A method for local micro-defect positioning and imaging based on nonlinear ultrasonic guided wave mixing

Abstract

This invention discloses a method for locating and imaging local micro-defects based on nonlinear ultrasonic guided wave mixing, belonging to the field of nondestructive testing technology. The method includes: screening guided wave modes on the material under test; exciting two fundamental frequency guided wave signals to form a mixing region in the material; measuring the propagation velocity of the fundamental frequency guided waves and calculating the mixing point position; adjusting the excitation delay to achieve mixing point movement and region scanning; acquiring signals and performing frequency domain analysis to extract the nonlinear mixing signal; and then performing defect determination and imaging. This invention utilizes the high sensitivity of nonlinear ultrasonic guided wave mixing to micro-damage, achieving precise location and imaging of early-stage micro-defects in materials, thus solving the problem of insufficient identification capability of traditional nondestructive testing methods for minute damage.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and in particular to a method for local micro-defect localization imaging based on nonlinear ultrasonic guided wave mixing. Background Technology

[0002] With the increasing demands for structural safety and reliability in fields such as aerospace, energy equipment, and transportation, materials are prone to early microscopic defects such as fatigue damage and creep voids during long-term service. These micro-defects are typically small in scale and hidden in distribution, but they gradually expand and evolve into macroscopic cracks during subsequent service, ultimately leading to structural failure. Therefore, achieving effective detection and localization of early micro-damage in materials is of great significance for structural health monitoring and life prediction.

[0003] Existing nondestructive testing methods mainly include ultrasonic testing, eddy current testing, and X-ray testing. Among them, traditional linear ultrasonic testing technology, which relies on wave reflection or scattering effects, has good detection capabilities for macroscopic defects, but is insensitive to small-sized microscopic damage, making it difficult to effectively identify early-stage damage. In recent years, nonlinear ultrasonic testing technology has gradually become a research hotspot due to its high sensitivity to changes in the microstructure of materials.

[0004] In nonlinear ultrasonic methods, guided wave technology is widely used for the inspection of plate-like structures due to its advantages such as long propagation distance and large coverage area. However, existing nonlinear guided wave-based inspection methods mostly focus on measuring the overall nonlinear response, making it difficult to achieve precise defect localization and imaging. In addition, in traditional methods, the nonlinear signal is often affected by the material state of other regions along the propagation path, resulting in low spatial resolution of the inspection results. Summary of the Invention

[0005] The main objective of this invention is to provide a local micro-defect localization imaging method based on nonlinear ultrasonic guided wave mixing, which can quickly and accurately locate and image early micro-damage to materials, such as fatigue microcracks and creep pores. The imaging results can provide a reference for the assessment of the service status of materials and the prediction of their service life.

[0006] Another objective of this invention is to propose a local micro-defect localization imaging device based on nonlinear ultrasonic guided wave mixing.

[0007] The third objective of this invention is to provide an electronic device.

[0008] A fourth objective of this invention is to provide a non-transitory computer-readable storage medium.

[0009] To achieve the above objectives, a first aspect of the present invention proposes a method for local micro-defect localization imaging based on nonlinear ultrasonic guided wave mixing, comprising:

[0010] S1. Perform waveguide mode screening on the material under test, select two waveguide modes that meet the phase velocity matching condition and the non-zero energy flow condition, and use them as the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode, respectively, and determine the mixing waveguide mode corresponding to the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode. S2, respectively excite the first fundamental frequency guided wave signal corresponding to the first fundamental frequency guided wave mode and the second fundamental frequency guided wave signal corresponding to the second fundamental frequency guided wave mode, so that the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal propagate in the material under test and form a mixing region in space; S3, by stepping and moving the receiving transducer, the propagation time of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal are collected respectively, and the corresponding propagation speed is calculated; S4. Calculate the position of the mixing point based on the propagation speed of the first and second fundamental frequency guided wave signals, the excitation delay, and the spacing between the excitation transducers. S5, by adjusting the excitation delay of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal, the mixing point moves within the area to be tested, and the receiving transducer is controlled to perform signal acquisition with the mixing point pair. S6, perform frequency domain analysis on the acquired signal and extract the nonlinear ultrasonic guided wave mixing signal corresponding to the mixing guided wave mode; S7. The nonlinear ultrasonic guided wave mixing signal is compared with the reference signal, and the defect is determined and the defect imaging is realized based on the intensity of the mixing signal in the area to be tested.

[0011] Optionally, waveguide mode screening can be performed on the material under test, including: Candidate guided wave mode pairs are selected iteratively, and the frequency and wave number of the mixing guided wave are calculated based on the phase velocity matching condition and the non-zero energy flow condition. The results are then verified to ensure that the frequency distribution of the guided wave mode meets the dispersion relation of the material to be tested for the corresponding thickness, thereby determining the first fundamental frequency guided wave mode and the second fundamental frequency guided wave mode.

[0012] Optionally, by stepping and moving the receiving transducer, the propagation time of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal are collected respectively, and the corresponding propagation speed is calculated, including: Control the receiving transducer to move a preset step size L along the direction of guided wave propagation. Record the arrival time difference Δt of the same fundamental frequency guided wave signal at different locations, and based on L The corresponding propagation speed is obtained by calculating / Δt.

[0013] Optionally, the mixer point position PL is calculated according to the following formula:

[0014] Where L is the distance between the two excitation transducers, V1 and V2 are the propagation speeds of the first and second fundamental frequency guided wave signals, respectively, and T1 and T2 are the corresponding excitation delays.

[0015] Optionally, the nonlinear ultrasonic guided wave mixing signal is a sum-frequency signal or difference-frequency signal generated by the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal under the nonlinear action of the material.

[0016] Optionally, the nonlinear ultrasonic guided wave mixing signal is compared with a reference signal, and defects are determined and imaged in the area to be tested based on the intensity of the mixing signal, including: The nonlinear ultrasonic guided wave mixing signal is compared with a reference signal; When the nonlinear ultrasonic guided wave mixing signal is approximately consistent with the reference signal, there is no defect in the determination plate; When the similarity between the nonlinear ultrasonic guided wave mixing signal and the reference signal is lower than a preset value, half of the maximum value of the nonlinear ultrasonic guided wave mixing signal in the scanning area is used as the judgment threshold. When the mixing signal intensity at a certain position is greater than the judgment threshold, it is determined that there is a defect; otherwise, it is determined that there is no defect.

[0017] To achieve the above objectives, a second aspect of the present invention provides a local micro-defect localization imaging device based on nonlinear ultrasonic guided wave mixing, comprising: The first module is used to screen the waveguide modes of the material under test, select two waveguide modes that meet the phase velocity matching condition and the non-zero energy flow condition, and use them as the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode, respectively, and determine the mixing waveguide mode corresponding to the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode. The second module is used to excite the first fundamental frequency guided wave signal corresponding to the first fundamental frequency guided wave mode and the second fundamental frequency guided wave signal corresponding to the second fundamental frequency guided wave mode, so that the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal propagate in the material under test and form a mixing region in space. The third module is used to collect the propagation time of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal by stepping the receiving transducer, and calculate the corresponding propagation speed. The fourth module is used to calculate the position of the mixing point based on the propagation speed of the first and second fundamental frequency guided wave signals, the excitation delay, and the spacing between the excitation transducers. The fifth module is used to move the mixing point within the test area by adjusting the excitation delay of the first and second fundamental frequency guided wave signals, and to control the receiving transducer to perform signal acquisition with the mixing point pair. The sixth module is used to perform frequency domain analysis on the acquired signals and extract the nonlinear ultrasonic guided wave mixing signal corresponding to the mixing guided wave mode; The seventh module is used to compare the nonlinear ultrasonic guided wave mixing signal with the reference signal, determine the defects in the area to be tested based on the intensity of the mixing signal, and realize defect imaging.

[0018] To achieve the above objectives, a third aspect of this application provides an electronic device, including a processor and a memory; wherein the processor runs a program corresponding to the executable program code stored in the memory to implement the method described in the first aspect.

[0019] To achieve the above objectives, a fourth aspect of this application provides a non-transitory computer-readable storage medium having a computer program stored thereon that, when executed by a processor, implements the method described in the first aspect.

[0020] The embodiments of this invention have the following beneficial effects: They achieve the localization and imaging of micro-defects based on two points: first, the nonlinear ultrasonic guided wave mixing signal is highly sensitive to changes in the internal microstructure of the material; second, the nonlinear ultrasonic guided wave mixing signal uniquely characterizes the material condition at the mixing point, independent of the material condition in other regions. Therefore, in practice, the mixing point position can be moved by time-division excitation of the fundamental frequency signal, further comparing the intensity of the nonlinear ultrasonic guided wave mixing signal at different mixing points with the location and image information of the defect. Compared with existing nondestructive testing methods, this method can achieve the detection and imaging of early-stage microstructural damage in materials, and the entire detection and evaluation process is computer-controlled, thus significantly improving detection accuracy and intelligence. Attached Figure Description

[0021] The above-described and additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, in which: Figure 1 A flowchart of a local micro-defect localization imaging method based on nonlinear ultrasonic guided wave mixing provided in an embodiment of the present invention; Figure 2 A diagram of an experimental setup for nonlinear ultrasonic guided wave counter-mixing provided in an embodiment of the present invention; Figure 3 A schematic diagram of the system structure for implementing a local micro-defect localization imaging method based on nonlinear ultrasonic guided wave mixing, as provided in an embodiment of the present invention; Figure 4(a) shows the scanning imaging results of a defective 6061 aluminum alloy plate by a local micro-defect localization imaging method based on nonlinear ultrasonic guided wave mixing provided in an embodiment of the present invention. Figure 4(b) is a schematic diagram showing the location and size of the actual defects in the defective 6061 aluminum alloy plate used in Figure 4(a). Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] This embodiment provides a local micro-defect localization imaging method based on nonlinear ultrasonic guided wave mixing, which can quickly and accurately locate and image early micro-damage to materials, such as fatigue microcracks and creep pores. The imaging results can provide a reference for the assessment of the service status of materials and the prediction of service life.

[0025] like Figure 1 As shown, the method includes the following steps: S1. Perform waveguide mode screening on the material under test, select two waveguide modes that meet the phase velocity matching condition and the non-zero energy flow condition, and use them as the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode, respectively, and determine the mixing waveguide mode corresponding to the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode.

[0026] In this embodiment, the guided wave mode is first screened for the material under test to determine the combination of guided wave modes suitable for nonlinear mixing detection. Specifically, guided wave dispersion curves are pre-established for the geometric dimensions, thickness, and material parameters of the material under test to describe the phase velocity and group velocity characteristics of the guided waves at different frequencies.

[0027] Based on this, the embodiments of this application select candidate guided wave mode pairs through an iterative method. For each pair of candidate guided wave modes, which are respectively designated as the first fundamental frequency guided wave mode and the second fundamental frequency guided wave mode, their propagation characteristics in the material are further calculated, and they are screened based on phase velocity matching conditions. The phase velocity matching conditions are used to ensure that the two fundamental frequency guided waves can continuously interact in space during propagation, thereby forming a stable nonlinear mixing effect.

[0028] Meanwhile, this application also introduces a non-zero energy flow condition to constrain the candidate mode pair, ensuring that the generated mixing guided wave mode has propagable energy characteristics, thereby enabling it to be effectively detected by the subsequent receiving transducer. Specifically, based on the selected first and second fundamental frequency guided wave modes, the frequency and wavenumber of the mixing guided waves that may be generated are calculated, and it is determined whether the corresponding mode satisfies the propagation condition that the energy flow is not zero.

[0029] Furthermore, in this embodiment, the calculated mixing guided wave frequency and wavenumber are substituted into the dispersion relation under the corresponding thickness condition of the material under test for verification. Only when the mixing guided wave modes simultaneously satisfy the dispersion relation constraint can the mode pair be determined as a valid mode pair. This determines the first fundamental frequency guided wave mode, the second fundamental frequency guided wave mode, and the corresponding mixing guided wave mode ultimately used for detection.

[0030] Through the above-described guided wave mode selection process, the embodiments of this application can select the optimal mode combination that satisfies the nonlinear mixing condition from a variety of possible guided wave modes, thereby providing a foundation for subsequent high-sensitivity detection and localization imaging of micro-defects.

[0031] S2, respectively excite the first fundamental frequency guided wave signal corresponding to the first fundamental frequency guided wave mode and the second fundamental frequency guided wave signal corresponding to the second fundamental frequency guided wave mode, so that the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal propagate in the material under test and form a mixing region in space.

[0032] In this embodiment of the application, after completing the waveguide mode screening and determining the first fundamental frequency waveguide mode, the second fundamental frequency waveguide mode and the corresponding mixing waveguide mode, the first fundamental frequency waveguide signal corresponding to the first fundamental frequency waveguide mode and the second fundamental frequency waveguide signal corresponding to the second fundamental frequency waveguide mode are excited respectively, so that the two fundamental frequency waveguide signals propagate along a predetermined path in the material under test and form a mixing region in space.

[0033] Specifically, two excitation transducers can be arranged at predetermined locations on the material under test to excite a first fundamental frequency guided wave signal and a second fundamental frequency guided wave signal, respectively. The two excitation transducers can be positioned on the same side or opposite sides of the material under test, preferably in a facing arrangement, so that the two fundamental frequency guided wave signals propagate towards each other, thereby forming a local wave coupling region within the material. To improve the uniformity and stability of the excited guided wave modes, in this embodiment, the installation angle, coupling method, and excitation parameters of the excitation transducers can be matched and set according to the selected guided wave mode type, center frequency, and propagation direction. If necessary, wedges, coupling layers, or guiding structures can also be used to reduce the generation of stray modes and improve the excitation purity of the target mode.

[0034] In this embodiment, both the first and second fundamental frequency guided wave signals are generated under computer control. Specifically, the computer can be electrically connected to the ultrasonic excitation device and send control commands to the corresponding excitation channel through a preset program to control the excitation of a single fundamental frequency signal or to control the excitation of two fundamental frequency signals according to a set timing sequence. Preferably, when it is necessary to measure or calibrate the propagation characteristics of a single fundamental frequency guided wave, the computer controls the excitation of one fundamental frequency signal while the other fundamental frequency signal is cut off or not excited. At this time, the receiving transducer collects the propagation response of the single fundamental frequency guided wave in the material under test so as to calculate its propagation speed, arrival time, and propagation path characteristics.

[0035] In further implementation, when a mixing region needs to be formed, the computer controls the first and second fundamental frequency guided wave signals to be emitted according to a preset excitation delay. Since the propagation speed, direction, and excitation sequence of the two fundamental frequency guided wave signals are controllable, their meeting point in the material under test can also be adjusted. After the two fundamental frequency guided wave signals meet in space and undergo nonlinear interaction, a mixing response related to the local state of the material is formed in the meeting region. This mixing region essentially corresponds to the mixing point or local mixing region in subsequent detection, and its position can be moved by adjusting the excitation delay, thereby enabling point-by-point scanning of different locations in the test area.

[0036] It should be noted that the mixing region formed in this embodiment mainly characterizes the nonlinear material properties of that local area. Therefore, the nonlinear ultrasonic guided wave mixing signal generated by this region can reflect the influence of local micro-defects, microcracks, creep pores, or early microscopic damage on the nonlinear response of the material in a relatively concentrated manner, while having a weaker correlation with the material state in other areas far from this mixing region. Based on this, this embodiment can utilize the local mixing regions formed by two fundamental frequency guided wave signals at different spatial locations to achieve highly sensitive detection and spatial localization of local micro-defects in the material under test.

[0037] Furthermore, in this embodiment, the computer can also control the excitation sequence, excitation amplitude, excitation frequency, and excitation delay of the first and second fundamental frequency guided wave signals according to a preset scanning strategy, so as to ensure that the mixing region moves in a predetermined manner within the target detection area. This not only provides a basis for subsequent propagation velocity measurement, mixing point location calculation, and transducer alignment, but also provides stable and repeatable excitation conditions for the entire local micro-defect localization imaging process.

[0038] S3, by stepping the receiving transducer, the propagation time of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal are collected respectively, and the corresponding propagation speed is calculated.

[0039] In this embodiment, to accurately obtain the actual propagation speeds of the first and second fundamental frequency guided wave signals in the material under test, a step-moving receiving transducer is used to measure the propagation time of the two fundamental frequency guided wave signals respectively. This method avoids the errors caused by relying solely on theoretical dispersion curves, making the subsequent calculation of the mixing point position more accurate, thereby improving the reliability of local micro-defect localization and imaging.

[0040] Specifically, in this embodiment, a receiving transducer is disposed on the surface of the material to be measured and connected to a motion mechanism. The motion mechanism, under computer control, drives the receiving transducer to move in steps along the propagation direction of the guided wave. Preferably, the direction of movement of the receiving transducer is consistent with the main propagation direction of the fundamental frequency guided wave signal to be measured, in order to reduce measurement errors and improve the accuracy of propagation time identification.

[0041] When measuring the propagation speed of the first fundamental frequency guided wave signal, the computer first controls the excitation of the first fundamental frequency guided wave signal, while the second fundamental frequency guided wave signal is either not excited or cut off, to avoid interference with arrival time identification when both signals act simultaneously. The receiving transducer acquires the propagation response of the first fundamental frequency guided wave signal at the first measurement position and records the time when the first fundamental frequency guided wave signal arrives at the receiving transducer. Subsequently, the computer controls a motion mechanism to move the receiving transducer along the propagation direction of the first fundamental frequency guided wave signal by a preset step size distance L. The receiving transducer again acquires the propagation response of the first fundamental frequency guided wave signal at the second measurement position and records its arrival time. Based on the arrival time difference Δt of the same first fundamental frequency guided wave signal at two different positions, and the stepping distance L of the receiving transducer... According to L / Δt is used to calculate the propagation speed of the first fundamental frequency guided wave signal in the material under test.

[0042] Using the same method as described above, this embodiment further measures the propagation speed of the second fundamental frequency guided wave signal. Specifically, the computer controls the excitation of the second fundamental frequency guided wave signal, while the first fundamental frequency guided wave signal is either not excited or cut off. The receiving transducer collects the propagation response of the second fundamental frequency guided wave signal at two different measurement locations and records the corresponding arrival times. The propagation speed is then measured based on the stepping distance L of the receiving transducer. The propagation speed of the second fundamental frequency guided wave signal is calculated by taking into account the arrival time difference Δt between the two measurement locations.

[0043] In this embodiment, the arrival time can be obtained by identifying characteristic wave packets of the received signal. For example, the peak time, envelope peak time, zero-crossing time, or the time with the greatest correlation to the excitation signal of the first valid wave packet in the received signal can be selected as the arrival time. To improve the accuracy of propagation speed calculation, the same fundamental frequency guided wave signal can be repeatedly acquired at multiple measurement locations, and the measurement results can be optimized by averaging, fitting, or outlier removal.

[0044] Furthermore, the preset step size described in this embodiment can be set according to the size of the material to be measured, the guided wave frequency, and the target measurement accuracy. A step size that is too small will increase the number of measurements and the detection time, while a step size that is too large may reduce the accuracy of the propagation velocity calculation. Therefore, it can be selected based on actual detection requirements. Preferably, the step size should ensure a sufficiently significant arrival time difference between two adjacent measurement positions to facilitate accurate subsequent calculation of the propagation velocity.

[0045] Through the above methods, the embodiments of this application obtain the actual propagation speeds of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal in the material under test. The propagation speed, as an important parameter for subsequent calculation of the mixing point location, reflects the true propagation characteristics of the guided wave under specific test material, specific thickness, and specific experimental setup conditions, thus providing a basis for precise control of the mixing area and accurate location of local micro-defects.

[0046] S4. Calculate the position of the mixing point based on the propagation speed of the first and second fundamental frequency guided wave signals, the excitation delay, and the spacing between the excitation transducers.

[0047] In this embodiment, after obtaining the propagation velocities of the first and second fundamental frequency guided wave signals in the material under test, the position of the mixing point is further calculated based on the propagation velocities of the two fundamental frequency guided wave signals, the corresponding excitation delay, and the distance between the two excitation transducers. This step quantitatively determines the location where the two fundamental frequency guided wave signals undergo nonlinear interaction in the material, thus providing a positional basis for subsequent transducer alignment, signal acquisition, and local micro-defect localization imaging.

[0048] Specifically, in this embodiment, the distance between the two excitation transducers is L, the propagation velocities of the first and second fundamental frequency guided wave signals are V1 and V2, respectively, and the excitation delays of the first and second fundamental frequency guided wave signals are T1 and T2, respectively. Based on the propagation process of the two fundamental frequency guided wave signals in the material under test and their encounter conditions, the mixing point position PL can be calculated. The mixing point position PL is calculated according to the following formula:

[0049] The mixing point position PL can be expressed as the distance from the first excitation transducer along the line connecting the two excitation transducers to the mixing point. In other words, in this embodiment, when the first fundamental frequency guided wave signal is excited by the first excitation transducer and propagates forward at a propagation speed V1, and the second fundamental frequency guided wave signal is excited by the second excitation transducer and propagates in a relative direction at a propagation speed V2, the spatial position where the two fundamental frequency guided wave signals meet and undergo nonlinear mixing within the material can be determined by the above formula.

[0050] In this embodiment, the formula is based on the following principle: when two fundamental frequency guided wave signals propagate to the same position in the material under test, they spatially overlap and generate nonlinear interaction in that local region. Since the excitation times of the two fundamental frequency guided wave signals may differ, the difference in propagation speed and their respective excitation delays must be considered simultaneously when calculating the mixing point location. By combining the propagation distance relationship with the propagation time relationship, the above expression for the mixing point location can be obtained. This expression comprehensively reflects the combined influence of the excitation transducer spacing, guided wave propagation characteristics, and excitation timing on the spatial location of the mixing point.

[0051] Furthermore, in this embodiment, when the propagation velocities V1 and V2 of the two fundamental frequency guided wave signals are obtained by actual measurement in the aforementioned steps, the calculation accuracy of the mixing point position PL can be significantly improved. Compared to directly using the phase velocity parameter in the theoretical dispersion curve, this embodiment uses the actual measured propagation velocity in the calculation, which can better reflect the influence of factors such as the actual state of the material under test, boundary conditions, transducer coupling state, and experimental device errors on guided wave propagation, thereby making the mixing point location more accurate.

[0052] In this embodiment, the excitation delays T1 and T2 are set and adjusted by a computer control system. By changing at least one parameter of T1 and T2, the calculated mixing point position PL can be changed. That is, given that the excitation transducer spacing L and propagation velocities V1 and V2 are known, the position of the mixing point can be controllably moved by adjusting the excitation timing of the two fundamental frequency guided wave signals. Based on this, this embodiment can precisely guide the mixing point to different positions within the test area, so as to perform point-by-point nonlinear response detection in the local area.

[0053] Furthermore, in this embodiment, to facilitate subsequent spatial alignment of the receiving transducer with the mixing point, the calculated mixing point position PL can be sent to the motion control module in real time. The motion control module then drives the receiving transducer to move to the position corresponding to the mixing point for signal acquisition. This method enables the receiving transducer to detect in the region where the mixing signal is strongest or most representative, which helps improve the reception quality of the mixing signal and the spatial resolution of defect imaging.

[0054] It should be noted that the mixing point position calculation in this embodiment is applicable not only to single fixed-position detection but also to continuous scanning scenarios. During continuous scanning, a set of excitation delay parameters can be pre-set, and the corresponding mixing point positions can be calculated sequentially to arrange multiple mixing points within the test area. This allows the entire test area to form a discrete or continuous scanning path, providing a data foundation for subsequent micro-defect location identification and image reconstruction.

[0055] In summary, in the embodiments of this application, by calculating the position of the mixing point based on the propagation speed, excitation delay, and transducer spacing, precise control of the mixing region of nonlinear ultrasonic guided waves can be achieved. This not only ensures the locality and specificity of the mixing signal source, but also provides key support for subsequent scanning detection, localization analysis, and imaging processing of local micro-defects.

[0056] S5, by adjusting the excitation delay of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal, the mixing point moves within the area to be tested, and the receiving transducer is controlled to perform signal acquisition with the mixing point pair.

[0057] In this embodiment of the application, after the mixing point position calculation is completed, the excitation delay of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal is adjusted so that the mixing point moves in the area to be tested according to a predetermined scanning path, and the receiving transducer and the mixing point pair are synchronously controlled to collect signals, thereby realizing point-by-point scanning of the area to be tested.

[0058] Specifically, in this embodiment, the computer control system pre-sets an adjustment strategy for the excitation delay. The adjustment strategy may be to adjust only the excitation delay T1 of the first fundamental frequency guided wave signal, adjust only the excitation delay T2 of the second fundamental frequency guided wave signal, or adjust both T1 and T2 simultaneously. Preferably, T1 and T2 can be adjusted step-by-step according to a set time interval, causing the meeting position of the two fundamental frequency guided wave signals in the material under test to change continuously or discretely, thereby causing the mixing point to gradually move along a predetermined direction within the test area.

[0059] In this embodiment, whenever the excitation delays T1 and T2 are adjusted, the computer recalculates the corresponding mixing point position based on the updated excitation delay parameters and the previously obtained propagation velocities V1 and V2 and the excitation transducer spacing L. Subsequently, this mixing point position information is sent to the motion control module, which drives the receiving transducer to move along the surface of the material under test, ensuring that the receiving transducer is spatially aligned with the current mixing point as much as possible. This method ensures that the receiving transducer always acquires signals near the location where the mixing effect is most significant, thereby improving the receiving sensitivity and detection stability of the mixing signal.

[0060] Furthermore, in this embodiment, the "set interval" can be determined based on the size of the area to be tested, the desired spatial resolution, and the required detection efficiency. When the set interval is small, the mixing point moves more precisely within the area to be tested, which is beneficial for obtaining higher resolution defect distribution information; when the set interval is large, the overall detection time can be shortened, and the scanning efficiency can be improved. Therefore, in this embodiment, the adjustment step size of the excitation delay can be flexibly set according to actual detection needs.

[0061] In this embodiment, the receiving transducer can be mounted on a controllable mobile platform, which is capable of moving in one or two dimensions. For a strip-shaped or unidirectional detection area, the receiving transducer can perform one-dimensional stepping motion along the waveguide propagation direction or the mixing point movement direction. For a detection area requiring area imaging results, the receiving transducer can also perform two-dimensional position adjustment within a plane to correspond with the mixing points at different scanning positions. After alignment, the receiving transducer acquires the response signal generated at the current mixing point and transmits the acquisition results to the data processing module for subsequent analysis.

[0062] In this embodiment, the data acquisition process can be repeated at each mixing point. That is, as the excitation delay parameters T1 and T2 change successively, the mixing point moves gradually within the test area, and the receiving transducer moves synchronously under the drive of the motion control module, completing one signal acquisition at each mixing point. By sequentially recording the positions of each mixing point and their corresponding nonlinear response data, the distribution of mixing signals at different locations within the test area can be established, providing a raw data foundation for subsequent defect determination and image reconstruction.

[0063] Furthermore, in this embodiment, the movement of the mixing point can be divided into two modes: unidirectional scanning and bidirectional scanning, depending on the scanning requirements. For example, based on the initial mixing point position, the excitation delay of the second fundamental frequency guided wave signal can be kept constant, while the excitation delay of the first fundamental frequency guided wave signal is gradually increased to move the mixing point in one direction. After completing the detection of the region in that direction, the excitation delay of the first fundamental frequency guided wave signal is kept constant again, while the excitation delay of the second fundamental frequency guided wave signal is gradually adjusted to move the mixing point in the other direction. Through the above method, scanning and detection can be performed on both sides of the initial mixing point as the center, thereby achieving coverage of a larger area to be tested.

[0064] It should be noted that, in the embodiments of this application, the alignment of the receiving transducer and the mixing point does not require absolute coincidence. As long as the receiving transducer is within the effective receiving range of the mixing signal, it can be considered that alignment with the mixing point has been achieved. To further improve the detection accuracy, the movement position of the receiving transducer can be compensated and corrected according to the effective receiving range of the transducer, the material attenuation characteristics, and the spatial distribution characteristics of the mixing signal.

[0065] Through the above steps, this embodiment of the application can utilize the adjustable excitation delay to achieve precise and controllable movement of the mixing point within the test area, and complete signal acquisition at each scanning position through synchronous alignment of the receiving transducer and the mixing point. Compared to detection methods with fixed excitation and receiving positions, this embodiment of the application can actively transfer the sensitive area of ​​nonlinear detection to different local positions of the material under test, thereby achieving point-by-point scanning, precise positioning, and imaging detection of local micro-defects.

[0066] S6. Perform frequency domain analysis on the acquired signal and extract the nonlinear ultrasonic guided wave mixing signal corresponding to the mixing guided wave mode.

[0067] In this embodiment of the application, after the signal acquisition at each mixing point is completed, the acquired time-domain signal is analyzed in the frequency domain to extract the nonlinear ultrasonic guided wave mixing signal corresponding to the mixing guided wave mode, thereby providing key feature parameters for subsequent defect determination and imaging.

[0068] Specifically, the signals acquired by the receiving transducer at each mixing point are time-domain signals containing multiple frequency components. These signals include not only the linear response components of the first and second fundamental frequency guided wave signals, but also mixing components generated due to material nonlinear effects. Therefore, it is necessary to decompose the time-domain signal using frequency domain analysis methods to identify and extract the target mixing signal.

[0069] In this embodiment, a Fast Fourier Transform (FFT) is preferably used to process the acquired time-domain signal. Specifically, the time-domain signal acquired at each mixing point is input to the data processing module, and the FFT is used to convert it to the frequency domain to obtain the corresponding spectral information. In the spectrum, spectral lines corresponding to the first fundamental frequency guided wave signal frequency f1, the second fundamental frequency guided wave signal frequency f2, and other frequency components can be identified.

[0070] Furthermore, in this embodiment, the nonlinear ultrasonic guided wave mixing signal mainly manifests as a sum-frequency signal or a difference-frequency signal generated by the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal under the nonlinear action of the material. The frequency of the sum-frequency signal is f1+f2, and the frequency of the difference-frequency signal is |f1|. Therefore, in the frequency domain analysis, the spectral line amplitudes located at the above-mentioned frequency positions can be extracted as characteristic parameters of the nonlinear mixing signal.

[0071] In this embodiment, to improve the accuracy of mixed signal extraction, the original time-domain signal can be preprocessed before performing the Fast Fourier Transform, such as time window truncation, noise reduction, bandpass filtering, or signal averaging, to reduce the impact of environmental and system noise on the spectral results. Simultaneously, during frequency domain analysis, the sampling length and sampling frequency can be reasonably set according to frequency resolution requirements to ensure accurate differentiation of sum-frequency and difference-frequency signals.

[0072] Furthermore, in this embodiment, for each mixing point, the amplitude of the mixing signal at the corresponding frequency can be extracted, and this amplitude is used as a quantitative index characterizing the nonlinear properties of the material at that location. Since microscopic defects such as microcracks and creep pores in the material can cause local nonlinear enhancement, the amplitude of the corresponding mixing signal will also increase accordingly. Based on this, by comparing and analyzing the amplitudes of the mixing signals at different mixing points, the damage distribution at different locations within the material under test can be effectively reflected.

[0073] It should be noted that, in the embodiments of this application, in addition to Fast Fourier Transform, Short Time Fourier Transform, Wavelet Transform or other frequency domain analysis methods can also be used to process the signal. As long as the effective extraction of the frequency components of the mixed signal can be achieved, they all fall within the protection scope of this application.

[0074] Through the above steps, the embodiments of this application can effectively separate the mixed guided wave signal generated by the nonlinear effect of the material from the complex received signal, making the detection results more sensitive to the microscopic damage characteristics of the material, thereby providing a reliable basis for subsequent defect judgment and imaging.

[0075] S7. The nonlinear ultrasonic guided wave mixing signal is compared with the reference signal, and the defect is determined and the defect imaging is realized based on the intensity of the mixing signal in the area to be tested.

[0076] In this embodiment of the application, after the nonlinear ultrasonic guided wave mixing signal is extracted, the nonlinear ultrasonic guided wave mixing signal is compared and analyzed with the reference signal. Based on the intensity of the mixing signal, the defect in the area to be tested is determined, and defect imaging is further realized.

[0077] Specifically, in this embodiment, the reference signal is a pre-acquired reference signal. This reference signal can originate from a nonlinear ultrasonic guided wave mixing signal obtained from a defect-free sample of the same material and thickness under the same testing conditions, or it can originate from a mixing signal corresponding to a known defect-free region in the material under test. The reference signal is used to characterize the nonlinear response level of the material under no obvious damage, thereby providing a comparative basis for subsequent defect determination.

[0078] In this embodiment, the nonlinear ultrasonic guided wave mixing signal acquired at each mixing point is compared point-by-point with the reference signal. If the nonlinear ultrasonic guided wave mixing signal at a certain point is approximately consistent with the reference signal, it indicates that the nonlinear response of the material at that point is not significantly abnormal, and it can be determined that there are no defects or identifiable micro-damage at that point. Here, "approximately consistent" can be understood as the two being within a preset allowable range in terms of amplitude, spectral characteristics, or overall similarity.

[0079] Furthermore, in this embodiment, when the similarity between the nonlinear ultrasonic guided wave mixing signal at a certain location and the reference signal is lower than a preset value, it is considered that there is an abnormal nonlinear response at that location, indicating that there is a significant difference between the local state of the material and the defect-free reference state. In this case, to further improve the consistency and operability of defect determination, this embodiment uses a threshold determination method to identify whether a defect exists at that location.

[0080] Specifically, in this embodiment, half the maximum value of the nonlinear ultrasonic guided wave mixing signal within the entire scanning area is used as the judgment threshold. When the mixing signal intensity at a certain location is greater than the judgment threshold, it is determined that a defect exists at that location; when the mixing signal intensity at a certain location is less than or equal to the judgment threshold, it is determined that no defect exists at that location. Through this judgment method, nonlinear enhancement regions caused by local microcracks, creep pores, or early microscopic damage can be distinguished from the overall scanning results. In this embodiment, the signal similarity can be obtained in various ways. For example, it can be calculated based on the amplitude difference, normalized difference, correlation coefficient, mean square error, or spectral overlap between the signal under test and the reference signal, and the result is compared with a preset value. Any signal that reflects the deviation of the nonlinear ultrasonic guided wave mixing signal at the test location from the reference signal can be used for similarity determination in this application.

[0081] Furthermore, after determining defects at each scanning position, a spatial distribution map of the test area can be constructed based on the location of each mixing point and its corresponding mixing signal intensity. Specifically, the spatial coordinates corresponding to each mixing point can be used as image position parameters, and the corresponding mixing signal intensity, signal deviation, or defect determination result can be used as image grayscale values, color values, or other characterization parameters, thereby forming a defect distribution image within the test area. This image can intuitively reflect the location, range, and relative intensity of defects within the test area.

[0082] In this embodiment, when the mixing signal intensity at multiple consecutive scanning positions within a local area exceeds the determination threshold, the continuous abnormal area can be identified as a defect image area, thereby further estimating the size and distribution range of the defect. Conversely, when abnormal signals only appear at isolated points and do not form a continuous distribution, further retesting or filtering can be performed based on actual detection needs to reduce the impact of random noise on the imaging results.

[0083] Through the above methods, the embodiments of this application can not only identify local micro-defects in the material under test based on the difference between the nonlinear ultrasonic guided wave mixing signal and the reference signal, but also reconstruct and display the detection results in the scanning area in the form of images, thereby realizing the localization and imaging of early micro-damage in the material. Compared with traditional methods that only output a single detection index, the embodiments of this application can more intuitively present the location and extent of defects, improving the interpretability of the detection results and their engineering application value.

[0084] The following section, using the scanning and imaging process of a 1mm thick 6061 aluminum alloy plate with localized defects, further illustrates the specific implementation process of the method of this invention. The experimental setup for nonlinear ultrasonic guided wave counter-mixing is shown in the diagram below. Figure 2 As shown, 1 and 2 are two excitation transducers, 3 is a receiving transducer, and 4 is a test sample; the schematic diagram of the system structure for realizing the local micro-defect localization imaging method based on nonlinear ultrasonic guided wave mixing is shown below. Figure 3 As shown.

[0085] (1) First, the guided wave modes present in the 1mm thick 6061 aluminum alloy plate are screened. According to the aforementioned nonlinear ultrasonic guided wave mixing mode screening method, the candidate guided wave mode pairs are iteratively analyzed to obtain the mode combination that satisfies the phase velocity matching condition and the non-zero energy flow condition. In this embodiment, the 1.13MHz S0 mode is selected as the first fundamental frequency guided wave mode, and the 1.82MHz S0 mode is selected as the second fundamental frequency guided wave mode. The mixing guided wave mode corresponding to the sum frequency signal generated by the two opposing mixing is the 2.95MHz S1 mode.

[0086] (2) The RAM-5000 high-energy ultrasonic testing system was used for the excitation and acquisition of ultrasonic signals. Two excitation transducers and one receiving transducer were set up in the experiment. The first excitation transducer was used to excite the first fundamental frequency guided wave signal, and the second excitation transducer was used to excite the second fundamental frequency guided wave signal. Both excitation transducers could obtain a relatively single target guided wave mode by adding a swashplate. The receiving transducer was preferably not equipped with a swashplate to avoid attenuating the mixing signal.

[0087] (3) The propagation speed of the first fundamental frequency guided wave signal is measured. The computer controls the first excitation transducer to excite the first fundamental frequency guided wave signal, while simultaneously controlling the second excitation transducer not to excite. The receiving transducer acquires the signal once at the current position and calculates the time it takes for the first fundamental frequency guided wave signal to reach the receiving transducer. Subsequently, the computer controls the receiving transducer to step a preset distance, acquire the first fundamental frequency guided wave signal again, and calculate its arrival time. Based on the step distance of the receiving transducer and the difference between the two arrival times, the propagation speed of the first fundamental frequency guided wave signal is obtained.

[0088] (4) Measure the propagation speed of the second fundamental frequency guided wave signal using the same method as in step (3). That is, the computer controls the second excitation transducer to excite the second fundamental frequency guided wave signal, while simultaneously controlling the first excitation transducer not to excite. The receiving transducer collects the response signals of the second fundamental frequency guided wave signal at two different locations, and calculates the propagation speed of the second fundamental frequency guided wave signal based on the step distance and the time difference between the two arrivals.

[0089] (5) After obtaining the propagation speeds of the first and second fundamental frequency guided wave signals, the position of the mixing point is calculated based on the distance between the two excitation transducers, the propagation speeds of the two fundamental frequency guided wave signals, and the corresponding excitation delays. The receiving transducer is then moved to the mixing point. The receiving transducer acquires the response signal at this position and extracts the nonlinear ultrasonic guided wave mixing and frequency signal through a fast Fourier transform.

[0090] (6) On this basis, apply a fixed delay to the first fundamental frequency guided wave signal and repeat step (5).

[0091] (7) The loop process (6) realizes the detection of the material in the region to the left of the initial mixing point. The number of loops depends on the size of the scanning area.

[0092] (8) Give the second fundamental frequency guided wave signal a fixed delay and repeat the process (5).

[0093] (9) The loop process (7) realizes the detection of the material in the region to the right of the initial mixing point. The number of loops depends on the size of the scanning area.

[0094] (10) Compare the acquired nonlinear ultrasonic guided wave mixing signal with the reference signal of the corresponding thickness material. If the difference between the two is small, it is considered that there is no defect in the scanned area; if the difference between the two is large, half of the maximum value of the nonlinear ultrasonic guided wave mixing signal in the measurement result is used as the judgment threshold to judge the defect in the scanned area. When the mixing signal intensity at a certain scanning position is greater than the judgment threshold, it is determined that there is a defect at that position; otherwise, it is determined that there is no defect at that position.

[0095] The scanning results and the actual defect results are shown in Figure 4(a) and Figure 4(b), respectively. Figure 4(a) is the defect image obtained by scanning, and Figure 4(b) is a schematic diagram of the location and size of the actual defect. It can be seen from the figures that the location and size of the scanned defect are basically consistent with the actual defect, thus verifying the reliability of the method.

[0096] This invention also provides a local micro-defect localization imaging device based on nonlinear ultrasonic guided wave mixing, the device comprising: The first module is used to screen the waveguide modes of the material under test, select two waveguide modes that meet the phase velocity matching condition and the non-zero energy flow condition, and use them as the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode, respectively, and determine the mixing waveguide mode corresponding to the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode. The second module is used to excite the first fundamental frequency guided wave signal corresponding to the first fundamental frequency guided wave mode and the second fundamental frequency guided wave signal corresponding to the second fundamental frequency guided wave mode, so that the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal propagate in the material under test and form a mixing region in space. The third module is used to collect the propagation time of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal by stepping the receiving transducer, and calculate the corresponding propagation speed. The fourth module is used to calculate the position of the mixing point based on the propagation speed of the first and second fundamental frequency guided wave signals, the excitation delay, and the spacing between the excitation transducers. The fifth module is used to move the mixing point within the test area by adjusting the excitation delay of the first and second fundamental frequency guided wave signals, and to control the receiving transducer to perform signal acquisition with the mixing point pair. The sixth module is used to perform frequency domain analysis on the acquired signals and extract the nonlinear ultrasonic guided wave mixing signal corresponding to the mixing guided wave mode; The seventh module is used to compare the nonlinear ultrasonic guided wave mixing signal with the reference signal, determine the defects in the area to be tested based on the intensity of the mixing signal, and realize defect imaging.

[0097] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0098] To implement the methods of the above embodiments, the present invention also provides an electronic device, which includes a memory and a processor; wherein the processor reads executable program code stored in the memory to run a program corresponding to the executable program code, so as to implement the various steps of the methods described above.

[0099] To implement the above embodiments, this application also proposes a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the method described in the foregoing embodiments.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0101] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0102] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A method for locating and imaging local micro-defects based on nonlinear ultrasonic guided wave mixing, characterized in that, Includes the following steps: Waveguide modes are screened for the material under test. Two waveguide modes that meet the phase velocity matching condition and the non-zero energy flow condition are selected as the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode, respectively. The mixing waveguide mode corresponding to the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode is determined. The first fundamental frequency guided wave signal corresponding to the first fundamental frequency guided wave mode and the second fundamental frequency guided wave signal corresponding to the second fundamental frequency guided wave mode are excited respectively, so that the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal propagate in the material under test and form a mixing region in space; By stepping and moving the receiving transducer, the propagation time of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal are collected respectively, and the corresponding propagation speed is calculated. The position of the mixing point is calculated based on the propagation speed of the first and second fundamental frequency guided wave signals, the excitation delay, and the spacing between the excitation transducers. By adjusting the excitation delay of the first and second fundamental frequency guided wave signals, the mixing point is moved within the test area, and the receiving transducer is controlled to perform signal acquisition with the mixing point pair. Frequency domain analysis is performed on the acquired signals to extract the nonlinear ultrasonic guided wave mixing signal corresponding to the mixing guided wave mode; The nonlinear ultrasonic guided wave mixing signal is compared with a reference signal, and the defect is determined and imaged based on the intensity of the mixing signal in the area under test.

2. The method according to claim 1, characterized in that, Waveguide mode screening of the material under test includes: Candidate guided wave mode pairs are selected iteratively, and the frequency and wave number of the mixing guided wave are calculated based on the phase velocity matching condition and the non-zero energy flow condition. The results are then verified to ensure that the frequency distribution of the guided wave mode meets the dispersion relation of the material to be tested for the corresponding thickness, thereby determining the first fundamental frequency guided wave mode and the second fundamental frequency guided wave mode.

3. The method according to claim 2, characterized in that, By using a step-moving receiving transducer, the propagation times of the first and second fundamental frequency guided wave signals are collected respectively, and the corresponding propagation velocities are calculated, including: Control the receiving transducer to move a preset step size L along the direction of guided wave propagation. Record the arrival time difference Δt of the same fundamental frequency guided wave signal at different locations, and based on L The corresponding propagation speed is obtained by calculating / Δt.

4. The method according to claim 3, characterized in that, The mixer point position PL is calculated according to the following formula: Where L is the distance between the two excitation transducers, V1 and V2 are the propagation speeds of the first and second fundamental frequency guided wave signals, respectively, and T1 and T2 are the corresponding excitation delays.

5. The method according to claim 4, characterized in that, The nonlinear ultrasonic guided wave mixing signal is the sum-frequency signal or difference-frequency signal generated by the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal under the nonlinear action of the material.

6. The method according to claim 5, characterized in that, The nonlinear ultrasonic guided wave mixing signal is compared with a reference signal. Based on the intensity of the mixing signal, defects in the area under test are determined and defect imaging is achieved, including: The nonlinear ultrasonic guided wave mixing signal is compared with a reference signal; When the nonlinear ultrasonic guided wave mixing signal is approximately consistent with the reference signal, there is no defect in the determination plate; When the similarity between the nonlinear ultrasonic guided wave mixing signal and the reference signal is lower than a preset value, half of the maximum value of the nonlinear ultrasonic guided wave mixing signal in the scanning area is used as the judgment threshold. When the mixing signal intensity at a certain position is greater than the judgment threshold, it is determined that there is a defect; otherwise, it is determined that there is no defect.

7. A local micro-defect localization imaging device based on nonlinear ultrasonic guided wave mixing, characterized in that, include: The first module is used to screen the waveguide modes of the material under test, select two waveguide modes that meet the phase velocity matching condition and the non-zero energy flow condition, and use them as the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode, respectively, and determine the mixing waveguide mode corresponding to the first fundamental frequency waveguide mode and the second fundamental frequency waveguide mode. The second module is used to excite the first fundamental frequency guided wave signal corresponding to the first fundamental frequency guided wave mode and the second fundamental frequency guided wave signal corresponding to the second fundamental frequency guided wave mode, so that the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal propagate in the material under test and form a mixing region in space. The third module is used to collect the propagation time of the first fundamental frequency guided wave signal and the second fundamental frequency guided wave signal by stepping the receiving transducer, and calculate the corresponding propagation speed. The fourth module is used to calculate the position of the mixing point based on the propagation speed of the first and second fundamental frequency guided wave signals, the excitation delay, and the spacing between the excitation transducers. The fifth module is used to move the mixing point within the test area by adjusting the excitation delay of the first and second fundamental frequency guided wave signals, and to control the receiving transducer to perform signal acquisition with the mixing point pair. The sixth module is used to perform frequency domain analysis on the acquired signals and extract the nonlinear ultrasonic guided wave mixing signal corresponding to the mixing guided wave mode; The seventh module is used to compare the nonlinear ultrasonic guided wave mixing signal with the reference signal, determine the defects in the area to be tested based on the intensity of the mixing signal, and realize defect imaging.

8. An electronic device, characterized in that, Including processor and memory; The processor reads executable program code stored in the memory to run a program corresponding to the executable program code, so as to implement the method as described in any one of claims 1-6.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1-6.

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