Rock microscale mineral compression-shear test system and method

Abstract

The present application provides a kind of rock microscale mineral compression-shear test system and method, its system includes: holding mechanism, normal loading component, tangential loading component and image acquisition system;When normal loading component loads, the rock slice sample clamped by clamping mechanism is abutted to the output end of tangential loading component, so as to apply shear load to rock slice sample under constant normal stress;Image acquisition system is set towards the main plane of rock slice sample, at least for obtaining the time sequence image of microcrack of pre-prepared notch of rock slice sample in compression-shear test process;Wherein, pre-prepared notch is pre-prepared in rock slice sample before compression-shear test, to form controllable crack initiation position at pre-prepared notch position for observation.The present application realizes stable, repeatable shear loading and failure whole process observation of rock slice sample under constant normal stress on microscale by independently decoupled normal loading component tangential loading component.

Description

Technical Field

[0001] This invention relates to the field of rock testing technology, and in particular to a mineral compression-shear testing system and method at the microscale of rocks. Background Technology

[0002] The microstructure of rocks significantly influences their macroscopic mechanical behavior, exhibiting remarkable multi-scale characteristics. Extensive engineering practice and laboratory experiments have shown that the diverse types and arrangements of microminerals are crucial causes of brittle fracture, slip failure, and age-related deformation in rocks. Grain size, grain boundary characteristics, foliation / bedding orientation, and the spatial distribution of microcracks determine the macroscopic strength and anisotropy of rocks. Particularly in metamorphic rocks with multiple mineral compositions, such as gneiss, slate, and phyllite, the bond-friction slip mechanical behavior of micro-interfaces of minerals like quartz, mica, and chlorite significantly affects the macroscopic mechanical behavior of rocks, leading to deformation and instability problems in engineering applications such as rock slopes, mine tunnels, and underground powerhouses.

[0003] Existing macroscopic mechanical testing methods, such as uniaxial / triaxial compression and direct shear devices, can obtain mechanical strength indices of rocks at the millimeter level in the laboratory. However, they are difficult to analyze the bonding-slip behavior and failure mechanisms of single mineral grains or microscopic weak surfaces at the microscale. At the same time, they cannot quantitatively distinguish the independent contributions of normal stress and shear stress to the slip failure of microcrystal interfaces.

[0004] Current micro- and nano-scale mechanical testing methods (such as nanoindentation) mainly obtain the vertical force-displacement response of micro-minerals, making it difficult to apply high-precision tangential displacement / force under controlled normal stress to achieve stable and repeatable compression-shear coupling loading.

[0005] If the relative orientation cannot be precisely set and maintained in the experiment, it is difficult to obtain comparable and repeatable parameters, resulting in large dispersion and poor accuracy of parameters such as shear strength and cohesion of the micro-mineral interface. Therefore, a compression-shear test system that can realize normal-tangential dual degrees of freedom of the mineral interface at the micrometer scale is needed. Summary of the Invention

[0006] This invention provides a mineral compression-shear testing system and method at the microscale of rocks, which addresses the deficiency in the prior art of lacking a compression-shear sample system that can achieve normal-tangential dual-degree-of-freedom loading of the mineral interface at the micrometer scale, and realizes a compression-shear testing system with complete decoupling and independent control of the normal and tangential directions.

[0007] This invention provides a mineral compression-shear testing system at the microscale of rocks, comprising: a clamping mechanism, a normal loading component, a tangential loading component, and an image acquisition system; The clamping mechanism is used to clamp the rock thin-section sample from the thickness direction of the rock thin-section sample. The tangential loading assembly is used to apply tangential pressure to the sidewall of the rock thin section sample in the thickness direction; The normal loading component is used to apply normal pressure to the sidewall of the rock thin section sample in the thickness direction. When the normal loading component is loaded, the rock thin section sample held by the clamping mechanism is pressed against the output end of the tangential loading component, thereby applying shear load to the rock thin section sample under constant normal stress. The image acquisition system is positioned toward the main plane of the rock thin section specimen and is used at least to acquire time-series images of microcracks that initiate during the compression-shear test of the pre-made notch of the rock thin section specimen. The thickness of the rock thin section specimen does not exceed 1.5 mm, and the pre-made notch is pre-made on the rock thin section specimen before the compression-shear test to form a controllable crack initiation position at the pre-made notch location for observation.

[0008] According to the present invention, a mineral compression-shear testing system at the microscale of rock further includes a mounting frame installed on the normal loading component, a clamping mechanism located within the mounting frame, and a tangential loading component disposed opposite to the normal loading component on the mounting frame, so that when the normal loading component is loaded, its output end drives the rock thin-section sample held by the clamping mechanism to move toward and press against the tangential loading component, thereby realizing normal loading on the rock thin-section sample.

[0009] According to the present invention, a mineral compression-shear testing system at the microscale of rock is provided, wherein the output end of the tangential loading component slides along the length direction of the loading surface of the rock thin section sample to achieve tangential loading on the rock thin section sample.

[0010] According to the present invention, a mineral compression-shear testing system at the microscale of rock is provided, wherein the output end of the tangential loading component is detachably fixed with a tangential friction element, and the tangential friction elements with different friction surface materials are configured based on the interface type of the rock thin-section sample.

[0011] According to the present invention, a mineral compression-shear testing system at the microscale of rock is provided, wherein the mounting frame is formed by four detachably fixed mounting plates, wherein two mounting plates corresponding to the main plane of the rock thin section sample are provided with openings to provide observation space for the image acquisition system.

[0012] According to the present invention, a mineral compression-shear testing system at the microscale of rock is provided, wherein the clamping mechanism includes a clamping base, the clamping base having a positioning groove for placing the rock thin-section sample, and the clamping base also having an adjustment component in the positioning groove to accommodate the installation of rock thin-section samples of different thicknesses.

[0013] According to the present invention, a mineral compression-shear testing system at the microscale of rock is provided, wherein the adjustment component includes a shim and a buffer liner respectively disposed on two opposite walls of the positioning groove, the buffer liner being configured to move along the width direction of the positioning groove to press the rock sheet sample placed in the positioning groove against the shim.

[0014] According to the present invention, a mineral compression-shear testing system at the microscale of rock is provided. The image acquisition system includes an optical microscope and a triaxial adjustment mechanism. The triaxial adjustment mechanism is used to control the movement of the optical microscope in the length, width and thickness directions of the rock thin section sample.

[0015] According to the present invention, a mineral compression-shear testing system at the microscale of rock is provided, which further includes a numerical control system. The numerical control system is electrically connected to the normal loading component, the tangential loading component and the image acquisition system to control the loading of the normal loading component and the tangential loading component, and to acquire the microcrack time-series images acquired by the image acquisition system.

[0016] This invention also provides a method for mineral compression-shear testing at the microscale of rocks, comprising: Obtain a rock thin section sample and make a one-sided notch on any sidewall of the rock thin section sample to form a pre-fabricated notch; The rock thin section sample with a notch is installed in the clamping mechanism; The normal loading component is controlled to load so that the installed rock thin section sample contacts the output end of the tangential loading component and maintains a constant preload. The image acquisition system is moved to a position where the pre-made notch of the rock thin section specimen is within its field of view in order to obtain a time-series image of the microcracks that initiate at the pre-made notch of the rock thin section specimen during the compression-shear test. The tangential loading component is controlled to apply shear load to the rock thin section specimen in a preset control mode, which is suitable for the corresponding type of micro-shear test. The microscopic shear test includes a microscopic direct shear test, which is used to obtain the peak stress when the rock thin section sample undergoes type II fracture or shear failure at the microscopic level, and to calculate the fracture toughness, interfacial shear strength and interfacial friction angle based on the peak stress.

[0017] The mineral compression-shear testing system and method at the microscale of rocks provided by this invention achieves stable and repeatable observation of the entire process of shear loading and failure of thin rock sections under constant normal stress at the microscale through independently decoupled normal loading and tangential loading components. Coupled with an image acquisition device, it captures time-series images of the dynamic propagation of microcracks originating from specific grain boundaries or bedding planes, thus providing a direct and reliable technical means for revealing the bond-slip failure mechanism of the microstructure of multi-mineral rocks. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is an overall structural diagram of the mineral compression and shear testing system at the rock microscale provided by the present invention; Figure 2 This is an overall structural diagram of the mineral compression-shear testing system at the microscale of rocks provided by the present invention from another perspective; Figure 3 This is a schematic diagram of the mineral compression and shear testing system at the microscale of rock provided by the present invention, mainly used to demonstrate the structure within the installation frame; Figure 4 The rock microscale mineral compression and shear testing system provided by this invention is mainly used to demonstrate the structural schematic diagram of the tangential loading component; Figure 5 The rock microscale mineral compression and shear test system provided by this invention is mainly used to show the planar schematic diagram of the installation frame, where (a), (b) and (c) are schematic diagrams of the top plate, side plate and bottom wall that make up the installation frame, respectively; Figure 6 The rock microscale mineral compression and shear testing system provided by this invention is mainly used to demonstrate the structural schematic diagram of the clamping mechanism; Figure 7 This invention provides a schematic diagram of the structure of a mineral compression-shear testing system at the microscale of rock, primarily used to demonstrate the image acquisition system. Figure 8 This is a schematic flowchart of the mineral compression-shear test method at the microscale of rock provided by the present invention; Figure 9 This is a schematic diagram of the stress analysis of the sample in the mineral compression-shear test method at the microscale of rock provided by the present invention; Figure 10 These are shear displacement-shear force images collected in the mineral compression-shear test method at the rock microscale provided by this invention; Figure 11 (1), (2), (3) and (4) are respectively Figure 10 The microscopic images corresponding to positions (1), (2), (3) and (4) in the image.

[0020] Figure label: 1. Rock thin section specimen; 11. Pre-fabricated notch; 2. Clamping mechanism; 21. Clamping base; 22. Positioning groove; 231. Gasket; 232. Buffer pad; 3. Normal loading assembly; 31. Normal linear loader; 32. Normal force sensor; 33. Lower bearing plate; 4. Tangential loading assembly; 41. Tangential loader; 411. Guide rail base; 412. Lead screw; 413. Moving slider; 414. Mounting port ; 415. Limiting end cap; 416. Lower limiting hole; 417. Mounting hole; 42. Tangential force sensor; 43. Tangential friction component; 5. Image acquisition system; 51. Optical microscope; 52. Three-axis adjustment mechanism; 521. X-axis linear moving guide rail; 522. Y-axis linear moving guide rail; 523. Z-axis linear moving guide rail; 53. Support base; 54. L-shaped plate; 6. Mounting frame; 7. Data measurement and control platform. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0022] The following is combined Figures 1 to 7 This invention introduces a mineral compression-shear testing system at the microscale of rocks, such as... Figure 1 As shown, it includes a clamping mechanism 2, a normal loading component 3, a tangential loading component 4, and an image acquisition system 5; The clamping mechanism 2 is used to clamp the rock thin-section sample 1 from the thickness direction. The tangential loading component 4 is used to apply tangential pressure to the sidewall of the rock thin section sample 1 in the thickness direction; The normal loading component 3 is used to apply normal pressure to the sidewall of the rock thin section sample 1 in the thickness direction. When the normal loading component 3 is loaded, the rock thin section sample 1 held by the clamping mechanism 2 is pressed against the output end of the tangential loading component 4, thereby applying shear load to the rock thin section sample 1 under constant normal stress. The image acquisition system 5 is positioned toward the main plane of the rock thin section sample 1 and is used at least to acquire the time sequence image of the microcracks that initiate during the compression-shear test of the pre-made notch 11 of the rock thin section sample 1. The thickness of the rock thin section sample 1 does not exceed 1.5 mm. The pre-made notch 11 is pre-made in the rock thin section sample 1 before the compression-shear test so as to form a controllable crack initiation position at the pre-made notch 11 for observation.

[0023] In metamorphic rocks with multiple minerals, such as gneiss, slate, and phyllite, the microstructural characteristics (grain size, grain boundary properties, foliation / bedding orientation, and spatial distribution of microcracks) significantly affect their macroscopic mechanical response. Existing experimental methods, uniaxial / triaxial compression or direct shear tests can only obtain macroscopic mechanical properties, making it difficult to analyze the bond-slip behavior of single mineral grains or microscopic weak planes. Micro- and nano-mechanical tests (such as nanoindentation) can only characterize local vertical force-displacement responses, failing to apply high-precision tangential displacement / force under controlled normal stress conditions, thus hindering the achievement of stable and repeatable compression-shear coupled loading.

[0024] Therefore, this invention proposes a mineral compression-shear testing system at the microscale of rocks for testing the micromechanical properties of rocks.

[0025] In particular, since the compression-shear testing system of the present invention is used to perform rock compression-shear tests at the microscale, the present invention is preferably applicable to rock thin-slab specimens 1 with a thickness not exceeding 1.5 mm prepared from layered rock. Unlike conventional rock specimens, rock thin-slab specimens 1 are difficult to support and place independently due to their thickness limitations. Therefore, the present invention provides a clamping mechanism 2 for holding the rock thin-slab specimen 1 so that the rock thin-slab specimen 1 can maintain a stable position during the compression-shear test and prevent it from rotating and / or warping during the compression-shear test.

[0026] Furthermore, since the length and width of rock thin section specimen 1 are typically much greater than its thickness, such as Figure 1 and Figure 2 As shown, the clamping mechanism 2 is configured to clamp the rock thin-section sample 1 from the thickness direction to optimize its stress.

[0027] Based on this, in order to conduct a compression-shear test on the rock thin section specimen 1, it is necessary to apply normal and tangential loads to the rock thin section specimen 1 fixed by the clamping mechanism 2. The normal load is that the load direction is perpendicular to any plane of the rock thin section specimen 1; the tangential load is that the load direction is parallel to any plane of the rock thin section specimen 1.

[0028] In order to apply a high-precision tangential load to the rock thin section specimen 1 under controlled normal stress conditions, this embodiment is provided with independent normal loading component 3 and tangential loading component 4, which are used to perform normal loading and tangential loading on the rock thin section specimen 1, respectively.

[0029] Among them, such as Figure 1As shown, the normal loading component 3 and the tangential loading component 4 are arranged opposite each other, and the clamping mechanism 2 is located between the normal loading component 3 and the tangential loading component 4. This arrangement ensures that when the rock thin-slice sample 1 is installed in the clamping mechanism 2, the normal loading component 3 and the tangential loading component 4 are located at opposite ends of the length or width of the rock thin-slice sample 1, and the output ends of both loading mechanisms are close to the rock thin-slice sample 1. Based on this, when the normal loading component 3 loads, its output end extends along the length / width direction of the rock thin-slice sample 1, driving the clamping mechanism 2 to move and causing the rock thin-slice sample 1 held by the clamping mechanism 2 to abut against the output end of the tangential loading mechanism, generating a constant preload on the rock thin-slice sample 1.

[0030] Based on this, the tangential loading component 4 is a displacement-controlled tangential force loading component. During loading, its output end is controlled to move at the contact surface with the rock thin section sample 1, applying shear displacement to the rock thin section sample 1, and finally achieving structural decoupling of the normal and tangential force transmission paths. This enables independent and precise control of normal stress and tangential stress at the micrometer scale, ensuring the stability and repeatability of the loading path.

[0031] like Figure 1 As shown, the compression-shear test system also includes an image acquisition system 5, which is positioned facing the main plane of the rock thin-section sample 1 to observe the cracks that initiate in the rock thin-section sample 1 during the compression-shear test and to observe the crack propagation at the grain boundaries. However, this observation of microcrack propagation at the rock grain boundary level greatly limits the field of view and depth of field of the image acquisition system 5. In order to enable it to acquire complete microcrack time-series images of the crack initiation process, in this embodiment, a pre-fabricated notch 11 is pre-formed on the rock thin-section sample 1 to form a controllable crack initiation position. Before the compression-shear test, the image acquisition system 5 is adjusted so that the pre-fabricated notch 11 is located at the center of its field of view to facilitate capturing the complete crack propagation process.

[0032] In one feasible implementation, such as Figure 1 As shown, the main plane of the rock thin section sample 1 held by the clamping mechanism 2 is set perpendicular to the horizontal plane. Correspondingly, the tangential loading component 4 and the normal loading component 3 are located at the upper and lower ends of the rock thin section sample 1, respectively, so that the image acquisition unit can be installed from one side to observe the main plane of the rock thin section sample 1.

[0033] In other feasible embodiments, the main plane of the rock thin section sample 1 held by the clamping mechanism 2 is set parallel to the horizontal plane. Correspondingly, the tangential loading component 4 and the normal loading component 3 are located at the left and right ends or the front and rear ends of the rock thin section sample 1, respectively, so that the image acquisition unit can observe the main plane of the rock thin section sample 1 from the upper end or the lower end of the rock thin section sample 1.

[0034] This invention enables stable and repeatable observation of the entire process of shear loading and failure of rock thin section specimen 1 under constant normal stress at the microscale through independently decoupled normal loading component 3 and tangential loading component 4. It also couples with an image acquisition device to capture the time-series images of the dynamic propagation of microcracks that originate from specific grain boundaries or bedding planes, thus providing a direct and reliable technical means for revealing the bond-slip failure mechanism of the microstructure of multi-mineral rocks.

[0035] The mineral compression-shear testing system at the microscale of rock of the present invention further includes an installation frame 6 installed on the normal loading component 3, the clamping mechanism 2 being located within the installation frame 6, and the tangential loading component 4 being arranged opposite to the normal loading component 3 on the installation frame 6, so that when the normal loading component 3 is loaded, its output end drives the rock thin-section sample 1 held by the clamping mechanism 2 to move toward and press against the tangential loading component 4, thereby realizing the normal loading of the rock thin-section sample 1.

[0036] like Figure 3 As shown, the compression-shear test system of the present invention also includes an installation frame 6. The installation frame 6 is generally in the shape of a rectangular box. The clamping mechanism 2 is installed inside the installation frame 6 and is configured such that when the rock thin sheet sample 1 is clamped by the clamping mechanism 2, the main plane of the rock thin sheet sample 1 is perpendicular to the horizontal plane. The installation frame 6 is supported by the normal loading component 3, and the normal loading component 3 and the tangential loading component 4 are respectively connected to opposite sides of the installation frame 6.

[0037] In one feasible implementation, such as Figure 1 As shown, the normal loading component 3 includes a normal linear loader 31 driven by a servo motor and a normal force sensor 32. The servo motor is connected to the normal linear loader 31 through a pulley structure, and the linear loader is moved in the vertical direction by the rotation of the motor.

[0038] Alternatively, the normal loading component 3 can also be other feasible high-precision linear drive components such as a linear motor.

[0039] In this embodiment, the normal linear loader 31 has a maximum loading force of 5000N, a linearity of 0.5%, a constant pressure holding error of ±10N, and a control cycle of 1 millisecond. It is used to provide constant, instantaneous normal loading stress, while the pressure and shear force cross sensitivity is 2.5%.

[0040] The mounting frame 6 is fixedly mounted on the housing of the normal linear loader 31, and the output end of the normal linear loader 31 extends into the mounting frame 6 through the reserved hole, so that the clamping mechanism 2 can be fixed to the output end of the linear loader within the mounting frame 6.

[0041] Preferably, such as Figure 2As shown, a lower pressure plate 33 is fixedly installed at the output end of the normal linear loader 31, and the lower pressure plate 33 forms a perpendicular contact with the rock thin section sample 1 installed on the clamping mechanism 2. A normal force sensor 32 is fixedly installed on the lower pressure plate 33 for real-time acquisition of normal load, and the clamping mechanism 2 is installed on the normal force sensor 32.

[0042] Optionally, in this embodiment, the tangential loading component 4 is installed on the lower end face of the top plate of the mounting frame 6, and the whole is located inside the mounting frame 6. The output end of the tangential loading component 4 faces downward. On this basis, the servo motor of the normal loading component 3 controls the normal linear loader 31 to rise, which can drive the clamping mechanism 2 and the rock thin section sample 1 clamped by the clamping mechanism 2 to rise to abut against the output end of the tangential loading component 4.

[0043] In the mineral compression-shear test system at the microscale of rock of the present invention, the output end of the tangential loading component 4 slides along the length direction of its loading surface with respect to the rock thin section sample 1 to achieve tangential loading on the rock thin section sample 1.

[0044] Optionally, the tangential loading component 4 in this embodiment includes a tangential loader 41 driven by a servo motor and a tangential force sensor 42. For example... Figure 4 As shown, the tangential loader 41 is a lead screw 412 slider structure driven by a servo motor. The servo motor directly drives the lead screw 412 to rotate through a coupling, so as to drive the slider on the lead screw 412 to make high-precision linear motion along the lead screw 412.

[0045] In other feasible implementations, the tangential loading component 4 may also be other high-precision linear drive structures.

[0046] Furthermore, the installation direction of the tangential loading component 4 is determined according to the clamping component, so that after installation, the slider slides along the length direction of the loading surface of the clamped rock thin section sample 1, thereby realizing tangential loading on the rock thin section sample 1.

[0047] In this embodiment, the tangential loading component 4 has a maximum loading force of 1000N, a linearity of 0.5%, a constant shear force holding error of ±5N, and a minimum loading step of 2 nanometers for the shear force axis, thereby achieving nanometer-level displacement loading and shear force control.

[0048] In this embodiment, the tangential loader 41 is as follows: Figure 4 As shown, it includes a guide rail base 411, a lead screw 412 rotatably connected to the guide rail base 411, and two movable sliders 413. One end of the guide rail base 411 has a servo motor drive mounting port 414, and the other end is bolted with a limit end cap 415. The limit end cap 415 serves as both a support base 53 for the lead screw 412 and a physical limit when the slider moves to its limit position, preventing overtravel.

[0049] Preferably, the lead screw 412 is a ball screw 412 to reduce friction, improve transmission accuracy and service life. The ball screw 412 has two nut seats that mesh with its threads. The two nut seats correspond one-to-one with the two movable sliders 413, and the nut seats are rigidly connected to the movable sliders 413. When the lead screw 412 rotates, the nut seats drive the movable sliders 413 to move linearly along the length of the guide rail, forming a controlled high-precision loading displacement.

[0050] The guide rail base 411 is made of high-strength aluminum alloy. The base has precision mounting grooves and screw holes for fixing the servo motor and lead screw 412. It also has a lower limit hole 416 for rigidly connecting to the top plate of the mounting frame 6 through screws or bolts, ensuring that no bending or torsional deformation will occur during tangential loading.

[0051] The movable slider 413 has a mounting hole 417 for mounting a tangential force sensor 42 to monitor the magnitude of the shear force.

[0052] Through the above methods, the normal loading component 3 and the tangential loading component 4 of the present invention can support various test modes such as monotonic shear, cyclic loading, rate step loading and normal disturbance coupling loading, which can simulate complex stress environments in engineering and expand the scope of application of microscopic rock mechanics research.

[0053] In the mineral compression-shear test system at the microscale of rock of the present invention, the output end of the tangential loading component 4 is detachably fixed with a tangential friction element 43, and the tangential friction element 43 with different friction surface materials is configured according to the interface type of the rock thin section sample 1.

[0054] like Figure 3 As shown, in this embodiment, the tangential force sensor 42 is used as the output end of the tangential loading component 4. The lower end of the tangential force sensor 42 is detachably equipped with a tangential friction component 43. The tangential friction component 43 is an assemblable modular structure, and is equipped with replacement parts for flat-head, ball-head or wedge-shaped pressure heads. The figure shows a flat-head tangential friction component 43 to adapt to rock thin section samples 1 with different interface types.

[0055] The vertical cross-section of the tangential friction element 43 is similar to a T-shape, that is, it has a large upper surface for easy installation, and at the same time has a small contact head for contacting the upper end face of the rock thin section sample 1. The vertical cross-section shape of the contact head of different tangential friction elements 43 is different.

[0056] Optionally, the tangential friction element 43 can be installed with the tangential force sensor 42 using any existing quick-release structure. In this embodiment, the tangential friction element 43 and the tangential sensor are detachably fixedly connected by screwing through a pre-drilled hole.

[0057] Preferably, the tangential friction element 43 can also be configured to be made of different friction pad materials to better adapt to different mineral interfaces and orientation tests.

[0058] In the mineral compression-shear test system at the microscale of rock of the present invention, the mounting frame 6 is formed by four detachably fixed mounting plates, wherein two mounting plates corresponding to the main plane of the rock thin section sample 1 are provided with openings to provide observation space for the image acquisition system 5.

[0059] In this embodiment, the mounting frame 6 is obtained by assembling four detachably fixed mounting plates. By removing the mounting frame 6, the tangential loading assembly 4, which is fixed to the top plate of the frame, including the servo motor, the tangential loader 41, the tangential sensor, and the tangential friction component 43 fixed to the tangential sensor, can be easily inspected or replaced.

[0060] The two mounting plates corresponding to the main plane of the rock thin section sample 1 after enclosure are designed with openings to reserve observation space for the image acquisition system 5; the mounting plate used to install the tangential loading component 4 after enclosure is provided with reserved holes that are compatible with the lower limiting hole 416; the mounting plate connected to the normal loading component 3 is provided with reserved holes at the center for the output end of the normal loading component 3 to extend into the mounting frame 6, and reserved holes for fixed installation with the outer shell of the normal loader, so that bolts or other fasteners can be used to achieve connection and fixation at the reserved holes.

[0061] A feasible mounting plate and reserved hole layout method is as follows: Figure 5 As shown, Figure 5 In the figures (a), (b), and (c), the top plate, side plate, and bottom plate of the mounting frame 6 are respectively. In other feasible embodiments, the reserved holes can also be adjusted according to requirements or installation methods to ensure the fastening of the mounting plate and the mounting frame 6 with the tangential loading component 4 and the normal loading component 3.

[0062] In the mineral compression-shear test system at the microscale of rock of the present invention, the clamping mechanism 2 includes a clamping base 21, on which a positioning groove 22 for placing the rock thin-slice sample 1 is provided. The clamping base 21 is also provided with an adjustment component in the positioning groove 22 to accommodate the installation of rock thin-slice samples 1 of different thicknesses.

[0063] like Figure 6 As shown, the clamping mechanism 2 in this embodiment includes a metal clamping base 21. The vertical cross-section of the clamping mechanism 2 is inverted T-shaped, so that it can be fixed to the output end of the normal loading device (normal force sensor 32 in this embodiment) by fasteners such as bolts through the large head at its lower end; and the small head at the upper end can clamp the rock thin section sample 1.

[0064] The upper end face of the small head of the clamping base 21 is provided with a positioning groove 22. Preferably, the positioning groove 22 is a long U-shaped groove, which facilitates the centering and fixing of the rock thin section sample 1.

[0065] Preferably, the clamping base 21 can also be configured as a modular structure, which facilitates the replacement of clamping bases 21 with different groove types, groove depths, groove widths and groove lengths to accommodate rock thin sheet specimens 1 of different sizes and shapes or other rock specimens that need to undergo compression and shear tests.

[0066] Preferably, the clamping base 21 is a metal base made of high-strength alloy material.

[0067] Furthermore, in order to make the positioning groove 22 suitable for the installation of rock thin sheet samples 1 with different thicknesses, an adjustment component is provided inside the positioning groove 22. In this embodiment, the adjustment component includes a shim 231. By replacing the shim 231 with a different thickness, it can be adapted to rock thin sheet samples 1 with different thicknesses.

[0068] Optionally, a re-adhesive layer is provided on one side of the gasket 231 to enable the gasket 231 to be fixedly installed and quickly replaced.

[0069] In one feasible implementation, a pad 231 can be attached to each of the two opposite sidewalls of the positioning groove 22, and the flexible pad 231 can contact the rock sample to improve the clamping stability.

[0070] In the mineral compression-shear test system at the microscale of rock of the present invention, the adjustment component includes a pad 231 and a buffer pad 232 respectively disposed on two opposite walls of the positioning groove 22. The buffer pad 232 is configured to move along the width direction of the positioning groove 22 to press the rock thin section sample 1 placed in the positioning groove 22 against the pad 231.

[0071] In this embodiment, such as Figure 6 As shown, the adjustment assembly includes a shim 231 and a buffer pad 232. The shim 231 is attached to one side wall of the positioning groove 22, and three buffer pads 232 are provided on the opposite side wall.

[0072] Specifically, the positioning groove 22 is used to install the buffer pad 232. The side wall of the groove has three threaded through holes spaced apart along its length. The buffer pad 232 is fixed to the front end of the fine-adjustment screw. The fine-adjustment screw is threaded to the clamping base 21 through the threaded through holes, so that the end with the buffer pad 232 is in contact with the rock thin section sample 1. By rotating the fine-adjustment screw, the length of the buffer pad 232 extending into the positioning groove 22 is adjusted so that the buffer pad 232 presses the rock thin section sample 1 against the pad 231, thereby achieving stable clamping of the rock thin section sample 1. The three buffer pads 232 spaced apart evenly distribute the loading stress, avoiding cracking or local damage to the rock thin section during loading.

[0073] In the mineral compression-shear test system at the microscale of rock of the present invention, the image acquisition system 5 includes an optical microscope 51 and a triaxial adjustment mechanism 52. The triaxial adjustment mechanism 52 is used to control the movement of the optical microscope 51 in the length, width and thickness directions of the rock thin section sample 1.

[0074] Optionally, the optical microscope 51 includes an objective / tube unit that works with a digital image correlation (DIC) algorithm to obtain local displacement / strain fields.

[0075] The three-axis adjustment mechanism 52 is used to drive the lens of the optical microscope 51 to move in the length, width and thickness directions of the installed rock thin section sample 1, thereby adjusting the field of view of the lens. It is suitable for rock thin section samples 1 with different pre-made opening positions and sizes.

[0076] In one feasible implementation, such as Figure 7 As shown, the three-axis adjustment mechanism 52 includes an X-axis linear moving guide rail 521, a Y-axis linear moving guide rail 522, and a Z-axis linear moving guide rail 523, which are used to control the movement of the lens of the optical microscope 51 in the length direction, thickness direction, and width direction of the rock thin section sample 1, respectively.

[0077] The triaxial adjustment mechanism 52 is mounted on the support base 53. Optionally, the support base 53 can be a metal support such as a portal frame or any other structure, providing a height foundation for the triaxial adjustment mechanism 52. This allows the optical microscope 51 connected to the triaxial adjustment mechanism 52 to be aligned with the portal frame support, which is a metal plate splicing base for the rock thin support base 53. The servo motor, which serves as the power source for the normal loading component 3, is installed inside the portal frame support. The normal loading device of the normal loading component 3 is located on one side of the portal frame support, making the overall structure of the compression-shear test system compact.

[0078] A Y-axis linear guide rail 522 is mounted on the top of the support base 53, an X-axis linear guide rail 521 is mounted on the Y-axis linear guide rail 522, and a Z-axis linear guide rail 523 is vertically mounted on the X-axis linear guide rail 521. An L-shaped plate 54 is fixed to the sliding block that defines the Z-axis linear guide rail, providing support for the installation of the optical microscope 51.

[0079] In addition, the triaxial adjustment mechanism 52 can smoothly scan in the X / Y directions and perform full-field stitching to obtain complete microstructural images of rock thin section samples, revealing the mechanisms of microcrack initiation, propagation and interface slip.

[0080] The mineral compression-shear test system at the microscale of rock of the present invention also includes a numerical control system. The numerical control system is electrically connected to the normal loading component 3, the tangential loading component 4 and the image acquisition system 5 to control the loading of the normal loading component 3 and the tangential loading component 4, and to acquire the microcrack time-series images acquired by the image acquisition system 5.

[0081] like Figure 1 As shown, the CNC system includes a data measurement and control platform 7, which is electrically connected to power sources such as the normal loading component 3, the tangential loading component 4, and the servo motor in the three-axis adjustment mechanism 52 via connecting cables, so as to precisely control the normal and tangential loading processes, as well as the position of the optical microscope 51.

[0082] Meanwhile, the data measurement and control platform 7 is also connected to the optical microscope 51 via a connecting cable to realize the acquisition of microcrack time sequence images.

[0083] Preferably, the image acquisition system 5, the normal loading component 3, and the tangential loading component 4 are synchronously triggered by electrical signals through the data measurement and control platform 7, thereby achieving consistency in the timing of load, displacement, and image, and better revealing the microcrack initiation, propagation, and interface slip mechanism.

[0084] This invention constructs a bidirectional independent servo loading system to achieve decoupling and independent control of normal and tangential stresses, enabling precise control of the compression-shear coupled loading path at the micrometer scale. It employs a high-precision linear motor and nanometer-level displacement control to simulate multiple working conditions, including constant displacement, constant force, cyclic loading, and rate step modes. The design of a small-scale rock sample holder ensures the stability of thin-sheet samples during loading, preventing rotation and warping. A synchronous acquisition platform based on X / Y / Z triaxial linear guides and an optical microscope 51 enables real-time imaging of crack initiation, grain boundary displacement, and interface damage during the stress process. Combined with the closed-loop control and high-speed synchronous acquisition technology of the data measurement and control platform 7, the consistency and repeatability of mechanical signals and microscopic images are achieved, thus realistically revealing the microscopic mechanical response mechanism of rocks under different loading conditions.

[0085] The following describes the mineral compression and shear test method at the microscale of rock provided by the present invention. The mineral compression and shear test method at the microscale of rock described below can be referred to in correspondence with the mineral compression and shear test system at the microscale of rock described above.

[0086] like Figure 8 As shown, the mineral compression-shear test methods at the microscale of rocks include: Step 801: Obtain a rock thin section sample and make a one-sided notch on any sidewall of the rock thin section sample to form a pre-fabricated notch; First, several thin rock sections with different bedding angles were prepared.

[0087] Optionally, in this embodiment, in order to study the microscopic properties of the bedding interface of anisotropic rocks, thin rock sections with horizontal bedding angles were prepared.

[0088] Specifically, based on research needs, typical rocks such as slate and phyllite are selected, and thin-sheet samples are prepared using wire cutting or ultrathin slicing techniques.

[0089] The geometric parameters of the rock samples include mineral composition, crystal orientation, bedding dip angle, crystal size, etc. Different types of samples can be designed according to different combinations of parameters to compare and analyze their mechanical differences.

[0090] The surface of the thin-sheet sample is ground and polished to obtain a rock sheet sample, so as to ensure that it has uniform contact with the output end of each loading mechanism during the compression-shear test and reduce the error caused by the interface effect.

[0091] Optionally, considering that the rough outer surface of the pre-processed thin sheet makes it difficult to observe the mineral crystals on the rock surface under a microscope, in this embodiment, sandpaper with roughness of 800c, 1000c, 1200c, 1500c and 2000c is used in sequence for polishing for 30 minutes each. Note that a flatness test is performed under a microscope after each polishing to observe the flatness after polishing. Then, diamond polishing fluid is used for surface polishing treatment. Diamond polishing fluid with particle sizes of 10μm, 5μm, 2.5μm, 1μm, 0.5μm and 0.25μm is used for polishing in sequence, with each step polishing for 30 minutes.

[0092] The rock thin section sample obtained by the above method can be observed to be clear and reflective to the naked eye. Discontinuous micro-layers can be clearly observed under light. Under a microscope, the mineral crystals on the rock surface and their weak cementation interfaces can be clearly observed.

[0093] Preferably, the grinding and polishing process should be such that the thin-section rock sample can be clearly identified by the characteristics of the thin-section bedding structure.

[0094] Finally, a pre-made notch is machined on one side of the rock thin section specimen, preferably one-third the length of the specimen, to form a controllable crack initiation location and meet the geometric conditions required for the shear test.

[0095] Alternatively, in another feasible embodiment, a cubic thin-film sample can also be used. In this embodiment, a micro-compression shear sample with a side length of 30 mm and a notch length of 10 mm is prepared.

[0096] Step 802: Install the rock thin section sample with a notch into the clamping mechanism; The pre-formed notch-processed rock thin-section sample is installed in the clamping mechanism and fixed by the clamping mechanism.

[0097] by Figure 6 Taking the clamping mechanism as an example, the rock thin-slice sample is placed in the positioning groove, and the rock thin-slice sample is clamped and fixed by the shims and fine-tuning screws. Then, the clamping base is installed on the normal force sensor by bolting, thus completing the installation of the rock thin-slice sample, so that the installed rock thin-slice sample is located in the working area of ​​the normal loader and the tangential loader.

[0098] Step 803: Control the normal loading component to load so that the installed rock thin section sample contacts the output end of the tangential loading component and maintains a constant preload. Then, pre-compression and contact determination are performed.

[0099] The output end of the control normal loading component moves toward the rock thin section sample, so as to drive the rock thin section sample to abut against the output end of the tangential loading component at a low speed.

[0100] Optionally, when the normal force sensor in the normal loading assembly detects a sudden change in the force-displacement curve or the contact stiffness exceeds the threshold, it is determined that the rock thin section sample has completed contact with the output end of the tangential loading assembly.

[0101] Afterward, the normal loading component is controlled to be in constant force mode, and a normal preload within a preset range is applied and maintained for a period of time to eliminate the small gaps between the mechanical parts of the clamping mechanism due to assembly, and to eliminate the initial relaxation effect, so as to ensure the compressive stability of the rock thin section specimen during the compression-shear test.

[0102] Step 804: Control the image acquisition system to move until the pre-made notch of the rock thin section specimen is within its field of view, so as to obtain a time sequence image of the microcracks that initiate at the pre-made notch of the rock thin section specimen during the compression-shear test. Then the image acquisition system is adjusted.

[0103] Start and control the image acquisition system so that the pre-made notch of the rock thin section sample is within the field of view of the image acquisition system.

[0104] by Figure 7 Taking the image acquisition system as an example, the lens position of the optical microscope is adjusted by a three-axis adjustment mechanism to ensure that its field of view covers the pre-made notch area of ​​the rock thin section sample. The microscope can be illuminated with bright field, dark field, or polarized light to enhance the contrast of grain boundary and interface features.

[0105] Optionally, hardware synchronization can be achieved through signal control equipment to ensure the temporal consistency between force-displacement data and microscope images during the compression-shear test.

[0106] Step 805: Control the tangential loading component to apply shear load to the rock thin section specimen in a preset control mode to suit the corresponding type of micro-shear test; The microscopic shear test includes a microscopic direct shear test, which is used to obtain the peak stress when the rock thin section sample undergoes type II fracture or shear failure at the microscopic level, and to calculate the fracture toughness, interfacial shear strength and interfacial friction angle based on the peak stress.

[0107] Among them, the micro-shear test includes the micro-direct shear test and the micro-tensile test.

[0108] Optionally, the preset control modes include constant displacement mode, constant force mode, cyclic mode and velocity step mode. Those skilled in the art can also predefine control modes based on experimental requirements.

[0109] In the constant displacement mode, the tangential loading component applies horizontal shear at a constant displacement rate to obtain the interfacial shear strength and friction angle of the rock thin section sample.

[0110] In constant force mode, the tangential loading component applies horizontal shear with a constant tangential force to observe the interfacial creep and time effect of rock thin section specimens.

[0111] In cyclic mode, the tangential loading component applies positive and negative symmetrical or asymmetrical shear cycles to study the fatigue characteristics and residual strength of rock thin section specimens.

[0112] In the velocity step mode, the tangential loading component adjusts the tangential loading rate during loading to study the rate sensitivity and interfacial dynamics characteristics of rock thin section samples.

[0113] Optionally, in the compression-shear test, under constant normal stress, the tangential loading component is controlled to apply shear load to the rock thin section specimen, and the tangential force and tangential displacement data are recorded as the shear force gradually increases to obtain the force-displacement curve. Simultaneously, microscopic images are acquired to obtain microcrack time sequence images.

[0114] When interface slippage, microcrack initiation, or shear failure occurs, the force-displacement curve will show a characteristic abrupt change, revealing the mechanism of grain displacement, crack propagation, and interface failure.

[0115] It should be noted that for traditional universal testing machines using lead screw or hydraulic drive, the error is mostly greater than 1µm, and the stiffness is mostly greater than 10. 8 The deformation is on the order of N / m, meaning that every 100N change in the testing machine will generate several micrometers of mechanical deformation, which cannot meet the requirements for accurately controlling the cracking of mineral crystal interfaces. However, the compression-shear testing system provided by this invention uses a displacement loading device based on a piezoelectric actuator with a Young's modulus of 105 GPa, achieving a displacement loading control accuracy of 1 nm, effectively solving the problem of insufficient accuracy in traditional loading equipment. Simultaneously, the device shell is made of high-strength stainless steel with a Young's modulus of 206 GPa, and finite element simulation calculations show that the overall stiffness of the loading device exceeds 10... 11 N / m, which means that when the axial load reaches 100N, the frame deformation is less than 1nm, effectively ensuring the loading accuracy.

[0116] In one specific implementation, a thin-section rock specimen for micro-compression-shear testing was prepared, and a schematic diagram of the pre-fabricated fracture stress analysis is shown below. Figure 9 As shown, the length of the sample L The pre-fabricated notch length is 30mm. a It is 10mm thick. B The thickness is 1.5 mm. Horizontal stratification, with a pre-made notch machined in the center of the thin sheet, followed by grinding and polishing of the sample surface until the stratification structure of the thin sheet can be clearly identified.

[0117] The prepared rock thin-section sample is placed in the positioning groove of the fixture, and coarse centering and clamping are achieved by adjusting the shims and fine-tuning the set screws. Then, the normal loading component is controlled to drive the indenter to press up at a low speed until it contacts the rock thin-section sample. Stress control is implemented through the normal force sensor until the predetermined normal stress that can achieve pure shear fracture is reached.

[0118] Adjust the position and focal length of the optical microscope to align it with and clearly observe the pre-fabricated notch area, and simultaneously start the synchronous acquisition of images and force-displacement signals. Then, control the tangential servo motor to apply shear displacement in a displacement control manner, with the step size set to 0.1 mm / step. The step size can also be modified according to the actual situation.

[0119] Real-time monitoring of shear force-displacement curves; when a sudden drop in shear force occurs, it is determined to be a stress relaxation response caused by crack propagation. The microscope is controlled by a three-dimensional sliding rail to perform X / Y / Z direction scanning, and the full-field imaging and crack propagation tracking at the corresponding moment are recorded.

[0120] In a specific experimental implementation, the shear force-displacement curve was monitored in real time on the data recording platform. When the shear force suddenly dropped, it indicated stress relaxation, meaning the crack was in a critical state. At this point, the crack morphology was observed and the maximum applied load was recorded using an image synchronous acquisition system. Considering the brittle fracture characteristics of rock, to accurately capture the critical stress during crack propagation, the displacement was stopped and held for 30 seconds for every 0.1 mm increase, and the full-field image at the corresponding moment was recorded, along with the shear force. When the shear force could no longer increase and crack propagation along the grain boundary was observed, the maximum load was recorded, capturing the crack initiation, grain boundary displacement, and interface failure processes. The rock thin-section samples were repeatedly assembled and loaded according to the above steps to obtain the physical and mechanical parameters under different working conditions.

[0121] Finally, the experimental loading curve and the corresponding microcrack time-series image were obtained as follows: Figure 10 and Figure 11 As shown. Among them, Figure 10 The red pentagram in the diagram represents the peak stress point, and the points marked (1) to (4) are consistent with... Figure 11 The correspondences between (1) and (4) are: Figure 11 The image acquisition points corresponding to the sub-image.

[0122] By combining the above loading methods with the shear displacement-shear force images obtained from the loading, the peak stress can be directly determined based on the experimental results. Furthermore, the mapping relationship between shear displacement and crack propagation length can be obtained from the image acquisition system, thereby inferring the microcrack propagation length under macroscopic stress. On this basis, the fracture toughness and fracture energy of micro-minerals, the shear strength of the mineral interface of the sample, and the friction angle of the mineral interface can be further calculated.

[0123] First, the calculation of fracture toughness and fracture energy based on linear elastic fracture mechanics is explained: Under peak load, the stress intensity factor reaches a critical value, called fracture toughness. Correspondingly, the energy release rate also reaches a critical value, called fracture energy. Fracture toughness and fracture energy are key parameters for evaluating a material's resistance to crack initiation and propagation.

[0124] Type II fracture toughness was obtained under peak load. and fracture energy The calculation formula is as follows: ; In the formula, This represents the peak load corresponding to the occurrence of Type II fracture or shear failure in the specimen during a micro-compression-shear test. Represents shape factor parameter ，S Indicates the span. b Indicates the thickness of the sample. h Indicates the height of the sample. aIndicates the length of the precast notch. This represents the elastic modulus of rock.

[0125] It is worth noting that at the microscale, due to the small sample size and the high precision requirements of the testing equipment, traditional methods such as direct shear tests can usually only fit microscopic parameters through the load-displacement curves of macroscopic interfaces. However, in this invention, based on the microscopic compression-shear testing system provided by this invention, by integrating a high-precision loading device and a real-time microscopic imaging system, it is possible to achieve microscopic analysis of individual minerals or bedding interfaces at the microscale. T The maximum value is obtained directly from experiments. During shear loading, crack behavior is captured simultaneously and the critical shear force is recorded directly. Thus, more accurate calculation results of type II fracture toughness are achieved by obtaining the shear strength of the crystal interface with higher precision.

[0126] Then, the calculation of the shear strength at the mineral interface is explained: Under shear stress, the material constitutive model at the mineral grain interface follows an ideal elastoplastic model. The stress-strain curve includes a linear variation stage and a stress-stable stage. Due to the very small thickness of the mineral grain interface, the plastic zone at the crack tip is banded, as shown in the image. Figure 9 As shown, the fracture conforms to the Dugdale-Barenblatt (DB model). Under the assumption of a small yield zone at the crack tip and uniform cohesion distribution within the yield zone, the relationship between the experimental peak load and the critical stress at interface failure was established. From this, the interface shear strength was derived. Theoretical calculation formula: ; In the formula, For far-field shear stress, For geometric or material correction factors associated with type II fracture, S Indicates the span. b Indicates the thickness of the sample. h Indicates the height of the sample.

[0127] The microscopic scale obtained directly through experiments using the above formulas The interfacial shear strength can then be calculated by substituting the values ​​into the equation.

[0128] Finally, the calculation of the friction angle at the mineral interface is explained: Based on the derivation above, the shear strength of the mineral interface under far-field stress can be obtained. By changing different selected normal stresses The peak shear strength of the specimens under different normal pressures was measured. The shear stress-shear displacement curve was plotted. This implementation method employs the approach recommended by the International Society for Rock Mechanics and Rock Engineering, conducting microscopic shear tests at three different normal stress levels to obtain the peak shear strength value. Subsequently, the relationship between the peak shear strength and normal stress is expressed according to the Mohr-Coulomb criterion. ; In the formula, , and These represent the shear strength, cohesion, and friction angle at the mineral interface, respectively. Indicates normal stress.

[0129] Peak shear strength was measured under different normal stress levels. Then, the shear strength of the mineral interface was calculated according to the method described above. And plot the shear strength of the microlayers. Different but constant normal stress The changing curves are fitted using the above formula to obtain the microscopic cohesion and friction angle of the mineral interface.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A mineral compression-shear testing system at the microscale of rocks, characterized in that, include: Clamping mechanism, normal loading component, tangential loading component, and image acquisition system; The clamping mechanism is used to clamp the rock thin-section sample from the thickness direction of the rock thin-section sample. The tangential loading assembly is used to apply tangential pressure to the sidewall of the rock thin section sample in the thickness direction; The normal loading component is used to apply normal pressure to the sidewall of the rock thin section sample in the thickness direction. When the normal loading component is loaded, the rock thin section sample held by the clamping mechanism is pressed against the output end of the tangential loading component, thereby applying shear load to the rock thin section sample under constant normal stress. The image acquisition system is positioned toward the main plane of the rock thin section specimen and is used at least to acquire time-series images of microcracks that initiate during the compression-shear test of the pre-made notch of the rock thin section specimen. The thickness of the rock thin section specimen does not exceed 1.5 mm, and the pre-made notch is pre-made on the rock thin section specimen before the compression-shear test to form a controllable crack initiation position at the pre-made notch location for observation.

2. The mineral compression-shear testing system at the microscale of rock according to claim 1, characterized in that, It also includes a mounting frame installed on the normal loading component, the clamping mechanism is located inside the mounting frame, and the tangential loading component is arranged opposite to the normal loading component on the mounting frame, so that when the normal loading component is loaded, its output end drives the rock thin section sample held by the clamping mechanism to move toward the tangential loading component and press against it, thereby realizing the normal loading of the rock thin section sample.

3. The mineral compression-shear testing system at the microscale of rock according to claim 2, characterized in that, The output end of the tangential loading component slides along its length direction relative to the loading surface of the rock thin section sample to achieve tangential loading on the rock thin section sample.

4. The mineral compression-shear testing system at the microscale of rock according to claim 3, characterized in that, The output end of the tangential loading component is detachably fixed with a tangential friction element, and the tangential friction elements with different friction surface materials are configured based on the interface type of the rock thin section sample.

5. The mineral compression-shear testing system at the microscale of rock according to claim 2, characterized in that, The mounting frame is formed by four detachably fixed mounting plates, with two mounting plates having openings corresponding to the main plane of the rock thin section sample to provide observation space for the image acquisition system.

6. The mineral compression-shear testing system at the microscale of rock according to claim 1, characterized in that, The clamping mechanism includes a clamping base, on which a positioning groove for placing the rock thin-section sample is provided. The clamping base is also provided with an adjustment component in the positioning groove to accommodate the installation of rock thin-section samples of different thicknesses.

7. The mineral compression-shear testing system at the microscale of rock according to claim 6, characterized in that, The adjustment assembly includes a pad and a buffer liner respectively disposed on two opposite walls of the positioning groove. The buffer liner is configured to move along the width direction of the positioning groove to press the rock sheet sample placed in the positioning groove against the pad.

8. The mineral compression-shear testing system at the microscale of rock according to claim 1, characterized in that, The image acquisition system includes an optical microscope and a triaxial adjustment mechanism, which is used to control the movement of the optical microscope in the length, width and thickness directions of the rock thin section sample.

9. The mineral compression-shear testing system at the microscale of rock according to claim 1, characterized in that, It also includes a numerical control system, which is electrically connected to the normal loading component, the tangential loading component and the image acquisition system to control the loading of the normal loading component and the tangential loading component, and to acquire the microcrack time sequence image acquired by the image acquisition system.

10. A method for testing mineral compression and shear at the microscale of rocks, characterized in that, include: Obtain a rock thin section sample and make a one-sided notch on any sidewall of the rock thin section sample to form a pre-fabricated notch; The rock thin section sample with a notch is installed in the clamping mechanism; The normal loading component is controlled to load the rock thin section sample so that the installed sample contacts the output end of the tangential loading component and maintains a constant preload. The image acquisition system is moved to a position where the pre-made notch of the rock thin section specimen is within its field of view in order to obtain a time-series image of the microcracks that initiate at the pre-made notch of the rock thin section specimen during the compression-shear test. The tangential loading component is controlled to apply shear load to the rock thin section specimen in a preset control mode, which is suitable for the corresponding type of micro-shear test. The microscopic shear test includes a microscopic direct shear test, which is used to obtain the peak stress when the rock thin section sample undergoes type II fracture or shear failure at the microscopic level, and to calculate the fracture toughness, interfacial shear strength and interfacial friction angle based on the peak stress.

Images