A method for imaging and detecting unknown irregular defects based on triple array signals

Abstract

The application discloses a kind of unknown irregular defect imaging detection methods based on triple array signal, belong to nondestructive testing technical field.Adopt by phased array ultrasonic detector, scanner, two identical phased array probes and matching wedge constitute detection system;Two phased array probes are connected scanner, symmetrically placed in the two sides of the region to be detected, independently move probe and obtain full matrix data with strong defect response in three signal acquisition modes;For each reconstruction point, 7 mode waves are screened to implement delay stacking composite imaging;The maximum and minimum amplitude of each reconstruction point in three groups of composite images are extracted for normalization processing, for each reconstruction point, higher amplitude in three normalization images is selected as the final amplitude of the point, thereby realizing the profile reconstruction and imaging representation of prior unknown irregular defect.The method can intuitively identify defect characteristics, and has higher quantitative accuracy, and has good engineering application prospect.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology and relates to an imaging detection method for unknown irregular defects based on triple array signals. Background Technology

[0002] Area-type defects, exemplified by cracks, have sharp endpoints and high stress concentrations, making them prone to propagation and ultimately leading to component fracture. They represent one of the most dangerous types of defects in engineering. Non-destructive testing (NDT) can detect defects without damaging the object being tested and perform quantitative characterization, aiding in the assessment of structural performance and remaining life. Among existing NDT methods, radiographic testing is insensitive to area-type defects and struggles to provide information on defect depth. In contrast, ultrasonic testing offers higher sensitivity and penetration, a wider detection range, and is more suitable for the detection and quantification of area-type defects.

[0003] With the development of ultrasonic imaging detection technology, the ability to characterize area-type defects has been continuously improved. Full-focusing methods and synthetic aperture focusing techniques perform time-delay superposition processing on array ultrasonic signals acquired by phased array ultrasonic probes, achieving point-by-point focusing within the detection range, thereby obtaining images with higher resolution. However, when using conventional phased arrays and full-focusing methods to detect prior unknown defects, the ultrasonic imaging results often only provide information about the defect endpoints, leading to misjudgments of defect type and quantity. To achieve accurate identification of area-type defect features, some signal post-processing techniques based on full-matrix capture data have been developed. By considering the orientation changes of area-type defects, the multi-mode full-focusing method can be applied to reconstruct the defect contour using mode waves under different acoustic beam paths; however, the selection of mode waves depends on certain prior defect information (Jin SJ, et al. Comparison of morphology characterization for regular cracks with multi-mode total focusing method. Far East NDT New Technology & Application Forum 2019. Qingdao, China). Based on this, selecting the strongest energy signal from different mode waves for composite processing helps to obtain the contour features of previously unknown area defects (Jin SJ, Liu CF, Shi SQ, Lin L, Luo ZB. Profile reconstruction and quantitative detection of planar defects with composite-mode total focusing method (CTFM). NDT&E Int 2021; 123:102518).

[0004] The aforementioned studies all focused on regular area-type defects. However, natural defects formed in actual components are complex and random in shape, exhibiting multifaceted characteristics, with the orientation of their branching surfaces varying within the range of -90° to 90°. After a single full-matrix data acquisition and direct summation of different mode waves, the branching characteristics and expansion trends of irregular defects can be roughly determined, but the contour reconstruction results are incomplete (Han XL, et al. Combination of direct, half-skip and full-skip TFM to characterize multi-faceted crack. 2015 IEEE International Ultrasonics Symposium Proceedings). Matched filtering further considers factors such as beam directivity, medium scattering, and diffusion attenuation, providing a statistical analysis model that fuses 21 modes, which helps to reconstruct the contours of unknown stress corrosion defects (Bevan RLT, Budyn N, Zhang J, Croxford AJ, Kitazawa S, Wilcox PD. Datafusion of multiview ultrasonic imaging for characterization of large defects. IEEE Trans on Ultrason Ferroelectr Freq Control 2020; 67(11):2387-2401). However, the above methods all acquire FMC data at a single location, which often makes it difficult to simultaneously acquire strong reflection signals from multiple surfaces of irregular natural defects, especially for approximately horizontal defect branch surfaces, where surface reflection waves cannot be obtained for imaging, resulting in incomplete defect contour reconstruction and reduced quantitative accuracy. Therefore, it is necessary to develop a contour reconstruction and imaging detection method suitable for prior unknown irregular defects to achieve defect property identification and accurate quantification and localization. Summary of the Invention

[0005] This invention provides an imaging detection method for unknown irregular defects based on triple array signals. The purpose is to address the difficulty in imaging and reconstructing the contours of prior unknown irregular defects with arbitrary orientation branch surfaces. Two phased array probes are connected to a scanner and symmetrically arranged on both sides of the area to be detected, forming different transmit and receive modes to acquire three sets of array signals. Through single-set array signal composite imaging, normalization processing, and triple normalized image fusion, the complete contour reconstruction and imaging detection of unknown irregular defects can be achieved.

[0006] The technical solution adopted in this invention is as follows:

[0007] An imaging detection method for unknown irregular defects based on triple array signals employs a detection system consisting of a phased array ultrasonic detector, a scanner, two identical phased array probes, and matching wedges. The two phased array probes are connected to the scanner and symmetrically arranged on both sides of the area to be detected, forming three sets of array signals in different transmit / receive modes. For each set of array signals, seven mode waves are selected based on the directivity of the mode waves to perform composite imaging. Based on this, the composite images are normalized using their respective maximum and minimum amplitude values. Finally, for each reconstruction point in the area to be detected, the higher amplitude value in the triple normalized image is selected as the final reconstruction amplitude for that point, thereby achieving contour reconstruction and imaging detection of the previously unknown irregular defect. The method comprises the following steps:

[0008] (a) Determination of detection parameters

[0009] Based on the material, shape, and size information of the test block, select a pair of phased array probes with identical center frequencies and array elements, as well as a pair of identical angle wedges;

[0010] (b) Acquisition of two sets of full matrix signals

[0011] Connect the phased array probe, angle wedge, and phased array ultrasonic testing instrument selected in step (a). Two phased array probes are connected to the scanner and symmetrically placed on both sides of the area to be tested, ensuring that the active axes of the phased array probes are in opposite directions. Move the two phased array probes independently to determine the acquisition positions with strong defect signal responses. Then, fix the phased array probes on the scanner to obtain a clear phased array probe spacing and their relative positions to the imaging area. Acquire full matrix data using the center of the defined imaging area as the reference point. The two phased array probes form three different array signal transmission and reception modes: self-transmitting and self-receiving mode for the left probe, self-transmitting and self-receiving mode for the right probe, and a one-transmitting and one-receiving mode for both probes. When both phased array probes have n array elements, three sets of full matrix data containing n² A-scan signals are acquired.

[0012] (c) Reconstructing the regional grid

[0013] A rectangular coordinate system is established, with the interface between the angle wedge and the test block as the x-axis, the projection point of the first element of the probe on the left test block as the origin, the direction from the lower end face to the upper end face of the angle wedge as the positive x-axis, and the depth direction of the test block as the positive y-axis. The detection area is divided into M×N rectangular grids, where M and N are the number of grid nodes in the horizontal and vertical directions, respectively. Each grid node is defined as an image reconstruction point, and the coordinates of any reconstruction point P are (a, b).

[0014] (d) Composite imaging of mode delay superposition and single array signal

[0015] For the self-transmitting and self-receiving mode of the phased array probe on the left side of the area to be detected, when the transmitting element i, the receiving element j, and the reconstruction point P are determined, a total of 21 different mode waves are generated, including 3 direct modes, 8 half-span modes, and 10 full-span modes. For the k-th mode wave, 1≤k≤21, the delayed superimposed imaging amplitude I at point P is... k (a,b) is given by equation (1);

[0016]

[0017] In the formula, A ij () represents the A-scan signal transmitted by the i-th array element and received by the j-th array element, t ij-k (a,b) represents the time taken for the k-th mode wave in the excitation signal of the i-th array element to propagate to point P and be received by the j-th array element;

[0018] The propagation time at point P varies for different wave modes. The corresponding time t is determined using Fermat's law and the coordinates of the transmitting and receiving array elements. ij-k When imaging with a single array signal, considering the repetition of the directivity of the mode waves and to reduce artifacts after delay superposition, for any reconstructed point P in the inspected area, only the strongest response signal among the seven mode waves (TT, LL, LT, TLT, TTT, LTT, TTL) is selected as the reconstructed amplitude I. l (a,b), where L represents longitudinal wave and T represents transverse wave;

[0019]

[0020] Similarly, when the self-transmitting and self-receiving mode of the right phased array probe is obtained, the reconstructed amplitude I at point P is... r (a,b), and the reconstructed amplitude I at point P in the one-to-one transmission and one-to-reception mode. lr (a,b);

[0021]

[0022]

[0023] (e) Normalization and triple image fusion

[0024] Based on this, for the images after the composite imaging of the triple array signals, the maximum and minimum values ​​of each reconstructed amplitude are extracted, and based on these values, minimum-maximum normalization processing is performed to normalize the amplitude of each reconstructed point in the same imaging area to the 0-1 interval.

[0025]

[0026] In the formula, G norm It is the normalized amplitude, G maxThe maximum value, G min It is the minimum amplitude;

[0027] By normalizing using equation (5), the normalized amplitude of the same reconstruction point P(a,b) is obtained respectively. and Then, the highest value among the three is taken as the reconstructed amplitude I of the triple array signal fusion image. p (a,b);

[0028]

[0029] (f) Qualitative and quantitative detection of defects

[0030] Repeat steps (d)-(e) to perform mode wave delay superposition, single array signal composite, normalization processing and triple array signal fusion imaging on the reconstructed area point by point, so as to obtain the contour reconstruction image of the unknown irregular defect and perform qualitative identification; finally, the -6dB method is used to quantify the depth, size and tilt angle of the defect.

[0031] The beneficial effects of this invention are as follows: The imaging detection method for unknown irregular defects based on triple array signals of this invention considers the multifaceted characteristics of natural defects. It utilizes a pair of phased array probes to independently acquire three sets of full-matrix data with strong defect signal responses on both sides of the area to be detected. Mode filtering, single-set array signal fusion, and normalized triple array signal fusion imaging are then performed to achieve contour reconstruction and quantitative detection of prior unknown defects. This method can present the characteristics of prior unknown irregular defects and can also perform complete contour reconstruction of regular area and volume defects, making it widely applicable. Furthermore, this method can be integrated into phased array ultrasonic testing instruments, demonstrating significant application prospects and promotional value. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the ultrasonic testing system used.

[0033] Figure 2 It is a drawing of an aluminum alloy test block with irregular root defects.

[0034] Figure 3 These are composite imaging results of a single array of signals for irregular defects. Among them, (a) is the self-transmitting and self-receiving mode of the left probe, (b) is the self-transmitting and self-receiving mode of the right probe, and (c) is the one-transmitting and one-receiving mode of the probe.

[0035] Figure 4 It is the result of composite imaging of triple array signals with irregular defects. Detailed Implementation

[0036] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0037] An imaging detection method for unknown irregular defects based on triple array signals, employing an ultrasonic testing system such as... Figure 1 As shown, this includes a phased array ultrasonic testing instrument, a scanner, a phased array probe, and a tilted plexiglass wedge. The specific testing and processing steps are as follows:

[0038] (a) The test block is an aluminum alloy block with a thickness of 25 mm. An irregular defect is machined on the bottom of the test block, consisting of two branches, each 4 mm long and with different orientations. The lower branch has an angle of 0°, and the upper branch has an angle of 45°, as shown below. Figure 2 As shown.

[0039] (b) Using a phased array ultrasonic testing instrument, two sets of 32-element phased array probes with a center frequency of 5MHz are used in conjunction with 45° wedges to detect defects. The sampling frequency is 100MHz, the longitudinal wave velocity of the wedge is 2330m / s, the transverse wave velocity of the aluminum alloy test block is 3100m / s, and the longitudinal wave velocity is 6300m / s.

[0040] (c) Using the full matrix capture function of the phased array ultrasonic testing instrument, array signals are acquired from both sides of the area to be inspected in three modes to obtain an A-scan signal matrix with strong defect response.

[0041] (d) Establish a rectangular coordinate system and divide the detection area into 100×100 rectangular grids. For each grid point in the area to be detected, calculate the propagation path and acoustic time of seven different modes of waves between each group of transmitting and receiving array elements under each signal acquisition mode.

[0042] (e) Figure 3 The results of composite imaging of single array signals for irregular defects are presented. Clearly, it is difficult to reconstruct the complete outline of the irregular defect in any of the three modes, which is detrimental to the accurate identification and quantitative detection of the defect's properties.

[0043] (f) Perform min-max normalization on the composite image of a single array signal, and then perform triple array signal composite imaging to obtain the following result: Figure 4 The image shown shows that the outline of the irregular defect has been completely reconstructed. Furthermore, calculations show that the upper branch length is 4.16 mm with an orientation angle of 46.64°, and the lower branch length is 3.98 mm with an orientation angle of 0.05°; all errors are within acceptable limits.

[0044] In summary, the method of the present invention achieves contour reconstruction and imaging detection of irregular area defects with small quantitative and positioning errors, meeting engineering requirements.

[0045] The descriptions of the exemplary embodiments presented above are merely illustrative of the technical solutions of the present invention and are not intended to be exhaustive or to limit the invention to the precise forms described. Obviously, those skilled in the art can make many changes and variations based on the above teachings. The exemplary embodiments were chosen and described to explain the specific principles of the invention and its practical applications, thereby enabling other those skilled in the art to understand, implement, and utilize the various exemplary embodiments of the invention and their various alternatives and modifications. The scope of protection of the present invention is intended to be defined by the appended claims and their equivalents.

Claims

1. A method for imaging and detecting unknown irregular defects based on triple array signals, characterized in that, A detection system consisting of a phased array ultrasonic detector, a scanner, two identical phased array probes, and an angle wedge is employed. The two phased array probes are connected to the scanner and symmetrically arranged on both sides of the area to be inspected, forming three sets of array signals in different transmit / receive modes. For each set of array signals, seven mode waves are selected based on the directivity of the mode waves to perform composite imaging. Based on this, the composite images are normalized using their respective maximum and minimum amplitude values. Finally, for each reconstruction point in the area to be inspected, the highest amplitude in the triple-normalized image is selected as the final reconstruction amplitude for that point, thereby achieving contour reconstruction and imaging detection of previously unknown irregular defects. The method employs the following steps: (a) Determination of detection parameters Based on the material, shape, and size information of the test block, select a pair of phased array probes with identical center frequencies and array elements, as well as a pair of identical angle wedges; (b) Acquisition of two sets of full matrix signals Connect the phased array probe, angle wedge, and phased array ultrasonic testing instrument selected in step (a). Two phased array probes are connected to the scanner and symmetrically placed on both sides of the area to be tested, ensuring that the active axes of the phased array probes are in opposite directions. Move the two phased array probes independently to determine the acquisition positions with defect signal responses. Then, fix the phased array probes on the scanner to obtain a clear phased array probe spacing and their relative positions to the imaging area. Acquire full matrix data using the center of the defined imaging area as the reference point. The two phased array probes form three different array signal transmission and reception modes: self-transmitting and self-receiving mode for the left phased array probe, self-transmitting and self-receiving mode for the right phased array probe, and a one-transmitting and one-receiving mode for both probes. When the number of array elements of both phased array probes is... n At that time, a total of three groups containing n 2 Full matrix data of each A-scan signal; (c) Reconstructing the regional grid Establish a rectangular coordinate system, with the interface between the angle wedge and the test block as the coordinate system. x Axis, let the first element of the phased array probe on the left side of the test block be in x The projection point of the axis is the origin, and the direction from the lower end face to the upper end face of the angle wedge is... x The positive axis and the depth direction of the test block are... y Establish a coordinate system along the positive axis and divide the area to be detected into... M × N A rectangular grid, in which M and N These represent the number of grid nodes in the horizontal and vertical directions, respectively; each grid node is defined as an image reconstruction point, and the coordinates of any reconstruction point P are ( a , b ); (d) Composite imaging of mode wave delay superposition and single array signal For the self-transmitting and self-receiving mode of the phased array probe on the left side of the area to be detected, in the transmitting array element i Receiver array element j When the reconstruction point P is determined, a total of 21 different mode waves are generated, including 3 direct modes, 8 half-span modes, and 10 full-span modes. For the first... k Type of wave, 1≤ k ≤21, the amplitude of the time-delayed superimposed image at point P. I k ( a , b The result is given by equation (1); (1) In the formula, A ij () is the first i Each array element is emitted, the first... j The A-scan signal received by each array element t ij-k ( a , b ) indicates the first i The excitation signal of each array element is the first k After the wave propagates to point P, it is... j The time taken for each array element to receive; The propagation time at point P varies for different wave modes. This time is determined by Fermat's principle and the coordinates of the transmitting and receiving array elements. t ij-k When imaging with a single array signal, considering the repetition of the directivity of the mode waves and to reduce artifacts after delay superposition, for any reconstruction point P in the detection area, only the strongest response signal among the seven mode waves (TT, LL, LT, TLT, TTT, LTT, TTL) is selected as the reconstruction amplitude. I l ( a, b ), where L represents longitudinal wave and T represents transverse wave; (2) Similarly, when the self-transmitting and self-receiving mode of the right phased array probe is obtained, the reconstructed amplitude at point P is... I r ( a, b ), and in the one-transmit-one-receive mode, the reconstructed amplitude of point P. I lr ( a, b ); (3) (4) (e) Normalization and triple image fusion Based on this, for the images after the composite imaging of the triple array signals, the maximum and minimum values ​​of each reconstructed amplitude are extracted, and based on these values, minimum-maximum normalization processing is performed to normalize the amplitude of each reconstructed point in the same imaging area to the 0-1 interval. (5) In the formula, G norm It is the normalized amplitude. G max It is the maximum amplitude value. G min It is the minimum amplitude; Through the normalization process of equation (5), the same reconstruction point P( a , b Normalized amplitude - I l ( a, b ), - I r ( a, b )and - I lr ( a, b Then, the highest value among the three is taken as the reconstructed amplitude of the triple array signal fusion image. I p ( a, b ); (6) (f) Qualitative and quantitative detection of defects Repeat steps (d)-(e) to perform mode wave delay superposition, single array signal composite, normalization processing and triple array signal fusion imaging on the reconstructed area point by point, so as to obtain the contour reconstruction image of the unknown irregular defect and perform qualitative identification; finally, the -6dB method is used to quantify the depth, size and tilt angle of the defect.

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