Multi-point superposition three-dimensional imaging method based on impact echo method

Abstract

The invention discloses a multi-point superposition three-dimensional imaging method based on an impact echo method, which is applied to the technical field of nondestructive testing and comprises the following steps: acquiring a four-channel time domain signal of each measuring point in a detection area by using a four-channel sensor impact echo detection system; taking the center of the detection area as the center of the top surface, respectively constructing a concrete three-dimensional discrete model corresponding to the four channels for each detection point, dividing the concrete three-dimensional discrete model into uniform cubic grid units, and calculating resonant frequency; carrying out normalization processing on the four-channel time domain signals, carrying out fast Fourier transform to obtain a normalized frequency domain spectrum, extracting amplitudes of cubic grid units based on resonant frequency, and superposing amplitude matrixes of the four channels under the same measuring point to obtain a defect amplitude enhancement matrix of each measuring point; superposing the enhanced matrix to obtain a global intensity matrix, performing normalization processing, mapping the global intensity matrix to an HSV color space, and generating a three-dimensional energy density distribution model; and performing multi-dimensional slice analysis on the model. According to the invention, the defect identification precision of the impact echo method is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nondestructive testing, and particularly relates to a multi-point superposition three-dimensional imaging method based on the impact echo method. Background Art

[0002] In modern structural engineering, evaluating the service life of a structure is an important aspect related to safety. For on-site inspection technologies of concrete structures, it provides an important basis for engineers to implement quality control of new projects, evaluate the state of existing buildings, and make decisions on the repair of damaged structures. The impact echo method is currently widely used in defect detection, but there are limitations in signal processing. After performing a fast Fourier transform on the time-domain data to obtain the frequency-domain data, due to the interference of complex factors such as internal pores, steel bars, and the external environment in the concrete during data acquisition, various spurious peaks often appear in the spectrum, affecting the judgment of defect frequencies by inspectors. The current mainstream approach is to construct defect images based on the frequency domain. However, current research on defect visualization mostly focuses on two-dimensional imaging or planar tomography imaging technologies. Two-dimensional images can only reflect the local wave field characteristics of a certain cross-section of the structure, making it difficult to analyze the interaction mechanism between stress waves and defects in three-dimensional space, unable to accurately identify damage distributed vertically and axially symmetrically, and the evaluation of internal damage of the structure is not accurate enough. Therefore, it is necessary to extend the research on defect visualization to the three-dimensional level.

[0003] Therefore, how to provide a multi-point superposition three-dimensional imaging method based on the impact echo method that can effectively analyze the interaction mechanism between stress waves and defects in three-dimensional space, accurately identify damage distributed vertically and axially symmetrically, and achieve accurate evaluation of internal damage of the structure is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention proposes a multi-point superposition three-dimensional imaging method based on the impact echo method.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A multi-point superposition three-dimensional imaging method based on the impact echo method, comprising: Step 1: Using four acceleration sensors as corner points and the impact point as the center, construct a four-channel sensor impact echo detection system based on an equilateral side length rectangular array, and collect the four-channel time-domain signals of each measurement point in the detection area when it is used as the impact point; Step 2: Using the center of the detection area as the center of the top surface, construct four concrete three-dimensional discrete models corresponding to the four channels for each measurement point, divide them into uniform cubic grid units, and calculate the resonant frequency of each cubic grid unit; Step 3: Normalize the amplitudes in the four-channel time-domain signals and perform fast Fourier transform to obtain four groups of normalized frequency-domain spectra corresponding to the four-channel time-domain signals. Based on the resonant frequency, extract the amplitudes of each cubic grid cell from the normalized frequency-domain spectra to obtain the amplitude matrix corresponding to the four channels at each measurement point. Superimpose the amplitude matrices of the four channels at the same measurement point to obtain the defect amplitude enhancement matrix for each measurement point; Step 4: Superimpose the defect amplitude enhancement matrices at all measurement points to obtain the global intensity matrix. After normalizing the amplitudes in the global intensity matrix again, map them to the HSV color space to generate a three-dimensional energy density distribution model; Step 5: Perform multi-dimensional slicing analysis on the three-dimensional energy density distribution model to quantitatively analyze the defects.

[0006] Optionally, in Step 1, the detection area is a grid detection area arranged above the area with defects inside the concrete structure in the form of a grid; among them, the corner points of each grid are used as measurement points.

[0007] Optionally, in Step 2, taking the center of the detection area as the center of the top surface, construct four concrete three-dimensional discrete models corresponding to the four channels for each measurement point respectively, specifically: The side lengths of the top surface and the bottom surface of the concrete three-dimensional discrete model are the side length of the grid detection area plus a preset length, and the depth is the same as the actual thickness of the concrete structure.

[0008] Optionally, in Step 2, the side length of the cubic grid cell satisfies the Nyquist sampling criterion, specifically: Among them, is the side length of the cubic grid cell; is the propagation speed of the P-wave in the measured concrete; is the sampling time interval.

[0009] Optionally, in Step 2, calculate the resonant frequency of each cubic grid cell as follows: Among them, is the resonant frequency of the cubic grid cell with the center coordinate of in the three-dimensional concrete discrete model at the k-th measurement point and the i-th channel acquisition point, i = 1, 2, 3, 4, corresponding to the four-channel acceleration sensor; is the propagation speed of the P-wave in the measured concrete; is the Euclidean distance between the center of the cubic grid cell and the impact point at the k-th measurement point; is the Euclidean distance between the center of the cubic grid cell and the i-th channel acquisition point at the k-th measurement point.

[0010] Optionally, in step 3, based on the resonance frequency, the amplitude of each cubic grid cell is extracted from the normalized frequency-domain spectrum to obtain the amplitude matrix corresponding to the four channels under each measuring point, specifically as follows: Each measuring point has four normalized frequency-domain spectra, respectively corresponding to the four-channel time-domain signals of the measuring point; Each measuring point has four three-dimensional discrete models of concrete, which are respectively constructed based on the four channels under the measuring point; Each three-dimensional discrete model of concrete contains multiple cubic grid cells, and each cubic grid cell has a resonance frequency; For the amplitude of each cubic grid cell in the three-dimensional discrete model of concrete at each measuring point, according to the measuring point and the corresponding channel in the three-dimensional discrete model of concrete, the normalized frequency-domain spectrum corresponding to the time-domain signal of the channel under the measuring point is determined, and the amplitude of the cubic grid cell is extracted from the normalized frequency-domain spectrum to obtain the amplitude matrix corresponding to the four channels under each measuring point.

[0011] Optionally, in step 3, the amplitude matrices of the four channels under the same measuring point are superimposed to obtain the defect amplitude enhancement matrix of each measuring point, as follows: Among them, is the defect amplitude enhancement matrix of the kth measuring point; is the amplitude matrix of the th channel under the kth measuring point.

[0012] Optionally, in step 4, the defect amplitude enhancement matrices of all measuring points are superimposed to obtain the global intensity matrix, as follows: Among them, is the global intensity matrix; is the number of measuring points; is the defect amplitude enhancement matrix of the kth measuring point.

[0013] Optionally, in step 4, the amplitude elements after normalization are mapped to the HSV color space, specifically as follows: The amplitude elements after normalization are mapped to the HSV color space in the order of red - yellow - green - blue to represent the amplitude from high to low, as follows: Among them, is the amplitude element in the global intensity matrix.

[0014] Optionally, in step 5, multi-dimensional slicing analysis is performed on the three-dimensional energy density distribution model to quantitatively analyze the defects, specifically as follows: Perform orthogonal slicing on the three-dimensional energy density distribution model along the X, Y, and Z axes, and extract two-dimensional projections , , , and perform multi-dimensional analysis of the defect condition through the principle of tomography.

[0015] As can be seen from the above technical solutions, compared with the prior art, the present invention proposes a multi-point superposition three-dimensional imaging method based on the impact echo method. By synchronously collecting impact echo signals through multiple channels and combining frequency domain feature extraction and amplitude enhancement mechanisms, the expansion from traditional two-dimensional imaging to three-dimensional imaging is realized, so as to more intuitively and accurately present the distribution range and buried depth position of internal defects in concrete. At the same time, the generated three-dimensional model can intercept profiles along the orthogonal planes in the X, Y, and Z axis directions, realize multi-dimensional analysis of the defect condition, provide more comprehensive defect information compared with traditional two-dimensional images, effectively overcome the situation that traditional two-dimensional imaging only presents the projection of defects in one direction and has insufficient recognition of complex defects, and improve the recognition accuracy of the impact echo method for defects. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0017] Figure 1 It is a schematic flow chart of the method of the present invention.

[0018] Figure 2 It is a schematic diagram of the layout of the grid detection area of the present invention and the acquisition sequence of the impact echo detection system of the four-channel sensor rectangular array.

[0019] Figure 3 It is a schematic diagram of the structure of the three-dimensional discrete model of concrete of the present invention.

[0020] Figure 4 Taking the kth measurement point and the acquisition point of channel i = 1 as an example of the present invention, it is a schematic diagram of calculating the resonance frequency of each cubic grid unit and assigning an amplitude.

[0021] Figure 5 It is a schematic diagram of the formation principle of the "spherical effect" of the present invention.

[0022] Figure 6 It is a schematic diagram of the superposition of the defect amplitude enhancement matrix of the present invention.

[0023] Figure 7 It is a schematic diagram of extracting the profile of the three-dimensional imaging model of the present invention. Detailed implementation mode

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] Embodiment 1: Embodiment 1 of the present invention discloses a multi-point superposition three-dimensional imaging method based on the impact echo method, as Figure 1 shown, including: Step 1: With four acceleration sensors as the corner points and the impact point as the center, a four-channel sensor impact echo detection system based on an equilateral rectangle array is constructed. The entire system takes the center of the rectangle, that is, the impact point, as the moving base point, and collects the four-channel time-domain signals of each measurement point in the detection area when it serves as the impact point.

[0026] As Figure 2 shown, the detection area is a grid detection area arranged above the area with defects inside the concrete structure in the form of a grid, and this detection area is sufficient to cover the entire defect; among them, the corner points of each grid serve as measurement points. In the present invention, the size of each grid is 3 cm × 3 cm.

[0027] Specifically, based on the orthogonal grid layout criterion, a grid detection area with a size of N×M is arranged above the defect, and the center of the grid detection area is used as the origin to establish a rectangular coordinate system, and record the coordinates of the impact point each time data is collected for subsequent calculation.

[0028] When collecting data, the four-channel sensor rectangular array acquisition system takes the center of the rectangle, that is, the impact point, as the moving base point, places the impact point on the measurement point for impact echo detection, and samples in the order from measurement point 1 to measurement point n and from measurement line 1 to measurement line n. Taking the center of the detection area as the coordinate origin, according to the grid size information, record the coordinates of the impact point, that is, the measurement point and the acquisition point each time the impact echo is detected. Since the distance between the acquisition point and the impact point is fixed, the coordinates of the acquisition point can be calculated from the coordinates of the impact point.

[0029] The coordinates of each channel sensor node are determined through rigid geometric relationships, as follows: Among them, is the impact point coordinate, which is the same as the measurement point coordinate; is the side length of the rectangular array of four-channel acceleration sensors, which is taken as 4 cm in the present invention. During detection, the impact point is placed on the measurement point, and the impact point coordinates and the four-channel time-domain signals are recorded through the synchronous trigger device , ensuring spatio-temporal consistency.

[0030] Step 2: Taking the center of the detection area as the center of the top surface, four three-dimensional concrete discrete models corresponding to the four channels are constructed for each measurement point, and divided into uniform cubic grid cells, and the resonance frequency of each cubic grid cell is calculated; all discrete models will be used as empty matrices for subsequent storage of amplitudes.

[0031] Taking the center of the detection area as the center of the top surface, four three-dimensional concrete discrete models corresponding to the four channels are constructed for each measurement point, specifically: The side lengths of the top and bottom surfaces of the three-dimensional concrete discrete model are the side length of the grid detection area plus a preset length, which is taken as 5 cm in the present invention, and the depth is the same as the actual thickness H of the concrete structure.

[0032] The side length of the cubic grid cell satisfies the Nyquist sampling criterion, specifically: wherein, is the side length of the cubic grid cell; is the propagation speed of the P-wave in the measured concrete; is the sampling time interval. Considering that the propagation speed of the P-wave in common concrete is approximately 4000 m / s, is usually taken as 2 μs, so , taking designed as 4 mm can meet the needs of most projects.

[0033] The present invention discretizes the concrete into numerous cube grid cells by using an imaging algorithm, aiming to design an empty matrix for storing the amplitudes extracted from the corresponding frequency-domain data of each grid cell. Each cubic grid cell is denoted as , Define the empty matrix (k is the measurement point number, i is the acquisition point number, is the center coordinate of the cubic grid, is the cubic grid cell with the center coordinate of in the three-dimensional concrete discrete model of the i-th acquisition point under the k-th measurement point; is the local zero matrix of the i-th acquisition point under the k-th measurement point composed of zero elements at , and each contains elements), which are used to calculate the resonant frequency and store the relevant amplitude in the subsequent steps, and perform matrix superposition.

[0034] Based on the coordinates of each impact point , and the corresponding four-channel acquisition point coordinates , calculate each cubic grid cell in different three-dimensional discrete models Resonant frequency ,as follows: in, The center coordinates of the 3D concrete discrete model of the i-th channel collection point at the k-th measurement point are The resonant frequencies of the cubic grid cells, i = 1, 2, 3, 4, correspond to the four-channel accelerometer; is the propagation velocity of the P wave in the concrete being tested; is the Euclidean distance between the center of the cube grid unit and the impact point at the kth measurement point; is the Euclidean distance between the center of the cube grid unit and the collection point of the i-th channel at the k-th measurement point.

[0035] like Figure 4 As shown, taking the kth measuring point, i=1 channel acquisition point as an example, based on the impact point coordinates , and the corresponding acquisition point coordinates of channel i=1 , calculate each cube grid unit The resonant frequency of channel i=1 .

[0036] Step 3: Normalize the four-channel time domain signal The amplitude in the four-channel time domain signal is obtained by fast Fourier transform to obtain four sets of normalized frequency domain spectra corresponding to the four-channel time domain signal. (Each measurement point has four sets of normalized frequency domain spectra corresponding to its four-channel time domain signals), based on the resonant frequency , the amplitude of each cubic grid unit is extracted from the normalized frequency domain spectrum to obtain the amplitude matrix corresponding to the four channels at each measuring point. The amplitude matrices of the four channels at the same measuring point are superimposed to obtain the defect amplitude enhancement matrix of each measuring point.

[0037] Based on the resonant frequency, the amplitude of each cubic grid unit is extracted from the normalized frequency domain spectrum, and the amplitude matrix corresponding to the four channels at each measurement point is obtained, specifically: Each measurement point has four normalized frequency domain spectra, corresponding to the four-channel time domain signals of the measurement point; Each measuring point has four concrete three-dimensional discrete models, which are constructed based on the four channels under the measuring point; Each concrete three-dimensional discrete model contains a plurality of cubic grid units, and each cubic grid unit has a resonant frequency; For the amplitude of each cubic grid unit in the concrete 3D discrete model at each measuring point, the normalized frequency domain spectrum corresponding to the time domain signal of the channel at the measuring point is determined according to the measuring point and the corresponding channel in the concrete 3D discrete model. The amplitude of the cubic grid unit is extracted from the normalized frequency domain spectrum to obtain the amplitude matrix corresponding to the four channels at each measuring point.

[0038] like Figure 4 As shown, at the kth measurement point, the collection point of channel i=1 For example, the resonant frequency of each cubic grid unit in the three-dimensional discrete model of the i=1 channel acquisition point is calculated. Then, from the normalized frequency domain spectrum Extract the resonant frequency Matched amplitude , and assigned to the corresponding cubic grid cells . Assign these magnitudes to the zero matrix In this way, we can get the amplitude matrix of i=1 at the kth measurement point, and based on this process, we can get the amplitude matrices of the other three i=2, 3, and 4 channel acquisition points respectively. The four amplitude matrices are superimposed to get the defect amplitude enhancement matrix of the kth measurement point. .

[0039] The present invention proposes a dynamic amplitude matching mechanism based on resonant frequency, realizes the automatic association between grid units and corresponding frequency components by traversing frequency domain data, and establishes a multi-dimensional mapping relationship between spatial coordinates, frequency characteristics and signal amplitude.

[0040] By superimposing the amplitude matrices of the four channels at the same measuring point, the defect amplitude enhancement matrix of each measuring point is obtained as follows: in, is the defect amplitude enhancement matrix of the kth measuring point; is the amplitude matrix of the i-th channel at the k-th measurement point.

[0041] Step 4: Superimpose the defect amplitude enhancement matrices at all measurement points to obtain a global intensity matrix. After normalizing the amplitude in the global intensity matrix again, map it to the HSV color space to generate a three-dimensional energy density distribution model.

[0042] The defect amplitude enhancement matrices at all measurement points are superimposed to obtain the global intensity matrix, as follows: in, is the global intensity matrix; is the number of measurement points; is the defect amplitude enhancement matrix obtained at the k-th measurement point.

[0043] As Figure 5 shown, from the calculation formula of the resonance frequency of each grid cell, it can be seen that if only the amplitude is extracted from a single set of frequency-domain data to generate an intensity matrix for 3D imaging, when the size of the grid cell is small and is a certain fixed value, there will be a large number of grid cells with equal resonance frequencies in the discrete model at this time. The connection lines of these grid cells can be approximated as a hemispherical surface with the center of the sphere O between the impact point and the acquisition point and a radius of R. The resonance frequencies of the grid cells passed by the trajectory of this hemispherical surface are almost equal. After extracting the amplitude from the spectrogram, these grid cells and their adjacent cells will have relatively small differences in their respective corresponding amplitudes, resulting in the same or similar colors in the energy density distribution map, that is, the 3D imaging of the defect. A spherical surface appears in the image, that is, the "spherical surface effect". Therefore, when using only a single set of frequency-domain data for imaging, there will be a large number of grid cells with resonance frequencies equal to the defect frequency. At this time, a spherical surface passing through the grid of the defect area will appear in the image, making it difficult to accurately judge the defect position from the image, and the visualization effect of the 3D model for internal defects is poor. To weaken the interference of the "spherical surface effect", the characteristics of the defect position can be highlighted by superimposing multiple intensity matrices. The principle is as follows: In the frequency-domain data obtained at different measurement points, the defect frequencies and amplitudes are different, but since the defect position is a strong reflection area, the amplitude of the defect in the frequency domain of each measurement point is higher than that of the defect-free area. Therefore, there will always be a spherical surface passing through the defect position when using a single set of frequency-domain data at different measurement points for imaging. When the number of measurement points, that is, the number of centers of the sphere, is increased to n, it is equivalent to increasing the number of spherical surfaces in the 3D imaging to n. When changing the measurement point, that is, changing the position of the impact point or the acquisition point, it is equivalent to changing the position of the center of the sphere. The coordinates of each measurement point, that is, the center of the sphere is at a different position. Therefore, when superimposing the intensity matrices, there will be partial overlap of these spherical surfaces, and the overlapping area is the defect position. The overlap of n spherical surfaces is equivalent to the superposition of the amplitudes of the cubic grid cells in the overlapping area, that is, the amplitude at the defect position is enhanced n times. At this time, the reflection intensity at the defect position is quite different from that at the defect-free position. When the re-normalized amplitude after superposition is subjected to color mapping, the defect boundary and burial depth can be clearly presented in the 3D discrete model. Based on the above description, when using a four-channel sensor to collect signals at a certain measurement point, step 3 essentially changes the position of the center of the sphere four times at this measurement point. This step can be regarded as a preliminary weakening of the "spherical surface effect". Therefore, when there are K measurement points, actually 4K amplitude matrices will be generated, that is, 4K spherical surfaces passing through the defect area will appear in the image. After superposition, the influence of the "spherical surface effect" can be effectively weakened.

[0044] Through matrix superposition and fusion, the present invention can break through the imaging limitation of a single set of data, further enhance the amplitude magnitude at the defect location, and highlight the difference between the defect area and the defect-free area. By coupling the acoustic signal intensity with the structural geometric parameters in three-dimensional space and constructing a three-dimensional model containing amplitude gradient information, the buried depth and boundary morphology of the defect can be intuitively displayed.

[0045] Map the amplitude elements after normalization processing to the HSV color space, specifically: Map the amplitude elements after normalization processing from high to low in the order of red - yellow - green - blue to the HSV color space, as follows: Among them, is the amplitude element in the global intensity matrix . Generate a three-dimensional energy density distribution model, which shows high-saturation red for the defect area and gradually changes to blue for the defect-free area.

[0046] As Figure 6 shown, to more intuitively display the matrix superposition effect, the projection of the "spherical effect" on a two-dimensional plane is used, and the impact point and single-channel acquisition points are used for display. In Figure 6 , the center of the circle is located between the impact point and the acquisition point. The radius of each circle in the figure is the approximate value of the sum of the distances between the center of each cubic grid in step 3 and the impact point and the acquisition point . The blue dashed circle represents the "spherical effect" that appears in the image when imaging with a single set of frequency-domain data for each measurement point. Taking the measurement point (center of the circle) as an example, when only using a set of data among the measurement points for imaging, the grids passed by the circular trajectory with as the center in the image all have the defect frequency as the resonance frequency, and the same amplitude is extracted from the frequency domain of . After color mapping, a ring approximately fitting the blue dashed line will appear in the image, and it is difficult to distinguish the actual position of the defect in the image. At this time, increasing the number of measurement points and changing the positions of the measurement points cause the ring positions to move. Since the rings all contain defect information, that is, they all pass through the defect area. Therefore, the overlapping part of numerous rings is the actual position of the defect. The ring overlap means that after superimposing all the amplitude matrices, the grid amplitudes in the defect area have been superimposed n times, and the amplitudes in this area have an obvious difference from those in the defect-free area. When re-normalizing the amplitudes and performing color mapping, a clear boundary and buried depth of the defect can be presented in the image.

[0047] Step 5: Perform multi-dimensional slicing analysis on the three-dimensional energy density distribution model to quantitatively analyze the defect.

[0048] Perform multi-dimensional slicing analysis on the three-dimensional energy density distribution model to quantitatively analyze defects, specifically as follows: As Figure 7 shown, perform orthogonal slicing on the three-dimensional energy density distribution model along the X, Y, and Z axes, and extract two-dimensional projections , , , and perform multi-dimensional analysis of the defect condition through the principle of tomography.

[0049] Specifically, by changing the position of the cutting plane on the three axes and observing the imaging situation from multiple angles, for the slices of the defect area, the size and burial depth of the projection of the defect in this direction will appear in the two-dimensional slice. Observe all two-dimensional slices passing through the defect area to determine the length, width, and burial depth of the defect in three-dimensional space.

[0050] Since the defect is inside the model, the color representing the defect position may be blocked by the color of the defect-free area during color mapping. Also, it is possible that the defect frequency amplitude is less than the plate thickness frequency amplitude in the frequency spectrum obtained after processing each group of time-domain data. At this time, it may be difficult to observe the color of the defect position in the three-dimensional image. Therefore, by performing orthogonal slicing on the three-dimensional model at different positions on the XYZ axes and observing the projections of the defect position at different positions in the three-axis directions, observe the imaging situation at the two-dimensional level to more intuitively judge the defect condition.

[0051] The present invention establishes a dynamic association mechanism between two-dimensional slices and three-dimensional models to support multi-dimensional data cross-verification. Through the spatial projection matrix conversion method, rapid reconstruction of any cutting plane is realized. The defect size and burial depth calculation model is constructed using the principle of tomography, and a dual diagnosis mode of "three-dimensional positioning + two-dimensional quantification" is established.

[0052] The embodiment of the present invention discloses a multi-point superposition three-dimensional imaging method based on the impact echo method. By synchronously collecting impact echo signals through multiple channels and combining frequency domain feature extraction and amplitude enhancement mechanisms, the expansion from traditional two-dimensional imaging to three-dimensional imaging is realized, so as to more intuitively and accurately present the distribution range and burial depth position of internal defects in concrete. At the same time, the generated three-dimensional model can intercept cross-sections along the orthogonal planes in the X, Y, and Z axis directions to realize multi-dimensional analysis of the defect condition, providing more comprehensive defect information compared with traditional two-dimensional images, effectively overcoming the situation that traditional two-dimensional imaging only presents the projection of defects in one direction and has insufficient recognition of complex defects, and improving the defect recognition accuracy of the impact echo method.

[0053] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts among the embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0054] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-point superposition three-dimensional imaging method based on the impact echo method, characterized in that Including: Step 1: With four acceleration sensors as the corners and the impact point as the center, construct a four-channel sensor impact echo detection system based on an equilateral rectangle array, and collect the four-channel time-domain signals of each measurement point in the detection area when it is used as the impact point; Step 2: With the center of the detection area as the center of the top surface, construct four concrete three-dimensional discrete models corresponding to the four channels for each measurement point respectively, divide them into uniform cubic grid cells, and calculate the resonant frequency of each cubic grid cell; Step 3: Normalize the amplitudes in the four-channel time-domain signals and perform a fast Fourier transform to obtain four sets of normalized frequency-domain spectra corresponding to the four-channel time-domain signals. Based on the resonant frequency, extract the amplitudes of each cubic grid cell from the normalized frequency-domain spectra to obtain the amplitude matrix corresponding to the four channels under each measurement point, and superimpose the amplitude matrices of the four channels under the same measurement point to obtain the defect amplitude enhancement matrix of each measurement point; Step 4: Superimpose the defect amplitude enhancement matrices of all measurement points to obtain the global intensity matrix, and after normalizing the amplitudes in the global intensity matrix again, map them to the HSV color space to generate a three-dimensional energy density distribution model; Step 5: Perform multi-dimensional slicing analysis on the three-dimensional energy density distribution model to quantitatively analyze the defects.

2. The multi-point superposition three-dimensional imaging method based on the impact echo method according to claim 1, characterized in that In Step 1, the detection area is a grid detection area arranged above the area with defects inside the concrete structure in a grid form; among them, the corners of each grid are used as measurement points.

3. A multi-point superposition three-dimensional imaging method based on the impact echo method according to claim 2, characterized in that, In Step 2, with the center of the detection area as the center of the top surface, construct four concrete three-dimensional discrete models corresponding to the four channels for each measurement point respectively, specifically: The side lengths of the top surface and the bottom surface of the concrete three-dimensional discrete model are the side length of the grid detection area plus a preset length, and the depth is the same as the actual thickness of the concrete structure.

4. A multi-point superposition three-dimensional imaging method based on the impact echo method according to claim 1, characterized in that In Step 2, the side length of the cubic grid cell satisfies the Nyquist sampling criterion, specifically: Among them, is the side length of the cubic grid cell; is the propagation speed of the P-wave in the concrete under test; is the sampling time interval.

5. A multi-point superposition three-dimensional imaging method based on the impact echo method according to claim 1, characterized in that In Step 2, calculate the resonant frequency of each cubic grid cell as follows: Among them, is the resonant frequency of the cubic grid unit with the central coordinate of in the three-dimensional concrete discrete model of the i-th channel acquisition point under the k-th measurement point, where i = 1, 2, 3, 4, corresponding to the four-channel acceleration sensor; is the propagation velocity of the P-wave in the measured concrete; is the Euclidean distance between the center of the cubic grid unit and the impact point under the k-th measurement point; is the Euclidean distance between the center of the cubic grid unit and the i-th channel acquisition point under the k-th measurement point.

6. A multi-point superposition three-dimensional imaging method based on the impact echo method according to claim 1, characterized in that In Step 3, based on the resonant frequency, extract the amplitudes of each cubic grid cell from the normalized frequency-domain spectra to obtain the amplitude matrix corresponding to the four channels under each measurement point, specifically: Each measurement point has four of the normalized frequency-domain spectra, corresponding to the four-channel time-domain signals of the measurement point respectively; Each measurement point has four concrete three-dimensional discrete models, constructed respectively based on the four channels under the measurement point; Each concrete three-dimensional discrete model contains multiple cubic grid cells, and each cubic grid cell has a resonant frequency; For the amplitude of each cubic grid cell in the concrete three-dimensional discrete model of each measurement point, determine the normalized frequency-domain spectrum corresponding to the time-domain signal of the corresponding channel under the measurement point according to the measurement point and the corresponding channel in the concrete three-dimensional discrete model, and extract the amplitude of the cubic grid cell from the normalized frequency-domain spectrum to obtain the amplitude matrix corresponding to the four channels under each measurement point.

7. A three-dimensional imaging method based on the impact echo method with multi-point superposition according to claim 1, characterized in that, In Step 3, superimpose the amplitude matrices of the four channels under the same measurement point to obtain the defect amplitude enhancement matrix of each measurement point as follows: Among them, is the defect amplitude enhancement matrix of the k-th measurement point; is the amplitude matrix of the -th channel under the k-th measurement point.

8. A three-dimensional imaging method based on the impact echo method with multi-point superposition according to claim 1, characterized in that, In step 4, the defect amplitude enhancement matrices under all measurement points are superimposed to obtain a global intensity matrix as follows: Among them, is the global strength matrix; is the number of measuring points; is the defect amplitude enhancement matrix of the k-th measuring point.

9. A three-dimensional imaging method based on impact echo method with multi-point superposition according to claim 1, characterized in that, In step 4, the amplitude elements after normalization are mapped to the HSV color space, specifically: The amplitude elements after normalization are mapped to the HSV color space in the order of red - yellow - green - blue to represent the amplitude from high to low as follows: Among them, is the amplitude element in the global intensity matrix.

10. A multi-point superposition three-dimensional imaging method based on the impact echo method according to claim 1, characterized in that, In step 5, multi - dimensional slicing analysis is performed on the three - dimensional energy density distribution model to quantitatively analyze the defects, specifically: Perform orthogonal slicing on the three-dimensional energy density distribution model along the X, Y, and Z axes, and extract two-dimensional projections , , , and perform multi-dimensional analysis of the defect condition through the principle of tomography.

Images