A method and system for measuring transient deformation of aggregate particles based on high-speed structured light

Abstract

The present invention discloses a method and system for measuring the transient deformation of aggregate particles based on high-speed structured light, and relates to the fields of geotechnical engineering, computer vision and structured light application technology. The method for measuring the transient deformation of aggregate particles mainly includes using a high-speed structured light uniaxial compression device to capture images of aggregate particles during crushing; using image processing technology to analyze changes in structured light patterns in the image and reconstructing them in three dimensions through an algorithm; using an algorithm based on three-dimensional digital image correlation technology to divide the three-dimensionally reconstructed particles into small units, and identifying corresponding units by comparing textures and curvatures; and calculating the three-dimensional displacement and strain field of particles during crack initiation and expansion. The present invention overcomes the shortcomings of the prior art, can capture the transient process of particle crack initiation, expansion, and crushing, and can accurately measure the displacement field and strain field, the change of particle crack length over time, and the pressure-displacement curve in this process.

Description

Technical Field

[0001] The present invention relates to the fields of geotechnical engineering, computer vision and structured light application technology, and in particular to a method and system for measuring transient deformation of aggregate particles based on high-speed structured light. Background Art

[0002] Aggregate particle crushing is a common phenomenon in geotechnical engineering applications, often occurring in actual construction processes such as piling, ground improvement, highway embankments, and heavy rockfill dams. Excessive stress can cause the deformation and crushing of gravel or sand particles, change the permeability, dilatancy and other properties of the soil, and cause changes in the macroscopic properties of geotechnical engineering, thereby affecting the long-term serviceability, safety and reliability of geotechnical infrastructure. By analyzing the deformation behavior of rock or soil during compression, its stability and bearing capacity can be evaluated, providing an important basis for engineering design and construction. Since aggregate particle crushing is a brittle failure and the damage is relatively rapid, in order to observe the particle crushing and explore the particle crushing mechanism, researchers began to introduce advanced three-dimensional imaging technology and digital image correlation technology into traditional geotechnical engineering experiments, using X-ray tomography technology to observe the crushing of aggregate particles under uniaxial compression, but this technology cannot capture the complete process of particle deformation and crushing. Some researchers used high-speed cameras to capture the process of particle deformation and crushing under uniaxial compression, but did not make quantitative measurements of the displacement field and strain field during particle deformation and crushing. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention proposes a method and system for measuring the transient deformation of aggregate particles based on high-speed structured light, which can achieve accurate capture and three-dimensional reconstruction of the rapid dynamic process of deformation and crushing of aggregate particles, and can quantitatively measure the displacement field and strain field in the particle crushing process. It has the advantages of simple operation, good reconstruction effect, and high measurement accuracy.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for measuring transient deformation of aggregate particles based on high-speed structured light, the method comprising the following steps:

[0006] S1. Build a high-speed structured light uniaxial compression device and use it to capture images of the deformation and crushing process of aggregate particles during compression;

[0007] S2. Using image processing technology to analyze changes in the structured light pattern of the image during the particle crushing process and realizing three-dimensional reconstruction of the particles during the crushing process through a structured light three-dimensional reconstruction algorithm based on the pattern changes;

[0008] S3, using an algorithm based on 3D digital image correlation technology to segment the 3D reconstructed particles into small units, and identifying corresponding units by comparing texture and curvature;

[0009] S4. Calculate the three-dimensional displacement field and strain field during the deformation and crushing of aggregate particles.

[0010] Preferably, the specific method of step S1 includes the following steps:

[0011] S2-1, calibrating the structured light system, that is, calibrating the geometric relationship between the structured light projector and the high-speed camera;

[0012] S2-2, projecting a preset structured light pattern with coded information onto aggregate particles undergoing a uniaxial compression test;

[0013] S2-3, capturing the complete process of deformation and crushing of particles during compression by controlling the loading force and rate of the particle uniaxial compressor and the image capture rate of the high-speed camera by a computer;

[0014] Preferably, the three-dimensional reconstruction of the aggregate particles in step S2 is specifically performed by comparing the pattern shape in the high-speed camera view with the designed shape of the pattern emitted from the structured light projector, and obtaining the three-dimensional spatial coordinates of the particle surface based on a three-dimensional reconstruction algorithm.

[0015] Preferably, the specific method of step S3 includes the following steps:

[0016] S3-1. The three-dimensional image of aggregate particles before compression is defined as the reference image and the calculation area is specified in the reference image to minimize the amount of calculation.

[0017] S3-2, the calculation area is further divided into small cells, and each cell in the reference image is used as a reference cell. The reference cells are used to search for the most similar cells in the deformed image, i.e., corresponding cells, and a search area is defined to limit the search range and speed up the calculation.

[0018] S3-3. Use the correlation coefficient to evaluate the similarity of units.

[0019] Preferably, the specific method of step S4 includes the following steps:

[0020] S4-1, perform the operation of step S3 on each unit in the aggregate particle to generate a three-dimensional displacement field (u x ,u y ,u z ).

[0021] S4-2, according to the obtained three-dimensional displacement field (u x ,uy ,u z ) to calculate the three-dimensional strain field (ε xx , ε yy , ε zz , ε xy , ε xz , ε yz ).

[0022] A transient deformation measurement system for aggregate particles based on high-speed structured light is composed of an image capture module, a three-dimensional reconstruction module, an image recognition module and a calculation module; the image capture module includes a high-speed structured light uniaxial compression device, which uses the high-speed structured light uniaxial compression device to capture a series of images of aggregate particles in the deformation and crushing process during compression; the three-dimensional reconstruction module performs three-dimensional reconstruction of aggregate particles in the deformation and crushing process by comparing the changes in the structured light pattern in the image captured by the image capture module based on a three-dimensional particle reconstruction algorithm; the image recognition module uses an algorithm based on three-dimensional digital image correlation technology to divide the image into small units, and identifies the corresponding units between two images by comparing the texture and curvature of the image; the calculation module is used to calculate the three-dimensional displacement of all units on the aggregate particles, and calculate the strain through the displacement, so as to construct the three-dimensional displacement field and strain field of the entire particle in the deformation and crushing process;

[0023] Preferably, the high-speed structured light uniaxial compression device is composed of a structured light projector, a high-speed camera, a particle uniaxial compressor and a computer; and the structured light projector, the high-speed camera and the particle uniaxial compressor are all connected to the computer, and the projection pattern of the structured light projector, the size of the image captured by the high-speed camera, the image acquisition rate and the loading force and rate of the particle uniaxial compressor can be controlled by the computer.

[0024] Compared with the prior art, the present invention provides a method and system for measuring transient deformation of aggregate particles based on high-speed structured light, which has the following beneficial effects:

[0025] The present invention realizes accurate capture and three-dimensional reconstruction of the rapid dynamic process of aggregate particle crushing through structured light imaging technology and high-speed cameras, and utilizes three-dimensional digital image correlation technology to process and analyze digital images to identify corresponding units between reference images and target images, thereby calculating the three-dimensional displacement field and strain field of particles during deformation and crushing to quantify strain localization, crack initiation, crack propagation and particle crushing. The present invention has the advantages of simple operation, fast measurement speed, good reconstruction effect and high measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the three-dimensional structure of the high-speed structured light uniaxial compression device in Example 1 of the present invention;

[0027] Figure 2 This is a flow chart of a method for measuring transient deformation of aggregate particles based on high-speed structured light in Example 2 of the present invention;

[0028] Figure 3 This is a schematic diagram of the structured light imaging technology in Example 2 of the present invention;

[0029] Figure 4 The image captured by the high-speed camera in Example 2 of the present invention;

[0030] Figure 5 Schematic diagram of corresponding units for identifying three-dimensional particles through an image recognition module in Example 2 of the present invention;

[0031] Figure 6 Partial displacement field and strain field at three typical moments in the particle crushing process measured in Example 2 of the present invention;

[0032] Figure 7 are the horizontal and vertical displacements of the particles under the vertical load measured in Example 2 of the present invention;

[0033] Figure 8 This is a graph showing the change in crack length over time of particles under uniaxial compression measured in Example 2 of the present invention;

[0034] In the figure: 1. Structured light projector; 2. High-speed camera; 3. Particle uniaxial compressor; 4. Computer. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0036] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0037] Embodiment 1:

[0038] A transient deformation measurement system for aggregate particles based on high-speed structured light consists of an image capture module, a three-dimensional reconstruction module, an image recognition module and a calculation module;

[0039] The image capture module includes a high-speed structured light uniaxial compression device, which uses the high-speed structured light uniaxial compression device to capture a series of images of aggregate particles during deformation and crushing during compression;

[0040] The three-dimensional reconstruction module performs three-dimensional reconstruction of aggregate particles in the deformation and crushing process by comparing the changes of the structured light pattern in the image captured by the image capture module based on the three-dimensional particle reconstruction algorithm;

[0041] The image recognition module uses an algorithm based on three-dimensional digital image correlation technology to divide the three-dimensionally reconstructed particles into small units, and identifies the corresponding units by comparing texture and curvature;

[0042] The calculation module is used to calculate the three-dimensional displacement of all units on the aggregate particles, and calculate the strain through the displacement, so as to construct the three-dimensional displacement field and strain field of the entire particle during the deformation and crushing process;

[0043] The high-speed structured light uniaxial compression device is composed of a structured light projector 1, a high-speed camera 2, a particle uniaxial compressor 3 and a computer 4. Figure 1 As shown; and the structured light projector 1, the high-speed camera 2 and the particle uniaxial compressor 3 are all connected to a computer 4, and the projection pattern of the structured light projector 1, the image size captured by the high-speed camera 2, the image acquisition rate and the loading force and rate of the particle uniaxial compressor 3 can be controlled by the computer 4.

[0044] Embodiment 2:

[0045] A method for measuring transient deformation of aggregate particles based on high-speed structured light, wherein the method uses the system in the above-mentioned embodiment 1 to measure the aggregate particle crushing process, and the process is as follows: Figure 2 The specific steps include:

[0046] The geometric relationship between the structured light projector and the high-speed camera is calibrated and calibrated. The principle of structured light 3D imaging technology is as follows Figure 3 A structured light projector is used to project a pixel sinusoidal moving pattern on the particle surface, and a high-speed camera will capture multiple distorted structured light patterns during this process, such as Figure 4 As shown. The i-th image I i The pattern in (x,y) can be represented as:

[0047]

[0048] Where I′(x,y), I″(x,y) and φ(x,y) represent the background light intensity, modulation intensity and pattern change map, and N is the number of captured images. The pattern change map φ(x,y) is determined by solving the N equations established for N images using the least squares method:

[0049]

[0050] To eliminate the 2π phase discontinuity, the integer map k(x,y) is added with 2π to obtain a continuous pattern change map Φ(x,y):

[0051] Φ(x,y)=φ(x,y)+2π×k(x,y) (Equation 3)

[0052] The pattern change map Φ(x,y) is converted into three-dimensional space coordinates (x,y,z) through a three-dimensional reconstruction algorithm based on the parameters obtained by the structured light system calibration. The pinhole imaging model is used to represent the high-speed camera and structured light projector. The following equation represents the transformation from the world coordinate system to the high-speed camera and structured light projector coordinate system and then to the two-dimensional image coordinate system:

[0053] s c [u c ,v c ,1] T =A c [R c ,t c ][x,y,z,1] T (Equation 4)

[0054] s p [u p ,v p ,1] T =A p [R p ,t p ][x,y,z,1] T (Equation 5)

[0055] The superscripts c and p denote the high-speed camera and structured light projector, respectively; s denotes the scaling factor; A and [R, t] denote the intrinsic and extrinsic matrices of the imaging lens, respectively, which transform points in three-dimensional space coordinates (x, y, z) into two-dimensional image coordinates (u, v); T is the number of pixels occupied by a sinusoidal pattern period. The intrinsic and extrinsic parameters are obtained by calibrating the structured light system. After the structured light system is calibrated, the pattern change map Φ(x, y) and the structured light projector pixels (u p , v p ) provides an additional equation. Since the pixel period of the designed sinusoidal pattern is T and has intensity variation in the upward direction, the linear constraint can be expressed as:

[0056]

[0057] By solving equations 4-6 simultaneously, the three-dimensional spatial coordinates of any point on the particle can be determined, thereby achieving three-dimensional reconstruction of the particle.

[0058] Define the three-dimensional image of aggregate particles before compression as the reference image, the image after deformation as the target image, and specify the calculation area in the reference image to minimize the amount of calculation. Based on the three-dimensional digital image correlation technology, the three-dimensional image is divided into small units through an algorithm, and the corresponding units between the reference image and the target image are identified by comparing their textures and curvatures. Figure 5 As shown. The normalized least square distance correlation function is introduced to evaluate the similarity of corresponding units, and its formula is as follows:

[0059]

[0060] Among them, f(x A ,y A ) and g(x B ,y B ) represent the image grayscale in the reference image and the target image respectively.

[0061] The displacement of the unit between the two 3D images is: x,i =x B -x A ,u y,i =y B -y A ,u z,i =z B -z A .

[0062] This process is repeated for each unit on the aggregate particle, and the three-dimensional displacement field (u x ,u y ,u z ), and the three-dimensional strain field is calculated using the Green strain tensor calculation formula through the three-dimensional displacement field. The Green strain tensor calculation formula is as follows:

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069] Figure 6The figure shows the partial displacement field and strain field at three typical moments in the particle crushing process. At the same time, the horizontal displacement and vertical displacement of the particle crushing process under vertical load can be calculated through the calculation module, such as Figure 7 As shown. Image recognition technology can be used to identify cracks in the reconstructed three-dimensional particles, and the crack length can be calculated through the calculation module. The change of crack length over time is shown in Figure 8 shown.

[0070] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for measuring transient deformation of aggregate particles based on high-speed structured light, characterized in that: The method comprises the following steps: S1. Build a high-speed structured light uniaxial compression device and use it to capture images of the deformation and crushing process of aggregate particles during compression; The specific method includes the following steps: S2-1, calibrating the structured light system, that is, calibrating the geometric relationship between the structured light projector and the high-speed camera; S2-2, projecting a preset structured light pattern with coded information onto aggregate particles undergoing a uniaxial compression test; S2-3, capturing the complete process of deformation and crushing of particles during compression by controlling the loading force and rate of the particle uniaxial compressor and the image capture rate of the high-speed camera by a computer; S2. Using image processing technology to analyze changes in the structured light pattern of the image during the particle crushing process and realizing three-dimensional reconstruction of the particles during the crushing process through a structured light three-dimensional reconstruction algorithm based on the pattern changes; S3, using an algorithm based on 3D digital image correlation technology to segment the 3D reconstructed particles into small units, and identifying corresponding units by comparing texture and curvature; The specific method includes the following steps: S3-1. Define the three-dimensional image of aggregate particles before compression as the reference image and specify the calculation area in the reference image to minimize the amount of calculation; S3-2, further dividing the calculation area into small units, each unit in the reference image is used as a reference unit, and the reference unit is used to search for the most similar unit in the deformed image, that is, the corresponding unit, and a search area is defined to limit the search range and speed up the calculation; S3-3, using correlation coefficient to evaluate the similarity of units; S4, calculate the three-dimensional displacement field and strain field during the deformation and crushing process of aggregate particles; The specific method includes the following steps: S4-1, performing the operation of step S3 on each unit in the aggregate particle to generate a three-dimensional displacement field (ux, uy, uz) of each unit on the particle during deformation and crushing; S4-2. Calculate the three-dimensional strain field (εxx, εyy, εzz, εxy, εxz, εyz) based on the obtained three-dimensional displacement field (ux, uy, uz).

2. The method for measuring transient deformation of aggregate particles based on high-speed structured light according to claim 1, characterized in that: The three-dimensional reconstruction of the aggregate particles in step S2 is specifically to obtain the three-dimensional spatial coordinates of the particle surface based on a three-dimensional reconstruction algorithm by comparing the pattern shape in the high-speed camera view with the designed shape of the pattern emitted from the structured light projector.

3. A dynamic deformation measurement system for aggregates based on high-speed structured light, characterized in that: The system is composed of an image capture module, a three-dimensional reconstruction module, an image recognition module and a calculation module; The image capture module includes a high-speed structured light uniaxial compression device, which uses the high-speed structured light uniaxial compression device to capture a series of images of aggregate particles during deformation and crushing during compression; The three-dimensional reconstruction module performs three-dimensional reconstruction of aggregate particles in the deformation and crushing process by comparing the changes of the structured light pattern in the image captured by the image capture module based on the three-dimensional particle reconstruction algorithm; The image recognition module uses an algorithm based on three-dimensional digital image correlation technology to divide the image into small units, and identifies the corresponding units between the two images by comparing the texture and curvature of the images; The calculation module is used to calculate the three-dimensional displacement of all units on the aggregate particles, and calculate the strain through the displacement, so as to construct the three-dimensional displacement field and strain field of the entire particle during the deformation and crushing process.

4. The aggregate dynamic deformation measurement system based on high-speed structured light according to claim 3 is characterized in that: The high-speed structured light uniaxial compression device is composed of a structured light projector (1), a high-speed camera (2), a particle uniaxial compressor (3) and a computer (4); the structured light projector (1), the high-speed camera (2) and the particle uniaxial compressor (3) are all connected to the computer (4), and the computer (4) can control the projection pattern of the structured light projector (1), the size of the image captured by the high-speed camera (2), the image acquisition rate and the loading force and rate of the particle uniaxial compressor (3).

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