Photoelastic test system and force chain dynamic evolution identification method based on same

Abstract

The invention relates to a photoelastic test system and a force chain dynamic evolution identification method based on the system.The system comprises a high-frequency power loading system, a boundary stress wave low-reflection test device and a data acquisition-analysis system.The boundary stress wave low-reflection test device comprises a model box system, and the model box system comprises a model box frame; a photoelastic sample is arranged in the model box frame, a power loading system is arranged above the model box system, optical systems are arranged on two sides of the model box system, the high-frequency power loading system comprises a voice coil motor, a power data acquisition instrument, a power sensor, an acceleration sensor and a temperature sensor, the voice coil motor is connected with the power data acquisition instrument, and the power data acquisition instrument is connected with the power sensor. The system further comprises a high-frequency image acquisition system and a data analysis system. Compared with the prior art, the high-frequency low-amplitude loading device has the advantages of realizing high-frequency low-amplitude loading and the like.

Description

Technical Field

[0001] The invention relates to the field of photoelastic test systems, and in particular to a photoelastic test system and a force chain dynamic evolution identification method based on the system. Background Art

[0002] The high-frequency vibration problem caused by high-speed trains in the geotechnical foundation under the track is a challenge that has attracted much attention in the field of rail transit engineering. Although the amplitude of high-frequency vibration is relatively small, as the speed of trains further increases, this vibration may become more significant, posing a potential threat to the long-term stability of the geotechnical foundation under the track.

[0003] Usually, geotechnical foundations under track use geotechnical granular materials that are easy to fill and compact, and these materials have significant discreteness. Previous studies have shown that geotechnical granular materials will show obvious strength attenuation under high-frequency and low-amplitude vibrations. However, there is still a lack of clear understanding of the mechanism of this strength attenuation, the appropriate description method, and effective countermeasures, which makes the track foundation face potential risks during its long-term service.

[0004] Photoelastic tests can directly obtain the visualization process of particle force and configuration development at the microscopic scale, providing an effective means to recognize and understand the multi-scale mechanical behavior of particles under high-frequency and low-amplitude vibration. At present, photoelastic instruments are mainly based on static tests, and on this basis, adaptive modifications have been made for geotechnical engineering. Almost all of them use motors as loading devices to directly or indirectly load the specimens from different directions. For example, the shear model of North Carolina State University uses a direct shear test box and loading rods and loading motors in the horizontal and vertical directions to achieve biaxial static loading. In terms of dynamic loading, existing equipment mainly focuses on impact loads. For example, the oblique impact photoelastic experiment of Duke University uses a two-dimensional copper disk or a similar heavy object as a force-applying object to impact the particle cluster and then embed it to generate an impact dynamic load; another example is the SHPB photoelastic experiment, which uses an impactor to impact a conductive rod to generate a high-intensity shock wave to achieve high-speed, short-term dynamic loading; another example is the impact photoelastic experiment of Vanderbilt University, which even uses a projectile fired by an air gun as the source of the impact load. In summary, existing photoelastic tests are mainly static or limited-number impact loading, do not involve stable cyclic dynamic loading, and cannot meet the requirements of high-frequency and low-amplitude loading. Summary of the invention

[0005] The purpose of the present invention is to provide a photoelastic test system and a force chain dynamic evolution identification method based on the system in order to achieve high-frequency low-amplitude loading and reduce the reflected waves generated by the sample at the device boundary during high-frequency dynamic loading.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A photoelastic test system capable of realizing high-frequency and low-amplitude loading, the system comprising a high-frequency power loading system, a boundary stress wave low-reflection test device and a data acquisition-analysis system, wherein the boundary stress wave low-reflection test device comprises a model box system, the model box system comprises a model box frame, the model box frame comprises a photoelastic sample, a power loading system is arranged above the model box system, optical systems are arranged on both sides of the model box system, the high-frequency power loading system comprises a voice coil motor, a power data acquisition instrument, a power sensor, an acceleration sensor and a temperature sensor, the voice coil motor is connected to the power data acquisition instrument, and the system also comprises a high-frequency image acquisition system and a data analysis system.

[0008] Furthermore, a loading bar is arranged on the top of the box frame, and the loading bar and the loading head end of the voice coil motor are at a certain distance from the loading bar, and the power sensor, acceleration sensor and temperature sensor are arranged on the voice coil motor.

[0009] Furthermore, the optical system includes a light source, a polarizer, a first 1 / 4 wave plate, a second 1 / 4 wave plate and an analyzer, wherein the light source, the polarizer and the first 1 / 4 wave plate are arranged on one side of the model box system, and the second 1 / 4 wave plate and the analyzer are arranged on the other side of the model box system.

[0010] Furthermore, the high-frequency image acquisition system is arranged on a side of the model box system where the second 1 / 4 wave plate and the analyzer are arranged.

[0011] Furthermore, the data analysis system includes a data acquisition device and a data processing host, the data acquisition device and the data processing host are connected to each other, and the data acquisition device is connected to a power sensor, an acceleration sensor and a temperature sensor.

[0012] Furthermore, boundary energy absorbing devices are provided on both sides and the bottom of the model box system, and the boundary energy absorbing devices are U-shaped components made of energy absorbing materials.

[0013] Another aspect of the present invention provides a method for identifying the dynamic evolution of a force chain based on the above-mentioned photoelastic test system capable of realizing high-frequency and low-amplitude loading. The method comprises the following steps:

[0014] The photoelastic specimen is marked with a cross and placed in the model box;

[0015] Adjust the up and down position of the power loading system until the loading head of the voice coil motor is a certain distance away from the loading bar on the top of the box frame;

[0016] Connect the power supply and start the data acquisition instrument of the data analysis system, start the data processing host of the data analysis system, reset the loading head of the voice coil motor, set the initial position of the motor to complete the motor initialization;

[0017] Control the angles of the polarizer and analyzer of the optical system, control the angles of the first 1 / 4 wave plate and the second 1 / 4 wave plate at the same time, and turn on the light source of the optical system;

[0018] Turn on the high-frequency image acquisition system, adjust the exposure and white balance values ​​in M ​​mode, set the voice coil motor to load at a given frequency and amplitude, and after the voice coil motor is activated, the high-frequency image acquisition system performs high-speed continuous shooting, and the obtained photos are transmitted to the data analysis system;

[0019] In the data analysis system, identification and data analysis are performed. The particle position and radius of the photo are identified as the particle geometric information. Based on the particle geometric information, the particle position matching algorithm is used to obtain the position change of the same marked particle in different states, and the displacement field of the particle system when the state changes is obtained;

[0020] Based on the particle geometry information, the positions where the particles contact each other are determined and the optical properties at the contact points are analyzed to obtain the effective contact relationship between the particles.

[0021] Through the force chain identification algorithm, the spatial distribution of force chains at different times is identified by combining particle geometry information, effective contact relationship and stress state, and the correlation analysis between particle motion and force chain evolution under high-frequency loads is realized.

[0022] Furthermore, the shooting frequency of the high-speed continuous shooting is not less than 10 times the loading frequency.

[0023] Furthermore, after the light source of the optical system is turned on, light is emitted from the light source and passes through the polarizer, the first 1 / 4 wave plate, the model box, the second 1 / 4 wave plate and the analyzer in sequence.

[0024] Furthermore, the angles of the polarizer and analyzer of the optical system are controlled, and the angles of the first quarter wave plate and the second quarter wave plate are controlled at the same time as follows:

[0025] Control the polarizer to rotate to 0 degrees, the analyzer to rotate to 90 degrees, the first 1 / 4 wave plate to rotate to 135 degrees, and the second 1 / 4 wave plate to rotate to 45 degrees; or control the polarizer to rotate or 180 degrees, the analyzer to rotate to 270 degrees, the first 1 / 4 wave plate to rotate to 315 degrees, and the second 1 / 4 wave plate to rotate to 225 degrees.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The U-shaped components made of energy-absorbing materials are arranged on both sides and the bottom of the model box in the test device adopted by the present invention, which reduces the reflected waves generated by the sample at the device boundary during high-frequency power loading, and realizes high-frequency and low-amplitude loading through the voice coil motor of the power loading system of the present invention. At the same time, at the data analysis level, the identification of the displacement field and the evolution analysis of the microscopic force chain structure are added on the basis of the currently widely used principal stress analysis, based on which the photoelastic test with high-frequency and low-amplitude loading and the efficient multi-scale analysis method are realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 are the particles identified in different states and their corresponding numbers, where Figure 1 (a) is the particles identified in state 1 and their corresponding numbers. Figure 1 (b) The particles identified in state 2 and their corresponding numbers. Figure 1 (c) Particles identified in state 3 and their corresponding numbers;

[0029] Figure 2 is the displacement field corresponding to the state change process, where Figure 2 (a) is the displacement diagram from state 1 to 2. Figure 2 (b) is the displacement diagram from state 2 to 3;

[0030] Figure 3 is the force chain of different states identified, where Figure 3 (a) is the state 1 force chain, Figure 3 (b) is the state 2 force chain, Figure 3 (c) is the state 3 force chain;

[0031] Figure 4 is the force chain and its displacement when the state changes, where Figure 4 (a) is the state 2 force chain and its displacement from state 1 to 2, Figure 4 (b) is the state 3 force chain and its displacement from state 2 to state 3;

[0032] Figure 5 It is a schematic diagram of the structure of the present invention;

[0033] Figure 6 It is a schematic diagram of the mechanical loading system;

[0034] Figure 7 It is a schematic diagram of the data analysis system;

[0035] In the figure, 1-optical system; 11-light source; 12-polarizer; 13-first 1 / 4 wave plate; 14-second 1 / 4 wave plate; 15-analyzer; 2-model box system; 21-model box frame; 22-photoelastic sample; 23-boundary energy absorption device; 3-high frequency image acquisition system; 4-power loading system; 41-voice coil motor; 42-power data acquisition instrument; 43-power sensor; 44-acceleration sensor; 45-temperature sensor; 5-data analysis system; 51-data acquisition instrument; 52-data processing host. DETAILED DESCRIPTION

[0036] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0037] The present invention proposes a photoelastic test system and a method for identifying the dynamic evolution of a force chain based on the system, which can realize high-frequency and low-amplitude loading. The photoelastic test system mainly includes a high-frequency dynamic loading system, a boundary stress wave low-reflection test device and a data acquisition-analysis system. The high-frequency dynamic loading system can achieve a cyclic loading of up to 50Hz, and the loading amplitude range is 0-1000N; it can obtain the applied power, loading end acceleration and loading device temperature in real time. The boundary stress wave low-reflection test device can effectively reduce the reflection of stress waves at the device boundary. The data analysis system can use the pictures collected by the high-frequency image acquisition system to obtain information such as particle position, particle contact relationship, and stress state at different times through image processing by computer vision technology, and combine the force characteristics and displacement field of the photoelastic particles to obtain the spatial distribution of the force chain at different times through the force chain identification algorithm; thereby realizing the correlation analysis of particle movement and force chain evolution under high-frequency load. The present invention helps to explore and understand the microscopic mechanism of the mechanical behavior of rock and soil granular materials under high-frequency vibration, thereby providing a new cross-scale idea for the design and maintenance of sub-track geotechnical foundations under higher-speed driving conditions.

[0038] like Figure 5 As shown, the system of the present invention includes a high-frequency power loading system 4, a boundary stress wave low reflection test device and a data acquisition-analysis system, wherein the boundary stress wave low reflection test device includes a model box system 2, the model box system 2 includes a model box frame 21, the model box frame 21 includes a photoelastic sample 22, a power loading system 4 is arranged above the model box system 2, and an optical system 1 is arranged on both sides of the model box system 2, the high-frequency power loading system 4 includes a voice coil motor 41, a power data acquisition instrument 42, a power sensor 43, an acceleration sensor 44 and a temperature sensor 45, the voice coil motor 41 is connected to the power data acquisition instrument 42, and the system also includes a high-frequency image acquisition system 3 and a data analysis system 5.

[0039] A loading bar is arranged on the top of the box frame 21 . The loading bar and the loading head end of the voice coil motor 41 are at a certain distance from the loading bar. The power sensor 43 , the acceleration sensor 44 and the temperature sensor 45 are arranged on the voice coil motor 41 .

[0040] The optical system 1 includes a light source 11, a polarizer 12, a first 1 / 4 wave plate 13, a second 1 / 4 wave plate 14 and an analyzer 15. The light source 11, the polarizer 12 and the first 1 / 4 wave plate 13 are arranged on one side of the model box system 2, and the second 1 / 4 wave plate 14 and the analyzer 15 are arranged on the other side of the model box system 2.

[0041] The high-frequency image acquisition system 3 is arranged on one side of the model box system 2 where the second 1 / 4 wave plate 14 and the analyzer 15 are arranged.

[0042] The data analysis system 5 includes a data acquisition device 51 and a data processing host 52 . The data acquisition device 51 and the data processing host 52 are connected to each other, and the data acquisition device 51 is connected to the power sensor 43 , the acceleration sensor 44 and the temperature sensor 45 .

[0043] Boundary energy absorbing devices 23 are provided on both sides and the bottom of the model box system 2 , and the boundary energy absorbing devices 23 are U-shaped components made of energy absorbing materials.

[0044] The schematic diagram of the high frequency power loading system (4) of the present invention is as follows Figure 6 The data analysis system diagram is shown in Figure 7 shown.

[0045] The present invention overcomes the defect that traditional photoelastic tests cannot perform stable cyclic loading, introduces an advanced dynamic loading system, realizes high-frequency and low-amplitude loading, takes into account the boundary reflection effect, and sets up a stress wave low-reflection device; at the same time, at the data analysis level, the identification of the displacement field and the evolution analysis of the mesoscopic force chain structure are added on the basis of the currently widely used principal stress analysis, based on which, a photoelastic test that can perform high-frequency and low-amplitude loading and an efficient multi-scale analysis method are realized.

[0046] In the present invention, the power loading system in the high-frequency and low-amplitude loading photoelastic test system can achieve a maximum cyclic loading of 50Hz, with a loading amplitude range of 0 to 1000N, and is implemented using a voice coil motor solution. The power loading system includes an acceleration sensor, a force sensor, and a temperature sensor, which can obtain the applied power, the acceleration of the loading end, and the temperature of the loading device in real time, thereby obtaining the macroscopic mechanical data required for the experiment.

[0047] The model box system can be adjusted in size according to the test requirements. The model box in the test device can be adjusted in size according to the test requirements. The maximum height and width of the model box are both 320mm (the maximum inscribed rectangle corresponding to the light-transmitting diameter of 500mm), and the maximum thickness is 20mm. It can be adjusted within this range to adapt to different particle sizes, thicknesses and component sizes.

[0048] The model box can be filled with photoelastic particles with different characteristics to achieve different experimental goals, mainly including the following: round particles with two different particle sizes, which can be used to simulate the mechanical response characteristics of binary particle materials under high-frequency dynamic loads, rectangular particles, and continua suitable for the size of the model box, which can be used to observe the stress distribution under concentrated loads, and damaged components including cracks, fissures, defects, etc., which are used to simulate the local stress distribution under damaged conditions.

[0049] The model box in the boundary stress wave low reflection test device can adjust the size according to the test requirements. U-shaped components made of energy-absorbing materials are arranged on both sides and the bottom of the model box to reduce the reflection waves generated by the sample at the device boundary when high-frequency dynamic loading occurs.

[0050] The data acquisition-analysis system can transmit images to the data processing host, and based on Python language and OpenCV computer vision methods, batch cropping, alignment, and exposure adjustment are performed, and then edge detection and Hough transform are performed, each particle is numbered, circular particles and cross marks on particles are identified, and the coordinates of the center of the photoelastic sample particle and the center of the cross mark and the particle radius are extracted, and the geometric information of the above particles is stored. It should be noted that although the physical size of the particle sample is known, due to the influence of factors such as shooting angle, focal length, and lens distortion, there are slight differences in the radius of the circular particles recognized by the computer. The error of this recognition is within 0.02.

[0051] The data acquisition-analysis system uses a particle matching algorithm based on the particle geometry information, and the morphology and statistical characteristics of the particle group to match the corresponding particle numbers between the two different states and mark them as the same particle. Since the recognition accuracy of the cross mark is higher than that of the circle, the difference vector of the cross mark coordinates of the particles in the two states is used as the displacement of the particle at this time step to obtain the displacement field of the particle system.

[0052] The data acquisition-analysis system can perform HSV channel separation on the image based on particle position and radius identification, and perform binarization after setting a threshold according to the optical characteristics of the image. A specific area can be selected for mean square gradient analysis to quantify the richness of the color of the photoelastic stripes in the area. First, each particle can be used as an analysis area to obtain the stress state of each particle, that is, the richer the stripes, the higher the value, and the higher the stress level; second, the area near the contact point between particles can be used as an analysis area to obtain the stress level of the contact point, and then judge the actual contact / force transfer relationship between the particles, that is, whether there is a sufficiently large contact force. This process converts optical information into mechanical information and obtains the contact network and stress field in the particle system.

[0053] The data acquisition-analysis system can identify the spatial distribution of force chains at a certain moment by combining particle geometry information (displacement field) and mechanical information (stress field) through a force chain identification algorithm.

[0054] The data acquisition and analysis system can comprehensively analyze the particle displacement / particle cluster morphology changes and the spatial distribution characteristics of the force chain at different times, and derive the time evolution characteristics of the force chain during dynamic loading.

[0055] The present invention also proposes a method for identifying the dynamic evolution of a force chain based on the above-mentioned photoelastic test system capable of realizing high-frequency and low-amplitude loading, the method comprising the following steps:

[0056] The photoelastic sample 22 is marked with a cross and then placed in the model box 21;

[0057] Adjust the up and down position of the power loading system 4 until the loading head end of the voice coil motor 41 is a certain distance away from the loading bar at the top of the box frame 21;

[0058] Connect the power supply and start the data acquisition instrument 51 of the data analysis system 5, start the data processing host 52 of the data analysis system 5, reset the loading head of the voice coil motor 41, set the initial position of the motor to complete the motor initialization;

[0059] Controlling the angles of the polarizer 12 and the analyzer 15 of the optical system 1, and controlling the angles of the first 1 / 4 wave plate 13 and the second 1 / 4 wave plate 14, and turning on the light source 11 of the optical system 1;

[0060] Turn on the high-frequency image acquisition system 3, adjust the exposure and white balance values ​​in the M mode, set the voice coil motor 41 to load at a given frequency and amplitude, and after the voice coil motor 41 is activated, the high-frequency image acquisition system 3 performs high-speed continuous shooting, and the obtained photos are transmitted to the data analysis system 5;

[0061] In the data analysis system 5, identification and data analysis are performed, and the particle position and radius are identified from the photo as the particle geometric information. Based on the particle geometric information, the position change of the same marked particle in different states is obtained through the particle position matching algorithm, and the displacement field of the particle system when the state changes is obtained;

[0062] Based on the particle geometry information, the positions where the particles contact each other are determined and the optical properties at the contact points are analyzed to obtain the effective contact relationship between the particles.

[0063] Through the force chain identification algorithm, the spatial distribution of force chains at different times is identified by combining particle geometry information, effective contact relationship and stress state, and the correlation analysis between particle motion and force chain evolution under high-frequency loads is realized.

[0064] Among them, the present invention first marks the photoelastic sample 22 with a cross and then puts it into the model box 21, checks with a level ruler to confirm that the model box is properly placed, and fastens the model box to the equipment, and places a loading bar on the top of the model box. Select a power loading system 4, and use bolts to adjust the upper and lower positions of the power loading system 4 until the end of its loading head is about 1 cm away from the loading. Connect the power supply and start the sensor data acquisition instrument 51 to confirm that the sensor displays the reading normally. Start the host 52, turn on the voice coil motor 41 control software, reset the loading head, set the motor initial position to complete the motor initialization. Turn on the polarizer 12, 15 rotation control software, rotate the polarizer 12 to 0 or 180 degrees, rotate the analyzer 15 to 90 or 270 degrees, and manually rotate the first 1 / 4 wave plate 13 to 135 or 315 degrees, and manually rotate the second 1 / 4 wave plate 14 to 45 or 225 degrees. Turn on the light source 11 and set it to white light.

[0065] Turn on the high-frequency image acquisition system camera 3, adjust the exposure in M ​​mode until the image is clear and bright, adjust and fix the white balance value until the image color is accurate, set the shooting mode to 120FPS high-speed continuous shooting, set the storage folder and other options to meet the various experimental requirements, and manually focus until the image is sharp before performing wire-controlled shooting.

[0066] The voice coil motor 41 is set to be loaded at a given frequency and amplitude, and high-speed continuous shooting is started after the voice coil motor 41 starts to move. In order to ensure sampling accuracy, the shooting frequency is generally not less than 10 times the loading frequency.

[0067] After the photos are transmitted to the data processing system, they are identified and analyzed:

[0068] Three typical states are selected to quantitatively analyze the displacement field and force chain evolution of the particles. Figure 1 The identified particles and their corresponding numbers in the three states. The particle numbers between different states have been matched, and the cross mark is drawn with a green dot in the center.

[0069] The transition from state 1 to state 2 is the process of load increase, and its corresponding displacement field is as follows: Figure 2 As shown in (a), it can be seen that the particles are displaced downward as a whole, among which the particles in the upper left area are displaced downward significantly, while the particles in the lower right area are slightly displaced to the right, and there is a shear band from the lower left to the upper right. State 2 to state 3 has the same load increase as state 1 to 2, and its corresponding displacement field is shown in Figure 2 As shown in (b), it can be seen that after the compaction of state 1-2, the overall displacement is Figure 2 (a) Decreased.

[0070] Depend on Figure 3 It can be seen that the final identified force chain is basically consistent with the intuitive judgment of the photoelastic particle stripes, reflecting the contact force transmission path and load-bearing structure of the particle system. As the external load level of the three states increases, the threshold for identifying high-stress particles increases accordingly.

[0071] There are 20 force chains in state 1. Figure 3 In the following changes, the new force chain is recorded starting from No. 21. From state 1 to state 2, such as Figure 3 (a) and (b) 3. The dominant long force chain structure in the particle system remains basically unchanged (3, 4, 6), some long force chains break during the evolution process (2, 5, 8, 9), most of the short force chains remain unchanged (1, 7, 12, 14, 17-19), and some force chains with lower stress levels withdraw from the load-bearing skeleton (11, 13, 15, 16, 20). The newly added force chains are mainly distributed at the specimen boundaries (21, 22, 24) and between the original force chains (23, 25, 26) to form lateral supports.

[0072] From state 2 to state 3, such as Figure 3 (b) and 3(c), the external load increase amplitude remains unchanged, the dominant long force chain structure remains basically unchanged (3, 4), some of the original force chains are extended (2, 5, 26), the long force chain is broken (9), most of the broken force chains remain the same (1, 6, 7, 14, 18, 19, 21, 22, 23, 24), some of the broken force chains disappear at a low stress level (8, 12, 17, 25), and the newly generated short force chains are still mainly concentrated at the edge (27) and between the existing force chain structures (28-30).

[0073] Separately extract and plot the displacement of particles on the force chain in state 2 and state 3 (corresponding to the previous state).

[0074] like Figure 4As shown in (a), from state 1 to state 2, the particles in the upper left corner area continue to move to the lower left and squeeze the side wall, the stress level increases to form new force chains 22 and 23, and the lower particles move to the lower right and squeeze the bottom layer to form new force chains 21 and 24; the original top long force chain 2 breaks when the particles move downward, and similarly, force chain No. 5 breaks when it moves to the lower right; parts of the long force chains No. 3 and No. 4 move towards each other and squeeze to form a lateral connecting force chain 27 during the period. Similarly, 25 is formed between No. 7 and No. 9.

[0075] like Figure 4 As shown in (b), from state 2 to state 3, the bottom particles continue to squeeze the bottom plate downward to form force chain 27, and the middle particles tend to move to the lower right and squeeze with the original skeleton to form force chains 28 and 29; the downward movement of force chain 7 squeezes it and the particles in 21 to form force chain 30.

[0076] Compared with the prior art, the present invention has the following advantages:

[0077] (1) Existing photoelastic testing equipment uses static or impact loads. The photoelastic experimental system mentioned in the present invention can achieve cyclic loading of up to 50Hz, with a loading amplitude range of 0 to 1000N. The loading end integrates a power sensor and an acceleration sensor, which can obtain the applied power and loading end acceleration in real time, regulate the load input from two dimensions, and can simulate more abundant load conditions.

[0078] (2) In the previous photoelastic experimental system, the morphological characteristics of the original force chain were directly recorded mainly through the camera system; the quantitative distribution of stress in the particle system was obtained through the average square gradient method; the principal stress direction, principal stress trace, shear stress field, etc. of the specimen were obtained through the phase shift method. The data analysis system mentioned in the present invention can obtain the displacement field in the particle system through particle position recognition, tracking, matching algorithm and particle morphological characteristics (or particle cluster morphological evolution characteristics) on the basis of the previous stage; identify the spatial distribution characteristics of the force chain based on the particle position, stress state and contact network; combine the particle displacement / particle cluster morphological changes at different times and the spatial distribution characteristics of the force chain, and further analyze the evolution characteristics and inducing factors of the microscopic force transmission skeleton.

[0079] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A photoelastic test system capable of realizing high-frequency and low-amplitude loading, characterized in that: The system comprises a high-frequency power loading system (4), a boundary stress wave low reflection test device and a data acquisition-analysis system, wherein the boundary stress wave low reflection test device comprises a model box system (2), the model box system (2) comprises a model box frame (21), the model box frame (21) comprises a photoelastic sample (22), a power loading system (4) is arranged above the model box system (2), and optical systems (1) are arranged on both sides of the model box system (2), the high-frequency power loading system (4) comprises a voice coil motor (41), a power data acquisition instrument (42), a power sensor (43), an acceleration sensor (44) and a temperature sensor (45), and the voice coil motor (41) is connected to the power data acquisition instrument (42), and the system further comprises a high-frequency image acquisition system (3) and a data analysis system (5).

2. A photoelastic test system capable of realizing high-frequency and low-amplitude loading according to claim 1, characterized in that: A loading bar is arranged on the top of the box frame (21), and the loading bar and the loading head end of the voice coil motor (41) are at a certain distance from the loading bar. The power sensor (43), the acceleration sensor (44) and the temperature sensor (45) are arranged on the voice coil motor (41).

3. A photoelastic test system capable of realizing high-frequency and low-amplitude loading according to claim 2, characterized in that: The optical system (1) comprises a light source (11), a polarizer (12), a first quarter wave plate (13), a second quarter wave plate (14) and an analyzer (15); the light source (11), the polarizer (12) and the first quarter wave plate (13) are arranged on one side of a model box system (2), and the second quarter wave plate (14) and the analyzer (15) are arranged on the other side of the model box system (2).

4. A photoelastic test system capable of realizing high-frequency and low-amplitude loading according to claim 3, characterized in that: The high-frequency image acquisition system (3) is arranged on a side of the model box system (2) where the second 1 / 4 wave plate (14) and the analyzer (15) are arranged.

5. The photoelastic test system capable of realizing high-frequency and low-amplitude loading according to claim 1, characterized in that: The data analysis system (5) comprises a data acquisition instrument (51) and a data processing host (52), wherein the data acquisition instrument (51) and the data processing host (52) are connected to each other, and the data acquisition instrument (51) is connected to a power sensor (43), an acceleration sensor (44) and a temperature sensor (45).

6. The photoelastic test system capable of realizing high-frequency and low-amplitude loading according to claim 1, characterized in that: Boundary energy absorbing devices (23) are provided on both sides and the bottom of the model box system (2), and the boundary energy absorbing devices (23) are U-shaped components made of energy absorbing materials.

7. A method for identifying the dynamic evolution of a force chain in a photoelastic test system capable of realizing high-frequency and low-amplitude loading according to claims 1 to 6, characterized in that: The method comprises the following steps: The photoelastic sample (22) is marked with a cross and then placed in a model box (21); Adjusting the up and down position of the power loading system (4) until the loading head end of the voice coil motor (41) is at a certain distance from the loading bar at the top of the box frame (21); Connecting a power source and starting a data acquisition device (51) of a data analysis system (5), starting a data processing host (52) of the data analysis system (5), resetting a loading head of a voice coil motor (41), setting an initial position of the motor, and completing motor initialization; Controlling the angles of the polarizer (12) and the analyzer (15) of the optical system (1), and simultaneously controlling the angles of the first quarter wave plate (13) and the second quarter wave plate (14), and turning on the light source (11) of the optical system (1); Turn on the high-frequency image acquisition system (3), adjust the exposure and white balance values ​​in the M mode, set the voice coil motor (41) to load at a given frequency and amplitude, and after the voice coil motor (41) is activated, the high-frequency image acquisition system (3) performs high-speed continuous shooting, and the obtained photos are transmitted to the data analysis system (5); In the data analysis system (5), identification and data analysis are performed, and the particle position and radius are identified from the photo as the particle geometric information. Based on the particle geometric information, the position change of the same marked particle in different states is obtained through the particle position matching algorithm, and the displacement field of the particle system when the state changes is obtained; Based on the particle geometry information, the contact positions of the particles are determined and the optical properties at the contact points are analyzed to obtain the effective contact relationship between the particles. Through the force chain identification algorithm, the spatial distribution of force chains at different times is identified by combining particle geometry information, effective contact relationship and stress state, and the correlation analysis between particle motion and force chain evolution under high-frequency loads is realized.

8. A method for identifying dynamic evolution of a force chain according to claim 7, characterized in that: The shooting frequency of the high-speed continuous shooting is not less than 10 times the loading frequency.

9. The photoelastic test system capable of realizing high-frequency and low-amplitude loading according to claim 7, characterized in that: After the light source (11) of the optical system (1) is turned on, light is emitted from the light source (11) and passes through the polarizer (12), the first quarter wave plate (13), the model box (21), the second quarter wave plate (14) and the analyzer (15) in sequence.

10. A method for identifying dynamic evolution of a force chain according to claim 9, characterized in that: The controlling of the angles of the polarizer (12) and the analyzer (15) of the optical system (1) and the simultaneous controlling of the angles of the first quarter wave plate (13) and the second quarter wave plate (14) are specifically as follows: The polarizer (12) is controlled to rotate to 0 degrees, the analyzer (15) is controlled to rotate to 90 degrees, the first quarter wave plate (13) is controlled to rotate to 135 degrees, and the second quarter wave plate (14) is controlled to rotate to 45 degrees; or the polarizer (12) is controlled to rotate or 180 degrees, the analyzer (15) is controlled to rotate to 270 degrees, the first quarter wave plate (13) is controlled to rotate to 315 degrees, and the second quarter wave plate (14) is controlled to rotate to 225 degrees.

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