Micromechanical test platform and method of granular materials based on optical measurement technology

Abstract

The present invention discloses a micromechanics testing platform and method for granular materials based on optical measurement technology. The testing platform is equipped with, from left to right, a polarized light source, a polarizer, a biaxial loading device, an LED light source, an analyzer, and the image acquisition system. The optical platform is also equipped with a control system electrically connected to the biaxial loading device. Based on optical measurement technology, this micromechanics testing platform for granular materials achieves shearing of a two-dimensional dense particle system through the movement of an adjustable biaxial loading device. By rotating the analyzer, it can switch between polarized and unpolarized light fields to acquire test images under different light fields. Contact force and dynamics analysis is performed by combining photoelasticity and digital image correlation techniques. This micromechanics testing platform for granular materials utilizes high-precision, high-frequency image acquisition technology to intuitively and synchronously acquire contact force and dynamics information of granular materials without contact.

Description

Technical Field

[0001] The present invention relates to the field of rock and soil testing technology, and in particular to a microscopic mechanics testing platform and testing method for granular materials based on optical measurement technology. Background Art

[0002] Granular materials are complex systems formed by the interaction of numerous discrete solid particles. Due to their highly heterogeneous internal structure, granular materials exhibit complex mechanical behaviors such as shear banding, dilatancy, and yielding when subjected to external forces. Numerous studies have demonstrated a close connection between the complex mechanical properties of granular materials and their microstructure. Therefore, studying the microdynamics, contact networks, and microstructure of granular materials provides a new avenue for uncovering their complex macroscopic and microscopic mechanical properties. Methods for studying the mechanical properties of granular materials include numerical simulation and physical testing. While numerical simulation has made significant progress in understanding the mechanisms of complex macroscopic phenomena in granular materials, conventional experimental methods (such as large-scale triaxial tests, ring shear tests, and direct shear tests) can only capture the macroscopic mechanical response of granular materials. At the microscopic level, due to the lack of experimental observations, some key mechanisms still require further investigation using sophisticated measurement techniques.

[0003] Photoelasticity is a stress measurement device that combines optics and mechanics. It determines the surface stress distribution by measuring interference fringes on the surface of a photoelastic specimen in a polarized light field. Due to its significant advantages in stress measurement, photoelasticity has been successfully applied to the study of granular materials, providing a technical basis for measuring force chain structures in two-dimensional granular systems. Digital image correlation (DIC) is a non-contact strain measurement technique that tracks or matches the position of identical pixels in images of the surface before and after deformation to obtain displacement and strain fields on the surface. DIC provides additional data for studying the deformation and rotation of granular materials, complementing the limitations of photoelasticity in dynamic measurements. However, combining these two techniques still presents challenges. For example, the polarization field generated by the photoelasticity instrument can interfere with DIC observations, resulting in distorted DIC images. Furthermore, the loading systems suitable for both photoelasticity and DIC are mostly uniaxial, primarily tensile and compressive, which cannot meet the complex biaxial or triaxial loading requirements of granular systems. Therefore, a test setup suitable for biaxial loading is required. Summary of the Invention

[0004] The purpose of the present invention is to provide a micromechanical testing platform and method for granular materials based on optical measurement technology to address the problems existing in the prior art.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A microscopic mechanical testing platform for granular materials based on optical measurement technology comprises an optical platform, a biaxial loading device is provided on the optical platform, a polarizer is provided on one side of the biaxial loading device, a polarized light source is provided on the side of the polarizer away from the biaxial loading device, a deflectable analyzer is provided on the other side of the biaxial loading device, an image acquisition system is provided on the side of the analyzer away from the biaxial loading device, and the image acquisition system is arranged toward the biaxial loading device; a plurality of LED light sources are also arranged in the area between the analyzer and the biaxial loading device, and a control system is also provided on the optical platform, which is electrically connected to the biaxial loading device.

[0007] This micromechanics test platform for granular materials is based on optical measurement technology. Through the movement of an adjustable biaxial loading device, it can achieve shearing of a two-dimensional dense particle system. By rotating the analyzer, it can switch between polarized light field and unpolarized light field to obtain test images under different light fields, and combine photoelastic technology and digital image correlation technology to perform contact force and dynamic analysis. This micromechanics test platform for granular materials uses high-precision, high-acquisition-frequency image acquisition technology to intuitively and synchronously obtain contact force and dynamic information of granular materials without contact.

[0008] The control system can control the biaxial loading device to apply multi-directional force loading to the particle sample. The image acquisition system can take pictures to obtain photoelastic images under different light fields. Under the action of the analyzer and the polarizer, the interference of the polarization field on DIC observation is reduced, thereby reducing imaging distortion.

[0009] Furthermore, the optical platform includes an independently arranged first optical platform and a second optical platform, the polarized light source, the polarizer and the biaxial loading device are all arranged on the first optical platform, and the analyzer and the image acquisition system are arranged on the second optical platform, which can prevent the deflection adjustment of the analyzer from affecting the biaxial loading device.

[0010] Furthermore, a supporting base plate is provided on the second optical platform, an arc-shaped groove is provided on the supporting base plate, an analyzer support plate is provided below the analyzer, one end of the analyzer support plate is rotatably connected to the supporting base plate, and a pulley or a slider is provided below the other end of the analyzer support plate, and the pulley or the slider is arranged in the arc-shaped groove and slides along the arc-shaped groove to facilitate the deflection of the analyzer.

[0011] Furthermore, the LED light sources are a pair arranged symmetrically, and the light is set toward the middle of the dual-axis loading device.

[0012] Furthermore, the biaxial loading device includes a supporting base arranged on the optical platform, a pair of parallel and vertically arranged organic glass baffles are provided on the supporting base, a side baffle is provided on one side of the pair of organic glass baffles, a first loading plate is provided on the other side, and a first loading assembly connected to the first loading plate is provided, a second loading plate and a second loading assembly connected to the second loading plate are provided above the pair of organic glass baffles; the first loading plate and the second loading plate are movably arranged between the pair of organic glass baffles, and the area enclosed by the supporting base, the side baffles, the first loading plate, the second loading plate and the pair of organic glass baffles form a sample placement cavity.

[0013] Furthermore, the first loading assembly includes a first bracket arranged on the optical platform, the first bracket is provided with a first stepper motor, the output end of the first stepper motor is connected to a first mechanical sensor, the first mechanical sensor is connected to the first loading plate through a force transmission rod, the first loading plate moves horizontally, and the first stepper motor and the first mechanical sensor are both electrically connected to the control system.

[0014] Furthermore, the second loading assembly includes a second bracket arranged on the optical platform, a second stepper motor is provided under the horizontal section of the second bracket, the output end of the second stepper motor is connected to a second mechanical sensor, the second mechanical sensor is connected to the second loading plate through a force transmission rod, the second loading plate moves vertically, and the second stepper motor and the second mechanical sensor are both electrically connected to the control system.

[0015] Furthermore, a top plate is provided above the pair of organic glass baffles, and one side of the top plate is detachably connected to the vertical section of the second bracket; a rack is provided on the outer side of the side baffle, and a slide body is provided on the vertical section of the second bracket, and a gear meshing with the rack is provided in the slide body.

[0016] Furthermore, the first loading assembly is detachably connected to the first loading plate via a quick-release clamp, and the second loading assembly is also detachably connected to the second loading plate via a quick-release clamp.

[0017] Furthermore, a test method for a micromechanical test platform of granular materials based on optical measurement technology is provided, the test method comprising the following steps:

[0018] Move the second loading plate to the top, remove the second loading plate, place the particle sample into the sample placement chamber, and then install the second loading plate; turn on the polarized light source, and place the analyzer in a position parallel to the polarized light source and the biaxial loading device;

[0019] The control system controls the first loading plate and the second loading plate to start moving, shears the two-dimensional dense particle system composed of photoelastic particles according to a set loading path, and obtains a macroscopic response of stress and deformation of the two-dimensional dense particle system by obtaining the forces applied to the first loading plate and the second loading plate;

[0020] When the load reaches a set load, the loading is stopped; and the image acquisition system is used to take a picture to obtain a photoelastic image of the two-dimensional dense particle system under a polarized light field;

[0021] Turn off the polarized light source and turn on the LED light source; rotate the analyzer 90°, and use the image acquisition system to take pictures again to obtain a photoelastic image of the two-dimensional dense particle system in a non-polarized light field for dynamic information analysis of the displacement and rotation of the particle sample.

[0022] Acquiring the contact force between particle samples through photoelastic imaging specifically includes the following steps:

[0023] Selecting a suitable brightness threshold to distinguish the particle sample from the background, thereby generating a binary image; then performing a Hough transform on the image after the binary image to determine the center position and radius of the particle sample;

[0024] Through the position of the particle sample, the geometric contact point between the particle samples is identified; then a brightness gradient threshold is set to determine the brightness gradient G at the contact point. 2 Whether it is greater than the threshold to determine the true contact point, the brightness gradient is calculated as follows:

[0025] .

[0026] With the contact force as a free parameter, the nonlinear least square method is used to obtain the optimal parameter of the contact force, so that the actual brightness value of each point of the particle sample is closest to the theoretical brightness value, thereby obtaining the contact force between the particle samples.

[0027] The strain field and particle dynamics information of particles obtained by digital image correlation technology include the following:

[0028] First, the photoelastic images acquired under a non-polarized light field are gridded. Then, correlation analysis is performed on the images before and after deformation based on the grid characteristics to obtain the motion trajectory and deformation of the particle specimen during loading, thereby obtaining the displacement, rotation, and strain fields of the particle specimen.

[0029] Compared with the prior art, the beneficial effects of the present invention are: 1. The microscopic mechanical test platform of granular materials is based on optical measurement technology. The shearing of a two-dimensional dense granular system is achieved through the movement of an adjustable biaxial loading device. By rotating the analyzer, it can switch between polarized light field and unpolarized light field to obtain test images under different light fields, and combine photoelastic technology and digital image correlation technology to perform contact force and dynamic analysis; this test method uses high-precision, high-acquisition frequency image acquisition technology without contact, and can intuitively and synchronously obtain the contact force and dynamic information of granular materials; 2. The control system can control the biaxial loading device to load the granular sample with forces in multiple directions. The image acquisition system can take pictures to obtain photoelastic images under different light fields. and the polarizer, the interference of the polarization field on DIC observation is reduced, and the imaging distortion is reduced; 3. Through the setting of two independent optical platforms, the vibration of the optical platform caused by the rotation of the analyzer around the axis can be avoided to affect the dual-axis loading device, which is beneficial to improve the accuracy and stability of the detection and avoid errors caused by manual operation as much as possible; 4. The setting of the arc groove and the pulley can allow the analyzer to deflect from a direction parallel to the dual-axis loading device to a direction perpendicular to the dual-axis loading device, thereby realizing the switching between polarized light field and non-deflected light field. This adjustment method is relatively simple and can be repeatedly operated without additional calibration adjustment; 5. Through the quick-release clamp, the two loading plates can be easily disassembled and the loading and removal of the particle sample can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the overall structure of the granular material micromechanics test platform based on optical measurement technology of the present invention;

[0031] Figure 2 A schematic diagram of the arrangement structure of the biaxial loading device of the present invention;

[0032] Figure 3 A schematic structural diagram of the connection between the dowel rod and the loading plate provided by the present invention;

[0033] In the figure: 1. Polarized light source; 2. Polarizer; 3. Analyzer; 4. Biaxial loading device; 5. Image acquisition system; 6. Control system; 7. First optical platform; 8. LED light source; 9. Second optical platform; 10. Support base; 11. Rotary bearing; 12. Second bracket; 13. Support base; 14. First stepper motor; 15. Second stepper motor; 16. First mechanical sensor; 17. Second mechanical sensor; 18. Force transmission rod; 19. Second loading plate; 20. First loading plate; 21. Side baffle; 22. Organic glass baffle; 23. Sample placement chamber; 24. Top plate; 25. Rack; 26. Slide trough body; 27. Fixing nut; 28. Sleeve connector; 29. ​​Arc groove; 30. Pulley; 31. First bracket. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first," "second," etc., etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] like Figure 1 and Figure 2 As shown, a micromechanical testing platform for granular materials based on optical measurement technology includes an optical platform, a biaxial loading device 4, a polarizer 2 disposed on one side of the biaxial loading device 4, a polarized light source 1 disposed on the side of the polarizer 2 away from the biaxial loading device 4, a deflectable analyzer 3 disposed on the other side of the biaxial loading device 4, an image acquisition system 5 disposed on the side of the analyzer 3 away from the biaxial loading device 4, and the image acquisition system 5 disposed toward the biaxial loading device 4. A plurality of LED light sources 8 are also disposed in the area between the analyzer 3 and the biaxial loading device 4. A control system 6 is also disposed on the optical platform, and the control system 6 is electrically connected to the biaxial loading device 4. In other words, the polarized light source 1, the polarizer 2, the biaxial loading device 4, the LED light source 8, the analyzer 3, and the image acquisition system 5 are disposed on the testing platform in order from left to right.

[0037] This microscopic mechanics test platform for granular materials is based on optical measurement technology. Through the movement of an adjustable biaxial loading device 4, shearing of a two-dimensional dense granular system is achieved. By rotating the analyzer 3, switching between polarized light field and unpolarized light field can be performed to obtain test images under different light fields. Contact force and dynamics analysis is performed by combining photoelastic technology and digital image correlation technology. This microscopic mechanics test platform for granular materials uses high-precision, high-acquisition-frequency image acquisition technology without contact, and can intuitively and synchronously acquire contact force and dynamics information of granular materials.

[0038] The polarized light source 1 is capable of generating polarized light, and the main function of the polarizer is to allow specific polarized light to pass through and block other polarized light waves, thereby converting an undefined or mixed polarized light beam into a clearly defined polarized light beam. The polarizer allows light in a specific direction to pass through due to its special transmission direction, while blocking light in other directions. This characteristic enables the polarizer to have significant effects in reducing reflections on smooth object surfaces, adjusting image contrast and color saturation, etc. For example, a circular polarizer can effectively reduce or even eliminate reflections on smooth surfaces of non-metallic surfaces (such as glass, plastic, etc.), while keeping the color and tone of the object itself unaffected, which is beneficial to the collection of photoelastic images of granular samples. In addition, the polarizer can also eliminate scattered light, making the field of view clear and natural.

[0039] The analyzer 3 is used to detect the polarization state of light after it passes through the biaxial loading device. It only allows light vibrating in a specific direction to pass through, and not light vibrating perpendicular to that direction. By rotating the analyzer, the polarization type of the light can be determined by observing the change in the intensity of the transmitted light.

[0040] The control system 6 can control the biaxial loading device 4 to apply multi-directional force to the particle sample. The image acquisition system 5 can take pictures to obtain photoelastic images under different light fields. Under the action of the analyzer and the polarizer, the interference of the polarization field on DIC observation is reduced, thereby reducing imaging distortion.

[0041] Furthermore, the optical platform includes an independently arranged first optical platform 7 and a second optical platform 9, the polarized light source 1, the polarizer 2, the biaxial loading device 4 and the LED light source 8 are all arranged on the first optical platform 7, and the analyzer 3 and the image acquisition system 5 are arranged on the second optical platform 9.

[0042] By setting up two independent optical platforms, the vibration of the optical platform caused by the rotation of the polarizer around the axis can be avoided, which may affect the dual-axis loading device, thereby improving the accuracy and stability of the detection and minimizing errors caused by manual operation.

[0043] Furthermore, a supporting base plate 10 is provided on the second optical platform 9, and an arc-shaped groove 29 is provided on the supporting base plate 10. A polarizer support plate is provided below the analyzer 3, and one end of the polarizer support plate is rotatably connected to the supporting base plate 10 through a rotary bearing 11. A pulley 30 is provided below the other end of the analyzer support plate, and the pulley 30 is arranged in the arc-shaped groove 29 and slides along the arc-shaped groove 29.

[0044] The arcuate slot 29 is a 90-degree arcuate slot, and the pulley 30 can slide within the arcuate slot 29. The pulley 30 slides from one end of the arcuate slot 29 to the other end, just enough to deflect the analyzer 3 from a direction parallel to the biaxial loading device 4 to a direction perpendicular to the biaxial loading device 4, thereby achieving switching between a polarized light field and an undeflected light field. This adjustment method is relatively simple and can be repeated without the need for additional calibration adjustments.

[0045] When it is necessary to collect images in a polarized light field, the analyzer 3 is returned to its original position, as shown in FIG. Figure 1 When it is necessary to capture an image without polarization, the analyzer 3 is rotated 90° along the arc groove 29.

[0046] In some embodiments, magnets are embedded at both ends of the arc-shaped groove 29, and magnets are also embedded at both ends of the pulley 30. When it approaches the end of the arc-shaped groove, it can be sucked in, which can play a fixing role and prevent it from shaking.

[0047] Furthermore, the LED light sources 8 are a pair of symmetrically arranged, with light directed toward the middle of the biaxial loading device. The pair of LED light sources 8 are supported by brackets and symmetrically arranged on both sides of the central axis of the entire test platform.

[0048] Furthermore, the biaxial loading device 4 includes a support base 13 arranged on the optical platform, and a pair of parallel and vertically arranged organic glass baffles 22 are provided on the support base 13, and a side baffle 21 is provided on one side of the pair of organic glass baffles 22, and a first loading plate 20 is provided on the other side, and a first loading assembly connected to the first loading plate 20, and a second loading plate 19 and a second loading assembly connected to the second loading plate 19 are provided above the pair of organic glass baffles 22; the first loading plate 20 and the second loading plate 19 are movably arranged between the pair of organic glass baffles 22, and the area enclosed by the support base 13, the side baffles 21, the first loading plate 20, the second loading plate 19 and the pair of organic glass baffles 22 form a sample placement cavity 23.

[0049] Specifically, the first loading assembly includes a first bracket 31 arranged on the optical platform, and a first stepper motor 14 is provided on the first bracket 31. The output end of the first stepper motor 14 is connected to a first mechanical sensor 16. The first mechanical sensor 16 is connected to the first loading plate 20 through a force transmission rod. The first loading plate 20 moves horizontally. The first stepper motor 14 and the first mechanical sensor 16 are both electrically connected to the control system 6.

[0050] The second loading assembly includes a second bracket 12 arranged on the optical platform, and a second stepper motor 15 is provided under the horizontal section of the second bracket 12. The output end of the second stepper motor 15 is connected to a second mechanical sensor 17. The second mechanical sensor 17 is connected to the second loading plate 19 through a force transmission rod 18. The second loading plate 19 moves vertically. The second stepper motor 15 and the second mechanical sensor 17 are both electrically connected to the control system 6.

[0051] Through the above arrangement, the area between the pair of organic glass baffles 22 is just formed under the enclosed by the support base 13, the side baffle 21, the first loading plate 20 and the second loading plate 19 to accommodate the particle sample. The particle sample placed therein can produce shear changes under the action of the first loading plate and the second loading plate.

[0052] On the one hand, the control system 6 can control the first loading plate 20 and the second loading plate 19 to move in the gap between a pair of the organic glass baffles 22 through instructions, and both the displacement and the loading speed can be controlled; on the other hand, it can obtain the force feedback from the first mechanical sensor 16 and the second mechanical sensor 17, that is, transmit the displacement and force of the top second loading plate and the left first loading plate to the control system.

[0053] The lower end surface of the organic glass baffle 22 is provided with a plurality of vertical connection holes, which can be fixedly connected to the support base through a connecting piece to maintain its vertical arrangement; the side baffle is directly in contact with the side of the organic glass baffle, which can prevent the particle sample from leaking and can bear a certain amount of force.

[0054] Force transmission rods 18 are provided at each end of the first and second force sensors 16, 17, respectively, to connect to their respective stepper motors and loading plates, ensuring better and more stable force transmission. The second bracket has vertical and horizontal sections to facilitate placement of the second loading plate from above a pair of organic glass baffles.

[0055] Furthermore, a top plate 24 is provided above the pair of organic glass baffles 22. One side of the top plate 24 is detachably connected to the vertical section of the second bracket 12. The top plate 24 is an L-shaped plate with a short vertical side that can be connected to the vertical section of the second bracket 12 via a connector. The long horizontal side is provided with a through slot for the second loading plate 19 to pass through. The provision of the top plate 24 can enhance the stability of the pair of organic glass baffles 22.

[0056] In some embodiments, a rack 25 is further provided on the outer side of the side baffle 21, and a slide trough body 26 is provided on the vertical section of the second bracket 12. A gear meshing with the rack 25 is provided in the slide trough body 26. This arrangement facilitates the loading and unloading of the side baffle 21 and the pair of organic glass baffles 22.

[0057] Furthermore, the first loading assembly is detachably connected to the first loading plate via a quick-release clamp, and the second loading assembly is also detachably connected to the second loading plate via a quick-release clamp, so as to fill the particle sample or discharge the particle sample.

[0058] Specific, combined Figure 3 As shown, the force transmission rod 18 is connected to each loading plate via a quick-release clamp (such as a sleeve connector 28), and a fixing nut 27 is placed on the force transmission rod; the fixing nut 27 can be tightened and loosened as needed. The quick-release clamp allows for easy disassembly of the two loading plates and the loading and removal of the particle sample. When the second loading plate 19 at the top is loaded to the very top, the fixing nut on the top is loosened to remove the second loading plate. The particle sample can then be poured into the sample placement cavity along the gap at the top of the two organic glass baffles, thereby achieving the loading of the particle sample. When the first loading plate on the left is loaded to the very outside, the fixing nut is loosened and the first loading plate is removed, and the sample slides out from the left, thereby achieving the unloading of the particle sample.

[0059] Furthermore, a test method for a micromechanical test platform of granular materials based on optical measurement technology is provided, the test method comprising the following steps:

[0060] Step 1: Move the second loading plate to the top, remove the second loading plate, load the particle sample into the sample placement chamber to obtain a two-dimensional dense particle system, and then install the second loading plate; turn on the polarization light source, and return the analyzer to a position parallel to the polarization light source and the biaxial loading device;

[0061] Step 2: Controlling the first loading plate and the second loading plate to start moving by the control system, shearing the two-dimensional dense particle system composed of photoelastic particles according to a set loading path, and obtaining a macroscopic response of stress and deformation of the two-dimensional dense particle system by obtaining the forces applied to the first loading plate and the second loading plate;

[0062] Step 3: When the set load is reached, the loading is stopped; and the image acquisition system is used to take a photo to obtain a photoelastic image of the two-dimensional dense particle system under the polarized light field;

[0063] Step 4: Turn off the polarized light source and turn on the LED light source; rotate the analyzer 90° and use the image acquisition system to take pictures again to obtain a photoelastic image of the two-dimensional dense particle system under a non-polarized light field for dynamic information analysis of the particle sample displacement and rotation;

[0064] Step 5: The particle sample is loaded again by controlling the control system, and steps 2, 3 and 4 are repeated to perform another round of loading test.

[0065] This test method combines photoelasticity and digital image correlation technology. Through high-precision, high-frequency image acquisition technology, it can intuitively and synchronously obtain the contact force distribution and dynamic information of granular materials without contact.

[0066] Furthermore, the contact force between the particle samples is obtained through the photoelastic image, which specifically includes the following steps:

[0067] Selecting a suitable brightness threshold to distinguish the particle sample from the background, thereby generating a binary image; then performing a Hough transform on the image after the binary image to determine the center position and radius of the particle sample;

[0068] Through the position of the particle sample, the geometric contact point between the particle samples is identified, that is, the point contact; then a brightness gradient threshold is set, and only the brightness gradient G at the contact point is 2 If the value is greater than the threshold, the contact point is a real contact point. The calculation formula of the brightness gradient is as follows:

[0069] .

[0070] Brightness gradient G 2 It is usually used to describe the speed and direction of brightness change at a certain point in an image. This calculation relies on two gradient components: horizontal gradient and vertical gradient. In the formula, i and j are positive integers, such as 1, 2, 3, 4...n. The subscript I represents the brightness value at a certain point in the image, and the subtraction represents the brightness change rate, such as I i+1，j -Ii-1，j Indicates the rate of change of image brightness in the horizontal direction, I i，j+1 -I i，j-1 Indicates the rate of change of image brightness in the vertical direction.

[0071] With the contact force as a free parameter, the nonlinear least square method is used to obtain the optimal parameter of the contact force, so that the actual brightness value of each point of the particle sample is closest to the theoretical brightness value, thereby obtaining the contact force between the particle samples.

[0072] The strain field and particle dynamics information of particles obtained by digital image correlation technology include the following:

[0073] First, the photoelastic images acquired under a non-polarized light field are gridded. Then, correlation analysis is performed on the images before and after deformation based on the grid characteristics to obtain the motion trajectory and deformation of the particle specimen during loading, thereby obtaining the displacement, rotation, and strain fields of the particle specimen.

[0074] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A microscopic mechanical testing platform for granular materials based on optical measurement technology, including an optical platform, characterized in that: The optical platform is provided with a biaxial loading device, a polarizer is provided on one side of the biaxial loading device, a polarized light source is provided on the side of the polarizer away from the biaxial loading device, a deflectable analyzer is provided on the other side of the biaxial loading device, an image acquisition system is provided on the side of the analyzer away from the biaxial loading device, and the image acquisition system is arranged toward the biaxial loading device; a plurality of LED light sources are also arranged in the area between the analyzer and the biaxial loading device, and a control system is also provided on the optical platform, and the control system is electrically connected to the biaxial loading device; The optical platform includes a first optical platform and a second optical platform that are independently arranged, the polarized light source, the polarizer and the biaxial loading device are all arranged on the first optical platform, and the analyzer and the image acquisition system are arranged on the second optical platform; A supporting base plate is provided on the second optical platform, an arc-shaped groove is provided on the supporting base plate, an analyzer support plate is provided below the analyzer, one end of the analyzer support plate is rotatably connected to the supporting base plate, and a pulley is provided below the other end of the analyzer support plate, the pulley is arranged in the arc-shaped groove and slides along the arc-shaped groove.

2. The granular material micromechanics test platform based on optical measurement technology according to claim 1 is characterized in that: The LED light sources are a pair that are symmetrically arranged, and the light is set toward the middle of the biaxial loading device.

3. The granular material micromechanics test platform based on optical measurement technology according to claim 1 is characterized in that: The biaxial loading device includes a supporting base arranged on the optical platform, a pair of parallel and vertically arranged organic glass baffles are provided on the supporting base, a side baffle is provided on one side of the pair of organic glass baffles, a first loading plate is provided on the other side, and a first loading assembly connected to the first loading plate is provided, a second loading plate and a second loading assembly connected to the second loading plate are provided above the pair of organic glass baffles; the first loading plate and the second loading plate are movably arranged between the pair of organic glass baffles, and the area enclosed by the supporting base, the side baffles, the first loading plate, the second loading plate and the pair of organic glass baffles form a sample placement cavity.

4. The granular material micromechanics test platform based on optical measurement technology according to claim 3 is characterized in that: The first loading assembly includes a first bracket arranged on the optical platform, a first stepper motor is provided on the first bracket, an output end of the first stepper motor is connected to a first mechanical sensor, the first mechanical sensor is connected to the first loading plate through a force transmission rod, the first loading plate moves horizontally, and the first stepper motor and the first mechanical sensor are both electrically connected to the control system.

5. The granular material micromechanics test platform based on optical measurement technology according to claim 3 is characterized in that: The second loading assembly includes a second bracket arranged on the optical platform, a second stepper motor is provided under the horizontal section of the second bracket, the output end of the second stepper motor is connected to a second mechanical sensor, the second mechanical sensor is connected to the second loading plate through a force transmission rod, the second loading plate moves vertically, and the second stepper motor and the second mechanical sensor are both electrically connected to the control system.

6. The granular material micromechanics test platform based on optical measurement technology according to claim 5 is characterized in that: A top plate is provided above the pair of organic glass baffles, and one side of the top plate is detachably connected to the vertical section of the second bracket; a rack is provided on the outer side of the side baffle, and a slide body is provided on the vertical section of the second bracket, and a gear meshing with the rack is provided in the slide body.

7. The granular material micromechanics test platform based on optical measurement technology according to claim 3 is characterized in that: The first loading assembly is detachably connected to the first loading plate via a quick-release clamp, and the second loading assembly is also detachably connected to the second loading plate via a quick-release clamp.

8. The test method of the granular material micromechanics test platform based on optical measurement technology according to any one of claims 3 to 7, characterized in that: The test method comprises the following steps: Move the second loading plate to the top, remove the second loading plate, place the particle sample into the sample placement chamber, and then install the second loading plate; turn on the polarized light source, and place the analyzer in a position parallel to the polarized light source and the biaxial loading device; The control system controls the first loading plate and the second loading plate to start moving, shears the two-dimensional dense particle system composed of photoelastic particles according to a set loading path, and obtains a macroscopic response of stress and deformation of the two-dimensional dense particle system by obtaining the forces applied to the first loading plate and the second loading plate; When the load reaches a set load, the loading is stopped; and the image acquisition system is used to take a picture to obtain a photoelastic image of the two-dimensional dense particle system under a polarized light field; Turn off the polarized light source and turn on the LED light source; rotate the analyzer 90°, and use the image acquisition system to take pictures again to obtain a photoelastic image of the two-dimensional dense particle system in a non-polarized light field for dynamic information analysis of the displacement and rotation of the particle sample.

Images