A method for detecting low-velocity impact damage in a solid plate based on nonlinear ultrasonic guided waves

Abstract

The application discloses a kind of based on nonlinear ultrasonic guided wave's solid plate low-speed impact damage detection method, belong to nondestructive testing technical field, this method includes the following steps: S1, detection preparation;S2, select base frequency wave;S3, select transducer;S4, signal excitation and reception;S5, low-speed impact damage detection;S6, data analysis and obtain conclusion.The application adopts the above-mentioned one based on nonlinear ultrasonic guided wave's solid plate low-speed impact damage detection method, optimizes transducer design, increases the flexibility of mode selection, accurately controls mixing frequency area, bidirectional reception specific mode guided wave, and reduces the influence of other mode guided wave, so as to improve detection efficiency and accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of nondestructive testing, and in particular relates to a method for detecting low-speed impact damage of a solid plate based on nonlinear ultrasonic guided waves. Background Art

[0002] Solid plate structures are widely used in fields such as shipbuilding, engineering, and aerospace. These structures are often subjected to low-velocity impacts during use, such as bird strikes during flight or the accidental dropping of maintenance tools. While these low-energy impacts may not cause immediate damage, they can cause subtle, hidden internal damage. Over time, these latent damages can gradually expand and eventually lead to structural failure. Therefore, effective impact damage detection of solid plates is crucial to ensuring the safety and reliability of structures.

[0003] Traditional nondestructive testing methods include radiography, magnetic particle testing, and penetrant testing. However, these methods are generally limited to detecting large-scale defects and struggle to detect subtle, early-stage damage. In contrast, ultrasonic testing (UT) is an ideal testing method due to its wide applicability, low cost, and high speed. Lamb waves, in particular, can propagate long distances in thin-walled structures without significant attenuation, making them ideal for detecting minute defects in such structures.

[0004] Nonlinear ultrasonic testing exploits the nonlinear effects of materials under load to detect internal defects or changes. Compared to traditional linear ultrasonic testing, nonlinear ultrasonic testing can more sensitively detect minute defects and offer higher detection accuracy. While existing technologies have made some progress in detecting low-velocity impact damage in solid plates, they still face numerous challenges in terms of detection accuracy, experimental conditions, data analysis, and broad application. Therefore, a new solution is urgently needed. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for detecting low-speed impact damage to solid plates based on nonlinear ultrasonic guided waves. This method optimizes the transducer design, increases the flexibility of mode selection, accurately controls the mixing region, bidirectionally receives specific mode guided waves, and reduces the influence of other mode guided waves, thereby improving detection efficiency and accuracy.

[0006] To achieve the above objectives, the present invention provides a method for detecting low-velocity impact damage of solid plates based on nonlinear ultrasonic guided waves, comprising the following steps:

[0007] S1. Preparation for testing;

[0008] Aluminum alloy plates with damage defects were produced, and a testing platform was built using the RAM-5000 SNAP nonlinear ultrasonic testing system as the main body;

[0009] S2, select the fundamental frequency wave;

[0010] Use software to draw the Lamb wave dispersion curve of the aluminum alloy plate, and obtain the phase velocity and group velocity of the fundamental wave based on the dispersion curve; calculate the location of the mixing area based on the selected fundamental wave;

[0011] S3, select transducer;

[0012] The transducer includes an exciting transducer and a receiving transducer, wherein the exciting transducer adopts a wedge transducer and the receiving transducer adopts a piezoelectric chip comb transducer;

[0013] S4, signal excitation and reception;

[0014] Select aluminum alloy plates without damage or defects for testing. First, perform a single excitation test, then a joint excitation test, and record the excitation test data of the aluminum alloy plates without damage or defects.

[0015] S5, low-speed impact damage detection;

[0016] Select the aluminum alloy plate with damage defects in S1, set at least one sampling point on the aluminum alloy plate with damage defects, repeat the individual excitation test and the common excitation test in S4 for the sampling point, and record the excitation test data of the sampling point;

[0017] S6. Data analysis and conclusions;

[0018] Compare the excitation test data of the aluminum alloy plate without damage defects in S4 with the excitation test data of the sampling point in S5. If the amplitude at a specific frequency is found to increase significantly, it indicates that the aluminum alloy plate has low-velocity impact damage at the location of the sampling point.

[0019] Preferably, in S2, the fundamental frequency wave is controlled to produce a mixing effect at a specified position by adjusting the excitation time difference.

[0020] Preferably, in S2, the fundamental frequency wave is screened out by using the non-zero energy flow criterion and phase velocity matching.

[0021] Preferably, in S2, the frequencies of the two fundamental waves selected are 1.1 MHz S0 mode and 2.78 MHz A1 mode respectively.

[0022] Preferably, in S3, a ruler is used to control the wedge transducer and the piezoelectric crystal comb transducer to be in a straight line and to maintain a fixed distance between them.

[0023] Preferably, in S3, the piezoelectric chip comb transducer includes comb wedges, the fingers of the comb wedges have the same length, and the period length of the comb wedges is equal to the wavelength of the specific mode Lamb wave.

[0024] Preferably, in S3, according to the difference frequency between the 2.78 MHz A1 mode and the 1.1 MHz S0 mode, the piezoelectric chip comb transducer selects the 1.7 MHz A0 mode as the receiving mode.

[0025] Therefore, the present invention adopts the above-mentioned method for detecting low-velocity impact damage of solid plates based on nonlinear ultrasonic guided waves. Compared with the existing technology, the present invention has the following significant beneficial effects:

[0026] (1) The present invention increases the range of mode selection by optimizing the transducer design, providing greater flexibility in selecting wave modes for specific application scenarios;

[0027] (2) The present invention can precisely control the position of the mixing area, thereby achieving accurate positioning of local damage;

[0028] (3) The piezoelectric chip comb transducer used in the present invention can effectively receive ultrasonic guided waves of a specific mode while reducing the influence of guided waves of other modes;

[0029] (4) The present invention can not only cover a larger inspection area, but also identify multiple defects simultaneously, thus improving the inspection efficiency and reducing the possibility of omissions;

[0030] (5) The transducer design adopted by the present invention can simultaneously receive guided waves from two opposite directions while reducing the influence of guided waves in other modes;

[0031] (6) The present invention adopts an improved transducer design to construct a relatively simple experimental platform, reducing the complexity and cost of the equipment.

[0032] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a front view of a damaged metal plate in a method for detecting low-velocity impact damage of a solid plate based on nonlinear ultrasonic guided waves according to the present invention;

[0034] Figure 2 This is a back view of a damaged metal plate in a method for detecting low-velocity impact damage of a solid plate based on nonlinear ultrasonic guided waves according to the present invention;

[0035] Figure 3 This is a Lamb wave phase velocity and group velocity dispersion curve of a solid plate low-speed impact damage detection method based on nonlinear ultrasonic guided waves of the present invention. Figure 3 a in the figure represents the Lamb wave phase velocity dispersion curve; Figure 3 b in the figure represents the Lamb wave group velocity dispersion curve;

[0036] Figure 4A transducer schematic diagram for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application;

[0037] Figure 5 A piezoelectric wafer comb transducer structure schematic diagram for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application;

[0038] Figure 6 A comb wedge structure schematic diagram for a piezoelectric wafer comb transducer for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application;

[0039] Figure 7 An opposite direction co-linear mixing schematic diagram for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application;

[0040] Figure 8 A time-domain waveform diagram and a frequency-domain diagram of a Lamb wave of a 1.1MHz S0 mode excited alone for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application, Figure 8 a in the above figure a indicates a time-domain waveform diagram, Figure 8 b in the above figure b indicates a frequency-domain diagram;

[0041] Figure 9 A time-domain waveform diagram and a frequency-domain diagram of a Lamb wave of a 2.78MHz A1 mode excited alone for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application, Figure 9 a in the above figure a indicates a time-domain waveform diagram, Figure 9 b in the above figure b indicates a frequency-domain diagram;

[0042] Figure 10 A time-domain waveform diagram and a frequency-domain diagram of a Lamb wave of two modes excited together for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application, Figure 10 a in the above figure a indicates a time-domain waveform diagram, Figure 10 b in the above figure b indicates a frequency-domain diagram;

[0043] Figure 11 A low-velocity impact damage aluminum alloy plate detection schematic diagram for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application;

[0044] Figure 12 A frequency-domain diagram of a detection excited together at a 4th point for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application;

[0045] Figure 13 A frequency-domain diagram of a detection excited alone at a 4th point for a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves of the present application, Figure 13a in the figure represents the frequency domain diagram of 1.1MHz S0 mode Lamb wave. Figure 13 b in the figure represents the frequency domain diagram of 2.78MHzA1 mode Lamb wave;

[0046] Figure 14 This is a frequency domain diagram of the common excitation detection at the fifth point of a solid plate low-velocity impact damage detection method based on nonlinear ultrasonic guided waves according to the present invention;

[0047] Figure 15 This is a frequency domain diagram of the fifth point of single excitation detection in a method for detecting low-speed impact damage of a solid plate based on nonlinear ultrasonic guided waves according to the present invention. Figure 15 a in the figure represents the frequency domain diagram of 1.1MHz S0 mode Lamb wave. Figure 15 b in FIG represents the frequency domain diagram of the 2.78 MHz A1 mode Lamb wave.

[0048] Reference numerals

[0049] 1. Comb-shaped wedge. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used in the present invention should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs.

[0051] Example 1

[0052] A method for detecting low-velocity impact damage of a solid plate based on nonlinear ultrasonic guided waves of the present invention comprises the following steps:

[0053] S1. Preparation for testing;

[0054] The present invention uses 6061 aluminum alloy plate as the test object. This material is widely used in aerospace, automobile manufacturing and other fields, and has good mechanical properties and processability.

[0055] To damage 6061 aluminum alloy plates, a drop-hammer impact system was constructed. The system consists of a punch (for impact generation), a high-speed camera (for recording the impact process), a data acquisition device (for collecting parameters such as impact force), and a control platform (for ensuring a stable impact process). The drop-hammer impact system generates impact energy by free-falling the punch from a specified height. Neglecting air resistance, the impact energy is equal to the potential energy at the punch height. A standard fixture ensures the stability of the impact process and eliminates interference from secondary impacts. Data uploaded to the data acquisition device from a PCB pressure sensor is used to calculate parameters such as impact velocity and energy.

[0056] like Figure 1-Figure 2 As shown in the figure, a 15J impact energy was used to impact a 6061 aluminum alloy plate. No obvious cracks were found on the surface after the impact, but there may be minor internal damage. Visual inspection was performed to confirm the condition of the front and back of the aluminum alloy plate to ensure that the impact damage met the test expectations.

[0057] Build a SNAP system, using the RAM-5000 SNAP nonlinear ultrasonic test system as the main body to build a detection platform for the excitation and reception of Lamb wave mixing signals.

[0058] S2, select the fundamental frequency wave;

[0059] Through the theoretical analysis of the nonlinear interaction of Lamb waves using the second-order perturbation method and the mode expansion method, it can be found that the displacement field of the mixing wave is a combination of a series of propagation modes with frequencies equal to the sum and difference of the frequencies of the two fundamental waves. The specific calculation method is as follows:

[0060] ;

[0061] in, z Direction is the direction of wave propagation, y The direction is perpendicular to the propagation direction and parallel to the plate thickness direction, t For time, and are the frequencies of the two fundamental waves, express m The wave structure of the order propagation mode, express m The amplitude of the first-order propagation mode.

[0062] Satisfies the following expression:

[0063] ;

[0064] in, is the composite energy flow of sum frequency and difference frequency modes, is the nonlinear surface driving force, is the nonlinear body driving force, and are the wave numbers of the fundamental frequency wave respectively.

[0065] when hour, It can be expressed as:

[0066] ;

[0067] The non-zero energy flow criterion is , the phase velocity matching condition is .

[0068] To ensure the existence of the mixing wave, the non-zero energy flow criterion and the phase velocity matching condition must be met simultaneously. Based on these two criteria, a suitable excitation signal pattern pair is selected. In the present invention, the S0 mode and the A1 mode are selected as the excitation signal pattern pair.

[0069] like Figure 3 As shown in the figure, the Lamb wave dispersion curve of a 6061 aluminum alloy plate was plotted using the Dispersion Calculator software. The dispersion curve shows how the phase velocity and group velocity vary with frequency in different modes. The phase velocity and group velocity at a specific frequency can be read from the dispersion curve. The frequencies of the two selected fundamental waves are 1.1 MHz (S0 mode) and 2.78 MHz (A1 mode). Based on the dispersion curve, the corresponding group velocity values ​​at these two frequencies are found. The theoretical group velocity for the 1.1 MHz S0 mode is approximately 4990.4 m / s, and the theoretical group velocity for the 2.78 MHz A1 mode is approximately 3658.48 m / s. Based on the group velocities of the two fundamental waves, their intersection position within the solid plate is calculated.

[0070] By controlling the excitation time difference, the two fundamental frequency waves meet at a specific location, generating a mixing effect. This transducer excitation time difference is achieved through the SNAP system. The SNAP system adjusts the Hanning window period so that the two fundamental frequency waves arrive simultaneously at a specific location (e.g., 127 mm), thus generating a mixing effect.

[0071] S3, select transducer;

[0072] like Figure 4As shown, the transducer consists of an excitation transducer and a receiving transducer. The excitation transducer uses a wedge-shaped transducer to excite Lamb wave signals of different frequencies. This has the advantage of effectively converting electrical signals into mechanical vibrations, thereby generating the desired Lamb wave. A 5-cycle Hanning window modulated sine signal (A1 mode) with a center frequency of 2.78 MHz is selected for the right-hand excitation, while a 5-cycle Hanning window modulated sine signal (S0 mode) with a center frequency of 1.1 MHz is selected for the left-hand excitation. These two frequencies were chosen based on their propagation characteristics in the 6061 aluminum alloy plate and the resulting frequency mixing effects.

[0073] like Figure 5-Figure 7 As shown, the receiving transducer uses a piezoelectric chip comb transducer to receive the mixed Lamb wave signal. The piezoelectric chip comb transducer consists of a comb wedge 1 and a piezoelectric chip bonded to the wedge. The comb wedge 1 consists of a series of parallel fingers with a certain spacing between the fingers. By designing the finger width and finger spacing, the reception of a specific mode of Lamb wave is achieved. The piezoelectric chip can convert mechanical vibrations into electrical signals or vice versa. Due to the geometric symmetry of the piezoelectric chip comb transducer and the uniform spacing between the fingers, it can receive both forward propagating and reversely reflected guided waves. The structure of the piezoelectric chip comb transducer includes a piezoelectric chip, an adhesive layer and a comb wedge 1. The geometric parameters of the comb wedge 1 include the finger length (aperture) W , refers to the number of bars n , long cycle L , finger width a and interdigital spacing b , where the period length is .

[0074] Comb wedge 1 each finger length W Due to the periodicity of the finger arrangement, the phase difference of the Lamb waves excited and received by adjacent finger electrodes It can be calculated by the following formula:

[0075] ;

[0076] in, is the angular frequency, For time, is the phase velocity.

[0077] Based on the output vector sum method, when the phase difference between adjacent fingers is When certain conditions are met, the total output reaches its maximum value. Specifically, when the phase difference When , the total output reaches its maximum value. Substituting the above phase difference formula, we get:

[0078] ;

[0079] wherein, is the wavelength, is the fundamental frequency.

[0080] Therefore, the basic condition that the piezoelectric wafer comb transducer needs to meet for receiving a specific mode of Lamb wave is that the periodic pitch length L of the piezoelectric wafer comb wedge 1 is equal to the wavelength of the specific mode of Lamb wave The design of this transducer allows it to receive a specific mode of Lamb wave, and different modes can be selected as needed. By adjusting the periodic pitch length (L) of the comb wedge 1 to be equal to the wavelength of the specific mode of Lamb wave, effective excitation and reception of different modes can be achieved. The periodic pitch length L of the piezoelectric wafer comb transducer selected in this embodiment is 1.52 mm.

[0081] The excitation modes are symmetric mode S0 (1.1 MHz) and anti-symmetric mode A1 (2.78 MHz). In order to receive the mixed frequency signal of these modes, especially the difference frequency signal (1.68 MHz) of the excitation frequency, a receiving mode needs to be selected. The piezoelectric wafer comb transducer with a pitch length of 1.52 mm has a frequency of 1.7 MHz in the anti-symmetric A0 mode, which is very close to the difference frequency signal (1.68 MHz) of the excitation frequency, so the anti-symmetric A0 mode is selected as the receiving mode.

[0082] In order to ensure that the two beams of Lamb wave propagate on the same path and meet at a predetermined location and mix, the relative position between the wedge transducer and the piezoelectric wafer comb transducer needs to be precisely controlled. A 300 mm ruler is used to control that the wedge transducer and the piezoelectric wafer comb transducer are always on the same line, and the distance between the two wedge transducers is determined by this length, thereby ensuring the realization of bidirectional reception, and maintaining high detection accuracy even in complex environments.

[0083] S4, signal excitation and reception;

[0084] A 395.5 mm 345 mm 6061 aluminum alloy plate with a specification of 1 mm is selected, and separate excitation detection is carried out. First, the Lamb wave of S0 mode at 1.1 MHz is excited separately, and then the Lamb wave of A1 mode at 2.78 MHz is excited separately, and the time domain and frequency domain patterns displayed by the oscilloscope are recorded.

[0085] As Figure 8-Figure 9As shown, when the Lamb wave of the 1.1MHz S0 mode is excited alone, only the fundamental wave of 1.1MHz and its harmonics (2.2MHz and 3.3MHz) have obvious peaks. When the Lamb wave of the 2.78MHz A1 mode is excited alone, only the fundamental wave of 2.73MHz has obvious peaks, and no other additional frequency components appear.

[0086] Then conduct a common excitation test, keep the transducer position unchanged, and excite the two frequencies of Lamb waves at the same time, and observe whether the difference frequency signal appears when the difference frequency is 1.68MHz in the frequency domain diagram. Figure 10 As shown in the figure, when the aluminum alloy plate is undamaged, the frequency domain diagram at 1.68 MHz has no obvious change, indicating that there is no mixing effect at this time.

[0087] S5, low-speed impact damage detection;

[0088] First, arrange sampling points, placing multiple sampling points at 10mm intervals from top to bottom on the damaged aluminum alloy plate. Then, acquire the mixing signal. Repeat the individual and combined excitation processes in S4 for each sampling point, ensuring that the transducer position remains unchanged during each test, ensuring that the low-velocity impact damage remains within the Lamb wave mixing region.

[0089] like Figure 11 Figure 2 shows a schematic diagram of an aluminum alloy plate damaged by low-velocity impact. The plate has a pit approximately 10 mm in size, representing the damage caused by the low-velocity impact. To perform detailed Lamb wave mixing detection, nine sampling points, numbered 1 to 9, were set from top to bottom at 10 mm intervals. Points 4 and 5 are located in the damaged area. Since the damage occurred between points 4 and 5, the mixing signals at these two points are of primary interest.

[0090] S6. Data analysis and conclusions;

[0091] Data obtained from the SNAP system was imported into Origin software for processing, and Lamb wave frequency domain waveforms were plotted to compare the frequency domain characteristics of the damage condition with and without damage. The frequency domain plots for individual and simultaneous excitation were compared, with particular attention paid to the presence and intensity of the difference frequency signal. A significant increase in amplitude at a specific frequency indicated the presence of low-velocity impact damage at that location. The combined test results confirmed that the Lamb wave mixing effect can effectively detect low-velocity impact damage in solid plates, and its sensitivity and accuracy were evaluated.

[0092] To verify whether the mixing signal actually carries damage information, it is necessary to compare the data from the damaged case with the undamaged case. The data from points 4 and 5 are compared with the frequency domain plot of the Lamb wave mixing signal from the undamaged case.

[0093] like Figure 12-13 As shown, the frequency at which the mixing signal waveform at point 4, marked by the mark, reaches its maximum amplitude is 1.229257 at 1.66083 MHz. In comparison, at the same frequency, the amplitude at point 4 when the 1.1 MHz S0 mode is excited alone is only 0.145837, while the amplitude when the 2.78 MHz A1 mode is excited alone is even lower, at 0.015828. This indicates that in the damaged area (point 4), the mixing of the two fundamental waves produces a significantly enhanced difference frequency signal (1.66083 MHz), proving that the mixing defect signal was successfully received at this point.

[0094] like Figure 14-15 As shown in Figure 3, analyzing the data at point 5, we also conducted tests with both single and co-excitation. Although point 5 also shows the presence of a mixed-frequency defect signal, its amplitude is smaller than that at point 4. This difference may reflect a change in the degree or location of the damage.

[0095] Therefore, the present invention adopts the above-mentioned method for detecting low-speed impact damage of solid plates based on nonlinear ultrasonic guided waves. This method optimizes the transducer design, increases the flexibility of mode selection, accurately controls the mixing area, bidirectionally receives specific mode guided waves, and reduces the influence of other mode guided waves, thereby improving detection efficiency and accuracy.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for detecting low-velocity impact damage of solid plates based on nonlinear ultrasonic guided waves, characterized in that: The following steps are involved: S1. Preparation for testing; The aluminum alloy plate was impacted with an impact energy of 15J to obtain the aluminum alloy plate with damage defects. The testing platform was built with the RAM-5000SNAP nonlinear ultrasonic testing system as the main body. S2, select the fundamental frequency wave; Use software to draw the Lamb wave dispersion curve of the aluminum alloy plate, and obtain the phase velocity and group velocity of the fundamental wave based on the dispersion curve; control the fundamental wave to produce a mixing effect at a specified location by adjusting the excitation time difference; the frequencies of the two fundamental waves selected are 1.1MHz S0 mode and 2.78MHz A1 mode; calculate the location of the mixing area based on the selected fundamental waves; S3, select transducer; The transducer includes an excitation transducer and a receiving transducer. The excitation transducer is a wedge transducer, and the receiving transducer is a piezoelectric chip comb transducer. The piezoelectric chip comb transducer consists of a comb wedge and a piezoelectric chip bonded to the wedge. The comb wedge is composed of a series of evenly spaced, parallel fingers. The fingers of the comb wedge are of the same length, and the period length of the comb wedge is equal to the wavelength of a specific Lamb wave mode. Based on the difference frequency between the 2.78MHz A1 mode and the 1.1MHz S0 mode, the piezoelectric chip comb transducer selects the 1.7MHz A0 mode as the receiving mode. The wedge transducer and the piezoelectric chip comb transducer are controlled to always be aligned, and the distance between the two wedge transducers is determined to ensure bidirectional reception. S4, signal excitation and reception; Select aluminum alloy plates without damage or defects for testing. First, perform a single excitation test, then a joint excitation test, and record the excitation test data of the aluminum alloy plates without damage or defects. S5, low-speed impact damage detection; Select the aluminum alloy plate with damage defects in S1, set at least one sampling point on the aluminum alloy plate with damage defects, repeat the individual excitation test and the common excitation test in S4 for the sampling point, and record the excitation test data of the sampling point; S6. Data analysis and conclusions; Compare the excitation test data of the aluminum alloy plate without damage defects in S4 with the excitation test data of the sampling point in S5. If the amplitude at a specific frequency is found to increase significantly, it indicates that the aluminum alloy plate has low-velocity impact damage at the location of the sampling point.

2. The method for detecting low-velocity impact damage of a solid plate based on nonlinear ultrasonic guided waves according to claim 1, characterized in that: In S2, the fundamental frequency wave is screened out by the non-zero energy flow criterion and phase velocity matching.

3. The method for detecting low-velocity impact damage of a solid plate based on nonlinear ultrasonic guided waves according to claim 1, characterized in that: In S3, a ruler is used to control the wedge transducer and the piezoelectric crystal comb transducer to be in a straight line and maintain a fixed separation distance.

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