Stress gradient automatic loading device and loading method

Abstract

The present invention discloses a stress gradient automatic loading device, including a rigid frame, four rigid loading side plates are arranged in the rigid frame, the four rigid loading side plates form a square loading cavity, the rigid frame is also provided with end covers for closing both ends of the square loading cavity, a force transmission component is matched and installed in the loading cavity, a cylindrical sample loading cavity is formed in the middle of the force transmission component, the force transmission component includes an elastic cylindrical sleeve, an elastic truncated cone sleeved outside the elastic cylindrical sleeve, and a square elastic body sleeved outside the elastic truncated cone, and also includes a loading system arranged in the rigid frame for applying force to the four rigid loading side plates respectively. The present invention also discloses a loading method using the above device. The present invention has the characteristics of simple structure, convenient operation, and can realize gradient loading of sample axial stress.

Description

Technical Field

[0001] The invention relates to a rock mass mechanical property testing device, in particular to a stress gradient automatic loading device and a loading method. Background Art

[0002] It has become a consensus among scientists around the world that humans must advance into the depths of the earth. The factors that currently restrict deep rock engineering are mainly "three highs and one disturbance", namely high geostress, high geotemperature, high osmotic pressure, and strong mining disturbance. The study of rock stability is the premise for deep engineering. To this end, scholars at home and abroad have widely explored the mechanical response of rocks under high geostress, high geotemperature, high osmotic pressure and mining disturbance. In the current research on the response of rocks to different influencing factors under high stress, the applied stress is usually constant. However, whether it is mining tunnels, chamber engineering, tunnel engineering, or civil air defense engineering, the pressure on the surrounding rock is gradient stress. Existing research has failed to reflect the actual stress condition of rocks, which has led to a disconnection between laboratory research and field application of rock mechanics, restricting the development of rock engineering. At present, the influence of other factors on rock mechanical properties and stability under stress gradient is limited to numerical calculation. The reason is that a set of key equipment for applying stress gradient in static and dynamic mechanical experiments of rocks has not been developed. Summary of the invention

[0003] The first technical problem to be solved by the present invention is to provide a stress gradient automatic loading device capable of applying gradient stress to a rock sample.

[0004] The second technical problem to be solved by the present invention is to provide a loading method using the above device.

[0005] In order to solve the above-mentioned first technical problem, the present invention adopts the following technical solution:

[0006] A stress gradient automatic loading device comprises a rigid frame, four rigid loading side plates are arranged in the rigid frame, the four rigid loading side plates surround a square loading cavity, the rigid frame is also provided with end covers for closing both ends of the square loading cavity, a force transmission component is matched and installed in the loading cavity, a cylindrical sample loading cavity is formed in the middle of the force transmission component, the force transmission component comprises an elastic cylindrical sleeve, an elastic truncated cone sleeved outside the elastic cylindrical sleeve, and a square elastic body sleeved outside the elastic truncated cone, and also comprises a loading system arranged in the rigid frame for applying force to the four rigid loading side plates respectively.

[0007] Furthermore, the loading system includes four hydraulic cylinders respectively arranged on the outer sides of four rigid loading side plates.

[0008] Furthermore, slide grooves are provided on the inner sides of the four rigid loading side plates, and the four rigid loading side plates are slidably connected in sequence through the slide grooves. The extension direction of the slide grooves on the rigid loading side plates on both sides of the hydraulic cylinder is parallel to the loading direction of the hydraulic cylinder.

[0009] Furthermore, the end cover is made of tempered glass.

[0010] Furthermore, the loading system also includes a hydraulic workstation, and four hydraulic cylinders are connected to the hydraulic workstation through branch pipes, and each branch pipe is provided with a pipeline switch and a pressure gauge.

[0011] A loading method, using the above-mentioned loading device, comprises the following steps:

[0012] Step 1: First, put the elastic frustum and the square elastic body on the elastic cylindrical sleeve in sequence to form a force transmission assembly, put the test sample into the elastic cylindrical sleeve, and finally place the force transmission assembly between four rigid loading side plates and fix the end cover on the rigid frame;

[0013] Step 2: Start the hydraulic workstation and the hydraulic control switch, so that the hydraulic oil is transmitted to the hydraulic cylinder along the branch pipe, and the hydraulic cylinder drives the rigid loading side plates to move toward each other, so as to pressurize the square elastic body in the loading cavity, and then pressurize the elastic frustum;

[0014] Step 3: When the sample needs to be subjected to axial stress gradient loading and axial uniform loading, adjust the pipeline switch and refer to the pressure gauge to make the pressure of the hydraulic cylinder equal to achieve circumferential uniform pressure loading of the sample. At the same time, due to the different axial outer diameters of the elastic truncated cone, the deformation of the elastic truncated cone is different, and the stress in the axial direction of the sample is also different, so that the axial stress gradient loading is achieved when the circumferential pressure of the sample section is the same;

[0015] When the specimen needs to be subjected to axial stress gradient loading and circumferential non-uniform loading, the pipeline switch is adjusted and the pressure of each hydraulic cylinder is made unequal by referring to the pressure gauge, thereby achieving different strains in different circumferential directions of the elastic frustum cross section. Due to the different deformations of the elastic frustum, the stress applied to the specimen is also different, thereby achieving axial stress gradient loading under different circumferential pressures of the specimen.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The present invention is based on elastic-plastic mechanics. By adjusting the pressure applied to each loading side plate by the loading system, uniform pressure or bias pressure loading is achieved around the elastic cylindrical sleeve, thereby achieving uniform pressure or bias pressure loading in the circumferential direction of the sample. In addition, due to the different axial outer diameters of the elastic truncated cone, the deformation of the elastic truncated cone is different, and the stress in the axial direction of the sample is also different, so the axial stress gradient loading of the sample can be achieved, providing an equipment basis for mechanical testing of materials such as rocks under stress gradient, and having the advantages of simple structure and reliable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of the invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] See also Figure 1 A stress gradient automatic loading device comprises a rigid frame 1, four rigid loading side plates 3 are arranged in the rigid frame 1, the four rigid loading side plates 3 surround a square loading cavity 6, the rigid frame 1 is also provided with end covers 14 closing both ends of the square loading cavity 6, a force transmission component is matched and installed in the loading cavity 6, a cylindrical sample loading cavity is formed in the middle of the force transmission component, the force transmission component comprises an elastic cylindrical sleeve 8, an elastic truncated cone 7 sleeved outside the elastic cylindrical sleeve 8 and a square elastic body 5 sleeved outside the elastic truncated cone 7, and also comprises a loading system arranged in the rigid frame 1 to apply force to the four rigid loading side plates 3 respectively.

[0021] Specifically, the loading system includes a hydraulic workstation 9 and four hydraulic cylinders 2 respectively arranged on the outside of four rigid loading side plates 3. Each hydraulic cylinder 2 is fixed on the rigid frame 1 and the loading rod is connected to the corresponding rigid loading side plate 3. The four hydraulic cylinders 2 are connected to the hydraulic workstation 9 through a branch pipe 12. Each branch pipe 12 is provided with a pipeline switch 13 and a pressure gauge 11. By adjusting the hydraulic cylinder 2 so that the forces applied to the two mutually perpendicular rigid loading side plates 3 are different, the loading of forces of different directions and sizes on the sample in the casing can be achieved.

[0022] The present invention is based on elastic-plastic mechanics. By adjusting the pressure applied to each loading side plate by the loading system, the uniform pressure or bias loading around the elastic cylindrical sleeve 8 is achieved, thereby achieving uniform pressure or bias loading in the circumferential direction of the sample. In addition, due to the different axial outer diameters of the elastic truncated cone 7, the deformation of the elastic truncated cone 7 is different, and the stress in the axial direction of the sample is also different, which can achieve axial stress gradient loading of the sample, providing an equipment basis for mechanical testing of materials such as rocks under stress gradient, and having the advantages of simple structure and reliable operation. In addition, by changing the cone angle of the truncated cone while ensuring that the diameter of the through hole in the middle of the truncated cone is equal, stress loading of different gradients can be achieved.

[0023] In this embodiment, the elastic cylindrical sleeve 8, the elastic truncated cone 7 and the square elastic body 5 can all be made of rubber material, and the end cover 14 can be made of tempered glass, so as to facilitate observation of the sample loading process.

[0024] It should be noted that in actual design, the elastic cone 7 is an elastic body with different diameters at both ends, and the diameter of the central through hole must be sufficient to ensure that the cylindrical sample is placed therein and subjected to a relatively small confining pressure. The inner diameter of the casing in its natural state is smaller than the diameter of the test sample, and the outer diameter of the casing is slightly larger than the inner diameter of the central through hole of the elastic cone 7 to avoid the appearance of wrinkles during the application of pressure.

[0025] Preferably, the elastic cylindrical sleeve 8, the elastic truncated cone 7 and the square elastic body 5 have the same length and both ends are respectively in contact with the end cover 14, thereby preventing the sleeve, the elastic truncated cone, etc. from lateral displacement during the process of applying force.

[0026] As a preferred solution of the present invention, in the loading device of this embodiment, the inner side surfaces of the four rigid loading side plates 3 are all provided with slide grooves 4, and the two four rigid loading side plates 3 are slidably connected in sequence through the slide grooves 4. The extension direction of the slide grooves 4 on the rigid loading side plates 3 on both sides of the hydraulic cylinder 2 is parallel to the loading direction of the hydraulic cylinder. The specific splicing method of the rigid loading side plates 3 is as follows: the four rigid loading side plates 3 are combined in pairs to form an L-shaped component, and the two rigid loading side plates 3 in the L-shaped component are slidably connected through the slide grooves, and the two free ends of the L-shaped component are slidably docked with the free end of the other L-shaped component through the slide grooves, thereby forming a square loading chamber 6. During loading, the hydraulic cylinder 2 drives the two relatively rigid loading side plates 3 to move toward each other along the slide grooves 4 to realize the loading of the sample. The rigid loading side plates 3 are slidably connected through the slide grooves, and the length and width of the loading chamber can be flexibly adjusted by adjusting the distance between the two relatively rigid loading side plates.

[0027] A loading method using the above loading device comprises the following steps:

[0028] When the specimen needs to be subjected to axial stress gradient loading and circumferential non-uniform loading, the pipeline switch is adjusted and the pressure of each hydraulic cylinder is made unequal by referring to the pressure gauge, thereby achieving different strains in different circumferential directions of the elastic frustum cross section. Due to the different deformations of the elastic frustum, the stress applied to the specimen is also different, thereby achieving axial stress gradient loading under different circumferential pressures of the specimen.

[0029] Step 1: First, the elastic truncated cone 7 and the square elastic body 5 are sequentially sleeved outside the elastic cylindrical sleeve 8 to form a force transmission assembly, and the sample to be tested is placed in the elastic cylindrical sleeve 8. Finally, the force transmission assembly is placed between the four rigid loading side plates 3 and the end cover 14 is fixed to the rigid frame;

[0030] Step 2: Start the hydraulic workstation 9 and the hydraulic control switch 10, so that the hydraulic oil is transmitted to the hydraulic cylinder 2 along the branch pipe 12, and the hydraulic cylinder 2 drives the rigid loading side plates 3 to move toward each other, so as to pressurize the square elastic body 5 in the loading cavity, and then pressurize the elastic truncated table 7;

[0031] Step 3: When the sample needs to be subjected to axial stress gradient loading and axial uniform loading, adjust the pipeline switch and refer to the pressure gauge 13 to make the pressure of the hydraulic cylinder 2 equal, so as to realize circumferential uniform pressure loading of the sample. At the same time, due to the different axial outer diameters of the elastic truncated cone 7, the deformation of the elastic truncated cone 7 is different, and the stress in the axial direction of the sample is also different, so as to realize axial stress gradient loading under the condition of the same circumferential pressure of the sample cross section;

[0032] When the sample needs to be subjected to axial stress gradient loading and circumferential non-uniform loading, the pipeline switch 11 is adjusted and the pressure of each hydraulic cylinder is made unequal by referring to the pressure gauge 13, thereby achieving different strains in different circumferential directions of the cross section of the elastic frustum 7. Due to the different deformations of the elastic frustum 7, the stress applied to the sample is also different, thereby achieving axial stress gradient loading under different circumferential pressures of the sample.

[0033] In this embodiment, the pressure coefficient (the ratio of lateral pressure to vertical pressure) can be adjusted by adjusting the pressure applied to the loading side plate. When the pressure coefficient is 1, that is, the pressure applied by the surrounding jacks is equal, the stress around the cylindrical sample loading cavity is the same. When the lateral pressure coefficient is not equal to 1, the force around the cylindrical sample loading cavity is different. The specific size and direction of the maximum stress are controlled by the ratio of the lateral pressure to the vertical pressure. By changing the pressure coefficient, the circumference of the same cross-section of the platform can be uniformly loaded or non-uniformly loaded. The size and direction of this non-uniform loading, such as the maximum principal stress and the minimum principal stress, can also be controlled.

[0034] The above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A stress gradient automatic loading device, comprising a rigid frame, wherein four rigid loading side plates are arranged inside the rigid frame, the four rigid loading side plates enclose a square loading cavity, and the rigid frame is also provided with end covers for closing both ends of the square loading cavity. Features: A force transmission component is matched and installed in the loading cavity, and a cylindrical sample loading cavity is formed in the middle of the force transmission component. The force transmission component includes an elastic cylindrical sleeve, an elastic truncated cone sleeved outside the elastic cylindrical sleeve, and a square elastic body sleeved outside the elastic truncated cone; and also includes a loading system arranged in the rigid frame and applying force to four rigid loading side plates respectively; The loading system includes four hydraulic cylinders respectively arranged on the outsides of four rigid loading side plates; Slide grooves are arranged on the inner sides of the four rigid loading side plates, and the four rigid loading side plates are slidably connected in sequence through the slide grooves. The extending direction of the slide grooves on the rigid loading side plates on both sides of the hydraulic cylinder is parallel to the loading direction of the hydraulic cylinder. The end cap is made of tempered glass; The loading system also includes a hydraulic workstation, to which four hydraulic cylinders are connected via branch pipes, each branch pipe being provided with a pipeline switch and a pressure gauge; The loading device is loaded as follows: Step 1: First, put the elastic frustum and the square elastic body on the elastic cylindrical sleeve in sequence to form a force transmission assembly, put the test sample into the elastic cylindrical sleeve, and finally place the force transmission assembly between four rigid loading side plates and fix the end cover on the rigid frame; Step 2: Start the hydraulic workstation and the hydraulic control switch, so that the hydraulic oil is transmitted to the hydraulic cylinder along the branch pipe, and the hydraulic cylinder drives the rigid loading side plates to move toward each other, so as to pressurize the square elastic body in the loading cavity, and then pressurize the elastic frustum; Step 3: When the sample needs to be subjected to axial stress gradient loading and axial uniform loading, adjust the pipeline switch and refer to the pressure gauge to make the pressure of the hydraulic cylinder equal to achieve circumferential uniform pressure loading of the sample. At the same time, due to the different axial outer diameters of the elastic truncated cone, the deformation of the elastic truncated cone is different, and the stress in the axial direction of the sample is also different, so that the axial stress gradient loading is achieved when the circumferential pressure of the sample section is the same; When the specimen needs to be subjected to axial stress gradient loading and circumferential non-uniform loading, the pipeline switch is adjusted and the pressure of each hydraulic cylinder is made unequal by referring to the pressure gauge, thereby achieving different strains in different circumferential directions of the elastic frustum cross section. Due to the different deformations of the elastic frustum, the stress applied to the specimen is also different, thereby achieving axial stress gradient loading under different circumferential pressures of the specimen.

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