Large field of view variable gravity photoelastic experiment apparatus and experimental method

Abstract

This invention specifically relates to a large field-of-view variable gravity photoelastic experimental apparatus and method, comprising: an adjustable tilt platform; an optical plate; a light source assembly; a polarization assembly, including a first polarizer and a second polarizer arranged opposite to each other; a particle container; and a gantry. This invention integrates the light source, polarizers, particle container, gantry, etc., onto the same optical plate, which tilts synchronously with the adjustable tilt platform. The gravity component can be adjusted within the range from Earth's gravity to zero gravity, avoiding the problem of repeated light adjustment and repositioning after changing the tilt angle, thus improving experimental efficiency and repeatability.

Description

Technical Field

[0001] This invention relates to the field of experimental mechanics and photoelasticity testing technology, specifically to a large field-of-view variable gravity photoelastic experimental apparatus and experimental method. Background Technology

[0002] Photoelasticity experiments utilize the stress birefringence effect generated in transparent photoelastic materials under stress to form stress-related photoelastic fringes in a polarized light field, thereby enabling visual analysis of the stress distribution within the sample. This method has been widely applied in fields such as stress analysis of complex structures, force chain observation in granular media, contact mechanics, and engineering model testing.

[0003] For particulate media, photoelastic experiments can visually display the transmission path and force chain structure of contact forces between particles, making them an important experimental method for studying particle accumulation, shearing, slippage, collapse, and local instability processes. Existing photoelastic testing apparatuses for particulate materials typically include a light source, polarizer, particle container, loading mechanism, and camera device, which can be used to observe the stress state of particulate systems under conventional gravity conditions. However, these apparatuses are usually based on a fixed optical path, a fixed platform, or a specific loading boundary, making it difficult to conduct photoelastic experiments under different equivalent gravity or different slope stress conditions.

[0004] On the other hand, low-gravity or microgravity particle experiments typically rely on drop towers, parabolic flight, space experimental platforms, or large-scale low-gravity simulation facilities. These methods involve complex equipment, high experimental costs, short experimental time windows, and inconvenience in repeating experiments, and are generally unsuitable for integration with large-field-of-view photoelastic observation systems. Therefore, current technologies cannot simultaneously meet the requirements of large-area photoelastic observation, controllable equivalent gravity components, stable optical path imaging, and continuous observation of the force chain evolution of particle systems. Summary of the Invention

[0005] To address the aforementioned problems, one objective of this invention is to provide a large field-of-view variable gravity photoelastic experimental instrument.

[0006] The second objective of this invention is to provide an experimental method using the aforementioned large field-of-view variable gravity photoelastic experimental apparatus.

[0007] The first technical solution adopted in this invention is: A large field-of-view variable gravity photoelastic experimental apparatus includes: Adjustable tilt platform; An optical flat plate is fixedly mounted on the adjustable tilt platform; The light source assembly is mounted on the optical plate; The polarization assembly includes a first polarizer and a second polarizer arranged opposite to each other, both mounted on the optical plate and located in the light output path of the light source assembly; A particle container, used to hold photoelastic particles or photoelastic samples, is mounted on the optical plate and located between the first polarizer and the second polarizer; and A gantry frame, fixedly mounted on the optical flat plate and spanning above the particle container, is used to install the loading mechanism; The adjustable tilt platform is used to adjust and lock the tilt angle to change the effective component of the gravity acting on the photoelastic particles or photoelastic sample in the experimental direction within the particle container. When the tilt angle of the adjustable tilt platform changes, the optical plate and the light source assembly, the first polarizer, the second polarizer, the particle container, and the gantry tilt synchronously to maintain a stable relative positional relationship between them.

[0008] Furthermore, in the aforementioned large field-of-view variable gravity photoelastic experimental instrument, the optical plate is provided with an array of mounting holes, and the light source assembly, the first polarizer, the second polarizer, the particle container, and the gantry are detachably fixed to the optical plate through the array of mounting holes.

[0009] Furthermore, the large field-of-view variable gravity photoelastic experimental instrument also includes multiple supports and limiting frames, which are used to support and assist in the fixed installation of the light source assembly, the first polarizer, the second polarizer, and the particle container on the optical plate.

[0010] Furthermore, in the aforementioned large field-of-view variable gravity photoelastic experimental instrument, the tilt angle adjustment range of the adjustable tilt platform is 0° to 90°.

[0011] Furthermore, in the aforementioned large field-of-view variable gravity photoelastic experimental instrument, the first polarizer and the second polarizer are circular polarizers with opposite rotation directions, which together constitute the polarized photoelastic optical path.

[0012] Furthermore, in the aforementioned large field-of-view variable gravity photoelastic experimental instrument, the optical plate is made of aluminum alloy and its surface is anodized.

[0013] Furthermore, in the aforementioned large field-of-view variable gravity photoelastic experimental instrument, the effective light-transmitting areas of the first and second polarizers are adapted to the internal cross-sectional area of ​​the particle container.

[0014] Furthermore, in the large field-of-view variable gravity photoelastic experimental instrument, the loading mechanism is one or more of a probe, indenter, penetration mechanism, force sensor, or displacement driving device, which is installed on the gantry frame and used to apply mechanical action to the photoelastic particles or photoelastic sample in the particle container.

[0015] Furthermore, the large field-of-view variable gravity photoelastic experimental instrument also includes an image acquisition device, which is fixedly mounted on the optical plate or the gantry frame, with its acquisition direction perpendicular to the plane where the particle container is located, for real-time recording of photoelastic stripe images inside the particle container.

[0016] The second technical solution adopted in this invention is: An experimental method using the large field-of-view variable gravity photoelastic experimental apparatus described in any one of the above claims, characterized by comprising the following steps: The light source assembly, the first polarizer, the particle container after the photoelastic particles or photoelastic sample are loaded, and the second polarizer are sequentially arranged on the optical plate, and an image acquisition device is also provided. Adjust the adjustable tilt platform to the target angle to set the required equivalent gravity conditions; Turn on the light source assembly so that the light passes sequentially through the first polarizer, the particle container, and the second polarizer; The photoelastic particles or photoelastic sample are loaded into the particle container by the loading mechanism. The photoelastic fringe images generated by the photoelastic particles or photoelastic samples during loading are recorded using an image acquisition device, which are used to analyze the stress distribution, contact force transmission and force chain evolution process under different equivalent gravity conditions.

[0017] The beneficial effects of the above technical solution are as follows: (1) The large field-of-view variable gravity photoelastic experimental instrument provided by the present invention integrates the light source, polarizer, particle container, gantry and other components onto the same optical plate and tilts synchronously with the adjustable tilt platform, thereby realizing the visualization observation of the stress distribution, contact force transmission and force chain evolution process inside the particle system under different equivalent gravity or slope stress conditions. This avoids the problem of repeated light adjustment and repositioning after changing the tilt angle, and improves the experimental efficiency and repeatability.

[0018] (2) The large field-of-view variable gravity photoelasticity experimental apparatus provided by this invention can change the effective component of gravity in the experimental direction by adjusting the platform tilt angle. It can simulate various working conditions such as microgravity, low gravity, and Earth gravity under ordinary laboratory conditions, with low cost and high repeatability. This invention can change the gravity component of the particle system along the experimental surface or slope direction by changing the tilt angle of the experimental cavity relative to the direction of Earth gravity. By continuously adjusting the ground and the optical plate, the evolution of particle force chains under different slopes, different equivalent gravity components, or different instability driving forces can be simulated. This invention does not rely on short-term low gravity facilities, but obtains continuous changes in the gravity component within the particle system through controllable attitude adjustment, thereby realizing low-cost, long-term, and repeatable equivalent variable gravity photoelasticity experiments.

[0019] (3) Many photoelastic experiments can only observe contact force chains in small areas, while problems such as asteroid surface soil, particle landslides, and slope instability often require observation of the overall particle response over a larger area. The large field-of-view variable gravity photoelastic experimental instrument provided by this invention uses a large-area optical plate, a large-size polarizer, and particle containers of corresponding size to form a large field-of-view observation area, which can conduct overall observation of the force chain network inside the particle system and reduce boundary effects.

[0020] (4) The large field of view variable gravity photoelastic experimental instrument provided by the present invention has an array of mounting holes on the optical plate that allow each component to be flexibly disassembled and its position adjusted, adapting to containers and loading devices of different sizes, and has strong expandability.

[0021] (5) The large field of view variable gravity photoelastic experimental instrument provided by the present invention can be equipped with a variety of loading mechanisms on the gantry, so as to realize the simultaneous observation of external mechanical action and photoelastic force chain, and provide complete data support for the study of the mechanical behavior of particle system.

[0022] (6) The experimental method provided by the present invention using a large field-of-view variable gravity photoelastic experimental instrument can continuously record the formation, reconstruction, fracture and restabilization process of the force chain of the particle system within a long time window, which is suitable for studying the mechanical behavior of particle media under slow loading or gradual instability conditions. Attached Figure Description

[0023] Figure 1 A schematic diagram of the disassembled structure of the large field-of-view variable gravity photoelastic experimental instrument provided by the present invention; Figure 2 This is a schematic diagram of an experiment in a zero-gravity state provided by the present invention; Figure 3 A schematic diagram of a standard gravity state experiment provided for this invention.

[0024] Explanation of reference numerals in the attached drawings: 1-Adjustable tilt platform, 2-Optical flat plate, 3-Bracket, 4-Limiting frame, 5-Light source assembly, 6-First polarizer, 7-Particle container, 8-Second polarizer, 9-Gantry. Detailed Implementation

[0025] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention. That is, the present invention is not limited to the described preferred embodiments, and the scope of the present invention is defined by the claims.

[0026] In the description of this invention, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance; those skilled in the art can understand the specific meaning of the above terms in this invention as appropriate.

[0027] like Figure 1 and Figure 2 As shown, this embodiment provides a large field-of-view variable gravity photoelastic experimental instrument, which includes an adjustable tilt platform 1, an optical plate 2, a light source assembly 5, a polarization assembly (including a first polarizer 6 and a second polarizer 8 arranged opposite to each other), a particle container 7, and a gantry 9.

[0028] Adjustable tilt platform 1 can be a manual worm gear tilting platform or an electric servo-driven tilting table, with the tilt angle (the angle between the inclined plane and the horizontal plane) adjustable from 0° to 90°. Figure 2 , 3 It features a self-locking function, allowing it to remain stably stationary at any angle. The optical plate 2 is a 900mm × 900mm aluminum alloy plate with an anodized black finish to reduce stray light reflection. The optical plate 2 is bolted to the inclined surface of the adjustable tilt platform 1.

[0029] An array of mounting holes is machined on the optical plate 2, and the hole spacing can be selected according to the actual use. The light source assembly 5, the first polarizer 6, the second polarizer 8, the particle container 7, and the gantry 9 are all vertically and detachably fixed to the optical plate 2 through the array of mounting holes. The adjustable tilt platform 1 is used to adjust and lock the tilt angle to change the effective component of the gravity acting on the photoelastic particles or photoelastic sample in the experimental direction. When the tilt angle of the adjustable tilt platform 1 changes, the optical plate 2 and the light source assembly 5, the first polarizer 6, the second polarizer 8, the particle container 7, and the gantry 9 on it tilt synchronously, maintaining a stable relative positional relationship between them, and the gravity component of the photoelastic particles or photoelastic sample can be adjusted within the range from Earth's gravity to zero gravity.

[0030] Specifically, the light source assembly 5 adopts an LED surface light source plus a uniform light plate structure to provide uniform backlight illumination. It can be a square light box with a light area of ​​500mm × 500mm. The first polarizer 6 and the second polarizer 8 are both circular polarizers with opposite rotation directions (for example, the first polarizer 6 is a left-handed circular polarizer, and the second polarizer 8 is a right-handed circular polarizer), and are located in the light output path of the light source assembly, together forming the circularly polarized photoelastic light path. The particle container 7 is used to contain photoelastic particles or photoelastic samples and is located between the first polarizer 6 and the second polarizer 8. The particle container 7 is a square box made of transparent acrylic or plexiglass, and its internal cross-sectional area is adapted to the effective light transmission area of ​​the first polarizer 6 and the second polarizer 8.

[0031] To facilitate stable installation, multiple brackets 3 and limiting frames 4 are also provided. The brackets 3 and limiting frames 4 are used to support and assist in fixing the light source assembly 5, the first polarizer 6, the second polarizer 8, and the particle container 7 onto the optical plate 2, respectively. The limiting frames on both sides are used to assist in fixing their lateral positions and prevent sliding or tipping when the tilt angle changes.

[0032] The gantry 9 has a U-shaped structure, consisting of two columns and a crossbeam. The bottom of the columns is fixed to the optical plate 2 with bolts, and the crossbeam spans directly above the particle container 7. A loading mechanism, such as one or more of a probe, indenter, penetration mechanism, force sensor, or displacement drive device, can be installed on the crossbeam of the gantry 9 to apply mechanical force to the photoelastic particles or photoelastic sample inside the particle container 7 for penetration experiments.

[0033] This embodiment also includes an image acquisition device (not shown in the figure). The image acquisition device can be an industrial camera. The camera is fixed to the optical flat plate 2, gantry 9 or other positions by a camera bracket. The lens (image acquisition direction) is vertically aligned with the center area of ​​the particle container 7 to record the photoelastic stripe image inside the particle container in real time.

[0034] Example of experimental method: The method for conducting microgravity equivalent simulation experiments using the above-mentioned experimental apparatus is as follows: (1) Device Assembly: Fix the optical plate 2 on the adjustable tilt platform 1. On the optical plate 2, install the light source assembly 5, the left-handed circular polarizer 6 (serving as the first polarizer), the particle container 7 containing photoelastic particles or photoelastic samples, and the right-handed circular polarizer 8 in sequence according to the optical path, and fix them using the bracket 3 and the limiting frame 4. Place the gantry 9 across the particle container 7 and install the loading mechanism (intrusion drive mechanism and force sensor). Adjust the camera position to achieve clear focus.

[0035] Sample preparation: A transparent acrylic box, measuring 500mm × 500mm × 8mm, was used as the particle container 7. The photoelastic particles were made of polyurethane, with dimensions of 20mm and 30mm and a thickness of 6mm. To reduce friction between particles and between particles and the container wall, a small amount of talc powder was evenly applied to the surface of the photoelastic particles. The photoelastic particles were then placed into the particle container 7, with the filling height approximately 15mm from the top edge of the container to ensure that the particles did not overflow during the immersion process.

[0036] (2) Adjust the adjustable tilt platform 1 to the target tilt angle (e.g., 89.4°) and lock it.

[0037] Specifically, three equivalent gravity states are set up, which are achieved by adjusting the angle between the adjustable tilt platform 1 and the horizontal plane: Inclination angle 0°: The plane of particle container 7 is perpendicular to the horizontal plane, simulating the Earth's (standard) gravity state, such as... Figure 3 As shown; Inclined at 60°: The plane of the particle container 7 forms a 30° angle with the horizontal plane to simulate a low-gravity state; Inclination angle 89.4°: The plane of particle container 7 forms a 0.6° angle with the horizontal plane to simulate microgravity. (For reference) Figure 2 The diagram shows a zero-gravity state.

[0038] The intrusion foot comes in four shapes: semi-circular, rectangular, triangular, and probe-shaped. The foot is 4mm thick and has a through hole at the rear end for fixed connection with the drive rod of the linear motor.

[0039] (3) Turn on the light source assembly 5 and the camera, so that the uniform backlight passes through the first polarizer 6 (left-handed circular polarizer), the photoelastic particle layer in the particle container 7, and the second polarizer 8 (right-handed circular polarizer) in sequence to form a circularly polarized photoelastic optical path. Record the contact force chain distribution of the particle system in the initial state.

[0040] Specifically, the natural light emitted by the light source becomes linearly polarized after passing through the first polarizer, and this polarized light is incident perpendicularly onto the stressed particle. Due to the stress birefringence effect of the particle, the incident linearly polarized light is decomposed into two components with mutually perpendicular vibration directions and different propagation speeds inside the particle. These two components create an optical path difference after passing through the particle, and then reach the second polarizer. Only the light component whose vibration direction is parallel to the polarization direction of the second polarizer can pass through, and finally form an image in the camera.

[0041] (4) Drive a linear motor (rated voltage 5V, thrust 2kg, speed 2mm / s) through the control board to make the intrusion sufficient to penetrate the photoelastic particle layer at a constant speed (e.g., 2mm / s).

[0042] Synchronous acquisition of force sensor signals: Two miniature force sensors (5mm in diameter, 3.5mm in diameter of sensing area, range 0.2N~10N, response time <10ms) record the force data during the intrusion process in real time, which is converted into force values ​​and output by a linear voltage conversion module.

[0043] The probe's force-displacement data and photoelastic stripe video are collected synchronously. After penetrating to a predetermined depth, the motor is stopped, and the video and force-time / force-depth data are saved.

[0044] (5) After the experiment, the adjustable tilt platform was adjusted to 60° and 0° in turn, and the above steps were repeated to obtain experimental data under low gravity and Earth gravity conditions respectively.

[0045] (6) Change the intrusion foot with different shapes and different proportions of particles (pure 20mm, pure 30mm, and a mixture of 20mm and 30mm in equal volumes, with a quantity ratio of approximately 9:4), and repeat the above steps. Repeat each working condition 3 times to ensure data reliability for subsequent data processing and analysis.

[0046] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A large field of view variable gravity photo-elastic experiment apparatus, characterized in that, include: Adjustable tilt platform (1); An optical flat plate (2) is fixedly mounted on the adjustable tilt platform (1); The light source assembly (5) is mounted on the optical plate (2); The polarization assembly includes a first polarizer (6) and a second polarizer (8) arranged opposite to each other, both mounted on the optical plate (2) and located in the light output path of the light source assembly (5); A particle container (7), used to hold photoelastic particles or photoelastic samples, is mounted on the optical plate (2) and located between the first polarizer (6) and the second polarizer (8); and A gantry frame (9) is fixedly mounted on the optical flat plate (2) and spans above the particle container (7) for mounting the loading mechanism; The adjustable tilt platform (1) is used to adjust and lock the tilt angle to change the effective component of the gravity of the photoelastic particles or photoelastic sample acting in the particle container (7) in the experimental direction. When the tilt angle of the adjustable tilt platform (1) changes, the optical plate (2) and the light source assembly (5), the first polarizer (6), the second polarizer (8), the particle container (7) and the gantry (9) on it tilt synchronously to maintain a stable relative positional relationship between them.

2. The large field-of-view variable gravity photoelastic experimental apparatus according to claim 1, characterized in that, The optical plate (2) is provided with an array of mounting holes. The light source assembly (5), the first polarizer (6), the second polarizer (8), the particle container (7) and the gantry (9) are fixedly mounted on the optical plate (2) in a detachable manner through the array of mounting holes.

3. The large field-of-view variable gravity photoelastic experimental apparatus according to claim 1, characterized in that, It also includes multiple brackets (3) and limiting brackets (4), the brackets (3) and the limiting brackets (4) being used to support and assist in fixing the light source assembly (5), the first polarizer (6), the second polarizer (8) and the particle container (7) on the optical plate (2).

4. The large field-of-view variable gravity photoelastic experimental apparatus according to claim 1, characterized in that, The tilt angle adjustment range of the adjustable tilt platform (1) is 0° to 90°.

5. The large field-of-view variable gravity photoelastic experimental apparatus according to claim 1, characterized in that, The first polarizer (6) and the second polarizer (8) are circular polarizers with opposite rotation directions, which together form a polarizing optical path.

6. The large field-of-view variable gravity photoelastic experimental apparatus according to claim 1, characterized in that, The optical flat plate (2) is made of aluminum alloy and its surface is anodized.

7. The large field-of-view variable gravity photoelastic experimental apparatus according to claim 1, characterized in that, The effective light-transmitting area of ​​the first polarizer (6) and the second polarizer (8) is adapted to the internal cross-sectional area of ​​the particle container (7).

8. The large field-of-view variable gravity photoelastic experimental apparatus according to claim 1, characterized in that, The loading mechanism is one or more of a probe, indenter, penetration mechanism, force sensor or displacement drive device, and is installed on the gantry (9) to apply mechanical action to the photoelastic particles or photoelastic sample in the particle container (7).

9. The large field-of-view variable gravity photoelastic experimental apparatus according to claim 1, characterized in that, It also includes an image acquisition device, which is fixedly mounted on the optical flat plate (2) or the gantry (9) and its acquisition direction is perpendicular to the plane where the particle container (7) is located, for real-time recording of photoelastic stripe images inside the particle container (7).

10. An experimental method using the large field-of-view variable gravity photoelastic experimental apparatus according to any one of claims 1 to 9, characterized in that, Includes the following steps: The light source assembly, the first polarizer, the particle container after the photoelastic particles or photoelastic sample are loaded, and the second polarizer are sequentially arranged on the optical plate, and an image acquisition device is also provided. Adjust the adjustable tilt platform to the target angle to set the required equivalent gravity conditions; Turn on the light source assembly so that the light passes sequentially through the first polarizer, the particle container, and the second polarizer; The photoelastic particles or photoelastic sample are loaded into the particle container by the loading mechanism. The photoelastic fringe images generated by the photoelastic particles or photoelastic samples during loading are recorded using an image acquisition device, which are used to analyze the stress distribution, contact force transmission and force chain evolution process under different equivalent gravity conditions.

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