Concrete internal crack detection method based on ultrasonic plane wave imaging technology

Abstract

The invention discloses a concrete internal crack detection method based on an ultrasonic plane wave imaging technology. The method comprises the following steps: establishing a concrete internal simulation model; scanning and imaging the concrete internal simulation model by adopting plane waves with different deflection angles; determining crack detection angles corresponding to different plane wave deflection angles; determining the actual crack angle according to the different plane wave deflection angles and the corresponding crack detection angles; performing composite plane wave imaging by taking the actual angle of the crack as the center to obtain a concrete internal crack image; and calculating the crack length according to the concrete internal crack image. According to the method, the internal crack of the concrete can be accurately calculated. Compared with a traditional composite plane wave imaging method, the method has the advantages that the concrete internal crack detection precision is greatly improved, and a theoretical basis is provided for concrete internal crack refined detection.

Description

Technical Field

[0001] The present invention relates to the field of nondestructive testing of construction projects, and in particular to a method for detecting internal cracks in concrete based on ultrasonic plane wave imaging technology. Background Art

[0002] Currently, quantitative detection of cracks within concrete relies on various image processing methods to identify ultrasonic imaging results. This method analyzes the magnitude and distribution of pixel values ​​to determine the crack's quantitative detection, which is significantly affected by pixel quality. However, in actual detection, the crack's inclination angle is unknown, and the plane wave scanning angle is primarily selected based on empirical experience. Because the concrete mesostructure generates strong structural noise, improperly selected scanning angles can produce artifacts with high amplitudes in non-crack directions, seriously affecting the accuracy of quantitative crack detection.

[0003] Ultrasonic fully focused imaging methods receive weak energy from target planes in different directions and are significantly affected by concrete structure noise. This makes them ineffective for detecting inclined cracks, resulting in poor image contrast. Reverse time migration (RTM) uses cross-correlation between forward and reverse wavefields, demonstrating good detection of inclined cracks. However, this method requires high accuracy in the numerical model and significant computing resources, making it unsuitable for real-time on-site detection.

[0004] Although traditional composite plane wave imaging can improve the signal-to-noise ratio and contrast of defects, in this algorithm, when [0°, )( > When multi-angle pixel value superposition is performed with scanning angles in the range of ≥0°), the crack direction is taken as the center, [0°, ) produces artifacts with strong pixel values. When the pixel values ​​are superimposed at scanning angles within the range of ≤0°, the crack endpoint is taken as the center. , 180°+ ] range produces artifacts with strong amplitude. Only when = When the direction of the artifact is consistent with the crack direction, the traditional composite plane wave imaging method will detect inclined cracks in concrete, and the error between the crack detection angle and the actual angle will be large, which will affect the accurate detection of the crack length. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the present invention provides a method for detecting internal cracks in concrete based on ultrasonic plane wave imaging technology, which solves the problem that the prior art is greatly affected by the concrete microstructure and has low accuracy in detecting crack angles and lengths.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solution: a method for detecting internal cracks in concrete based on ultrasonic plane wave imaging technology, comprising: Establish a concrete interior simulation model; Plane waves with different deflection angles are used to scan and image the concrete internal simulation model; Determine the crack detection angle corresponding to different plane wave deflection angles; Determine the actual angle of the crack based on different plane wave deflection angles and their corresponding crack detection angles; Composite plane wave imaging is performed with the actual crack angle as the center to obtain the crack image inside the concrete; Calculate the crack length based on the crack image inside the concrete.

[0007] The beneficial effects of the present invention are: 1. By adopting multi-angle plane wave scanning imaging, signals are transmitted and received from multiple angles, which can reduce blind spots in the imaging process, help to more accurately locate the characteristics of the target, avoid ignoring edges and corners, increase the accumulation of effective signals, improve image quality, achieve full coverage of the detection target, and provide more comprehensive image information for concrete crack detection.

[0008] 2. By adopting different identification methods to determine the final actual angle of the crack, and combining the results of multiple detection methods, they can verify and complement each other. At the same time, they can more accurately determine the actual position and direction of the crack, reduce the error that may be caused by a single perspective, and calculate a more accurate crack detection angle, providing a reliable basis for the subsequent determination of the actual angle of the crack, greatly improving the accuracy of concrete internal crack detection, and providing a theoretical basis for the refined detection of concrete internal cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A flowchart of a method for detecting internal cracks in concrete based on ultrasonic plane wave imaging technology is provided in an embodiment; Figure 2 Schematic diagram of the concrete interior simulation model; Figure 3 Schematic diagram of target coverage under a single plane wave deflection angle; Figure 4 Schematic diagram of the bwlabel function 8-element connectivity rule identification method; Figure 5 This is a comparison chart of ultrasonic images generated by the method provided by the present invention and the traditional method. DETAILED DESCRIPTION

[0010] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0011] like Figure 1 As shown, in one embodiment of the present invention, a method for detecting internal cracks in concrete based on ultrasonic plane wave imaging technology includes the following steps: S1. Establish a concrete internal simulation model; like Figure 2 As shown in the figure, the detection signal uses a Ricker wavelet with a center frequency of 100 kHz. A total of 16 array elements are set with an array element spacing of 10 mm. From left to right, all 16 array elements receive and form the original fully focused data. In order to avoid numerical dispersion, the sampling interval is set to 5×10 -7 s, the maximum grid size is 2 mm, the crack length is set to 60 mm, and the coordinates of the center of the inclined crack are (340, 150).

[0012] S2, using plane waves with different deflection angles to scan and image the concrete internal simulation model, and obtaining scanning images corresponding to different plane wave deflection angles; S3, determining crack detection angles corresponding to different plane wave deflection angles; S3-1. Determine the target coverage under a single plane wave deflection angle. The coverage area is as follows: Figure 3 As shown, its calculation expression is:

[0013] in, is the coordinate of the first excitation element (the first excitation element refers to the first unit in the array probe to be excited during ultrasonic plane scanning. The ultrasonic imaging system realizes beam formation and scanning by controlling the delay time of different units. Specifically, by changing the relative delay of each excitation electrical signal, the position of the transmitted beam can be changed, thereby realizing scanning in different directions. The first excitation element is the starting point of this process, which determines the starting position and direction of the beam scan. For example, in linear scanning, the first excitation element is usually located at one end of the array, and then the adjacent units are excited in turn to form a linear scanning path. In phased array scanning, the direction of the beam can be changed by controlling the excitation time difference of each unit, thereby covering a wider scanning range). is the coordinate of the target scattering point, is the plane wave deflection angle, represents the tangent function, For the N The coordinates of the receiving array elements; S3-2. Create a single angle detection area matrix, the expression of which is:

[0014] in, is the single angle detection area matrix; S3-3. Correct the detection area and obtain the corrected single-angle pixel matrix of the detection area. The expression is:

[0015] in, is the single angle pixel matrix after correction of the detection area, N is the number of receiving array elements, j is the receiving element index, The deflection angle is Time j The echo signal received by the receiving array elements is It means that the plane wave propagates to the target scattering point and is j The flight time consumed by each receiving element; S3-4, normalizing the corrected single-angle pixel matrix of the detection area; S3-5, using the bwlabel function to label the connected regions in the normalized single-angle pixel matrix to obtain a labeled detection region matrix; like Figure 4 As shown, when marking, the elements with pixel values ​​greater than 0.5 are marked as 1, and the rest are marked as 0. After marking the connected area, the detection area matrix is ​​recorded as , the identification unit matrix is IE ; S3-6, identifying the local crack area in the detection area matrix after marking; S3-7. The local crack area is identified by linear fitting method, principal component analysis method and maximum length search method respectively to obtain the crack detection angle.

[0016] Among them, the linear fitting method uses the least squares method to calculate the crack detection angle, and its expression is:

[0017]

[0018]

[0019] in, is the crack detection angle obtained by linear fitting method, represents the inverse tangent function, represents the slope of the linear fitting line, is the number of elements in the local crack region, is the index of the element in the local crack region, The local crack area The coordinates of the elements, b is the intercept of the linear fitting line, is the average value of the horizontal coordinates of all elements in the local crack area.

[0020] The specific method of obtaining the crack detection angle using principal component analysis is as follows: A. Obtain the coordinate set matrix of the local crack area X , whose expression is:

[0021] B. The matrix X Subtract the average value of the local crack area coordinates and center it. The expression is:

[0022] in, is the centered coordinate set matrix, is the average value of the ordinates of all elements in the local crack area; C. Calculate the principal component direction, matrix The eigenvector corresponding to the maximum eigenvalue of is the principal component direction, and its expression is:

[0023] Where, the superscript T represents the transpose of the matrix. is the principal component direction, is the maximum eigenvalue; D. Calculate the crack detection angle based on the two components of the principal component direction:

[0024] in, represents the crack detection angle obtained by principal component analysis, 、 The two components are the principal component directions.

[0025] The specific method of obtaining the crack detection angle using the maximum length fitting method is: I. Extract the horizontal and vertical coordinates corresponding to the maximum pixel point in the local crack area ; II. Calculate the projection lines at different trial angles. The expression is:

[0026]

[0027] in, The trial angle is The ordinate of a point on the projection line of The trial angle is The horizontal coordinate of a point on the projection line of The trial angle is The intercept of the projected line; III. Calculate the projection length at different trial angles. The expression is:

[0028] in, The trial angle is The projection length under The local crack area is at the test angle of The maximum coordinate on the projection line of The local crack area is at the test angle of The minimum coordinate on the projection line of ; IV. Calculate the crack detection angle based on the projection length at different test angles. The expression is:

[0029] in, is the crack detection angle obtained by the maximum length fitting method, Indicates the value when the projection length is maximum.

[0030] S4. determining the actual angle of the crack according to different plane wave deflection angles and their corresponding crack detection angles; The absolute distances between the different plane wave deflection angles obtained by the linear fitting method, principal component analysis method, and maximum length search method and the corresponding crack detection angles are calculated respectively. When the absolute distance is the smallest, the crack detection angle at this time is set as the actual crack angle, and its expression is:

[0031] in, is the actual angle of the crack, represents the crack detection angle calculated by any method when the absolute distance is minimum, Indicates the absolute value. Indicates the value when the absolute distance is minimum.

[0032] S5. Perform composite plane wave imaging with the actual crack angle as the center to obtain an image of the crack inside the concrete; This embodiment uses The center is set as the pixel, the spacing is set to 1° for composite plane wave imaging, the number of single deflections is C, and the value of C is 15. This multi-angle pixel superposition method can improve the problem of artifacts in the crack direction and avoid the problem of inaccurate crack length detection.

[0033] S6. Calculate the crack length based on the image of the crack inside the concrete: S6-1. Calculate the projection line of the actual angle of the crack. The expression is:

[0034]

[0035] in, is the equation of the projection line of the actual angle of the crack (it can also be expressed as the ordinate of a point on the projection line of the actual angle of the crack), Indicates the horizontal coordinate of a point on the projection line of the actual angle direction of the crack. is the intercept of the projection line of the actual angle direction of the crack, are the horizontal and vertical coordinates corresponding to the maximum pixel value of the crack area in the concrete internal crack image obtained by composite plane wave imaging with the actual crack angle as the center, is the maximum pixel value of the crack area in the concrete internal crack image obtained by composite plane wave imaging with the actual crack angle as the center; S6-2. Calculate the crack length using the expression:

[0036] in, is the crack length, is the maximum coordinate of the crack area on the projection line of the actual crack angle in the concrete internal crack image obtained by composite plane wave imaging with the actual crack angle as the center, It is the minimum coordinate of the crack area on the projection line of the actual crack angle in the concrete internal crack image obtained by composite plane wave imaging with the actual crack angle as the center.

[0037] In order to verify the effectiveness and outstanding effect of the method proposed in the present invention, this embodiment takes a crack with a length of 60 mm and a crack angle of 9.6° and 20° as an example, and uses the traditional composite plane wave imaging technology and the method proposed in the present invention to perform crack detection tests. The angle scanning range is -30° to 30°, and the scanning interval is 1°. The generated ultrasonic image comparison is shown in the figure below. Figure 5 As shown. Figure 5 It can be seen that the crack angle detection error of the composite plane wave imaging method is larger than that of the improved method proposed in the present invention.

[0038] In summary, the present invention can more accurately calculate internal cracks in concrete. Compared with the traditional composite plane wave imaging method, it greatly improves the accuracy of internal crack detection in concrete and provides a theoretical basis for refined detection of internal cracks in concrete.

Claims

1. A method for detecting internal cracks in concrete based on ultrasonic plane wave imaging technology, characterized in that: include: Establish a concrete interior simulation model; Plane waves with different deflection angles are used to scan and image the concrete internal simulation model; Determine the crack detection angle corresponding to different plane wave deflection angles; Determine the actual angle of the crack based on different plane wave deflection angles and their corresponding crack detection angles; Composite plane wave imaging is performed with the actual crack angle as the center to obtain the crack image inside the concrete; Calculate the crack length based on the crack image inside the concrete.

2. The method according to claim 1, characterized in that The specific method for determining the crack detection angle corresponding to the plane wave deflection angle is: Determine the target coverage under a single plane wave deflection angle, and its expression is: in, is the coordinate of the first excitation element, is the coordinate of the target scattering point, is the plane wave deflection angle, represents the tangent function, For the N The coordinates of the receiving array elements; Create a single angle detection area matrix, the expression is: in, is the single angle detection area matrix; Correct the detection area and obtain the corrected single-angle pixel matrix of the detection area. The expression is: in, is the single angle pixel matrix after correction of the detection area, N is the number of receiving array elements, j is the receiving element index, The deflection angle is Time j The echo signal received by the receiving array elements is It means that the plane wave propagates to the target scattering point and is j The flight time consumed by each receiving element; Normalize the single-angle pixel matrix after correction of the detection area; The bwlabel function is used to mark the connected areas in the normalized single-angle pixel matrix to obtain the marked detection area matrix; identifying local crack regions in the marked detection region matrix; The linear fitting method, principal component analysis method and maximum length search method are used to identify cracks in the local crack area and obtain the crack detection angle.

3. The method according to claim 2, characterized in that The linear fitting method uses the least squares method to calculate the crack detection angle, and its expression is: in, is the crack detection angle obtained by linear fitting method, represents the inverse tangent function, represents the slope of the linear fitting line, is the number of elements in the local crack region, is the index of the element in the local crack region, The local crack area The coordinates of the elements, is the average value of the horizontal coordinates of all elements in the local crack area.

4. The method according to claim 2, characterized in that The specific method of obtaining the crack detection angle using principal component analysis is as follows: Get the coordinate set matrix of the local crack area X , whose expression is: The matrix X Subtract the average value of the local crack area coordinates and center it. The expression is: in, is the centered coordinate set matrix, is the average value of the ordinates of all elements in the local crack area; Calculate the principal component direction, the expression is: Where, the superscript T represents the transpose of the matrix. is the principal component direction, is the maximum eigenvalue; Calculate the crack detection angle based on the two components of the principal component direction: in, represents the crack detection angle obtained by principal component analysis, 、 The two components are the principal component directions.

5. The method according to claim 2, characterized in that The specific method of obtaining the crack detection angle using the maximum length fitting method is: Extract the horizontal and vertical coordinates corresponding to the maximum pixel point in the local crack area ; Calculate the projection line of different trial angles, the expression is: in, The trial angle is The ordinate of a point on the projection line of The trial angle is The horizontal coordinate of a point on the projection line of The trial angle is The intercept of the projected line; Calculate the projection length at different trial angles, the expression is: in, The trial angle is The projection length under The local crack area is at the test angle of The maximum coordinate on the projection line of The local crack area is at the test angle of The minimum coordinate on the projection line of ; The crack detection angle is calculated based on the projection length at different test angles, and its expression is: in, is the crack detection angle obtained by the maximum length fitting method, Indicates the value when the projection length is maximum.

6. The method according to claim 2, characterized in that The specific method for determining the actual crack angle based on different plane wave deflection angles and their corresponding crack detection angles is as follows: The absolute distances between the different plane wave deflection angles obtained by the linear fitting method, principal component analysis method, and maximum length search method and the corresponding crack detection angles are calculated respectively. When the absolute distance is the smallest, the crack detection angle at this time is set as the actual crack angle, and its expression is: in, is the actual angle of the crack, represents the crack detection angle calculated by any method when the absolute distance is minimum, Indicates the absolute value. Indicates the value when the absolute distance is minimum.

7. The method according to claim 6, characterized in that The specific method for calculating the crack length is: The projection line to calculate the actual angle of the crack is expressed as: in, is the equation of the projection line in the actual angle direction of the crack, is the horizontal coordinate of a point on the projection line of the actual angle direction of the crack, is the intercept of the projection line of the actual angle direction of the crack, is the coordinate corresponding to the maximum pixel value of the crack area in composite plane wave imaging; Calculate the crack length, the expression is: in, is the crack length, For composite plane wave imaging of crack region on the straight line The maximum coordinate of the projection on For composite plane wave imaging of crack region on the straight line The minimum coordinate of the projection.

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