Micro damage detection method based on ultrasonic phased array tail wave interference

Abstract

A tiny damage detection method based on ultrasonic phased array tail wave interference comprises the steps that A, an ultrasonic phased array probe or a set of piezoelectric wafers are adopted to form phase control emission, and a phase control ultrasonic field is formed in a detected area under the excitation delay rule; step B, acquiring an ultrasonic signal from an ultrasonic phased array probe or a piezoelectric wafer through an ultrasonic field, and determining and extracting a tail wave signal; c, measuring the phase difference change of the tail wave by adopting a stretching method, analyzing the tail wave signal, and calculating the numerical value of the waveform expansion coefficient of the relative wave velocity variation; step D, by collecting tail wave signals of small damages with different sizes, continuously repeating calculation in the step B and the step C to obtain multiple groups of relative wave velocity variation values, and performing value fitting on the relative wave velocity variation; e, repeating the measurement and calculation of the step B and the step C for the objects with the same material and the same structure, and combining the step D to obtain the size of the micro damage; and early-stage accurate identification of tiny damage is realized.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and in particular to a method for detecting minute damage based on ultrasonic phased array wake wave interferometry. Background Technology

[0002] In the aerospace, energy and power, rail transportation, and petrochemical industries, metallic materials (such as aluminum alloys and titanium alloys) and composite materials (such as carbon fiber reinforced polymers) are the main materials used to manufacture components. These components, such as aircraft skins, pipes, and bridges, are exposed to complex and variable environments such as alternating loads, corrosion, and temperature changes over long periods. This makes them prone to developing minute damage (such as microcracks) ranging in size from 0.1 mm to 1 mm, which tends to propagate gradually along stress concentration areas. Due to the small initial size and dispersed distribution of these minute damages, if not detected in time, they can rapidly propagate along stress concentration areas, leading to fatigue fracture and seriously threatening structural safety. Therefore, early and accurate detection of minute damage is crucial for ensuring structural reliability and achieving early warning of failures, and is of great significance for extending the service life of components and optimizing maintenance costs.

[0003] Currently, non-destructive testing methods for minor damage mainly include conventional testing methods (optical, penetrant, X-ray, eddy current) and ultrasonic testing methods (traditional ultrasound, nonlinear ultrasound, and novel ultrasound), but all of them have certain limitations: 1. Conventional non-destructive testing methods, (1) Optical testing: Microcracks are detected by light reflection or interference principle. Although the AOI automatic optical testing of patent CN202111399828.5 and the laser interference technology of CN202310704245.1 can achieve a resolution of tens of micro-nano level, they are greatly affected by light intensity, have poor detection effect on components with high surface roughness, and are difficult to detect internal damage.

[0004] (2) Penetrant testing: A penetrant is inserted into the microcracks, and then observed with the naked eye or a microscope (e.g., patents CN202110891704.2, CN201910162017.X). Although the penetrant method is simple to operate, its detection efficiency is low. Moreover, it requires the use of chemical reagents, which can easily cause environmental pollution. In addition, it cannot detect deep damage.

[0005] (3) X-ray detection: It can effectively detect internal micro-cracks, but there are radiation hazards, and the equipment is large and has poor mobility, making it difficult to meet the needs of on-site detection.

[0006] (4) Eddy current detection: non-contact detection, but only applicable to conductive materials, highly susceptible to environmental electromagnetic interference, and has a high false alarm rate.

[0007] 2. Ultrasonic testing methods: Ultrasonic testing is an important means of detecting minute damage, but traditional ultrasonic testing methods and existing improved methods have significant shortcomings: (1) Traditional ultrasonic testing: Based on the linear response caused by the reflection of sound waves at the defect, macroscopic defects are identified. The smallest detectable defect size is about half the wavelength of the ultrasonic wave. However, for micro-damage, the reflected signal is extremely weak, making it difficult to effectively identify early micro-cracks.

[0008] (2) Nonlinear ultrasonic testing: Although nonlinear ultrasonic parameters can characterize minute damage, nonlinear signals are easily affected by instrument noise and the microstructure of the material itself (such as grain boundaries), thus reducing the detection accuracy.

[0009] (3) Existing new ultrasonic methods: electromagnetic ultrasound (such as patent CN202210728123.1): combined with nonlinear acoustic resonance technology, but the energy conversion efficiency is low, resulting in insufficient sensitivity for detecting microcracks; Laser ultrasound (such as patent CN202310401042.5): locates microcracks by changing the transmission component, but the device is complex and the excitation source and detection position need to be manually adjusted according to the size of the metal component to be tested. Moreover, the echo signal is easily submerged in the environmental noise. Acoustic emission technology (such as patent CN202210866405.8): It can detect microcracks by collecting acoustic signals, but the signals are weak, easily affected by external interference such as mechanical vibration, and have many limitations such as variable propagation paths.

[0010] 3. Other novel detection methods, (1) Detection methods requiring special instruments: Patent CN201910476251.X achieves detection by analyzing mass spectrometry characteristic peak information, but requires bombarding the sample with ions once and collecting secondary ions, making the equipment complex; Patent CN202410802064.7 proposes infrared laser digital holography technology for the detection of micro defects in response to the limitations of infrared / near-infrared imaging; Patent CN202310392156.8 proposes laser infrared thermal imaging technology to detect micro defects; Patent CN202310440008.9 proposes an electromagnetic non-destructive testing method, which uses a flexible double-layer wire structure magnetizer to detect micron-level cracks in curved workpieces.

[0011] (2) Detection methods combined with artificial intelligence: Patents CN202311662461.0 and CN202110265616.1 combine image processing with machine learning to determine the existence of cracks by extracting image features; Patent 202411749433.7 proposes a microcrack identification method based on deep learning, which achieves accurate identification by extracting microcrack detail features.

[0012] The above methods can be classified into two categories: one category relies on special equipment such as infrared imaging and laser interferometers, which has shortcomings such as high cost, complex adjustment and limited applicable scenarios; the other category combines machine learning / deep learning with image feature extraction, which is currently a research hotspot, but the recognition method is not yet fully mature due to the influence of image clarity and feature extraction effect.

[0013] In summary, existing methods for detecting minute damage suffer from insufficient resolution, susceptibility to interference, and limited applicability. This is particularly true in the field of ultrasonic testing, where traditional linear methods struggle to identify minute damage, while nonlinear and novel ultrasonic methods still suffer from signal interference and low sensitivity. Therefore, there is an urgent need for a highly sensitive, interference-resistant, and applicable nondestructive testing method for minute damage in a variety of materials. Summary of the Invention

[0014] To address the shortcomings of existing technologies, this invention provides a method for detecting minute damage based on ultrasonic phased array wakewave interferometry. This invention utilizes the deflection and focusing technology of an ultrasonic phased array (PAUT) to achieve spatial modulation of the sound field energy. Combined with wakewave interferometry (CWI) theory, a feature extraction model for the scattered field of minute damage is established, enhancing the detection capability of ultrasonic signals for minute damage on aluminum skin surfaces. Its core advantage lies in establishing a quantitative mapping relationship between waveform characteristic parameters and damage size, enabling the detection of minute damage that conventional phased array techniques cannot effectively identify. This provides a novel detection scheme with high sensitivity and strong noise resistance for structural health monitoring, achieving early and accurate identification of minute damage.

[0015] To achieve the above objectives, the technical solution adopted by the present invention is: a method for detecting minute damage based on ultrasonic phased array tailwave interference, comprising the following steps: Step A, using an ultrasonic phased array probe or a phased emission composed of a set of piezoelectric crystals, a phased ultrasonic field is formed in the test area under the excitation delay rule; Step B: Acquire ultrasonic signals from an ultrasonic phased array probe or a piezoelectric crystal using a phased ultrasonic field, determine and extract the wake signal; Step C: Measure the phase difference change of the wake wave using the stretching method, analyze the wake wave signal, and calculate the value of the relative wave velocity change, i.e., the waveform stretching coefficient. Step D: By collecting wake signals from micro-damage of different sizes, repeatedly perform the calculations in Steps B and C to obtain multiple sets of relative wave velocity change values, and then perform numerical fitting on the relative wave velocity change values. Step E: For objects of the same material and structure, repeat the measurements and calculations of steps B and C, and combine them with step D to obtain the dimensions of the minor damage.

[0016] The method for forming a phased ultrasonic field within the measured area described in step A is as follows: An independent piezoelectric crystal or a single piezoelectric crystal in a group of piezoelectric crystals within an ultrasonic phased array probe is called an array element. The key to forming a phased ultrasonic field is precisely controlling the emission time of a single array element. When N array elements are delayed and the resulting beam deflection angle is γ, and the beam is focused at a distance F from the focal point P to the center of the array element group, the excitation delay between the nth (n=1,2,3,…,N) array element and the (n-1)th array element is Δτ. n Determined by the following formula: △τ n = △τ0+ [c△τ2 0(N – 2n)] / 2Ftan 2 γ (1); Where Δτ0 = dsinγ / c, d is the spacing between array elements, γ is the beam deflection angle, c is the sound velocity of ultrasound in the material, N is the total number of excited array elements, n is the serial number of the excited array element, and F is the focal length.

[0017] Step B involves acquiring ultrasonic signals from an ultrasonic phased array probe or piezoelectric crystal and determining and extracting the wake signal. The method is as follows: Based on the principle of path superposition, the wavefield u(t) obtained by superimposing the wavelets of all paths is expressed as follows: u(t) = Σ M S M (t) (2); Where M represents the path of the sound beam propagation within the ultrasonic field, and S... M u(t) represents the ultrasonic wave that randomly travels from the excitation point through the transmission path M to the signal receiving point. Therefore, u(t) includes both the direct wave and the scattered wave. When the mean free path of the scattered wave is less than one wavelength, the change in the wave field is mainly reflected in the phase change. During propagation, if the wave velocity changes, a disturbance τ will be generated in time along a certain path M in the entire propagation path. M The perturbed wave field is represented as: u M (t) = Σ M S M (t - τ M (3); Where, τ M It is the time-varying disturbance τ generated by the ultrasonic wave along a certain propagation path M. M The main dependence on the propagation path M indicates that the phase change of the wave path before and after the disturbance is related to the change of M. In order to realize that the wake signal is a superimposed signal formed by multiple scatterings after passing through the damaged area, the wake time window should be selected later. In this way, the waveform signal is less affected by clutter, and the phase difference of the signal waveform can be accurately identified within the selected window.

[0018] Step C uses the stretching method to measure the phase difference change of the wake wave, performs wake wave signal analysis, and calculates the relative wave velocity change, i.e., the waveform scaling factor, as follows: The wake wave waveform obtained in the initial state is used as the reference waveform, denoted as u0(t). The scaling factor ε is applied to the reference waveform within the time window [t]. A , t B By stretching or compressing within the [t], a tailwave signal u0[t(1+ε)] in another state is obtained. The scaling factor ε represents the relative wave velocity change between the two tailwave waveforms. The cross-correlation coefficient CC(ε) of the two waveform signals is shown in the following equation: CC(ε)=∫t B t A u0[t(1+ε)]u0(t)dt / { ∫t B t A u2 0[t(1+ε)]dt ∫t B t A u2 0(t)dt} 0.5 (4); Among them, [t A , t B The time interval from which the wake signal is extracted from the acquired ultrasound signal is denoted as u0(t), where u0(t) is the wake signal acquired in the initial state, and ε is the scaling factor. When the cross-correlation coefficient CC(ε) reaches its maximum value, the corresponding scaling factor ε is... max The relative change in wave velocity between the two waveforms is shown in the following formula: ε max = △v / v (5; In the formula: △v is the change in wave velocity between the two waveforms, and v is the sound wave propagation speed before the waveform change; During the analysis, the reference signal and multiple sets of disturbance signals were cross-correlated, and the calculated CC(ε) was obtained. max ) represents the similarity of each group of signals; but when CC(ε) max When the value is too small, the stretching method will no longer be applicable. To determine the change in relative velocity, a stepwise wake wave interferometry method is introduced. Instead of directly comparing the entire change process of the reference signal and the disturbance signal, it is divided into multiple parts, denoted by Q, and the ε of each part is solved step by step. i Finally, the total change in relative velocity is obtained as follows: △v / v = [(1-ε1) (1-ε2)…(1-ε i )] -1 -1 (6); Where: ε i It is the scaling factor for the i-th part, i=1,2,…Q.

[0019] The method in step D is as follows: as the external tensile force increases, micro-damage gradually forms and its size continues to grow. By collecting the tailwave signals of micro-damage at different sizes, the calculations in steps B and C are repeated continuously to obtain multiple values ​​of ∆v / v. The ∆v / v is then numerically fitted, and the fitting results show the relationship between the micro-damage in the measured area and the tailwave parameters.

[0020] The method in step E is as follows: repeat the measurement and calculation of steps B and C for objects of the same material and structure to obtain the ∆v / v value. Combine the fitting curve of ∆v / v obtained in step D to obtain the size of the minor damage.

[0021] The beneficial effects of this invention are as follows: First, a PAUT-CWI detection method combining phased array ultrasonic testing (PAUT) and wakewave interferometry (CWI) has been established. Compared with the current wakewave interferometry detection method based on a single piezoelectric crystal, it has the advantages of more concentrated detection energy and higher detection reachability. The deflection and focusing detection method of the phased array can enhance the energy of the incident sound beam, which is beneficial to the acquisition and identification of wakewave signals. The deflection of the sound beam can not only expand the scanning range of the sound beam, but also increase the reachability of the sound beam, making it suitable for the detection of workpieces with complex geometries.

[0022] Second, the relationship between wake wave parameters and minor damage was established based on the CWI signal processing algorithm: Simulation and experiments show that as the external loading force gradually increases, Δv / v fits into an approximately linearly increasing line segment, and R... 2 All values ​​are greater than 0.9904. Compared to nonlinear ultrasonic testing of minute damage, this method does not require consideration of instrument nonlinear interference, and has the advantages of low computational cost and accurate detection results.

[0023] Third, this method is not only applicable to the detection of minor damage in metallic materials, but also to the detection of minor damage in non-metallic materials, such as composite materials.

[0024] In summary, this invention is based on the PAUT-CWI method and focuses on the formation of phased acoustic fields, the acquisition of wake signals, and the analysis of wake signals. It establishes the relationship between wakes and micro-damages, and realizes the identification and detection of micro-damages within materials. Attached Figure Description

[0025] Figure 1 The flowchart of the PAUT-CWI detection method of the present invention is shown below; Figure 2 This is a three-dimensional finite element model diagram of the aluminum alloy in an embodiment of the present invention; Figure 3 This is a waveform diagram of the beam when it is not deflected according to an embodiment of the present invention; Figure 4 This is a waveform diagram of the beam deflection at 45° according to an embodiment of the present invention. Figure 5 This is a signal diagram collected by the receiving end in an embodiment of the present invention; Figure 6 This is a diagram of the direct wave signal in the received signal according to an embodiment of the present invention; Figure 7 This is a schematic diagram comparing the tailwave signals of different types of damage in an embodiment of the present invention; Figure 8 This is a curve showing the Δv / v numerical fitting of a 1MHz signal according to an embodiment of the present invention. Figure 9 This is a schematic diagram of the fatigue machine applying force to the test block according to an embodiment of the present invention; Figure 10 This is a schematic diagram of phased array detection of the substrate according to an embodiment of the present invention; Figure 11 This is a scan of the received signal A collected by the phased array instrument when the applied force is at its maximum in this embodiment of the invention; Figure 12 These are tailwave signal diagrams under different loading forces according to embodiments of the present invention; Figure 13 This is a numerical fitting curve of ∆v / v obtained from a phased array experiment according to an embodiment of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, such as... Figure 1As shown, a micro-damage detection method based on ultrasonic phased array wake wave interferometry (PAUT-CWI) has the following specific steps: Select a material to be tested, and form an ultrasonic field (such as a deflection-focused sound field) in the material to be tested using an ultrasonic phased array probe or a phased emission system composed of a group of multiple piezoelectric crystals. The ultrasonic phased array probe or the receiving piezoelectric crystal collects the received signal. There are three ways to generate a phased emission sound field: (1) Use one ultrasonic phased array probe to form a self-transmitting and self-receiving mode to collect ultrasonic signals; (2) Use two ultrasonic phased array probes to form a one-transmitting and one-receiving mode to collect ultrasonic signals; (3) If using A phased-array transmitter system composed of a set of piezoelectric crystals acquires ultrasonic signals at the receiving point using a single piezoelectric crystal, forming a multi-transmitter-one-receiver mode. The system acquires ultrasonic signals and extracts wake signals from the received signals through phase analysis. The system uses a stretching method to measure the phase difference change of the wake and calculates the relative wave velocity change. Wake signals from micro-damages of different sizes are acquired, and multiple sets of relative wave velocity change values ​​are obtained and numerically fitted. For materials of the same material and structure, ultrasonic received signals are acquired, wake signals are extracted, and the relative wave velocity change is calculated. The micro-defect size is obtained by combining the relative wave velocity numerical fitting curve.

[0028] Example 1: Verifying the feasibility of this method using simulation software includes the following steps: Step A: Material selection: 7075 super-hard aluminum alloy, its finite element model is as follows. Figure 2 As shown. In Figure 2 The 3D model adopts a rectangular thin-plate structure with dimensions of 200mm × 60mm × 3mm. The detection sensors employ a multi-transmitter, single-receiver configuration. The excitation sensors consist of eight piezoelectric crystals, each with a fixed spacing of d = 0.5mm, arranged in a distributed linear pattern. Their specific positions are: (-87.5mm, 1.75mm, 0) (-87.5mm, 1.25mm, 0) (-87.5mm, 0.75mm, 0) (-87.5mm, 0.25mm, 0) (-87.5mm, -0.25mm, 0) (-87.5mm, -0.75mm, 0) (-87.5mm, -1.25mm, 0) (-87.5mm, -1.75mm, 0). The excitation signal is transmitted to the model vertically within the plate. Figure 2 At point S; the receiving sensor is a piezoelectric crystal, in Figure 2Point P in the model is located at (87.5mm, 0, 0). The excitation and receiving sensors are both mounted on the same surface. The damage is located in the middle of the plate. Considering the initial length of the damage and the minimum damage size to be detected in the simulation, the damage size is set to the micrometer level. The damage is located at the origin of the three-dimensional coordinate system and lies on the same plane as the excitation and receiving sensors. The overall three-dimensional damage model is obtained by combining the undamaged aluminum structure with each damaged structure and performing a three-dimensional Boolean operation. Multiple aluminum damage models are established by continuously adjusting the damage size. This invention establishes a total of 10 damage models with different sizes ranging from 20μm to 200μm.

[0029] The excitation signal adopts a time-delay excitation mode to achieve beam deflection and focusing effect. The excitation delay of a single array element is calculated and determined using formula (1). The center frequency of the probe is 1MHz. During the signal propagation process, the beam propagation state can be observed during the fluctuation process, such as... Figure 3 and Figure 4 As shown. Figure 3 In the image, the initial wave is excited from the excitation source and propagates uniformly and stably along the white circular wavefront. Along the line connecting the center of the transmitting array element and the receiving point, blue and red hues appear on the white wavefront, indicating that the energy of the ultrasonic beam is amplified in these areas. The beam propagates along the central axis without deflection. Figure 4 In the image, the blue and red wavefronts do not appear on the line connecting the center of the transmitting array element and the receiving point, but rather at a 45° angle to it. This indicates the generation of a phased acoustic field, causing the detection beam to form the main beam at a 45° angle to the line connecting the center of the transmitting array element and the receiving point, thus enhancing the ultrasonic detection energy. This also proves that the beam deflection state has reached the preset state.

[0030] Step B: Acquisition of the wake signal. Figure 5 The receiver collected 10 different sizes of full-window damage signals. Figure 6 for Figure 5 The direct wave signal in the middle. Figure 6 This indicates that the phases of the direct wave signals are completely coincident, making it impossible to distinguish the specific signals corresponding to different types of damage. Since the signal waves analyzed in traditional ultrasonic testing are also direct waves, traditional ultrasonic testing methods are ineffective in detecting this level of damage under these circumstances.

[0031] Figure 7 These are five types of micro-damage tailwave signals. (From...) Figure 7 It can be seen that as the damage gradually expands from 20μm to 100μm, the tailwave signals of the five damage models change in both phase and amplitude. Therefore, the tailwave method can achieve a micrometer-level sensitivity for detecting minute damage.

[0032] Step C: Using the 20μm damaged tailwave waveform signal as the reference signal, use formula (4) to calculate the cross-correlation coefficient between the 40-200μm damaged tailwave waveform signal and the reference signal, and use formula (6) to calculate the relative wave velocity change (∆v / v), i.e. the waveform scaling coefficient, to obtain the pairwise waveform relationship.

[0033] Step D: Use polynomial fitting to perform curve fitting on the ∆v / v value, and the result is as follows. Figure 8 The red dashed line in the figure represents the R-squared value of the fitted curve. 2 A value of 0.9904 indicates a good fit.

[0034] Example 2: The feasibility of this method was verified by a fatigue tensile testing machine, including the following steps: Step A: The experimental specimens were made of the same 7075 aluminum material as in the simulation experiment. A narrow V-shaped notch was prepared on the experimental specimen using wire cutting. A fatigue tensile testing machine was used to load this V-shaped notch, thereby obtaining multiple specimens with different degrees of damage, such as... Figure 9 As shown. Figure 9 In this experiment, the fatigue tensile testing machine was set to apply a fixed force at a rate of 5 mm / s, initially set at 8 kN. Subsequent specimens with different damage sizes were prepared by gradually increasing this fixed force, with each increase of 0.1 kN resulting in the preparation of a damaged specimen. A total of eight damaged specimens and one control specimen were prepared with fixed forces ranging from 8 kN to 8.7 kN, all with plate dimensions of 390 mm × 40 mm × 2 mm. During the loading process in the fatigue tensile testing machine, the different fixed forces applied to the specimens caused varying degrees of damage, manifested as different degrees of deformation and cracks at the V-shaped notch. Cracks at the V-shaped notch are typically more complex; therefore, to facilitate subsequent numerical analysis, the magnitude of the fixed force was used to represent the different degrees of micro-damage present on the specimens. The phased-array ultrasonic field was generated by an ultrasonic phased array probe 5L32-A11, and the wedge was an SA11-IHC. The Omniscan MX2 phased array instrument, which receives ultrasonic signals via a self-transmitting and self-receiving method, performs tests on nine test blocks, such as... Figure 10 As shown. Figure 10 In this case, the detection signal frequency is 5MHz, and the signal delay is set in the same way as in Example 1. The excitation time of a single array element is determined by formula (1).

[0035] Step B: Acquisition of the wake signal. Figure 11 When the applied force is at its maximum, the A-scan of the received signal acquired by the phased array instrument shows the relationship between the amplitude of the received ultrasonic pulse and the transit time (ultrasonic path). Figure 12 yes Figure 11 The wake signal collected in the middle. Figure 12 Phase difference between mid-tail band waveforms and Figure 7 The observed patterns are consistent, with the phases all exhibiting a linear, gradual shift backward.

[0036] Step C: Using the tailwave signal collected from the blank board without defects as the reference signal, the cross-correlation coefficient between the remaining eight groups of tailwaves with micro-damage and the reference signal is calculated using formula (4) and the value of the relative wave velocity change (∆v / v) is calculated using formula (6) to obtain the pairwise waveform relationship.

[0037] Step D: Same as in Example 1, perform curve fitting on the ∆v / v value, and the result is as follows. Figure 13 The red dashed line in the figure represents the R-squared value of the fitted curve. 2 The value is 0.9956. The calculation result is consistent with the preset damage size.

[0038] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications, equivalent substitutions and variations without departing from the spirit and scope of the invention, and such modifications, equivalent substitutions and variations all fall within the scope defined by the appended claims.

Claims

1. A method for detecting minute damage based on ultrasonic phased array wake wave interferometry, characterized in that, Includes the following steps: Step A: Using an ultrasonic phased array probe or a phased emission device composed of a set of piezoelectric crystals, a phased ultrasonic field is formed in the measured area under the excitation delay rule; Step B: Acquire ultrasonic signals from an ultrasonic phased array probe or a piezoelectric crystal using a phased ultrasonic field, determine and extract the wake signal; Step C: Measure the phase difference change of the wake wave using the stretching method, analyze the wake wave signal, and calculate the value of the relative wave velocity change, i.e., the waveform stretching coefficient. Step D: By collecting wake signals from micro-damage of different sizes, repeatedly perform the calculations in Steps B and C to obtain multiple sets of relative wave velocity change values, and then perform numerical fitting on the relative wave velocity change values. Step E: For objects of the same material and structure, repeat the measurements and calculations of steps B and C, and combine them with step D to obtain the dimensions of the minor damage.

2. The method for detecting minute damage based on ultrasonic phased array wake wave interferometry according to claim 1, characterized in that, The method for forming a phased ultrasonic field within the measured area described in step A is as follows: An independent piezoelectric crystal or a single piezoelectric crystal in a group of piezoelectric crystals within an ultrasonic phased array probe is called an array element. The key to forming a phased ultrasonic field is precisely controlling the emission time of a single array element. When N array elements are delayed and the resulting beam deflection angle is γ, and the beam is focused at a distance F from the focal point P to the center of the array element group, the excitation delay between the nth (n=1,2,3,…,N) array element and the (n-1)th array element is Δτ. n Determined by the following formula: △τ n = △τ0 + [c△τ2 0(N – 2n)] / 2Ftan 2 γ (1) ; Where Δτ0 = dsinγ / c, d is the spacing between array elements, γ is the beam deflection angle, c is the sound velocity of ultrasound in the material, N is the total number of excited array elements, n is the serial number of the excited array element, and F is the focal length.

3. The method for detecting minute damage based on ultrasonic phased array wake wave interferometry according to claim 1, characterized in that, Step B involves acquiring ultrasonic signals from an ultrasonic phased array probe or piezoelectric crystal and determining and extracting the wake signal. The method is as follows: Based on the principle of path superposition, the wavefield u(t) obtained by superimposing the wavelets of all paths is expressed as follows: u(t) = Σ M S M (t) (2); Where M represents the path of the sound beam propagation within the ultrasonic field, and S... M u(t) represents the ultrasonic wave that randomly travels from the excitation point through the transmission path M to the signal receiving point. Therefore, u(t) includes both the direct wave and the scattered wave. When the mean free path of the scattered wave is less than one wavelength, the change in the wave field is mainly reflected in the phase change. During propagation, if the wave velocity changes, a disturbance τ will be generated in time along a certain path M in the entire propagation path. M The perturbed wave field is represented as: you M (t) = Σ M S M (t - τ M ) (3); Where, τ M It is the time-varying disturbance τ generated by the ultrasonic wave along a certain propagation path M. M The main dependence on the propagation path M indicates that the phase change of the wave path before and after the disturbance is related to the change of M. In order to realize that the wake signal is a superimposed signal formed by multiple scatterings after passing through the damaged area, the wake time window should be selected later. In this way, the waveform signal is less affected by clutter, and the phase difference of the signal waveform can be accurately identified within the selected window.

4. The method for detecting minute damage based on ultrasonic phased array wake wave interferometry according to claim 1, characterized in that, Step C uses the stretching method to measure the phase difference change of the wake wave, performs wake wave signal analysis, and calculates the relative wave velocity change, i.e., the waveform scaling factor, as follows: The wake wave waveform obtained in the initial state is used as the reference waveform, denoted as u0(t). The scaling factor ε is applied to the reference waveform within the time window [t]. A , t B By stretching or compressing within the [t], a tailwave signal u0[t(1+ε)] in another state is obtained. The scaling factor ε represents the relative wave velocity change between the two tailwave waveforms. The cross-correlation coefficient CC(ε) of the two waveform signals is shown in the following equation: CC(ε) =∫t B t A u0[t(1+ε)]u0(t)dt / {∫t B t A u2 0[t(1+ε)]dt ∫t B t A u2 0(t)dt} 0.5 (4); Among them, [t A , t B The time interval from which the wake signal is extracted from the acquired ultrasound signal is denoted as u0(t), where u0(t) is the wake signal acquired in the initial state, and ε is the scaling factor. When the cross-correlation coefficient CC(ε) reaches its maximum value, the corresponding scaling factor ε is... max The relative change in wave velocity between the two waveforms is shown in the following formula: e max = △v / v (5); In the formula: △v is the change in wave velocity between the two waveforms, and v is the sound wave propagation speed before the waveform change; During the analysis, the reference signal and multiple sets of disturbance signals were cross-correlated, and the calculated CC(ε) was obtained. max ) represents the similarity of each group of signals; but when CC(ε) max When the value is too small, the stretching method will no longer be applicable. To determine the change in relative velocity, a stepwise wake wave interferometry method is introduced. Instead of directly comparing the entire change process of the reference signal and the disturbance signal, it is divided into multiple parts, denoted by Q, and the ε of each part is solved step by step. i Finally, the total change in relative velocity is obtained as follows: △v / v = [(1-ε1) (1-ε2)…(1-ε i )] -1 -1 (6); Where: ε i It is the scaling factor for the i-th part, i=1,2,…Q.

5. The method for detecting minute damage based on ultrasonic phased array wake wave interferometry according to claim 1, characterized in that, The method in step D is as follows: as the external tensile force increases, micro-damage gradually forms and its size continues to grow. By collecting the tailwave signals of micro-damage at different sizes, the calculations in steps B and C are repeated continuously to obtain multiple values ​​of ∆v / v. The ∆v / v is then numerically fitted, and the fitting results show the relationship between the micro-damage in the measured area and the tailwave parameters.

6. The method for detecting minute damage based on ultrasonic phased array wake wave interferometry according to claim 1, characterized in that, The method in step E is as follows: repeat the measurement and calculation of steps B and C for objects of the same material and structure to obtain the ∆v / v value. Combine the fitting curve of ∆v / v obtained in step D to obtain the size of the minor damage.

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