A Jack for Mitigating Impact Loads and a Loading Method

Abstract

The present invention provides a jack for mitigating impact loads and a loading method. The jack includes a cylinder body, an upper piston, an upper piston rod, and a lower piston. The upper piston divides the cylinder body into an upper oil cylinder and a lower oil cylinder, and the upper piston rod extends out of the cylinder body from the upper end of the upper oil cylinder. A lower piston hole is correspondingly formed in the middle of the lower end face of the upper piston, the lower piston extends into the lower piston hole, and the lower end is integrally connected to the bottom surface of the lower oil cylinder through a lower piston rod. Oil through holes are respectively provided on the side walls of the upper and lower oil cylinders. Before loading, the upper piston is located in the middle of the cylinder body, and a single oil pump is used to simultaneously fill the upper oil cylinder and the lower oil cylinder with low-compressibility hydraulic oil at equal flow rate and equal pressure, maintain the hydraulic pressure of one oil cylinder in a constant steady state, and uniformly reduce the hydraulic pressure of the other oil cylinder, and use the pressure difference between the two oil cylinders to apply a load to the test piece. The present invention greatly reduces the impact load generated by the conventional loading method of the jack, and can obtain the load-deformation curve after the failure of the test piece, especially for high-strength and brittle materials.

Description

Technical Field

[0001] The present invention belongs to the field of solid mechanics tests, relates to a loading device for mechanical tests, and specifically is a jack for mitigating impact loads and a loading method thereof. Background Art

[0002] At present, a hydraulic jack is a commonly used loading device for solid mechanics tests. A manual oil pump, an electric oil pump or an electro-hydraulic servo system is used to fill hydraulic oil into the lower oil cylinder of the jack. The hydraulic pressure makes the piston together with the piston rod push outwards, so as to apply a tensile force or a pressure to the test piece. For an ordinary double-acting jack, the area of the lower oil cylinder is larger than that of the upper oil cylinder. The lower oil cylinder transfers the load to the piston (rod) through hydraulic transmission to generate force. The function of the upper oil cylinder is to reset the piston rod ejected after the test and cannot bear high pressure. During the loading process, there is no oil pressure in the hydraulic oil of the upper oil cylinder, and the valve is in the open oil return state. In solid mechanics tests, for brittle materials, when the test piece is extremely close to the moment of failure at the ultimate load, the deformation energy of the jack and the test bench frame is instantaneously released and acts on the test piece. The piston rod of the jack quickly pops forward under the action of hydraulic pressure and impacts the damaged test piece after failure, causing its fragments to fly, which poses a safety hazard. When a rock specimen is stressed and suddenly ruptures, non-linear mutation phenomena such as the generation, expansion and fracture of internal micro-cracks occur. The main reasons are that the stiffness of the testing machine is smaller than that of the rock specimen or the control accuracy of the testing machine is not high. However, the electro-hydraulic servo rigid testing machine developed for this purpose is still not easy to obtain the load-deformation curve after the failure of all rocks, especially for rocks of high strength and brittle materials. Summary of the Invention

[0003] To solve the above problems, the present invention provides a jack for mitigating impact loads and a loading method thereof. The jack is a double-acting jack with equal double outputs, and can transfer the load to the test piece through the low-compressibility hydraulic oil, the piston and the piston rod by the pressure difference between the two oil cylinders. When the test piece fails instantaneously, the reduced load is transferred to the pressure relief oil cylinder through the piston of the jack, and the hydraulic pressure of the pressure relief oil cylinder supports the piston to limit the ejection of the piston, thereby greatly mitigating the impact of the load on the test piece.

[0004] To achieve the above technical purpose, the present invention provides a jack for mitigating impact loads. The jack includes a cylinder body, an upper piston, an upper piston rod and a lower piston. The upper piston divides the cylinder body into an upper oil cylinder and a lower oil cylinder. The upper piston rod is placed on the upper end surface of the piston and is integrally connected with the upper piston. The upper piston rod extends out of the cylinder body from the upper end of the upper oil cylinder. The lower piston is placed at the central position of the lower oil cylinder. A lower piston hole is correspondingly opened in the middle of the lower end surface of the upper piston. The lower piston extends into the lower piston hole and is integrally connected with the bottom surface of the lower oil cylinder through the lower piston rod. An upper oil passage hole is provided on the side wall of the upper oil cylinder, and a lower oil passage hole is provided on the side wall of the lower oil cylinder.

[0005] Further technical solution of the present invention: The diameters of the upper piston rod, the lower piston and the lower piston rod are equal.

[0006] Preferred technical solution of the present invention: A two-way high-pressure sealing ring is provided between the upper piston and the cylinder block, a sealing ring is provided between the lower piston and the lower piston hole, and a through-hole is provided in the middle of the lower piston rod. The through-hole passes through the lower piston, the lower piston rod and the oil cylinder base to communicate with the atmosphere.

[0007] In order to achieve the above technical purpose, the present invention also provides a jack loading method for reducing impact load, which is characterized in that the above-mentioned jack for reducing impact load is used for loading, and the upper piston rod of the jack acts on the surface of the test piece. The specific steps are as follows:

[0008] (1) Before loading, place the upper piston of the jack in the middle of the oil cylinder, and use an oil pump to simultaneously fill the upper oil cylinder and the lower oil cylinder of the jack with low-compressibility hydraulic oil of equal flow rate and equal pressure, so that the output force of the upper piston rod of the jack is greater than the estimated failure load of the test piece;

[0009] (2) While ensuring that the pressure oil cylinder is always in a constant pressure and stable state, close the oil filling pipeline of the pressure relief oil cylinder so that the end face of the piston rod is in pre-contact with the pressure receiving surface of the test piece; The constant pressure and stable state of the pressure oil cylinder can be maintained by using a ball screw for pressurization and a hydraulic servo control method, or other conventional methods can also be used;

[0010] (3) Slowly open the pressure relief valve of the pressure relief oil cylinder to uniformly reduce the hydraulic pressure of the pressure relief oil cylinder, and the pressure difference between the pressure oil cylinder and the pressure relief oil cylinder acts on the test piece to apply pressure or tension.

[0011] Further technical solution of the present invention: The output force areas of the top surface and the bottom surface of the upper piston are equal.

[0012] Further technical solution of the present invention: When the pressure difference between the pressure oil cylinder and the pressure relief oil cylinder acts on the test piece to apply pressure in step (3), the pressure relief oil cylinder in step (2) is the upper oil cylinder of the jack, and the pressure oil cylinder is the lower oil cylinder of the jack; When the pressure difference between the pressure oil cylinder and the pressure relief oil cylinder acts on the test piece to apply tension in step (3), the pressure relief oil cylinder in step (2) is the lower oil cylinder of the jack, and the pressure oil cylinder is the upper oil cylinder of the jack.

[0013] The jack cylinder body of the present invention is divided into upper and lower oil cylinders by an upper piston. A lower piston with a piston rod diameter equal to that of the piston is arranged in the lower oil cylinder. A lower piston hole is opened in the middle and lower part of the upper piston to make the force output areas on the top and bottom surfaces of the piston equal. The loading method is to simultaneously fill the upper oil cylinder and the lower oil cylinder with low-compressibility hydraulic oil of equal flow rate and equal pressure. By keeping one of the oil cylinders in a constant pressure-stabilized state and uniformly discharging the pressure of the other oil cylinder, the pressure difference between the two oil cylinders causes the load to be transmitted to the test piece through the low-compressibility hydraulic oil, the piston, and the piston rod. During the loading process, the hydraulic pressure in the pressurizing oil cylinder is constant, and the force output is constant, which is jointly borne by the pressure-relieving oil cylinder and the test piece. At the moment when the test piece is damaged, the reduced load is transmitted to the pressure-relieving oil cylinder through the jack piston, and the jacking action of the hydraulic pressure in the pressure-relieving oil cylinder restricts the ejection of the piston, greatly slowing down the impact of the load on the test piece, thereby obtaining the stress-strain relationship curve of the material throughout the process. The larger the force output area of the jack, the smaller the failure load of the test piece, the smaller the pressure difference causing the failure of the test piece, and the more obvious the blocking effect, and the better the effect of slowing down the impact load. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic structural diagram of the jack of the present invention;

[0015] Figure 2 is Figure 1 the sectional view taken along AA' in

[0016] Figure 3 is Figure 1 the sectional view taken along BB' in

[0017] In the figure: 1 - cylinder body, 2 - piston rod, 3 - upper oil cylinder, 4 - upper piston, 5 - lower oil cylinder, 5-1 - bottom cover, 6 - lower piston, 7 - lower piston hole, 8 - vent hole, 9 - upper oil passage hole, 10 - lower oil passage hole, 11 - lower piston rod. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The present invention will be further described below in conjunction with the embodiments and the drawings. The following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the present invention claimed, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0019] The present invention will be further described below in conjunction with the drawings and the embodiments. Attached Figures 1 to 3These are all the drawings of the embodiments, which are drawn in a simplified manner and are only used to clearly and concisely illustrate the purpose of the embodiments of the present invention. The technical solutions shown in the drawings below are the specific solutions of the embodiments of the present invention and are not intended to limit the scope of the present invention claimed. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0020] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0021] An embodiment provides a jack for mitigating impact loads, such as Figures 1 to 3 shown. The jack includes a cylinder body 1, an upper piston 4, an upper piston rod 2, and a lower piston 6. The upper piston 4 divides the cylinder body 1 into an upper oil cylinder 3 and a lower oil cylinder 5. The upper piston rod 2 is placed on the upper end face of the piston 4 and is integrally connected with the upper piston 4. The upper piston rod 2 extends out of the cylinder body 1 from the upper end of the upper oil cylinder 3. The lower piston 6 is placed at the central position of the lower oil cylinder 5. A lower piston hole 7 is correspondingly opened in the middle of the lower end face of the upper piston 4. The lower piston 6 extends into the lower piston hole 7, and the lower end is integrally connected with the bottom surface of the lower oil cylinder 5 through a lower piston rod 11. An upper oil passage hole 9 is provided on the side wall of the upper oil cylinder 3, and a lower oil passage hole 10 is provided on the side wall of the lower oil cylinder 5. The diameters of the upper piston rod 2, the lower piston 6, and the lower piston rod 11 are equal. A two-way high-pressure sealing ring is provided between the upper piston 4 and the cylinder body. A sealing ring is provided between the lower piston 6 and the lower piston hole 7. A through hole 8 is provided in the middle of the lower piston rod 11. The through hole 8 passes through the lower piston 6, the lower piston rod 11, and the oil cylinder base and is connected to the atmosphere.

[0022] The design of the jack in the present invention: Determine the jack output according to the designed maximum load. Considering the maximum oil pressure of the electro-hydraulic servo system and the installation space of the jack, determine the piston output area of the jack. Draw up the diameter of the piston rod according to the use of the piston rod, then obtain the piston diameter, and obtain the diameters of the lower piston and the lower piston hole. Calculate the wall thickness of the jack according to the mechanical principle, and select the material and seal of the jack.

[0023] The processing of the jack is divided into three parts. According to the design drawing of the jack, the upper part of the jack cylinder is integrally machined; the upper piston 4 and the upper piston rod 2 are integrally machined, and a lower piston hole 7 is turned in the middle and lower part of the upper piston 4; the jack base is integrally machined, and the diameters of the lower piston 6 and the piston rod 11 are equal. A double-direction high-pressure seal is arranged between the upper piston 4 and the cylinder block 1, a high-pressure seal is arranged between the lower piston 6 and the lower piston hole 7, and an oil passage hole is opened in each of the upper oil cylinder 3 and the lower oil cylinder 5.

[0024] The main parameters of the jack in the embodiment: the body height is 440 mm, the outer diameter of the oil cylinder is 377 mm, the inner diameter of the oil cylinder is 280 mm, the diameter of the piston rod is 130 mm, the length of the lower piston is 150 mm, the diameter is 130 mm, the thickness of the piston is 200 mm, the stroke is 200 mm, the extended height is 640 mm., the thickness of the bottom cover is 103 mm. The rated pressure is 63 MPa, the rated output force is 2766 kN, and the self-weight is 330 kg.

[0025] The lithology and size of the test specimen in the embodiment: quartzite, the cross-sectional diameter of the test specimen is 50 mm and the height is 100 mm, the estimated uniaxial compressive strength of failure is 280 MPa, and the corresponding hydraulic pressure of the jack oil cylinder is 9.0 MPa; The specific process of loading the test specimen with the jack in the embodiment is as follows:

[0026] (1) Install the jack at the preset position and connect it to the electro-hydraulic servo control system;

[0027] (2) Place the test specimen on the steel pad for test loading or fix it on the fixture;

[0028] (3) Adjust the height of the reaction frame and the position of the upper piston 4 of the jack so that the upper piston 4 of the jack is located in the middle of the cylinder block 1 and make the end face of the upper piston rod 2 in pre-contact with the compression surface of the test specimen;

[0029] (4) Open the oil passage valves of the upper oil cylinder 3 and the lower oil cylinder 5 of the jack, and fill low-compressibility hydraulic oil through the hydraulic servo control system until the output force of the jack is greater than the estimated failure load of the test specimen. The estimated value of the failure load of the test specimen can be calculated by conventional methods. For example, for quartzite, the maximum hydraulic pressure in the oil cylinder is 12 MPa;

[0030] (5) Close the inlet valve of the pressure relief oil cylinder and always keep the pressure in the pressurizing oil cylinder in a constant and stable state during the test;

[0031] (6) Start the acquisition system for the test, operate the hydraulic servo control system to slowly open the hydraulic pressure of the pressure relief oil cylinder, and control the unloading rate at 0.3 - 0.5 MPa / s to make the hydraulic pressure be slowly and uniformly unloaded;

[0032] (7) When the deformation of the test specimen has an accelerating trend, further reduce the pressure relief speed of the pressure relief oil cylinder, control the rate at 0.1 - 0.2 MPa / s until the test specimen fails;

[0033] After the specimen is damaged, according to the test requirements, the pressure relief speed of the piston jack should be reduced again. When the specimen deformation reaches a certain value or is completely damaged, the test can be ended.

[0034] During the loading process of the embodiment, the whole-process stress-strain relationship curve of the material was obtained.

[0035] It should be noted that similar reference numerals and letters indicate similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0036] As described above, these are only two embodiments of the present invention, and the description is relatively specific and detailed. However, it should not be construed as a limitation to the scope of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the appended claims.

Claims

1. A jack loading method for mitigating impact loads, characterized in that: A jack for mitigating impact loads is used for loading, and the upper piston rod of the jack acts on the surface of the test piece; the jack for mitigating impact loads includes a cylinder body (1), an upper piston (4), an upper piston rod (2) and a lower piston (6). The upper piston (4) divides the cylinder body (1) into an upper oil cylinder (3) and a lower oil cylinder (5). The upper piston rod (2) is placed on the upper end face of the piston (4) and is integrated with the upper piston (4). The upper piston rod (2) extends out of the cylinder body (1) from the upper end of the upper oil cylinder (3). The lower piston (6) is placed at the central position of the lower oil cylinder (5). A lower piston hole (7) is correspondingly opened in the middle of the lower end face of the upper piston (4). The lower piston (6) extends into the lower piston hole (7), and the lower end is integrated with the bottom surface of the lower oil cylinder (5) through a lower piston rod (11). An upper oil passage hole (9) is provided on the side wall of the upper oil cylinder (3), and a lower oil passage hole (10) is provided on the side wall of the lower oil cylinder (5). The diameters of the upper piston rod (2), the lower piston (6) and the lower piston rod (11) are equal. A double-direction high-pressure sealing ring is provided between the upper piston (4) and the cylinder body. A sealing ring is provided between the lower piston (6) and the lower piston hole (7). A through air hole (8) is provided in the middle of the lower piston rod (11). The air hole (8) penetrates through the lower piston (6), the lower piston rod (11) and the oil cylinder base and is communicated with the atmosphere. The specific steps of the loading method are as follows: S1. Before loading, place the upper piston of the jack in the middle of the oil cylinder, and use an oil pump to simultaneously fill the upper oil cylinder and the lower oil cylinder of the jack with low-compressibility hydraulic oil of equal flow rate and equal pressure, so that the output force of the upper piston rod of the jack is greater than the estimated failure load of the test piece. S2. While ensuring that the pressure cylinder is always in a constant pressure and stable state, close the oil filling pipeline of the pressure relief cylinder so that the end face of the piston rod is in pre-contact with the pressure-receiving surface of the test piece; the output force areas of the top surface and the bottom surface of the upper piston are equal. S3. Slowly open the pressure relief valve of the pressure relief cylinder to uniformly reduce the hydraulic pressure of the pressure relief cylinder, and the pressure difference between the pressure cylinder and the pressure relief cylinder acts on the test piece to apply pressure or tension.

2. The jack loading method for mitigating impact loads according to claim 1, characterized in that: When the pressure difference between the pressure cylinder and the pressure relief cylinder acts on the test piece to apply pressure in step S3, the pressure relief cylinder in step S2 is the upper oil cylinder of the jack, and the pressure cylinder is the lower oil cylinder of the jack; when the pressure difference between the pressure cylinder and the pressure relief cylinder acts on the test piece to apply tension in step S3, the pressure relief cylinder in step S2 is the lower oil cylinder of the jack, and the pressure cylinder is the upper oil cylinder of the jack.

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