lamb wave detection.

[0053] In this embodiment, the structure of the acoustic filter metamaterial is firstly designed. In order to achieve the above purpose, it is necessary to design an acoustic filter metamaterial so that the fundamental frequency is in the passband range and the double frequency is in the band gap range. In this embodiment, the acoustic black hole structure is combined with the phononic crystal to design an acoustic filter metamaterial. The unit cell structure of the acoustic filter metamaterial is as follows: Figure 3 As shown, specifically, its unit cell structure consists of two parts: a substrate 1 and an acoustic black hole structure 2, and the acoustic black hole structure is attached to the middle position of the substrate.

[0054] In this embodiment, the lattice constant is set to a=4 mm, the substrate thickness is set to H=2 mm, and the thickness of the acoustic black hole structure gradually changes according to the parabolic law, and its expression is:

[0055]

[0056] Where h(x) represents the thickness of the contour of the acoustic black hole structure, h0 and h1 represent the minimum thickness and maximum thickness of the acoustic black hole structure respectively, l represents the length of the connection between the acoustic black hole structure and the substrate, and x represents the distance to the minimum thickness position, i.e., the origin O.

[0057] In this embodiment, h0=0.5 mm, h1=3.5 mm, l=3 mm.

[0058] In this embodiment, the substrate 1 is made of aluminum and the acoustic black hole structure 2 is made of steel, because both materials are relatively easy to obtain and convenient to process and manufacture. Specific material parameters are shown in Table 1. In Table 1, ρ is density, E is Young's modulus, and υ is Poisson's ratio.

[0059] Table 1 Material parameters

[0060]

[0061] In this embodiment, the finite element method is used to calculate the band structure and frequency response of the acoustic filter metamaterial. The band structure of the acoustic filter material is as follows: Figure 4a The frequency response curve is shown as Figure 4b As shown. Figure 4a It can be seen that the designed metamaterial has two band gaps along the x-direction in the frequency range of 0-500kHz. The first band gap is located between the third and fourth energy bands, with a band gap range of 271.6-360.9kHz and a bandwidth of 89.3kHz. The second band gap is located between the fourth and fifth energy bands, with a band gap range of 394.7-478.9kHz and a bandwidth of 84.2kHz.

[0062] And from Figure 4bIt can be seen from the frequency response curve that there are two attenuation zones in the corresponding 0-500kHz frequency range, with the maximum attenuation reaching 89dB and 113dB respectively. The frequency range of the two attenuation zones is Figure 4a The band gaps shown in are basically the same.

[0063] In this embodiment, the excitation frequency of the selected signal is 220kHz, and the corresponding double frequency is 440kHz. Therefore, the fundamental frequency is in the passband region and the double frequency is in the second band gap range. This shows that the designed acoustic filtering metamaterial can allow the fundamental frequency Lamb wave to pass through while preventing the propagation of the double frequency Lamb wave.

[0064] In this embodiment, after calculating the band structure and frequency response of the acoustic filter metamaterial, the displacement field distribution of the fundamental frequency and the double frequency is analyzed to study the propagation characteristics of Lamb waves in the acoustic filter metamaterial; the displacement field distribution of the fundamental frequency and the double frequency Lamb waves when propagating in the acoustic filter metamaterial is shown in FIG5 , where: Figure 5a represents the fundamental frequency Lamb wave, Figure 5b represents the double frequency Lamb wave. It can be clearly seen that the fundamental frequency Lamb wave can pass through the metamaterial and continue to propagate along the plate, while the double frequency Lamb wave cannot propagate through the metamaterial. That is, the metamaterial can effectively filter out the system nonlinearity in non-linear ultrasonic Lamb wave detection, thereby improving the detection sensitivity and accuracy of microcracks.

[0065] In addition, the band gap range can be changed by adjusting the structural type, structural parameters and material properties of the acoustic filtering metamaterial to meet different application requirements.

[0066] Then, in order to verify that the acoustic filtering metamaterial can improve the nonlinear ultrasonic Lamb wave detection capability, microcrack nonlinear ultrasonic Lamb wave detection was carried out, and the performance of the designed acoustic filtering metamaterial was evaluated using time-domain finite element simulation.

[0067] In this embodiment, two finite element models are constructed in the simulation process, namely: a model without an acoustic filter metamaterial structure attached, and a model with an acoustic filter metamaterial structure attached. On the left side of the model, i.e., the input end, the same 5-cycle Hanning window modulated sinusoidal pulse signal with a frequency of 220kHz is applied to the two models, and on the right side of the model, i.e., the output end, the displacement time domain signals are extracted respectively. In order to analyze the influence of the presence / absence of the acoustic filter metamaterial on the detection signal, the output time domain signal is processed respectively, and the fundamental frequency Lamb wave component and the double frequency Lamb wave component are obtained based on the extracted time domain signal, and the nonlinear acoustic parameters are calculated and compared to verify the effectiveness of the acoustic filter metamaterial in improving the sensitivity and accuracy of nonlinear Lamb wave detection.

[0068] In this embodiment, the specific implementation of the verification process is as follows:

[0069] First, in a lossless manner, the effectiveness of acoustic filtering metamaterials in filtering out system nonlinearity is verified. The excitation signal contains a fundamental frequency component and a double frequency component related to system nonlinearity. The fundamental frequency Lamb wave time domain signal and the double frequency Lamb wave time domain signal are extracted from the detection signal, as shown in Figure 6. Figure 6a 1 is a diagram of the baseband Lamb wave signal received respectively with and without the acoustic filtering metamaterial when the system nonlinearity is considered in the embodiment; and Figure 6b Figures 2 and 3 are the received double frequency Lamb wave signal diagrams with and without the acoustic filtering metamaterial respectively when considering the system nonlinearity in the embodiment; it can be seen from the two figures that after the acoustic filtering metamaterial is attached, the amplitude of the fundamental frequency Lamb wave is slightly reduced, and there is a certain phase delay, but it has little effect on the detection result; and the amplitude of the double frequency Lamb wave is significantly reduced, indicating that the acoustic filtering metamaterial can effectively filter out the system nonlinearity.

[0070] In this embodiment, in order to prove that acoustic filtering metamaterials can improve the accuracy of nonlinear ultrasonic Lamb wave detection of microcracks, a microcrack model is constructed and contact nonlinearity is introduced, while the inherent double frequency component in the excitation signal is removed, that is, the influence of system nonlinearity is not considered.

[0071] In this embodiment, the reverse pulse technology is used to excite two signals with opposite phases, and the two received signals are added to eliminate the base frequency Lamb wave component, and then the double frequency Lamb wave component is obtained through digital filtering.

[0072] In this embodiment, the comparison of the normalized second harmonic components generated by the system nonlinearity and the contact nonlinearity when there is / is no acoustic filtering metamaterial is as follows: Figure 7 As shown, it can be clearly seen that when there is no acoustic filtering metamaterial, the system nonlinearity is greater than the contact nonlinearity. After attaching the acoustic filtering metamaterial structure, the system nonlinearity is significantly reduced compared to the contact nonlinearity, and the signal-to-noise ratio of the ultrasonic signal is improved, which is conducive to accurately distinguishing the nonlinear response caused by microcracks, thereby improving the accuracy of nonlinear ultrasonic Lamb wave detection of microcracks.

[0073] In this embodiment, in order to further prove that acoustic filtering metamaterials can improve the sensitivity of nonlinear ultrasonic detection of microcracks, different microcrack lengths L are set in the model considering system nonlinearity and contact nonlinearity. L is divided into 0 mm, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, and 1.0 mm, and the variation of nonlinear acoustic parameters with different microcrack lengths is studied.

[0074] In this embodiment, when there is / is no acoustic filtering metamaterial, the variation curve of the normalized nonlinear acoustic parameter β with the microcrack length L is as follows: Figure 8As shown in the figure, in the case of no acoustic filtering metamaterial, as the microcrack length L increases from 0mm to 1.0mm, the normalized nonlinear acoustic parameter β increases by 31.4%; when the acoustic filtering metamaterial structure is attached, the normalized nonlinear acoustic parameter β increases by 1005.9%, which indicates that the attached acoustic filtering metamaterial can make the Lamb wave more sensitive to the change of microcrack length, thereby improving the sensitivity of nonlinear ultrasonic Lamb wave detection of microcracks.

[0075] In summary, a nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials in this embodiment uses an acoustic filtering metamaterial that combines an acoustic black hole structure and a phononic crystal, and integrates the acoustic filtering metamaterial into the detection model, aiming to achieve regulation of elastic waves using a simple structure, effectively filtering out the system nonlinearity in nonlinear ultrasonic Lamb wave detection, and improving the sensitivity and accuracy of microcrack detection. This method provides an efficient and accurate technical means for early diagnosis and safety assessment of microcracks, and has great application prospects.

[0076] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials, characterized in that: The method comprises the following steps: S1. Combining acoustic black hole structure and phononic crystal to build acoustic filtering metamaterial structure; S2. Construct a finite element model for nonlinear ultrasonic Lamb wave detection of microcracks, and integrate the acoustic filter metamaterial structure into it to obtain a finite element model for nonlinear ultrasonic Lamb wave detection based on acoustic filter metamaterial; S3. Use the constructed nonlinear ultrasonic Lamb wave detection finite element model of microcracks to perform microcrack detection.

2. The nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials according to claim 1 is characterized in that: The acoustic filtering metamaterial structure in S1 is formed by arranging unit cell structures, and the unit cell structure includes a substrate and an acoustic black hole structure, and the acoustic black hole structure is attached to the middle position of the substrate.

3. The nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials according to claim 2 is characterized in that: The process of S1 building an acoustic filtering metamaterial structure includes: combining an acoustic black hole structure with a phononic crystal, and adjusting the structural parameters and material properties of the acoustic filtering metamaterial so that the fundamental frequency is located in the passband and the double frequency is located in the band gap; the structural parameters are the dimensions of the acoustic filtering metamaterial structure, and the dimensions include the lattice constant, the substrate thickness, the minimum thickness and the maximum thickness of the acoustic black hole structure, and the length of the connection between the acoustic black hole structure and the substrate; the material properties are the types of materials corresponding to the substrate and the acoustic black hole structure in the acoustic filtering metamaterial structure.

4. The nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials according to claim 3 is characterized in that: The thickness of the acoustic black hole structure changes gradually according to the parabolic law, and its expression is: Where h(x) is the thickness of the acoustic black hole structure contour, h0 and h1 represent the minimum thickness and maximum thickness of the acoustic black hole structure, respectively, l represents the length of the connection between the acoustic black hole structure and the substrate, and x represents the distance to the minimum thickness position, i.e., the origin O.

5. The nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials according to claim 3 is characterized in that: The substrate material in the acoustic filtering metamaterial structure is aluminum, and the acoustic black hole structure material is steel.

6. The nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials according to claim 3 is characterized in that: The base frequency is 220kHz, and the corresponding double frequency is 440kHz.

7. The nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials according to claim 1 is characterized in that: The S2 integrates the acoustic filtering metamaterial structure into the microcrack nonlinear ultrasonic Lamb wave detection finite element model by means of attachment.

8. The nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials according to claim 1, characterized in that: The specific process of performing microcrack detection in S3 is as follows: first, the excitation signal is input into the microcrack nonlinear ultrasonic Lamb wave detection finite element model, the system nonlinearity and the contact nonlinearity caused by the microcracks are analyzed, and the displacement time domain signal is output. Based on the displacement time domain signal, the fundamental frequency Lamb wave component and the double frequency Lamb wave component can be obtained, and then the nonlinear acoustic parameters are calculated, and the nonlinear acoustic parameters are the microcrack detection results.

9. The nonlinear ultrasonic Lamb wave detection method for microcracks based on acoustic filtering metamaterials according to claim 8, characterized in that: The fundamental frequency Lamb wave component and the double frequency Lamb wave component are extracted from the displacement time domain signal by using the reverse pulse technology.

10. A nonlinear ultrasonic Lamb wave detection system for microcracks based on acoustic filtering metamaterials, characterized in that: The system is operated by a nonlinear ultrasonic Lamb wave detection method for microcracks based on an acoustic filtering metamaterial as described in any one of claims 1 to 9, and the system includes an acoustic filtering metamaterial structure building module, a model building and optimization module, and a microcrack detection module; The acoustic filtering metamaterial structure building module is used to combine the acoustic black hole structure and the phononic crystal to build an acoustic filtering metamaterial structure; The model building and optimization module is used to build a finite element model for nonlinear ultrasonic Lamb wave detection of microcracks based on acoustic filtering metamaterials, and integrate the acoustic filtering metamaterial structure into it to obtain a finite element model for nonlinear ultrasonic Lamb wave detection based on acoustic filtering metamaterials; The microcrack detection module is used to perform microcrack detection using the constructed microcrack nonlinear ultrasonic Lamb wave detection finite element model based on acoustic filtering metamaterials.

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