Particle material micromechanics test platform and method based on optical measurement technology

Abstract

The invention discloses a granular material micromechanics test platform and method based on an optical measurement technology, the test platform is provided with a polarized light source, a polarizer, a biaxial loading device, an LED light source, an analyzer and an image acquisition system from left to right in sequence, and the optical platform is also provided with a control system. And the control system is electrically connected with the biaxial loading device. The granular material micromechanics test platform is based on an optical measurement technology, shearing of a two-dimensional dense particle system is achieved through movement of the adjustable biaxial loading device, switching between a polarized light field and an unpolarized light field can be achieved by rotating the polarization analyzer, so that test images under different light fields are obtained, and the test precision is improved. A photoelastic technology and a digital image related technology are combined to carry out contact force and dynamics analysis; according to the granular material micromechanics test platform, contact force and dynamic information of the granular material can be visually and synchronously obtained through a high-precision and high-acquisition-frequency image acquisition technology without contact.

Description

Technical Field

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

[0002] Granular materials are complex systems formed by the interaction of a large number of discrete solid particles. Due to the high heterogeneity of their internal structure, granular materials will exhibit complex mechanical behaviors under the action of external forces, such as shear bands, dilatancy, and yielding. A large number of studies have shown that there is a close relationship between the complex mechanical properties of granular materials and their microstructures. Therefore, studying the microdynamics, contact network, and microstructure of granular materials provides a new way to reveal the complex macro- and micro-mechanical properties of granular materials. The research methods for the mechanical properties of granular materials include numerical simulation and physical experiments. Although numerical simulation has made significant progress in the study of the mechanism of complex macroscopic phenomena of granular materials; from the experimental point of view, conventional experimental methods (such as large triaxial tests, ring shear, and direct shear tests) can only obtain the macroscopic mechanical response of granular materials; at the micro- and micro-level, due to the lack of experimental observations, some key mechanisms still need to be combined with sophisticated measurement test techniques for more in-depth research.

[0003] Photoelasticity is a stress measurement device that combines optics and mechanics. It determines the surface stress distribution by measuring the interference fringes on the surface of the photoelastic sample in the polarized light field. Due to its significant advantages in measuring stress, photoelasticity has been successfully applied to the study of granular materials, providing technical support for the measurement of force chain structures in two-dimensional granular systems. Digital Image Correction (DIC) is a non-contact strain measurement technology that obtains the displacement field and strain field of the object surface by tracking or matching the position of the same pixel point in the image before and after the deformation of the object surface. DIC technology provides additional data for studying the deformation and rotation of granular materials, making up for the shortcomings of photoelasticity in dynamic measurement. However, there are still challenges in the combined use of these two technologies. For example, the polarization field generated by the photoelasticity will interfere with DIC observations, resulting in DIC imaging distortion. On the other hand, the loading systems suitable for photoelasticity and DIC are mostly unidirectional loading mainly based on tension and compression, which cannot meet the complex biaxial or triaxial loading requirements in granular systems. It is necessary to design a set of test devices suitable for biaxial loading. Summary of the invention

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

[0005] To achieve the above object, the technical solution adopted by the present invention is: A microscopic mechanical testing platform for granular materials based on optical measurement technology comprises an optical platform, wherein a biaxial loading device is arranged on the optical platform, a polarizer is arranged on one side of the biaxial loading device, a polarized light source is arranged on the side of the polarizer away from the biaxial loading device, a deflectable analyzer is arranged on the other side of the biaxial loading device, an image acquisition system is arranged 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 arranged on the optical platform, and the control system is electrically connected to the biaxial loading device.

[0006] This granular material micromechanics test platform is based on optical measurement technology. Through the movement of an adjustable biaxial loading device, it can achieve shearing of a two-dimensional dense granular system. By rotating the analyzer, it can switch between polarized light fields and unpolarized light fields to obtain test images under different light fields, and combine photoelastic technology and digital image correlation technology to perform contact force and dynamics analysis. This granular material micromechanics test platform uses high-precision, high-acquisition-frequency image acquisition technology without contact, and can intuitively and synchronously acquire the contact force and dynamics information of granular materials.

[0007] The control system can control the biaxial loading device to load the particle sample with forces in multiple directions. 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, and imaging distortion is reduced.

[0008] Furthermore, the optical platform includes a first optical platform and a second optical platform which are independently arranged; the polarized light source, the polarizer and the biaxial loading device are all arranged on the first optical platform; the analyzer and the image acquisition system are arranged on the second optical platform, so as to avoid the deflection adjustment of the analyzer affecting the biaxial loading device.

[0009] 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, a pulley or a slider is provided below the other end of the analyzer support plate, 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.

[0010] Furthermore, the LED light source is a pair that is symmetrically arranged, and the light is set toward the middle of the dual-axis loading device.

[0011] 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 and a first loading assembly connected to the first loading plate are provided on the other side, 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.

[0012] 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.

[0013] Furthermore, the second loading assembly includes a second bracket arranged on the optical platform, a second stepper motor is provided below 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.

[0014] 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 in the vertical section of the second bracket, and a gear meshing with the rack is provided in the slide body.

[0015] 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.

[0016] Furthermore, a test method for a micromechanics test platform of granular materials based on optical measurement technology comprises the following steps: Move the second loading plate to the top, remove the second loading plate, load the particle sample into the sample placement cavity, and then install the second loading plate; turn on the polarized light source, and return the analyzer to 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 the 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 loading reaches the set load, the loading is stopped; the image acquisition system is used to take pictures to obtain a photoelastic image of the two-dimensional dense particle system under the polarized light field; The polarized light source is turned off and the LED light source is turned on; the analyzer is rotated 90° and the image acquisition system is used again to take pictures to obtain a photoelastic image of the two-dimensional dense particle system in a non-polarized light field for dynamic information analysis of particle sample displacement and rotation.

[0017] Acquiring the contact force between particle samples through photoelastic images specifically includes the following steps: Selecting a suitable brightness threshold to distinguish between the particle sample and 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; 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: .

[0018] The contact force is taken as a free parameter and the optimal parameter of the contact force is obtained using the nonlinear least square method, 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.

[0019] The strain field and particle dynamics information of particles obtained by digital image correlation technology include the following: Firstly, the photoelastic images acquired under the non-polarized light field are gridded. Then, the images before and after deformation are correlated and analyzed according to the grid characteristics. The motion trajectory and deformation of the particle sample during loading are obtained, thereby obtaining the displacement, rotation and strain field of the particle sample.

[0020] 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. Through the movement of an adjustable biaxial loading device, the shearing of a two-dimensional dense granular system is realized. By rotating the analyzer, it is possible to switch between polarized light fields and unpolarized light fields to obtain test images under different light fields, and combine photoelastic technology and digital image correlation technology to perform contact force and dynamic analysis; the test method uses high-precision, high-acquisition frequency image acquisition technology without contact, and can intuitively and synchronously acquire 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 acquire 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 of 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

[0021] Figure 1 It is a schematic diagram of the overall structure of the micromechanics test platform of granular materials based on optical measurement technology of the present invention; Figure 2 A schematic diagram of the arrangement structure of the biaxial loading device of the present invention; Figure 3 A schematic diagram of the structure of the connection between the force transmission rod and the loading plate provided by the present invention; 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, rotating 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 cavity; 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

[0022] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "middle", "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships 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 direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0024] like Figure 1 and Figure 2 As shown, a microscopic mechanical test platform for granular materials based on optical measurement technology includes an optical platform, a biaxial loading device 4 is provided on the optical platform, a polarizer 2 is provided on one side of the biaxial loading device 4, a polarized light source 1 is provided on the side of the polarizer 2 away from the biaxial loading device 4, a deflectable analyzer 3 is provided on the other side of the biaxial loading device 4, an image acquisition system 5 is provided on the side of the analyzer 3 away from the biaxial loading device 4, and the image acquisition system 5 is arranged toward the biaxial loading device 4; a plurality of LED light sources 8 are also arranged in the area between the analyzer 3 and the biaxial loading device 4, and a control system 6 is also provided on the optical platform, and the control system 6 is electrically connected to the biaxial loading device 4. That is, 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 arranged in sequence from left to right on this test platform.

[0025] The microscopic mechanics test platform for 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 4. By rotating the analyzer 3, the polarized light field and the unpolarized light field can be switched to obtain test images under different light fields, and the contact force and dynamics analysis can be performed in combination with photoelastic technology and digital image correlation technology. The microscopic mechanics test platform for granular materials uses high-precision, high-acquisition-frequency image acquisition technology without contact, and can intuitively and synchronously acquire the contact force and dynamics information of granular materials.

[0026] 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 through 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 smooth surface reflections on non-metallic surfaces (such as glass, plastic, etc.), while keeping the color and tone of the object itself unaffected, which is conducive to the collection of photoelastic images of particle samples. In addition, the polarizer can also eliminate scattered light, making the field of view clear and natural. ‌ The analyzer 3 can be used to detect the polarization state of light after passing through the biaxial loading device. It can only allow light vibrating in a specific direction to pass through, but not light vibrating perpendicular to the direction to pass through. By rotating the analyzer, the change in the intensity of the transmitted light can be observed to determine the polarization type of the light.

[0027] The control system 6 can control the biaxial loading device 4 to apply multi-directional force loading 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, and imaging distortion is reduced.

[0028] 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.

[0029] By setting up two independent optical platforms, it is possible to avoid vibration of the optical platform caused by the rotation of the analyzer around the axis and affect the dual-axis loading device, which is beneficial to improving the accuracy and stability of detection and avoiding errors caused by manual operation as much as possible.

[0030] Furthermore, a supporting base plate 10 is provided on the second optical platform 9, and an arc groove 29 is provided on the supporting base plate 10. An analyzer support plate is provided below the analyzer 3, and one end of the analyzer support plate is rotatably connected to the supporting base plate 10 through a rotating 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 groove 29 and slides along the arc groove 29.

[0031] The arc groove 29 is a 90-degree arc groove, and the pulley 30 can slide in the arc groove 29. The pulley 30 slides from one end of the arc groove 29 to the other end, which just allows the analyzer 3 to deflect from a direction parallel to the biaxial loading device 4 to a direction perpendicular to the biaxial loading device 4, thereby realizing the switching between the polarized light field and the non-deflected light field. This adjustment method is relatively simple and can be repeatedly operated without additional calibration adjustment.

[0032] When it is necessary to collect images in a polarized light field, the analyzer 3 is returned to its original position, as shown in Figure 1 When it is necessary to capture an image without polarization, the analyzer 3 is rotated 90° along the arc groove 29.

[0033] In some embodiments, magnets are embedded at both ends of the arc groove 29, and magnets are also embedded at both ends of the pulley 30. When it is close to the end of the arc groove, it can be sucked, which can play a fixing role and prevent it from shaking.

[0034] Furthermore, the LED light source 8 is a pair of symmetrically arranged light sources, and the light is arranged 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.

[0035] Furthermore, the biaxial loading device 4 includes a supporting base 13 arranged on the optical platform, a pair of parallel and vertically arranged organic glass baffles 22 are provided on the supporting base 13, a side baffle 21 is provided on one side of the pair of organic glass baffles 22, a first loading plate 20 is provided on the other side, and a first loading assembly connected to the first loading plate 20, a second loading plate 19 is provided above the pair of organic glass baffles 22, and a second loading assembly connected to the second loading plate 19; 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 supporting base 13, the side baffle 21, the first loading plate 20, the second loading plate 19 and the pair of organic glass baffles 22 forms a sample placement cavity 23.

[0036] 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.

[0037] The second loading assembly includes a second bracket 12 arranged on the optical platform, a second stepper motor 15 is provided below 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, and the second stepper motor 15 and the second mechanical sensor 17 are both electrically connected to the control system 6.

[0038] Through the above arrangement, the area between the pair of organic glass baffles 22 is just formed under the enclosure of 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.

[0039] 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.

[0040] 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.

[0041] The first mechanical sensor 16 and the second mechanical sensor 17 are provided with force transmission rods 18 at both ends to connect with the respective stepping motors and loading plates, and can transmit the force better and more stably. The second bracket has a vertical section and a horizontal section to arrange the second loading plate from above a pair of organic glass baffles.

[0042] Furthermore, a top plate 24 is provided above the pair of organic glass baffles 22, and 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, having a short vertical side, which can be connected to the vertical section of the second bracket 12 through a connector, and a through slot is provided on the long horizontal side, through which the second loading plate 19 can pass. The provision of the top plate 24 can improve the stability of the pair of organic glass baffles 22.

[0043] 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. Such an arrangement facilitates the loading and unloading of the side baffle 21 and the pair of plexiglass baffles 22.

[0044] 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.

[0045] Specific, combined Figure 3 As shown, the force transmission rod 18 is connected to each loading plate through 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. Through the quick-release clamp, the two loading plates can be easily disassembled and the particle sample can be loaded and removed. When the second loading plate 19 at the top is loaded to the top, the fixing nut on the top is loosened to remove the second loading plate, and then the particle sample can be poured into the sample placement cavity along the gap at the top of the two organic glass baffles, thereby realizing the loading of the particle sample; when the first loading plate on the left is loaded to the outermost part, the fixing nut is loosened and the first loading plate is removed, and the sample slides out from the left, thereby realizing the unloading of the particle sample.

[0046] Furthermore, a test method for a micromechanics test platform of granular materials based on optical measurement technology comprises the following steps: Step 1: Move the second loading plate to the top, remove the second loading plate, load the particle sample into the sample placement cavity to obtain a two-dimensional dense particle system, and then install the second loading plate; turn on the polarized light source, and return the analyzer to a position parallel to the polarized light source and the biaxial loading device; Step 2: Control the first loading plate and the second loading plate to start moving through the control system, shear the two-dimensional dense particle system composed of photoelastic particles according to the set loading path, and obtain the 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; Step 3: When the set load is reached, the loading is stopped; the image acquisition system is used to take a photo to obtain a photoelastic image of the two-dimensional dense particle system under a polarized light field; 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 the photoelastic image of the two-dimensional dense particle system under the non-polarized light field for dynamic information analysis of particle sample displacement and rotation; 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.

[0047] This test method combines photoelastic technology and digital image correlation technology. Through high-precision and high-acquisition frequency image acquisition technology, it can intuitively and synchronously obtain the contact force distribution and dynamic information of granular materials without contact.

[0048] Furthermore, the contact force between the particle samples is obtained through the photoelastic image, which specifically includes the following steps: Selecting a suitable brightness threshold to distinguish between the particle sample and 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; 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: .

[0049] 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 depends on the gradient components in two directions: 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 -I i-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.

[0050] The contact force is taken as a free parameter and the optimal parameter of the contact force is obtained using the nonlinear least square method, 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.

[0051] The strain field and particle dynamics information of particles obtained by digital image correlation technology include the following: Firstly, the photoelastic images acquired under the non-polarized light field are gridded. Then, the images before and after deformation are correlated and analyzed according to the grid characteristics. The motion trajectory and deformation of the particle sample during loading are obtained, thereby obtaining the displacement, rotation and strain field of the particle sample.

[0052] Although 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 the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A micromechanical test platform for granular materials based on optical measurement technology, including an optical platform, characterized in that: 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, and the control system is electrically connected to the biaxial loading device.

2. The micromechanics test platform for granular materials based on optical measurement technology according to claim 1 is characterized in that: The optical platform comprises a first optical platform and a second optical platform which are independently arranged; the polarized light source, the polarizer and the biaxial loading device are all arranged on the first optical platform; the analyzer and the image acquisition system are arranged on the second optical platform.

3. The micromechanics test platform for granular materials based on optical measurement technology according to claim 2 is characterized in that: 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, 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.

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

5. The micromechanics test platform for granular materials based on optical measurement technology according to claim 1, 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 and a first loading assembly connected to the first loading plate are provided on the other side, 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.

6. The micromechanics test platform for granular materials based on optical measurement technology according to claim 5, 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.

7. The micromechanics test platform for granular materials based on optical measurement technology according to claim 5, characterized in that: The second loading assembly includes a second bracket arranged on the optical platform, a second stepper motor is provided below 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.

8. The micromechanics test platform for granular materials based on optical measurement technology according to claim 7, 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 in the vertical section of the second bracket, and a gear meshing with the rack is provided in the slide body.

9. The micromechanics test platform for granular materials based on optical measurement technology according to claim 5, 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.

10. The test method of the micromechanics test platform of granular materials based on optical measurement technology according to any one of claims 5 to 9, characterized in that: The test method comprises the following steps: Move the second loading plate to the top, remove the second loading plate, load the particle sample into the sample placement cavity, and then install the second loading plate; turn on the polarized light source, and return the analyzer to 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 the macroscopic response of stress and deformation of the two-dimensional dense particle system by obtaining the force applied to the first loading plate and the second loading plate; When the loading reaches the set load, the loading is stopped; the image acquisition system is used to take pictures to obtain a photoelastic image of the two-dimensional dense particle system under the polarized light field; The polarized light source is turned off and the LED light source is turned on; the analyzer is rotated 90° and the image acquisition system is used again to take pictures to obtain a photoelastic image of the two-dimensional dense particle system in a non-polarized light field for dynamic information analysis of particle sample displacement and rotation.

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