Method for accurately positioning closed crack through nonlinear ultrasonic full-focusing imaging and imaging device

Abstract

The invention discloses a method for accurately positioning a closed crack through nonlinear ultrasonic full-focusing imaging and an imaging device.According to the method, parallel excitation is adopted, the number M of scanning times is determined, N array elements of a phased array probe are selected, and all the array elements receive response signals from a detection area after excitation each time; the captured time domain signal is recorded in an echo matrix S. The method comprises the following steps: 1, extracting a nonlinear signal; 2, establishing a coordinate system, discretizing a scanning area, and setting each grid point as a virtual focus point; 3, calculating the delay time of the virtual focus point to each array element; 4, array element signal delay correction; 5, calculating imaging data; and 6, traversing scanning times, and superposing second harmonic amplitude imaging data of M times of scanning to synthesize a comprehensive detection image. The method has the technical effects that imaging is clear, closed cracks in the material are specifically and prominently shown, the positions of the cracks in the material are accurately detected, and missing detection is avoided.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology for materials, specifically relating to a nonlinear ultrasonic full-focusing imaging method, imaging device, electronic device, and storage medium. Background Technology

[0002] Ultrasonic testing, as an important non-destructive testing method, is widely used to detect internal defects such as cracks in structural components. In actual testing, structural components are usually in a non-service state (i.e., zero-load condition), and cracks in the stable propagation stage are often closed. Due to residual stress, the two interfaces of a closed crack are in close contact. When ultrasonic waves propagate to such closed cracks, they propagate directly through the interface, unlike open cracks where strong scattering occurs at the crack tip or edge where air gaps exist. This phenomenon makes it difficult for traditional ultrasonic testing to effectively identify closed cracks, potentially leading to missed detections or underestimation of their size.

[0003] The nonlinear response of ultrasound is an effective method for detecting and evaluating closed cracks. Its basic principle is that when a high-energy ultrasonic beam propagates through a material containing a closed crack, the contact interface of the crack undergoes "clapping" behavior (i.e., opening-closing nonlinear vibration) under acoustic excitation. This nonlinear vibration generates higher and lower harmonic components different from the incident fundamental frequency; this phenomenon is called contact acoustic nonlinearity (CAN). By analyzing these nonlinear acoustic signals, effective detection of closed cracks can be achieved.

[0004] Currently, the linear ultrasonic full-focusing imaging method widely used in engineering typically employs a single-element excitation-detection strategy. This strategy generates relatively weak excitation wave energy, making it difficult to effectively excite the nonlinear response of micro-defects (such as closed cracks) within materials. Therefore, it is unsuitable for nonlinear ultrasonic imaging detection. Chinese patent document CN 118393006 A discloses a nonlinear ultrasonic imaging and evaluation method for micro-cracks. It acquires the guided wave signal of the target structure under ultrasonic excitation using a full-matrix acquisition method. For the target structure, based on the ultrasonic excitation signal, it constructs a dispersive harmonic dictionary and a non-dispersive harmonic dictionary for different propagation distances. Based on the dispersive harmonic dictionary and the guided wave signal, it solves for the sparse coefficients. Based on the non-dispersive harmonic dictionary and the sparse coefficients, it obtains the reconstructed non-dispersive second harmonic signal. Based on the reconstructed non-dispersive second harmonic signal, it obtains the full-focusing image of the target structure. Its core innovation lies in establishing a dispersive harmonic dictionary to solve the detection error problem caused by wave velocity changes when ultrasonic guided waves propagate in plate-like structures. However, this patent cannot solve the difficulty of detecting deep cracks within cubic materials. Summary of the Invention

[0005] To address the problems existing in the prior art, the technical problem to be solved by this invention is to provide a method for precise localization of closed cracks using nonlinear ultrasonic total focusing imaging. This method can reveal hidden closed cracks, achieving clear imaging and precise localization of closed cracks within materials, and has stronger engineering applicability. This invention also provides a nonlinear ultrasonic total focusing imaging device, electronic device, and storage medium.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for precise localization of closed cracks using nonlinear ultrasonic full-focusing imaging. This method employs parallel excitation, determines the number of scans M, selects N array elements of a phased array probe, and after each excitation, all array elements receive response signals from the detection area. The captured time-domain signals are recorded in the echo matrix S. The method includes the following steps:

[0008] Step 1: Extract the nonlinear signal

[0009] The echo matrix S from the positive phase excitation + The echo matrix S of the anti-phase excitation - By adding the two signals together, a nonlinear ultrasonic signal matrix U is obtained. n This represents the nonlinear signal received by the nth array element;

[0010] Step 2: Establish a coordinate system and discretize the scanned area.

[0011] With the center point of the bottom surface of the ultrasonic probe as the origin, the x-axis is set along the array element arrangement direction, and the material depth direction perpendicular to the x-axis and away from the ultrasonic probe is set as the z-axis, establishing a rectangular coordinate system in the wave propagation plane; the detection area is divided into grids, and each grid point is set as a virtual focal point P(x p ,z p );

[0012] Step 3: Calculate the delay time of the virtual focal point to each array element.

[0013] Calculate the time delay t of the ultrasonic wave propagating from excitation point P to any array element k. pk ; Traverse all N array elements of the phased array probe, calculate the delay time of each virtual aggregation point P at each array element, and save the delay time as a matrix:

[0014] DT = [t pn ] Z×X×N

[0015] In the formula, N is the number of array elements, and z and X are the number of rows and columns of virtual cluster points in the detection area;

[0016] Step 4, Array element signal Un Delay correction

[0017] For each virtual focal point, the signal U of each array element is adjusted according to the delay time. n Perform delay correction, and then convert the corrected array element signals U n By superimposing and synthesizing, the synthesized signal at each virtual focal point is obtained, which is equivalent to a nonlinear sound source at that location:

[0018]

[0019] In the formula, U n [tt pn ] is the nonlinear signal after correction of the nth array element;

[0020] Traverse all virtual focal points P in the scanning area to obtain the nonlinear sound source F(x,z,m) at all virtual focal point locations;

[0021] Step 5: Calculate imaging data

[0022] The nonlinear sound source signal is subjected to Fourier transform to obtain the frequency information of the nonlinear sound source at all virtual aggregation points; the characteristic parameters of typical nonlinear signals are extracted for imaging.

[0023] By traversing all virtual focal points P in the scanning area, the second harmonic amplitude imaging data H(x,z,m) of all virtual focal points are obtained.

[0024] Step 6: Iterate through the number of scans, and combine the second harmonic amplitude imaging data from M scans to create a comprehensive detection image.

[0025] Preferably, the method further includes a step of optimization using phase coherence weighted imaging:

[0026] Step 1 also includes step 101, calculating the phase of the received signal of the array element.

[0027] For the even harmonic signal U of array element n n (t) Perform Hilbert transform:

[0028]

[0029] In the formula, |h| is the magnitude of the signal. The phase angle of the signal;

[0030] Step 5 also includes step 501, calculating the phase coherence factor.

[0031] Calculate the signal U of each array element n Standard deviation of phase at the virtual focal point:

[0032]

[0033] In the formula, Let be the variance of the real part of the phase. Let be the variance of the imaginary phase. The standard deviation of the phase;

[0034] After normalizing the phase standard deviation calculated by the formula, the annular coherence factor is constructed:

[0035]

[0036] Then, construct the symbolic coherence factor using the symbolic function:

[0037]

[0038] Step 5 also includes step 502, phase coherence factor weighting.

[0039] The CCF and SCF are fused with a weight of β∶(1-β) to weight the original second harmonic amplitude imaging matrix H(x,z,m), resulting in the optimized imaging matrix J(x,z,m).

[0040] J(x,z,m)=(β*CCF+(1-β)*SCF)*H(x,z,m)

[0041] In the formula, β is the weighting coefficient of the annular coherence factor relative to the phase coherence factor.

[0042] Secondly, the present invention provides a nonlinear ultrasound total focusing imaging device, comprising the following parts:

[0043] The nonlinear signal extraction unit is used to extract the ultrasonic positive phase excitation echo matrix S. + and the anti-phase excitation echo matrix S - The sums are used to obtain a nonlinear ultrasound signal matrix U, where the nonlinear signal U received by the nth element is... n ;

[0044] The scanning area is discretized into units to establish a Cartesian coordinate system in the wave propagation plane, with the center point of the ultrasonic probe's bottom surface as the origin, the x-axis defined along the array element arrangement direction, and the material depth direction perpendicular to the x-axis and away from the ultrasonic probe defined as the z-axis. The detection area is then divided into a grid, with the grid spacing determined according to the imaging resolution. Each grid point is designated as a virtual focal point P(x). p ,z p );

[0045] The delay time calculation unit is used to calculate the time it takes for the ultrasonic wave to travel from the excitation point P to any array element k, thus obtaining the delay time t of the signal received by array element k. pk; Traverse all N array elements of the phased array probe, calculate the delay time of all virtual aggregation points P at each array element in turn, and save it as matrix DT;

[0046] The array element signal delay correction unit is used to adjust the signal U of each array element according to the delay time of each virtual focus point. n Perform delay correction, and then convert the corrected array element signals U n By superimposing and synthesizing, and traversing all virtual focal points P in the scanning area, the nonlinear sound sources F(x,z,m) at all virtual focal point P locations are obtained.

[0047] The computational imaging data unit is used to perform Fourier transform on the nonlinear sound source signal to obtain the frequency of the nonlinear sound source, and extract typical nonlinear signal characteristic parameters for imaging; it traverses all virtual focal points P in the scanning area to obtain the second harmonic amplitude imaging data H(x,z,m) of all virtual focal points.

[0048] The M-scan imaging data synthesis unit is used to superimpose the second harmonic amplitude imaging data H(x,z,m) of all virtual focal points in the M scans to obtain the synthesized nonlinear ultrasound total focusing imaging detection image matrix I(x,z).

[0049] Preferably, it includes a phase coherence weighted imaging optimization unit:

[0050] The array element receives signal phase calculation unit, used for the even harmonic signal U of the nth array element. n (t) Perform a Hilbert transform to obtain the phase angle of the signal.

[0051] The phase coherence factor calculation unit is used to calculate the phase coherence factors CCF(x,z,m) and SCF(x,z,m) at the virtual focal point of the m-th scan result;

[0052] The phase coherence factor weighting unit is used to weight the original second harmonic amplitude imaging matrix H(x,z,m) to obtain the optimized imaging matrix J(x,z,m).

[0053] Thirdly, the present invention provides an electronic device including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the electronic device enables the electronic device to implement any of the nonlinear ultrasonic total focusing imaging methods for precisely locating closed cracks provided in the embodiments herein.

[0054] Fourthly, the present invention provides a computer-readable storage medium storing a computer program that, when executed by a computing device, enables the computing device to implement any of the nonlinear ultrasonic total focusing imaging methods for precisely locating closed cracks as described in the embodiments herein.

[0055] The technical effects of this invention are:

[0056] This invention employs a parallel excitation strategy to excite a high-energy ultrasonic beam, thereby inducing a strong nonlinear response in closed cracks within the tested component. A pulse inversion technique is used to extract the nonlinear signal, and a full-focusing imaging algorithm based on this nonlinear signal is constructed. The core steps of the algorithm include coordinate system establishment, region discretization, delay calculation, signal synthesis and harmonic imaging, phase coherence weighted imaging, and multi-scan mode image fusion. The resulting image is clear, specifically highlighting closed cracks within the material and accurately detecting their location, avoiding missed detections. Attached Figure Description

[0057] The accompanying drawings of this invention are described below:

[0058] Figure 1 A schematic diagram illustrating the discretization of the scanned area;

[0059] Figure 2 A flowchart for generating a nonlinear ultrasound total focusing imaging detection image matrix;

[0060] Figure 3 This is a photograph of the actual aluminum block sample.

[0061] Figure 4 Dimensioning diagram for the cut and tested sample;

[0062] (a) 3D dimensioning, (b) 2D dimensioning, (c) Actual drawing of the cut sample;

[0063] Figure 5 for Figure 4 Microscopic ultrasonic C-scan images of the cut and inspected sample;

[0064] Figure 6 This is a layout diagram of the test platform of the present invention;

[0065] Figure 7 The detection imaging images of sample 1 and sample 2 for this invention;

[0066] Figure 8 for Figure 7 Enlarged local images of each crack in the image:

[0067] (a) Magnified view of crack 1-A; (b) Magnified view of crack 2-A; (c) Magnified view of crack 2-B;

[0068] Figure 9 This is a full-matrix, full-focus imaging map;

[0069] Figure 10 A schematic diagram of a nonlinear ultrasound total focusing imaging device is provided as an exemplary embodiment of the present invention;

[0070] Figure 11 A schematic diagram of a nonlinear ultrasound total focusing imaging device optimized using phase coherence weighted imaging;

[0071] Figure 12 This is a schematic diagram of the structure of an electronic device provided as an exemplary embodiment of the present invention. Detailed Implementation

[0072] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0073] The present invention provides a method for precise localization of closed cracks using nonlinear ultrasonic full-focusing imaging, which employs parallel excitation, determines the number of scans M, selects N array elements of a phased array probe, and determines the ultrasonic scanning method.

[0074] Ultrasonic scanning methods include plane wave scanning or multiple focal point scanning, using a parallel excitation strategy (i.e., simultaneously opening multiple ultrasonic excitation channels) to excite a high-energy ultrasonic beam, thereby inducing a strong nonlinear response of a closed crack in the tested component;

[0075] For a phased array probe containing N array elements, after each excitation, all array elements will receive response signals from the detection area, and the captured time-domain signals are recorded in the echo matrix S.

[0076] In the embodiment, the phased array probe has 64 array elements. The number of scans in the single crack example is 5, and the number of scans in the double crack example is 35. The scanning method is focused scanning.

[0077] Then, the following steps are included:

[0078] Step 1: Extract the nonlinear signal

[0079] Extracting nonlinear signals using the pulse inversion method:

[0080] To obtain effective nonlinear ultrasound signals, each detection requires two excitations, with a phase difference of 180 degrees between the two excitation signals, referred to as positive-phase excitation and negative-phase excitation, respectively. The echo matrix S of the positive-phase excitation... + The echo matrix S of the anti-phase excitation - Adding them together yields the nonlinear ultrasound signal matrix U, U n This represents the nonlinear signal received by the nth array element, or simply the array element signal U. n ;

[0081] Step 2: Establish a coordinate system and discretize the scanned area.

[0082] like Figure 1 As shown, a rectangular coordinate system is established in the wave propagation plane, with the center point of the bottom surface of the ultrasonic probe as the origin, the x-axis set along the array element arrangement direction, and the material depth direction perpendicular to the x-axis and away from the ultrasonic probe set as the z-axis. The detection area is divided into grids, with the grid spacing determined according to the imaging resolution. Each grid point is set as a virtual focal point P(x). p ,z p ), to calculate the delay time of all virtual focal points for each array element.

[0083] Step 3: Calculate the delay time of the virtual focal point to each array element.

[0084] With virtual focal point P(x) p ,z p Taking this as an example, calculate the time it takes for the ultrasonic wave to travel from excitation at point P to any array element k, that is, the delay t between the signal being sent to the virtual focal point P and then traveling from point P to the received signal at any array element k. pk .

[0085] Figure 1 In the diagram, path a represents the path of the ultrasonic signal propagating from each array element to point P. Under parallel excitation (plane wave excitation or focused wave excitation) mode, each array element has an excitation delay Δt. n The time it takes for the signal of the nth element to propagate to point P after excitation is t. an The time t an With the coordinates of each array element (x) n ,z n ), virtual focal point coordinates (x) p ,z p And related to wave speed c:

[0086]

[0087] Path a(a1…a N The arrival time of the ultrasonic wave is the minimum time required for all array element signals to propagate to point P.

[0088]

[0089] Equation (2), k represents any one of the array elements, k∈(1,2…N).

[0090] The path b is the distance the ultrasonic wave travels from point P to any array element k, and the required propagation time is t. bk :

[0091]

[0092] In equation (3), the coordinates (x) k ,z k Let be the coordinates of any array element k among all array elements.

[0093] The total delay of the received signal at point P for any array element k is:

[0094] t pk =t ak +t bk (4)

[0095] Following the above method, traverse all N array elements of the phased array probe, calculate the delay time of all virtual aggregation points P at each array element, and save it in matrix form:

[0096] DT = [t pn ] Z×X×N (5)

[0097] In equation (5), N is the number of array elements, and Z and X are the number of rows and columns of virtual cluster points in the detection area.

[0098] It should be noted that the delay time matrix DT can be pre-calculated and stored for later use, which helps to improve detection efficiency.

[0099] Step 4, Array element signal U n Delay correction

[0100] For each virtual focal point, the signal U of each array element is adjusted according to the delay time. n Perform delay correction, and then convert the corrected array element signals U n By superimposing and synthesizing, a synthesized signal is obtained at each virtual focal point. This synthesized signal can be physically equivalent to a nonlinear sound source at that location.

[0101]

[0102] In equation (6), U n [tt pn ] is the nonlinear signal after delay correction of the nth array element.

[0103] By traversing all virtual focal points P in the scanning area, the nonlinear sound source F(x,z,m) at the positions of all virtual focal points is obtained.

[0104] Step 5: Calculate imaging data

[0105] Step 51: Perform Fourier transform on the nonlinear sound source signal to obtain the frequency information of the nonlinear sound source at all virtual aggregation points;

[0106] Because nonlinear ultrasonic testing typically uses multi-cycle excitation signals, the source signal has a long duration in the time domain. If imaging is performed by directly extracting the time-domain amplitude using the linear ultrasonic full-focusing algorithm, it will result in low imaging resolution. Therefore, a Fourier transform is performed on the nonlinear sound source signal:

[0107]

[0108] In equation (7), T is the duration of the excitation signal.

[0109] Step 52: Extract typical nonlinear signal feature parameters for imaging.

[0110] In this embodiment, the second harmonic amplitude of each virtual focal point is extracted, and the second harmonic amplitude is used for imaging:

[0111]

[0112] In equation (8), H(x) p ,z p ,m) represents the second harmonic amplitude at point P during the m-th scan.

[0113] Traverse all virtual focal points P in the scanning area to obtain the second harmonic amplitude imaging data H(x,z,m) of all virtual focal points.

[0114] Imaging can also use other nonlinear signals, such as zero-frequency static components, third harmonics, or other higher harmonics. In this embodiment, the second harmonic has a large amplitude and strong signal, which is beneficial for imaging.

[0115] Step 6: Iterate through the scans, and combine the second harmonic amplitude imaging data from M scans to create a comprehensive detection image.

[0116] To improve the detection capability of closed cracks, repeated scanning using multi-angle plane waves or multiple focal points can be employed. Each scan repeats the above process to acquire second harmonic amplitude imaging data H(x,z,m) under the corresponding conditions. Finally, a comprehensive detection image is synthesized by superimposing the second harmonic amplitude imaging data H(x,z,m) from each scan. If there are M scans in total, the resulting composite nonlinear ultrasonic total focusing imaging image matrix is:

[0117]

[0118] In equation (9), H(x,z,m) represents the second harmonic amplitude imaging data of the m-th scan.

[0119] This multi-scan mode image synthesis helps improve the defect signal-to-noise ratio and detection reliability.

[0120] like Figure 2As shown, the nonlinear ultrasound total focusing imaging detection image matrix I(x,z) is generated, which also includes the calculation of phase coherence factor and phase coherence weighting, according to the following process:

[0121] S201. Input parameters, including the number of scans M, the number of array elements N, and the Z rows and X columns of the discretized scan range;

[0122] S202. Initialize the parameters of S201 sequentially according to the number of scans m, the discretized z rows, x columns and array elements n, and enter the four-fold loop;

[0123] S203. Obtain the phase information of the signal received by array element n;

[0124] Because nonlinear ultrasound signals are weak and susceptible to noise interference, resulting in a generally low signal-to-noise ratio, artifacts frequently appear in the imaging results, severely affecting the accuracy and reliability of interpretation. To improve imaging quality, this embodiment introduces a phase coherence imaging algorithm to weight the imaging results, thereby suppressing noise interference, reducing artifacts, and improving image reliability and clarity.

[0125] The basic principle of phase coherence imaging algorithms is to use the phase information of the signals received by each array element to evaluate the phase consistency at different locations within the imaging region. Since a closed crack can be regarded as the source of nonlinear ultrasonic signals, the phase consistency of the nonlinear signals received by each array element is high at the crack location, and the algorithm will enhance the amplitude in that region; while at locations far from the crack, the phase consistency decreases, and the signal amplitude is suppressed.

[0126] Based on the above principle, the phase information of each array element signal is extracted using Hilbert transform:

[0127] According to the literature “Comparison of ultrasonic array imaging algorithms for nondestructive evaluation[J]”, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2013, 60(8):1732-1745. and the literature “Research on phase coherence imaging noise reduction of austenitic stainless steel welds[C]”, Chen Yao et al., Proceedings of the 2017 Far East Nondestructive Testing New Technology Forum, 2017:679-683:

[0128] In step 1 above, after obtaining the nonlinear ultrasonic signal matrix Un, phase information can be extracted for the even harmonic signal U of array element n. n (t) Perform Hilbert transform:

[0129]

[0130] In equation (10), |h| is the magnitude of the signal. The phase angle of the signal.

[0131] This operation can be pre-calculated and stored in step 1 for later use. This step only reads the phase of each array element signal.

[0132] S204. Read the delay matrix DT and retrieve the signal delay of array element n.

[0133] S205, The superposition of the delayed N element signals yields the nonlinear sound source signal F(x). p ,z p ,t);

[0134] The nonlinear sound source is calculated based on equation (6).

[0135] S206: Does the number of array elements N need to be traversed? If yes, then execute S206; otherwise, repeat the process n times.

[0136] S207. Extract the phase of the nonlinear signal and calculate the phase coherence factors CCF(x,z,m) and SCF(x,z,m);

[0137] According to the phase information of equation (10) and Further calculation of the standard deviation of the phase of each array element signal at the virtual focal point:

[0138]

[0139] In equation (11), Let be the variance of the real part of the phase. Let be the variance of the imaginary phase. This represents the standard deviation of the phase.

[0140] After normalizing the phase standard deviation calculated by equation (11), the circular coherence factor (CCF) is constructed:

[0141]

[0142] Then, the sign coherence factor (SCF) is constructed using the sign function:

[0143]

[0144] S208, sound source signal F(x) p ,z p The second harmonic amplitude H(x) is extracted by Fourier transform of t) p ,z p ,t);

[0145] The amplitude of the second harmonic is calculated based on equations (7) and (8).

[0146] S209, phase coherence factor weighting, to obtain imaging data;

[0147] A phase coherence imaging algorithm is introduced to perform weighted processing on the imaging data.

[0148] This invention employs the two phase coherence factors mentioned above to optimize the imaging results. Each factor has its own characteristics in imaging optimization: the SCF factor can significantly improve the amplitude and resolution of defect echoes, but it is sensitive to phase errors and easily introduces high-frequency noise; the CCF factor has a higher tolerance for phase errors, improving defect display while offering better noise control. To balance the advantages of both, this embodiment fuses the CCF and SCF factors with a weight of 0.7:0.3, weighting the original second harmonic amplitude imaging matrix H(x,z,m) to obtain the optimized imaging matrix J(x,z,m):

[0149] J(x,z,m)=(0.7*CCF+0.3*SCF)*H(x,z,m) (14);

[0150] If S210 and column x have been traversed, execute S211; otherwise, loop through column x.

[0151] If S211 and z lines have been traversed, execute S212; otherwise, loop through z and execute.

[0152] S212. Accumulate the imaging data J(x,z,m) to obtain the comprehensive detection image data I(x,z);

[0153] To improve the detection capability of closed cracks, repeated scanning using multi-angle plane waves or multiple focal points is employed. Each scan repeats the above process to acquire imaging results under corresponding conditions. Finally, the results of each scan are superimposed to create a comprehensive detection image. If there are a total of M scans, the resulting comprehensive nonlinear ultrasonic total focusing imaging detection image matrix is:

[0154]

[0155] In equation (15), J(x,z,m) represents the result of the m-th scan.

[0156] This multi-scan mode image synthesis helps improve the defect signal-to-noise ratio and detection reliability.

[0157] S213. Does the scan count m involve traversal? If yes, execute S214; otherwise, repeat the process in the loop until m is reached.

[0158] S214. Output imaging data I(x,z) and display the imaging using imaging data I(x,z).

[0159] This method is used to detect closed cracks.

[0160] 1. Sample preparation

[0161] This experiment follows the relevant provisions on pre-existing fatigue cracks in the national standard GB / T 6398-2017. It uses aluminum block specimens with through notches and prepares closed cracks through a three-point bending loading method.

[0162] Two types of samples, such as Figure 3 As shown, the first type is a single-sided, single-notch specimen, with the notch located at the center of the bottom of the specimen, and is numbered 1; the second type is a single-sided, double-notch specimen, with the two notches located at the bottom of the specimen and centrally symmetrically distributed, with a notch tip spacing of 30 mm, and is numbered 2. The specimen dimensions are all 256 mm × 60 mm × 60 mm, with a notch width of 3.75 mm and a height of 9 mm.

[0163] The fatigue test parameters are set as follows: minimum load F min = -34.5kN, stress ratio R = 10, loading frequency f = 15Hz. After approximately 150,000 to 200,000 cycles of loading, fatigue cracks with a length of 15 to 20 mm were successfully pre-induced in two specimens.

[0164] To accurately measure the crack length, after completing the nonlinear ultrasonic testing experiment of this invention, according to... Figure 4 Based on the specified dimensions, a 20mm wide crack section is cut out centered on the notch. A 4mm thick test sample is then cut out from the middle of the width direction. This location usually corresponds to the longest fatigue crack propagation area.

[0165] Ultrasonic scanning (C-scan) microscopy requires the sample to be thinned before inspection. C-scan imaging utilizes ultra-high frequency ultrasonic waves driven by a stepper motor to perform a two-dimensional scan of the workpiece surface. During inspection, the probe records ultrasonic data at various locations and generates a two-dimensional image. Based on the principle of sound wave reflection, internal defects in the material are identified. The inspection results are as follows: Figure 5 As shown (the C-scan inspection dimensions were calibrated by the testing company), the image clearly shows the length and direction of the entire fatigue crack, but it cannot distinguish between the open and closed portions. Based on the crack propagation characteristics in this specimen, it can be concluded that the leading edge along the crack propagation direction is the closed crack region.

[0166] 2. Experimental process of this invention

[0167] This experiment was conducted on a Verasonics phased array ultrasonic experimental platform. The overall experimental setup is as follows: Figure 6 As shown. A 64-element phased array probe (hereinafter referred to as the probe) manufactured by IMASONIC was used for testing. This probe has a center frequency of 5MHz, a -6dB relative bandwidth of 64%, an element width of 0.4mm, and a spacing of 0.5mm. The experiment used a self-transmitting and self-receiving mode for signal acquisition.

[0168] Regarding the excitation signal, to balance the probe's frequency response characteristics and the effect of nonlinear harmonic generation, the excitation waveform was set to a 10-cycle, 3MHz Hanning window amplitude-modulated sine wave. This parameter helps enhance the system's receiving sensitivity to second harmonic signals, providing an effective signal for generating nonlinear imaging.

[0169] In this experiment, the probe center was precisely aligned directly above the notch in the specimen, and data acquisition was performed using the focusing mode. The specific scanning parameters for single-crack and double-crack specimens in the focusing mode are listed in Table 1.

[0170] Table 1. Focusing mode scanning parameters of the experiment

[0171]

[0172] 3. Comparison of the detection results of this invention with existing detection technologies.

[0173] Existing technologies use linear ultrasound full-matrix-full-focus detection (which belongs to phased array detection), and their results are compared and analyzed with the imaging results of the method invented in this invention:

[0174] Figure 7 The nonlinear ultrasonic full-focus imaging results of the focusing pattern scanning of sample 1 and sample 2 are presented in this invention. Figure 7 (a) and Figure 7 (b) shows the imaging results of the second harmonic amplitude of sample 1 and sample 2. Figure 7 (c) and Figure 7 (d) shows the nonlinear ultrasonic imaging results of specimen 1 and sample 2 after the introduction of the phase coherence algorithm. It can be seen that the phase coherence algorithm effectively improves the signal-to-noise ratio of the nonlinear ultrasonic imaging results.

[0175] Figure 8 From Figure 7 (a) and Figure 7(b) shows local imaging images of each crack. Based on the mechanical characteristics of fatigue-propagating cracks, along the crack propagation direction, the closer to the closed crack zone, the greater the compressive force, while the closer to the opening, the smaller the compressive force. Regions with higher compressive forces require higher-energy ultrasound to elicit significant nonlinear effects, while regions with lower compressive forces require relatively lower ultrasound energy. Therefore, although the crack tip is the location with the strongest nonlinear characteristics, its ultrasonic nonlinear response amplitude is not necessarily the largest. Based on this mechanism, in Figure 8 In the local imaging, the extreme points that conform to the above response characteristics are identified as the locations of closed crack tips. Specifically, in the imaging of crack 1-A, the second peak is identified as the crack tip; while cracks 2-A and 2-B do not exhibit multi-peak characteristics, so their maximum response points are identified as the tip locations. The comparison data between this identification result and the C-scan detection result is shown in Table 2 (from the top surface as the starting point, the scale is downward).

[0176] Table 2 Comparison of the results of focused scanning and C-scan detection in this invention (unit: mm)

[0177]

[0178] Note: C-scan images can clearly show the length and direction of the entire fatigue crack, but cannot distinguish between the open and closed portions. The crack propagation characteristics of the specimens detected by this invention show that the leading edge along the crack propagation direction is the closed crack region. The detection results of this invention provide crucial evidence for locating closed cracks.

[0179] from Figure 8 As can be seen, this invention can accurately identify the location of the extension tip of a closed crack based on the peak characteristics of the second harmonic amplitude imaging diagram, thereby achieving precise positioning of the closed crack.

[0180] Figure 9 (a) Figure 9 (b) shows the FMC-TFM imaging results for samples 1 and 2. Because the crack propagation direction is nearly straight and the gap at the crack opening is extremely small, the reflected signal is extremely weak. Therefore, neither the open nor closed portion of the crack can be effectively identified in FMC-TFM imaging. In contrast, this invention can effectively detect and locate closed cracks.

[0181] like Figure 10 As shown, the nonlinear ultrasound total focusing imaging device 100 of the present invention includes the following parts:

[0182] The nonlinear signal extraction unit 110 is used to extract the ultrasonic positive phase excitation echo matrix S + and the anti-phase excitation echo matrix S -The sums are used to obtain a nonlinear ultrasound signal matrix U, where the nonlinear signal U received by the nth element is... n ;

[0183] The scanning area discretization unit 120 is used to establish a rectangular coordinate system in the wave propagation plane, with the center point of the bottom surface of the ultrasonic probe as the origin, the x-axis set along the array element arrangement direction, and the material depth direction perpendicular to the x-axis and away from the ultrasonic probe set as the z-axis. The detection area is divided into a grid, with the grid spacing determined according to the imaging resolution. Each grid point is set as a virtual focal point P(x). p ,z p );

[0184] The delay time calculation unit 130 is used to calculate the time it takes for the ultrasonic wave to propagate from the excitation point P through the virtual focal point P to any array element k, thus obtaining the delay time t of the signal received by array element k. pk ; Traverse all N array elements of the phased array probe, calculate the delay time of all virtual aggregation points P at each array element in turn, and save it as matrix DT;

[0185] The array element signal delay correction unit 140 is used to adjust the array element signal U according to the delay time of each virtual focus point. n Perform delay correction, and then convert the corrected array element signals U n By superimposing and synthesizing, and traversing all virtual focal points P in the scanning area, the nonlinear sound sources F(x,z,m) at all virtual focal point P locations are obtained.

[0186] The computational imaging data unit 150 is used to perform Fourier transform on the nonlinear sound source signal to obtain the frequency of the nonlinear sound source, and extract typical nonlinear signal characteristic parameters for imaging; it traverses all virtual focal points P in the scanning area to obtain the second harmonic amplitude imaging data H(x,z,m) of all virtual focal points.

[0187] The M-scan imaging data synthesis unit 160 is used to superimpose the second harmonic amplitude imaging data H(x,z,m) of all virtual focal points in the M-scan to obtain the synthesized nonlinear ultrasound total focusing imaging detection image matrix I(x,z).

[0188] Preferably, such as Figure 11 The nonlinear ultrasound total focusing imaging device 100 shown also includes a unit for phase coherence weighted imaging optimization:

[0189] The array element receiving signal phase calculation unit 111 is used for the even harmonic signal U of the nth array element. n (t) Perform a Hilbert transform to obtain the phase angle of the signal.

[0190] The phase coherence factor calculation unit 151 is used to calculate the phase coherence factors CCF(x,z,m) and SCF(x,z,m) of the scan result at the virtual focal point;

[0191] The phase coherence factor weighting unit 152 is used to weight the original second harmonic amplitude imaging matrix H(x,z,m) to obtain the optimized imaging matrix J(x,z,m).

[0192] The nonlinear ultrasound total focusing imaging device 100 provided by this invention can execute the method for accurately locating closed cracks using nonlinear ultrasound total focusing imaging as described in the embodiments herein, and possesses the corresponding functional modules and beneficial effects of this method invention. Contents not described in detail in the device embodiments of this invention can be referred to the descriptions in the method invention embodiments.

[0193] Figure 12 This is a schematic diagram of an electronic device provided in an embodiment of the present invention, used to exemplarily illustrate the electronic device for implementing the method of precise localization of closed cracks using nonlinear ultrasonic total focusing imaging provided in the embodiments of the present invention. The electronic device 200 can be a portable mobile terminal, such as a smartphone, in-vehicle terminal, tablet computer, MP3 player, MP4 player, laptop computer, or desktop computer. The electronic device 200 may also be referred to as user equipment, portable terminal, laptop terminal, desktop terminal, or other names.

[0194] Typically, electronic device 200 includes one or more processors 201 and memory 202.

[0195] The processor 201 may be a central processing unit (CPU) or other form of processing unit with data processing and / or instruction execution capabilities, and may control other components in the electronic device 200 to perform desired functions.

[0196] The memory 202 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. Volatile memory may include, for example, random access memory (RAM) and / or cache memory. Non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium. The processor 201 can execute the program instructions to implement the method for precise localization of closed cracks using nonlinear ultrasonic total focusing imaging provided in this embodiment of the invention, and can also implement other desired functions. Various contents such as input signals, signal components, and noise components may also be stored in the computer-readable storage medium.

[0197] The method for accurately locating closed cracks using nonlinear ultrasonic full-focus imaging provided in this embodiment of the invention may include: 1. extracting nonlinear signals; 2. establishing a coordinate system and discretizing the scanning area; 3. calculating the delay time of the virtual focal point to each array element; 4. array element signal U. n 5. Delay correction; 6. Calculation of imaging data; 7. Number of traversal scans; 8. Synthesis of second harmonic amplitude imaging data from M scans into a comprehensive detection image. This also includes calculating the phase of the received signal from the array elements, calculating the phase coherence factor, and calculating the phase coherence factor weighting. It should be understood that the electronic device 200 can also perform other preprocessing methods related to this invention.

[0198] Electronic device 200 may also include input device 203 and output device 204, which are interconnected via a bus system and / or other forms of connection mechanism (not shown).

[0199] In addition, the input device 203 may include, for example, the array elements of a phased array probe, a keyboard, a mouse, etc.

[0200] The output device 204 may include, for example, a display, a speaker, a printer, and a communication network and its connected remote output devices. The output device 204 can output various information to the outside, including nonlinear ultrasound total focusing images.

[0201] Of course, for the sake of simplicity, Figure 12 Only the components of the electronic device 200 relevant to the present invention are shown, omitting components such as buses, input / output interfaces, etc. In addition, the electronic device 200 may include any other suitable components depending on the specific application.

[0202] This invention also provides a computer program product, comprising a computer program or computer program instructions, which, when executed by a computing device, cause the computing device to implement the method for precise localization of closed cracks using nonlinear ultrasonic total focusing imaging provided in this invention. The computer program product can be written with program code for performing the operations of this invention using any combination of one or more programming languages.

[0203] Furthermore, embodiments of the present invention may also provide a computer-readable storage medium storing computer program instructions thereon, which, when executed by a computing device, cause the computing device to implement the method for precise localization of closed cracks using nonlinear ultrasonic total focusing imaging provided in embodiments of the present invention.

[0204] The method for accurately locating closed cracks using nonlinear ultrasonic full-focus imaging provided in this invention embodiment may include: 1. extracting nonlinear signals; 2. establishing a coordinate system and discretizing the scanning area; 3. calculating the delay time of the virtual focal point to each array element; 4. array element signal U. n The process includes: 5. Delay correction; 6. Calculation of imaging data; 7. Number of traversal scans; and 8. Synthesis of second harmonic amplitude imaging data from M scans into a comprehensive detection image. It also includes calculating the phase of the received signal from the array elements, calculating the phase coherence factor, and calculating the phase coherence factor weighting.

[0205] Computer-readable storage media may take the form of any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may, for example, include, but is not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatuses, or devices, or any combination thereof. More specific examples of readable storage media (a non-exhaustive list) include: electrical connections having one or more wires, portable disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

Claims

1. A method for precisely locating closed cracks using nonlinear ultrasonic full focus imaging, using parallel excitation, determining the number of scans M, selecting a phased array probe of N elements, after each excitation all elements receive a response signal from the detection area, the captured time domain signals are recorded in an echo matrix S, characterized in that, The method comprises the following steps: Step 1, extracting a nonlinear signal The nonlinear ultrasound signal matrix U, U n is obtained by adding the echo matrix S + from positive excitation and the echo matrix S - from negative excitation, U n denotes the nonlinear signal received by the nth element. Step 2, establishing a coordinate system and discretizing a scanning area With the center point of the bottom surface of the ultrasonic probe as the origin, an x-axis is set along the array arrangement direction, and a z-axis is set as the material depth direction perpendicular to the x-axis and away from the ultrasonic probe, to establish a rectangular coordinate system in the wave propagation plane; the detection area is divided into grids, and each grid point is set as a virtual focusing point P(x p ,z p ) Step 3, calculating a delay time of each array element with respect to a virtual focus point The delay time t of the ultrasonic wave from the excitation to any element k via P point pk ; all phased array probe N elements are traversed, and the delay time of all virtual focus points P at each element is calculated in turn, and the delay time is saved as a matrix: DT = [t pn ] Z×X×N wherein N is the number of array elements, z and X are the number of rows and columns of the virtual focus points in the detection area; Step 4, array element signal U n Delay correction For each virtual focus point, the time-delayed signals U n are corrected according to the time delay, and then the corrected signals U n are superimposed to obtain the composite signal at each virtual focus point, which is equivalent to a nonlinear sound source at that position: In the formula, U n [t-t pn ] is the corrected non-linear signal of the nth array element. All virtual focus points P in the scanning area are traversed to obtain a nonlinear sound source F(x, z, m) of all virtual focus point positions; Step 5, calculating imaging data The nonlinear sound source signal is subjected to Fourier transform to obtain frequency information of the nonlinear sound source of all virtual focus points; and typical nonlinear signal characteristic parameters are extracted for imaging; All virtual focus points P in the scanning area are traversed to obtain a second harmonic amplitude imaging data H(x, z, m) of all virtual focus points; Step 6, traversing the scanning times, and superimposing and synthesizing a second harmonic amplitude imaging data of M scanning times to obtain a comprehensive detection image.

2. The method of claim 1, wherein the non-linear ultrasound full-focusing imaging precisely locates the closed crack. The method comprises the following steps: In step 1, step 101, a phase of a signal received by an array element is calculated For even order harmonic signal U of array element n n (t) performing a Hilbert transform: where |h| is the modulus of the signal, is the phase angle of the signal; In step 5, step 501, a phase coherence factor is calculated The signal U of each array element is calculated n Standard deviation of the phase at the virtual focus point: wherein is the variance of the real part phase, is the variance of the imaginary part phase, is the standard deviation of the phase; The phase standard deviation obtained by calculation is normalized to construct a ring-shaped coherence factor: A sign coherence factor is constructed by using a sign function: In step 5, step 502, the phase coherence factor is weighted The CCF and the SCF are fused according to a weight ratio of β:(1-β), and a second harmonic amplitude imaging matrix H(x, z, m) is weighted to obtain an optimized imaging matrix J(x, z, m): J(x, z, m) = (β*CCF + (1-β)*SCF)*H(x, z, m) wherein β is a weight coefficient of the ring-shaped coherence factor with respect to the phase coherence factor.

3. The method of nonlinear ultrasonic total focusing imaging for precise location of closed cracks according to claim 1 or 2, characterized in that, In step 3, the delay time t of the ultrasonic wave from the start of excitation, propagating via point P to any element k is calculated pk : Path a is the path of the ultrasonic signal propagating from each array element to point P. In parallel excitation mode, each array element has an excitation delay Δt. n The time it takes for the signal of the nth element to propagate to point P after excitation is t. an The time t an and the coordinates of each array element (x) n ,z n ), virtual focal point coordinates (x) p ,z p And related to wave speed c: Path a (a1...a N The ultrasound wave arrival time on path a (a1...a is the minimum value of the times required for the signals from all the elements to propagate to point P: wherein k represents any array element in all array elements, and k ∈ (1, 2…N). The distance b is the path of the ultrasound wave from point P to any element k, the required propagation time being t bk : where the coordinates (x k ,z k ) are the coordinates of any element k of all elements. A total delay of a signal received by any array element k at a point P is: t pk = t ak + t bk .

4. The method of claim 3, wherein the non-linear ultrasound full-focusing imaging precisely locates the closed crack. The nonlinear sound source signal is subjected to Fourier transform to obtain frequency information of the nonlinear sound source of all virtual focus points: wherein T is a duration length of an excitation signal; The typical nonlinear signal characteristic parameters are extracted as follows: A second harmonic amplitude of each virtual focus point is extracted, and the second harmonic amplitude is used for imaging: where H(x p ,z p ,m) is the second harmonic amplitude at point P at the mth scan.

5. The method of claim 3, wherein the non-linear ultrasound full-focusing imaging precisely locates the closed crack. A superimposed and synthesized nonlinear ultrasonic full-focus imaging detection image matrix is: wherein H(x, z, m) represents a second harmonic amplitude imaging data of the mth scanning.

6. A nonlinear ultrasonic full-focusing imaging apparatus, characterized by, The method comprises the following parts: a nonlinear signal extraction unit (110) for adding the ultrasonic in-phase excitation echo matrix S + and the anti-phase excitation echo matrix S - to obtain a nonlinear ultrasonic signal matrix U, wherein the nth element of the nonlinear ultrasonic signal matrix U n received by the nth element The scanning area discretization unit (120) is configured to complete the following: taking the center point of the bottom surface of the ultrasonic probe as the origin, setting the x-axis along the arrangement direction of the array elements, setting the z-axis perpendicular to the x-axis and away from the material depth direction of the ultrasonic probe, and establishing a rectangular coordinate system in the wave propagation plane. The detection area is grid divided, and the grid spacing is determined according to the imaging resolution. Each grid point is set as a virtual focus point P(x p ,z p ). The delay time calculation unit (130) is configured to calculate the time from the start of excitation of the ultrasonic wave to the propagation of the ultrasonic wave to any array element k via the virtual focus point P, to obtain the delay time t of the array element k receiving signal pk ; all phased array probe N elements are traversed, and the delay time of all virtual focus points P at each array element is calculated in turn and saved as a matrix DT; The array element signal delay correction unit (140) is configured to delay each virtual focus point according to a delay time to obtain a plurality of array element signals U n The array element signal delay correction unit (140) is configured to delay each virtual focus point according to a delay time to obtain a plurality of array element signals U n The array element signal delay correction unit (140) is configured to delay each virtual focus point according to a delay time to obtain a plurality of array element signals U An imaging data calculation unit (150) is configured to subject a nonlinear sound source signal to Fourier transform to obtain a frequency of a nonlinear sound source, extract typical nonlinear signal characteristic parameters for imaging, traverse all virtual focus points P in a scanning area, and obtain a second harmonic amplitude imaging data H(x, z, m) of all virtual focus points; An M-time scanning imaging data synthesis unit (160) is configured to superimpose a second harmonic amplitude imaging data H(x, z, m) of all virtual focus points in M-time scanning to obtain a synthesized nonlinear ultrasonic full-focus imaging detection image matrix I(x, z).

7. The nonlinear ultrasonic full-focusing imaging apparatus of claim 6, wherein, The method comprises a phase coherence weighting imaging optimization unit: An array element received signal phase calculation unit (111) is configured to calculate the phase of the even harmonic signal U of the nth array element n (t) performing Hilbert transform to obtain the phase angle of the signal A phase coherence factor calculation unit (151) is configured to calculate a phase coherence factor CCF(x, z, m) and a sign coherence factor SCF(x, z, m) of a virtual focus point in a result of the mth scanning; A phase coherence factor weighting unit (152) is configured to weight the primary second harmonic amplitude imaging matrix H(x, z, m) to obtain an optimized imaging matrix J(x, z, m).

8. An electronic device comprising a memory and a processor, characterized in that: The memory stores a computer program, and when the computer program is executed by the processor, the electronic device implements the method for precisely positioning a closed crack by nonlinear ultrasonic full-focus imaging according to any one of claims 1-5.

9. A computer readable storage medium having stored therein a computer program, characterized in that: The computer program, when executed by the computing device, causes the computing device to implement the method for precisely positioning a closed crack by nonlinear ultrasonic full-focus imaging according to any one of claims 1-5.

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