Engineering material structure micro-damage detection method and device based on broadband nonlinear Lamb waves

Abstract

The invention discloses an engineering material structure micro-damage detection method based on broadband nonlinear Lamb waves. The engineering material structure micro-damage detection method comprises the steps that an active Lamb wave excitation device and a sensor are arranged on an engineering material structure; driving the active Lamb wave excitation device to generate broadband excitation with a preset bandwidth, and collecting a response signal of the broadband excitation through a sensor; extracting a fundamental wave and a second harmonic from the response signal, the second harmonic representing a nonlinearity of a response of the broadband excitation generated by the micro-damage, the nonlinearity being a contact acoustic nonlinearity caused by the micro-damage under the broadband excitation; and analyzing the response signal by a non-linearity indicator to quantify the non-linearity. According to the method, the micro-crack damage in the aluminum alloy sheet is detected by using the broadband nonlinear Lamb wave, and the method is effective in the aspect of high-sensitivity damage identification. The invention further discloses a corresponding device.

Description

Technical Field

[0001] This application belongs to the field of structural damage detection, and particularly relates to a damage detection method and device based on Lamb waves. Background Art

[0002] Fiber-reinforced composite materials have been widely used in the fields of aerospace, shipbuilding, and automobiles due to their excellent properties such as high specific stiffness, specific strength, light weight, and corrosion resistance. However, due to their complex structural characteristics, artificial defects are likely to occur during the manufacturing process, and accidental damage is likely to occur during use. These factors may pose a potential threat to the service performance of composite structures. In particular, impact damage (such as delamination microdamage) caused by accidental impact, which is almost invisible or completely invisible. As the service time of the structure extends, the damage may gradually expand and eventually lead to catastrophic consequences. The mechanism of second harmonic generation caused by delamination microdamage is different from that of microstructural defects in isotropic materials. The interaction between Lamb waves and the delamination microdamage interface belongs to the contact acoustic nonlinear phenomenon. The dynamic wave load can cause the breathing effect of delamination damage, which is the main reason for the generation of the second harmonic component. Ng et al. used a sensor network to sequentially scan the delamination microdamage in a composite material structure by driving and receiving dual Lamb waves, and proposed a damage location imaging algorithm using non-linear combined frequency waves to determine the damage location. This method may become a baseline-free damage detection technology. Shan et al. further explored the characteristics of the second harmonic B2 mode Lamb wave from the aspects of cumulative characteristics, robustness to beam divergence, and excitability through theoretical and numerical simulation methods. Finally, the omnidirectional cumulative effect of the quasi-phase-matched second harmonic B2 mode Lamb wave was confirmed by monitoring the material degradation in the thermal aging experiment of carbon fiber reinforced polymer matrix composite (CFRP). Existing work only diagnoses and locates inherent delamination microdamage, but lacks research on the influence of anisotropy on second harmonic Lamb waves in composite plates and the strength of the nonlinear response to the degree of delamination damage.

[0003] Under the stimulation of a high enough vibration power (such as the excitation of active ultrasonic guided waves), microcracks inside the material may exhibit "breathing motion" (i.e., periodic closing-opening behavior), interfacial frictional interaction, and hysteresis effects caused by energy dissipation at the micro and mesoscopic scales. These nonlinear behaviors can induce various classical nonlinear responses, such as material nonlinearity and Contact Acoustic Nonlinearity (CAN). Among them, material nonlinearity mainly comes from the inherent nonlinear elastic properties of the material and local stress concentration caused by fatigue cracks, and its manifestations usually include the nonlinearity of the stress-strain relationship and the change of acoustic parameters. While CAN comes from the contact nonlinearity generated during the breathing motion and frictional interaction of microcracks. Under the action of ultrasonic excitation, the crack may exist in three states: completely closed, partially closed / opened, or completely opened, and the CAN effect will be enhanced or inhibited due to the change of the contact state between the crack interfaces. Therefore, these defects at the micro and mesoscopic scales can be used as the main source of high-order harmonic vibration components. Since these vibration components have a lower attenuation rate and stronger scattering characteristics compared with traditional linear Lamb waves, nonlinear features can be extracted to obtain the defect information of the structure.

[0004] In practical engineering applications, due to the influence of environmental factors (such as temperature, stress distribution changes, etc.), it is difficult to accurately predict the resonance frequencies of some local defects. In this case, only using single-frequency or narrowband excitation cannot effectively stimulate the nonlinear response, resulting in incomplete detection of structural defects and omission of key information. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies in the prior art and propose to use a broadband signal as the excitation source to improve the comprehensive detection ability for micro defects.

[0006] To this end, some embodiments of the present application propose a method for detecting microdamage in engineering material structures based on broadband nonlinear Lamb waves, which includes the steps of: setting an active Lamb wave excitation device and a sensor on the engineering material structure; driving the active Lamb wave excitation device to generate a broadband excitation with a preset bandwidth, and collecting the response signal of the broadband excitation through the sensor; extracting the fundamental wave and the second harmonic from the response signal, where the second harmonic represents the nonlinearity of the response of the broadband excitation generated by the microdamage, and the nonlinearity is the contact acoustic nonlinearity caused by the microdamage under the broadband excitation; analyzing the response signal through a nonlinear index to quantify the nonlinearity, and the nonlinear index is defined as: Wherein, and respectively represent the average values of the normalized amplitudes of the fundamental wave and the second harmonic.

[0007] In some embodiments, the preset bandwidth of the broadband excitation signal is 200 kHz.

[0008] In some embodiments, the frequency range of the broadband excitation signal is 200 - 400 kHz or 300 - 500 kHz or 400 - 600 kHz.

[0009] In some embodiments, the engineering material structure is an isotropic material.

[0010] In some embodiments, the engineering material structure is an anisotropic material, especially a composite material, particularly a CFRP material.

[0011] In some embodiments, the degree of the microdamage is determined based on the following relationship: as the degree of the microdamage increases, the generated nonlinear response gradually weakens, and the nonlinear response shows a downward trend.

[0012] In some embodiments, the microdamage is a microcrack.

[0013] Some other embodiments of the present application propose a microdamage detection device for an engineering material structure based on broadband nonlinear Lamb waves, which includes an active Lamb wave excitation device and a sensor disposed on the engineering material structure; a control unit that drives the active Lamb wave excitation device to generate a broadband excitation with a preset bandwidth, and an acquisition unit that acquires a response signal of the broadband excitation through the sensor; and an analysis unit, where the analysis unit is configured to: extract a fundamental wave and a second harmonic from the response signal, the second harmonic represents the nonlinearity of the response of the broadband excitation generated by the microdamage, and the nonlinearity is contact acoustic nonlinearity caused by the microdamage under the broadband excitation; analyze the response signal through a nonlinear index to quantify the nonlinearity, and the nonlinear index is defined as: Wherein, and respectively represent the average values of the normalized amplitudes of the fundamental wave and the second harmonic.

[0014] The effective effect of the present application is that:

[0015] Microcrack damage inside an aluminum alloy thin plate is detected by using broadband nonlinear Lamb waves, which is effective in high-sensitivity damage identification and expands the application prospect of nonlinear Lamb waves in the field of microdamage detection.

[0016] Through the extraction and analysis of broadband nonlinear Lamb wave signals, not only the high-precision detection of micro-damage in aluminum alloy thin plates is realized, but also the damage degree of different aluminum alloy thin plates can be quantitatively evaluated, laying a foundation for constructing a more perfect damage quantification evaluation system. This achievement has important reference value for the health monitoring and remaining life assessment of engineering structures.

[0017] This method has successfully detected the delamination micro-cracks inside the CFRP plate, verifying the applicability of broadband nonlinear Lamb waves in the identification of artificial defects in anisotropic materials. This method provides theoretical support for the detection of micro-damage in composite materials based on nonlinear Lamb waves, and helps to promote the application and development of this technology in the fields of aerospace, high-end manufacturing, etc.

[0018] By extracting and calculating the nonlinear parameter β’ WB,CAN , the evolution degree of internal damage in the structure can be quantitatively characterized, and a higher-precision damage assessment can be achieved. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the finite element model of an aluminum alloy thin plate according to an embodiment of the present application.

[0020] Figure 2a It shows a schematic diagram of the nonlinear response of an aluminum alloy thin plate in the time domain under a broadband excitation of 400 kHz - 600 kHz.

[0021] Figure 2b It is Figure 2a a schematic diagram of the frequency domain response of

[0022] Figure 2c It shows a schematic diagram of the nonlinear response of a CFRP plate in the time domain under a broadband excitation of 400 kHz - 600 kHz.

[0023] Figure 2d It is Figure 2c a schematic diagram of the frequency domain response of

[0024] Figure 3a It is a schematic diagram of the nonlinear response of an aluminum alloy thin plate with a 20 nm micro-damage under a frequency excitation of 200 kHz - 400 kHz.

[0025] Figure 3b It is a schematic diagram of the nonlinear response of an aluminum alloy thin plate with a 200 nm micro-damage under a frequency excitation of 200 kHz - 400 kHz.

[0026] Figure 3c It is a schematic diagram of the nonlinear response of an aluminum alloy thin plate with a 2000 nm micro-damage under a frequency excitation of 200 kHz - 400 kHz.

[0027] Figure 3dSchematic diagram of the nonlinear index of aluminum alloy thin plates with different degrees of damage under the excitation of 200 kHz - 400 kHz frequencies.

[0028] Figure 4a Schematic diagram of the nonlinear response of a 20 nm micro-damage of an aluminum alloy thin plate under the excitation of 300 kHz - 500 kHz frequencies.

[0029] Figure 4b Schematic diagram of the nonlinear response of a 200 nm micro-damage of an aluminum alloy thin plate under the excitation of 300 kHz - 500 kHz frequencies.

[0030] Figure 4c Schematic diagram of the nonlinear response of a 2000 nm micro-damage of an aluminum alloy thin plate under the excitation of 300 kHz - 500 kHz frequencies.

[0031] Figure 4d Schematic diagram of the nonlinear index of aluminum alloy thin plates with different degrees of damage under the excitation of 300 kHz - 500 kHz frequencies.

[0032] Figure 5a Schematic diagram of the nonlinear response of a 20 nm micro-damage degree of an aluminum alloy thin plate under the excitation of 400 kHz - 600 kHz frequencies.

[0033] Figure 5b Schematic diagram of the nonlinear response of a 200 nm micro-damage degree of an aluminum alloy thin plate under the excitation of 400 kHz - 600 kHz frequencies.

[0034] Figure 5c Schematic diagram of the nonlinear response of a 2000 nm micro-damage degree of an aluminum alloy thin plate under the excitation of 400 kHz - 600 kHz frequencies.

[0035] Figure 5d Nonlinear response of an aluminum alloy thin plate with different degrees of damage under the excitation of 400 kHz - 600 kHz frequencies:

[0036] Figure 6a Schematic diagram of the nonlinear response of a CFRP plate under the excitation of a 200 kHz - 400 kHz broadband.

[0037] Figure 6b Schematic diagram of the nonlinear response of a CFRP plate under the excitation of a 300 kHz - 500 kHz broadband.

[0038] Figure 6c Schematic diagram of the nonlinear response of a CFRP plate under the excitation of a 400 kHz - 600 kHz broadband.

[0039] Figure 6d Schematic diagram of the nonlinear response of a CFRP plate under the excitation of broadband with different frequencies. Detailed implementation manners

[0040] The following describes in detail the specific implementation manners of the present application with reference to the accompanying drawings.

[0041] Some embodiments of the present application propose a method for detecting micro-damage in an engineering material structure based on broadband non-linear Lamb waves, which includes the steps of: arranging an active Lamb wave excitation device and a sensor on the engineering material structure; driving the active Lamb wave excitation device to generate a broadband excitation with a preset bandwidth, and collecting a response signal of the broadband excitation through the sensor; extracting the fundamental wave and the second harmonic from the response signal, where the second harmonic represents the non-linearity of the response of the broadband excitation generated by the micro-damage, and the non-linearity is the contact acoustic non-linearity caused by the micro-damage under the broadband excitation; analyzing the response signal through a non-linearity index to quantify the non-linearity, and the non-linearity index is defined as: Wherein, and respectively represent the average values of the normalized amplitudes of the fundamental wave and the second harmonic.

[0042] Some other embodiments of the present application propose a device for detecting micro-damage in an engineering material structure based on broadband non-linear Lamb waves, which includes an active Lamb wave excitation device and a sensor arranged on the engineering material structure; a control unit for driving the active Lamb wave excitation device to generate a broadband excitation with a preset bandwidth, and an acquisition unit for collecting a response signal of the broadband excitation through the sensor; and an analysis unit configured to: extract the fundamental wave and the second harmonic from the response signal, where the second harmonic represents the non-linearity of the response of the broadband excitation generated by the micro-damage, and the non-linearity is the contact acoustic non-linearity caused by the micro-damage under the broadband excitation; analyze the response signal through a non-linearity index to quantify the non-linearity, and the non-linearity index is defined as: Wherein, and respectively represent the average values of the normalized amplitudes of the fundamental wave and the second harmonic.

[0043] 1. Principle:

[0044] Broadband signals can excite multiple propagation modes within a wider frequency range, covering multiple potential non-linear coupling frequencies, thereby enhancing the excitation effect of second and higher harmonics. This characteristic enables broadband excitation to stably trigger CAN even in the presence of uncertainties in structural parameters. Additionally, broadband excitation also has significant advantages in the micro-damage detection of composite structures. Its multi-modal excitation characteristic allows it to simultaneously excite multiple guided wave modes, thus enhancing the detection ability of the non-linear behavior of different types of damage. This not only improves the sensitivity of non-linear Lamb waves to micro-damage but also alleviates the damage mode coupling problem caused by material anisotropy, thereby enhancing the accuracy and robustness of defect identification.

[0045] The non-linear information contained in the signal can be quantified by using non-linear indices. Currently, the commonly used classical non-linear index β' is used to evaluate material non-linearity and CAN caused by cracks, and its definition is:

[0046]

[0047] where A1 and A2 are the amplitudes under the fundamental wave and the second harmonic respectively. To distinguish it from material non-linearity, a new non-linear index β' is proposed for specifically quantifying the second harmonic generation caused by CAN, CAN and its definition is:

[0048]

[0049] In fact, the definitions of the above non-linear indices are applicable to single-frequency or narrowband excitation because they tend to represent a single non-linear response more concentratedly. Therefore, a non-linear index suitable for quantifying the second harmonic generated by broadband excitation is proposed, and its definition is:

[0050]

[0051] where and represent the average values of the normalized amplitudes of the fundamental wave and the second harmonic respectively. β' WB,CAN can more accurately quantify the broadband non-linear response caused by CAN under broadband excitation.

[0052] 2. Numerical Modeling

[0053] A two-dimensional numerical model of an aluminum alloy thin plate with dimensions of 2mm×100mm is established, for example, for dynamic simulation in the commercial software ABAQUS / Explicit. In this model, a micro-crack is set at the center of the model, the crack length is 1mm, and three different crack widths of 10 1 nm, 10 2 nm, and 10 3nm is used to simulate different degrees of damage of the material. At the same time, a two-dimensional numerical model of a GFRP composite laminate with a ply angle of [0° / 90° / 90° / 0°] is established. Tables 1 and 2 respectively give the mechanical properties of the aluminum alloy thin plate and GFRP. Nodes are defined at 30 mm and 40 mm away from the microcrack as the receivers and generators of the excitation signal. The model uses displacement excitation, with the direction along the positive x-axis and the excitation displacement being 0.1 mm. A total of three broadband excitations are set: 200 - 400 kHz, 300 - 500 kHz, and 400 - 600 kHz. The finite element (FE) model selects a four-node bilinear plane stress quadrilateral element (CPS4R) with enhanced hourglass control of second-order integration and reduced accuracy. A pair of frictionless, tangential and normal hard contacts are set on the surface where the microcracks interact, and at the same time, the mesh of the microcrack part of the model is refined. When sufficient vibration excitation is applied, the surfaces where the microcracks interact will undergo tension and compression, thus causing a local CAN effect. Figure 1 Shows a schematic diagram of the two-dimensional numerical model of the aluminum alloy thin plate with microcracks. The red dots and blue dots on the model respectively represent the excitation device of the active Lamb wave and the sensor signal receiving device, and the arrow represents the excitation direction, which is along the positive X-axis direction. Figure 1 Also shows three different crack widths set in this application to simulate different degrees of damage. The model schematic diagram and the finite element contour plot jointly show the "breathing" motion generated by the microcracks under high-frequency excitation.

[0054] Table 1 Material parameters of the aluminum alloy thin plate model

[0055]

[0056] Table 2 Material parameters of the carbon fiber reinforced matrix composite

[0057]

[0058] 3. Validation of the effectiveness of the finite element model

[0059] Figure 2a and Figure 2c respectively represent the nonlinear responses of the aluminum alloy thin plate and the CFRP plate in the time domain under broadband excitation of 400 kHz - 600 kHz, where the red and blue dashed lines respectively represent the cases with prefabricated microdamage. It can be seen from the figure that the amplitude of the time-domain curve in the damaged state is significantly greater than that in the undamaged state. This is because the microcracks generate a breathing effect under broadband excitation of 400 kHz - 600 kHz, resulting in a large amplitude of the second harmonic component in the time-domain response due to the interaction between the interfaces during each contact, which causes local energy dissipation. At the same time, it shows obvious second harmonic characteristics in the Figure 2b and Figure 2d frequency-domain responses. FromFigures 2a to 2d As shown, it can be concluded that the non-linear response generated by CAN will produce signature features in the time domain and frequency domain, namely larger time-domain amplitudes and obvious higher harmonics. These features allow us to quickly detect the presence of cracks in materials.

[0060] In addition, by comparing Figure 2a and Figure 2c as well as Figure 2b and Figure 2d , it can be found that the non-linear response generated by CAN is completely different in isotropic and anisotropic materials. In isotropic materials, the amplitudes of each wave packet show good correspondence and regularity in the undamaged and damaged states, but in anisotropic materials, there is no obvious corresponding relationship, especially in the frequency domain, there is no good discrimination. Therefore, it can be determined that this is also a key point and difficulty in the current detection of micro-damage in composite material structures using non-linear Lamb waves.

[0061] 4. Influence of damage degree of isotropic materials on frequency-domain non-linear response: Taking an aluminum alloy thin plate as an example

[0062] Figures 3a to 3d shows the frequency-domain non-linear response of an aluminum alloy thin plate with micro-cracks of 20nm, 200nm, and 2000nm widths under a frequency excitation of 200kHz - 400kHz. It can be seen from the figure that the fundamental wave generates various frequency characteristics in the range of 200kHz - 400kHz, and smaller but more diverse frequency characteristics are generated in the corresponding second-harmonic frequency band (500kHz - 700kHz) and third-harmonic frequency band (800kHz - 1000kHz). By quantifying the amplitudes of these frequency characteristics using the above formula (3), the Figure 3d graphical results can be obtained. From Figure 3d , it can be found that under the excitation of the 200kHz - 400kHz frequency band, as the damage degree increases, the non-linear response shows a downward trend. This is because as the damage degree increases, the contact time of the crack interaction surface under the same displacement excitation becomes shorter and shorter, so the non-linear response gradually weakens.

[0063] Figures 4a to 4d , Figures 5a to 5dThe frequency-domain nonlinear responses of aluminum alloy sheets with three damage degrees are respectively shown under the excitation of 300 kHz - 500 kHz and 400 kHz - 600 kHz frequencies. It can be found that, similar to the case under the excitation of 200 kHz - 400 kHz frequencies, rich frequency characteristics also appear at the second and third harmonic bands, and with the increase of the frequency band, the frequency characteristics of the high harmonic bands are more abundant and concentrated. This feature is more obvious under the excitation of the 300 kHz - 500 kHz frequency band. Therefore, it can be found that the distinguishability of cracks with different damage degrees is the most obvious under the excitation of the 300 kHz - 500 kHz frequency band, and there are trends in the other two cases, but no obvious distinguishability is shown. Thus, it can be seen that the excitation situation of the 300 kHz - 500 kHz frequency band is better than the other two cases. However, due to the increase of frequency, the fundamental wave and the high harmonic responses are gradually separated, and the phenomenon of unstable frequency change appears in the middle frequency band. This may be one of the factors interfering with the reading of the nonlinear response. However, for these three cases, they are not affected by the interference brought by the middle frequency perturbation and can still effectively quantify the nonlinear responses of different damage degrees.

[0064] 5. Nonlinear Responses of CFRP Plates under Different Wide-Frequency Excitations

[0065] In Figures 6a to 6d the frequency-domain nonlinear responses of CFRP plates with 20 nm delamination microdamage are shown under the excitation of 200 kHz - 400 kHz, 300 kHz - 500 kHz and 400 kHz - 600 kHz frequencies. According to Figure 6a , Figure 6b , Figure 6c shown, no matter under the excitation of which frequency band, the second harmonic shows rich frequency characteristics. Compared with the amplitude of the nonlinear response of the aluminum alloy sheet, the response amplitude in CFRP is stronger than that of the aluminum alloy sheet. This may be because the anisotropic material properties of CFRP enhance the degree of nonlinear response therein. Especially under the excitation of the 300 kHz - 500 kHz frequency band, the amplitude of one of the frequencies in its nonlinear response has reached the same level as the amplitude of the fundamental wave, showing extremely strong nonlinearity.

[0066] For the factors found in aluminum alloy thin plates that are interfered by intermediate frequencies with increasing frequency, they do not exist under the excitation of two frequency bands of 200 kHz - 400 kHz and 300 kHz - 500 kHz, which is also attributed to its extremely strong nonlinear response characteristics. However, in the case of 400 kHz - 600 kHz, it is more severely interfered, and there is even an extremely strong peak in the frequency band of 600 kHz - 900 kHz. This may be because under broadband excitation, the intermodulation effect between multiple frequency components will generate intermediate frequencies, and these frequencies may not belong to the simple multiples of the fundamental wave or harmonics. These newly generated frequency components may overlap with the second harmonic or affect the clarity of the frequency-domain signal, resulting in the masking or misjudgment of the second harmonic signal. Therefore, the second harmonic characteristics may be blurred during frequency-domain analysis, causing inaccurate identification of damage characteristics.

[0067] Similarly, the nonlinear responses in three cases are quantified using formula (3), as Figure 6d shown. The same as the previous analysis, under the excitation of the 300 kHz - 500 kHz frequency band, the degree of nonlinear response is higher, and it also has excellent second harmonic discrimination. The excitation cases of the 200 kHz - 400 kHz and 400 kHz - 600 kHz frequency bands have their own advantages and disadvantages. The former has better discrimination, and the latter has a higher degree of nonlinear response. Therefore, it can be concluded that the excitation case of the 300 kHz - 500 kHz frequency band is the preferred one among these three frequency band excitation cases. And as the frequency band increases, while the degree of nonlinear response increases, the discrimination of the second harmonic will also decrease. In order to detect micro-damage inside isotropic and anisotropic materials in this application, an aluminum alloy thin plate model considering different damage degrees is constructed in ABAQUS / Explicit. The nonlinear responses are systematically studied by exciting the damage model with three frequency bands of 200 kHz - 400 kHz, 300 kHz - 500 kHz, and 400 kHz - 600 kHz respectively. At the same time, the influence of different frequency excitations on the nonlinear response of CFRP is analyzed. Finally, the nonlinear responses of the two are quantified and compared.

[0068] Through the above experiments, the applicant found that the non-linear response generated by CAN will produce signature features in the time domain and frequency domain, namely, larger time-domain amplitudes and obvious higher harmonics. As the degree of damage increases, the non-linear response formed by CAN will gradually weaken. For the same degree of damage, stronger non-linear behavior is exhibited under the excitation of the 300 kHz - 500 kHz frequency band. Wide-band excitation will bring richer non-linear information at higher harmonics, but it will also bring more interference information. Therefore, it is necessary to select an appropriate frequency range for wide-band excitation. The above has been described with reference to the accompanying drawings and embodiments. However, it should be understood that those of ordinary skill in the art can make various modifications and changes to the present invention without departing from the technical idea of the present invention as described in the scope of the following claims.

Claims

1. A method for detecting micro-damage in engineering material structures based on broadband non-linear Lamb waves, characterized in that: Including the steps: Providing an active Lamb wave excitation device and a sensor on the engineering material structure; Driving the active Lamb wave excitation device to generate a broadband excitation with a preset bandwidth, and collecting the response signal of the broadband excitation through the sensor; Extracting the fundamental wave and the second harmonic from the response signal, where the second harmonic represents the nonlinearity of the response of the broadband excitation generated by the microdamage, and the nonlinearity is the contact acoustic nonlinearity caused by the microdamage under the broadband excitation; Analyze the response signal through a non - linear index to quantify the non - linearity, the non - linear index being defined as: where and represent the average values of the normalized amplitudes of the fundamental wave and the second - harmonic wave, respectively.

2. The method for detecting micro-damage of engineering material structures based on broadband nonlinear Lamb waves according to claim 1, wherein: The preset bandwidth of the broadband excitation signal is 200 kHz.

3. The method for detecting micro-damage of engineering material structures based on broadband nonlinear Lamb waves according to claim 1, wherein: The frequency range of the broadband excitation signal is 200 - 400 kHz or 300 - 500 kHz or 400 - 600 kHz.

4. The method for detecting microdamage of engineering material structures based on broadband nonlinear Lamb waves according to claim 1, wherein: The engineering material structure is an isotropic material.

5. The method for detecting microdamage of engineering material structures based on broadband nonlinear Lamb waves according to claim 1, characterized in that: The engineering material structure is an anisotropic material, especially a composite material, particularly a CFRP material.

6. The method for detecting micro-damage of engineering material structures based on broadband nonlinear Lamb waves according to claim 1, wherein: Determining the degree of the microdamage based on the following relationship: as the degree of the microdamage increases, the generated nonlinear response gradually weakens, and the nonlinear response shows a downward trend.

7. The method for detecting micro-damage of engineering material structures based on broadband nonlinear Lamb waves according to claim 1, characterized in that: The microdamage is a microcrack.

8. An engineering material structure micro-damage detection device based on broadband nonlinear Lamb waves, characterized in that: Including the active Lamb wave excitation device and the sensor provided on the engineering material structure; A control unit for driving the active Lamb wave excitation device to generate a broadband excitation with a preset bandwidth, and a collection unit for collecting the response signal of the broadband excitation through the sensor; And An analysis unit configured to: extract the fundamental wave and the second harmonic from the response signal, where the second harmonic represents the nonlinearity of the response of the broadband excitation generated by the microdamage, and the nonlinearity is the contact acoustic nonlinearity caused by the microdamage under the broadband excitation; Analyze the response signal through a non - linear index to quantify the non - linearity, where the non - linear index is defined as: where and represent the average values of the normalized amplitudes of the fundamental wave and the second - harmonic wave, respectively.

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