Specimen assembly for testing static / dynamic compression and tensile mechanical properties based on small-sized specimens

Abstract

The present invention relates to a specimen assembly for testing static / dynamic compression-tensile mechanical properties based on small-sized specimens, belonging to the technical field of research on material mechanical properties. The specimen assembly is composed of a specimen assembled with two fixtures; the specimen includes two loading sections, two transition sections and a testing section. The loading sections are isosceles trapezoids, the transition sections are frustums of cones, and the testing section is cylindrical. The two ends of the testing section are correspondingly connected to the two loading sections through the two transition sections to form an I-shaped structure; the fixture is a cylinder with a radial groove penetrating through the end face, and the two ends of the bottom surface of the groove are respectively processed into inclined surfaces that match the waists of the isosceles trapezoids in the specimen. The width of the groove is equal to the thickness of the isosceles trapezoid in the specimen; by applying axial compression loading to the fixture in the specimen assembly, the specimen can be made to produce a longitudinal tensile effect, thereby enabling the study of the tensile properties of small-sized specimens under static / dynamic loading conditions.

Description

Technical Field

[0001] The present invention relates to a specimen assembly for testing static / dynamic compression and tensile mechanical properties based on small-sized specimens, and belongs to the technical field of research on mechanical properties of materials. Background Art

[0002] With the development of technology, new materials are increasingly widely used in industry. In the actual applications and test processes of industrial projects such as aerospace, petroleum, chemical engineering, shipbuilding, machinery, electronics, and electric power, metallic materials and non-metallic materials, etc. often serve under different working conditions. Therefore, researchers need to conduct tests and studies on the mechanical behaviors under different loading conditions. However, due to the limitations of material size and the cost of rare and precious metal materials, the processing and design of conventional tensile specimens have become difficult for many scholars, and it has become an inevitable trend to carry out research on the static and dynamic mechanical behaviors of small-sized specimens.

[0003] Combined with the current specimen structures and loading methods used for research on mechanical properties of materials, some scholars have attempted to conduct tensile tests on specimens of micro-sized on micro-devices, but only carried out tensile tests on small-sized specimens under quasi-static conditions. In addition, the data measured by using the Hopkinson bar experimental device for dynamic tensile tests on materials has relatively large errors. Usually, the Hopkinson bar experimental device is used to study the dynamic compression performance of materials, and the size of the specimens for testing is large and the specimens need to be thread-processed, especially for rare and precious materials, which requires a large cost. Summary of the Invention

[0004] Aiming at the problems existing in the current research on the static / dynamic mechanical properties of small-sized specimens, the present invention provides a specimen assembly for testing static / dynamic compression and tensile mechanical properties based on small-sized specimens. Through the innovative "I"-shaped specimen design and the cylindrical fixture cooperating therewith, applying axial compression loading to the fixture by using the Hopkinson bar experimental device or a material testing machine can cause the specimen to produce a longitudinal tensile effect, and thus the tensile performance research of the specimen under static / dynamic loading conditions can be realized, which has an important guiding role for obtaining the static and dynamic mechanical behaviors of small-sized materials and rare and precious metals, saves costs, and has great economic benefits.

[0005] The object of the present invention is achieved by the following technical solutions.

[0006] A specimen assembly for testing static / dynamic compression and tensile mechanical properties based on small-sized specimens, the specimen assembly comprising a specimen and a fixture;

[0007] The specimen includes two loading sections, two transition sections, and one test section. Among them, the loading sections are isosceles trapezoids, the transition sections are frustums of cones, and the test section is cylindrical. The two ends of the test section are correspondingly connected to the two loading sections through the two transition sections to form an I-shaped structure;

[0008] The fixture is a cylinder with a radial groove penetrating through its end face, and the two ends of the bottom surface of the groove are respectively processed into inclined surfaces that fit with the waists of the isosceles trapezoids in the specimen. The width of the groove is equal to the thickness of the isosceles trapezoid in the specimen;

[0009] The specimen is assembled with the two fixtures. The two waists on one side of the two isosceles trapezoids in the specimen are correspondingly attached to the two inclined surfaces in one fixture, and the two waists on the other side of the two isosceles trapezoids in the specimen are correspondingly attached to the two inclined surfaces in the other fixture. The cylindrical part in the specimen is located in the groove of the fixture and does not contact the bottom surface of the groove.

[0010] Furthermore, the outer circumferential surfaces of the transition sections are processed in a fillet way at the joints with the loading sections and the test section.

[0011] Furthermore, the angle between the waist and the lower base (i.e., the bottom surface with the longer side length) of the isosceles trapezoid in the specimen is 45°, and at the same time, the slope of the inclined surface of the groove in the fixture is 45°.

[0012] Furthermore, the length of the cylindrical part in the specimen is 0.4 - 0.5 times the diameter of the fixture; in addition, the diameter of the cylindrical part in the specimen is more preferably 2 - 4 mm.

[0013] Furthermore, the material strength of the fixture should be greater than or equal to the material strength of the Hopkinson bar. The same material as the Hopkinson bar can be selected, which can reduce the influence on waves during the test and has sufficient strength.

[0014] Furthermore, in order to ensure good contact between the fixture and the Hopkinson bar and reduce test errors, the absolute value of the difference between the diameter of the fixture and the diameter of the Hopkinson bar is less than or equal to 5 mm.

[0015] Furthermore, grease or lubricating oil is applied between the contact surfaces of the waist of the isosceles trapezoid in the specimen and the inclined surface in the fixture to reduce the error influence on the test data caused by the friction between the specimen and the fixture during the test.

[0016] Furthermore, the distance between the large end of the inclined surface of the groove in the fixture and the other end face of the fixture without the processed groove is not less than 2 mm; the wall thickness of the groove in the fixture is not less than 2 mm, preferably 2 - 6 mm.

[0017] Furthermore, the length of the bottom surface of the groove in the fixture (i.e., the distance between the two small ends of the inclined surfaces in the groove in the radial direction of the fixture) is 0.7 - 0.8 times the diameter of the fixture.

[0018] Beneficial effects:

[0019] (1) The loading section of the specimen in the present invention is designed as an isosceles trapezoid, and the angle between the waist and the lower base is designed to be 45°. Meanwhile, the fixture is designed with an inclined plane with a slope of 45° to cooperate with it. At this time, the axial compressive loading force can be made equal to the transverse tensile force of the specimen, which is convenient for calculation and analysis in the test.

[0020] (2) The height of the isosceles trapezoid of the loading section in the specimen of the present invention is greater than or equal to 3 mm, so as to ensure good cooperation between the inclined plane bearing the load and the fixture, and at the same time, ensure that the loading section has sufficient strength during the process of the specimen bearing a large compressive load, so that the small-sized specimen fails by fracture in the test area during the compression and tension process.

[0021] (3) The designed transition section in the specimen of the present invention can play a role in the transition during the stress transfer process and avoid sudden increase in stress, especially during the dynamic test. The transition section is processed in the way of fillet. On the one hand, the connection between the loading section and the transition section is a fillet, which can reduce the stress concentration at the right angle caused by the cross-section change of different parts during the test; on the other hand, the connection between the test section and the transition end is a fillet, which can ensure that the tensile stress is mainly concentrated in the test section area during the dynamic compression and tension process, and thus ensure that the failure mainly occurs in the test section area.

[0022] (4) The test section of the specimen in the present invention is designed as a cylinder. Compared with the rectangular design, it avoids certain errors in the measured data due to local stress concentration during the tensile process of the specimen. In addition, the size of the test section in the specimen is optimized. On the one hand, it ensures that the specimen can undergo tensile failure in the test, and on the other hand, it avoids the specimen from breaking quickly during the loading process, which is not convenient for signal acquisition when the specimen fails.

[0023] (5) In the fixture of the present invention, the distance between the large end of the inclined plane of the groove and the end face of the fixture is limited, mainly to ensure that the fixture has sufficient strength during the static / dynamic loading process, so that the specimen fails by fracture during the compression and tension process; the setting of the wall thickness parameter of the groove is mainly to ensure that the fixture has sufficient strength and does not deform during the static / dynamic loading process, and plays a role in limiting the "I"-shaped specimen.

[0024] (6) In the specimen assembly of the present invention, lubricating grease or lubricating oil is applied to the contact surface between the specimen and the fixture, and the material and diameter of the fixture are limited, all of which are to minimize the test error.

[0025] In summary, in the specimen assembly of the present invention, the loading section of the specimen is designed as an isosceles trapezoid, and at the same time, a groove with a corresponding inclined plane is machined on the fixture. The contact assembly between the specimen and the fixture is realized through the ingeniously designed inclined plane. Thus, through the axial compression loading of the fixture, the specimen can produce a longitudinal tensile effect. Furthermore, the Hopkinson bar experimental device can be used to study the dynamic tensile properties of small-sized specimens, and at the same time, a material testing machine can be used to study the static tensile properties of small-sized specimens, which well realizes the static / dynamic tensile property test research of small-sized specimens. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of the specimen described in Example 1; where a is the front view, b is the left view, and c is the top view.

[0027] Figure 2 It is a schematic structural diagram of the fixture described in Example 1; where a is the front view, b is the left view, and c is the top view.

[0028] Figure 3 It is a structural diagram of the device for studying the mechanical properties of the specimen assembly described in Example 1 by using the Hopkinson bar experimental device technology; where 1 - bullet, 2 - incident bar, 3 - strain gauge Ⅰ, 4 - specimen assembly, 5 - strain gauge Ⅱ, 6 - transmission bar, 7 - Wheatstone bridge Ⅱ, 8 - ultra-high-speed digital camera, 9 - Wheatstone bridge Ⅰ, 10 - photoelectric switch, 11 - wire, 12 - ultra-dynamic strain gauge, 13 - oscilloscope, 14 - computer Ⅰ, 15 - computer Ⅱ.

[0029] Figure 4 It is a force-displacement curve obtained during the static compression and tensile process of the specimen described in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The present invention will be further described below in conjunction with the drawings and specific embodiments. Among them, the methods are conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified. In addition, in the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and 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.

[0031] Example 1

[0032] Taking small-sized 943 armor steel as the research object, the steps for studying its static / dynamic compression and tensile mechanical properties are as follows:

[0033] (1) Use the electrical discharge wire cutting process to machine an I-shaped structural specimen from small-sized armor steel material; wherein, the specimen is composed of a loading section, a transition section, a test section, a transition section, and a loading section in sequence. Both loading sections are isosceles trapezoids with an upper base × lower base × height × thickness = 8 mm × 14 mm × 3 mm × 8 mm. The transition section is a frustum of a cone, and the connections between both ends of the frustum and the loading section as well as the transition section are machined into chamfers with R = 2 mm. The test section is a cylinder with a height of 10 mm and a diameter of 4 mm, as Figure 1 shown;

[0034] Machine two fixtures using the same material as the Hopkinson bar with a diameter of 20 mm (the material is 18Ni300 martensitic steel); wherein, the fixture is a cylinder with a radial groove processed on one end face. The diameter of the cylinder is 20 mm and the total height is 8 mm. The two ends of the bottom surface of the groove are respectively processed into inclined planes with a slope of 45°. The width of the groove is 8 mm and the depth is 2 mm. The length of the bottom surface of the groove (i.e., the distance between the small ends of the two inclined planes) is 14 mm. The distance between the large end of the inclined plane in the groove and the other end face of the cylinder without the processed groove is 3 mm, as Figure 2 shown;

[0035] (2) Polish the surfaces of the specimen and the fixtures respectively to make their surface finish reach 0.4 - 0.6, and then clean and dry them with alcohol for standby;

[0036] (3) Assemble the specimen and the two fixtures together. The two waists on one side of the two isosceles trapezoids in the specimen are correspondingly attached to the two inclined planes in one fixture, and the two waists on the other side of the two isosceles trapezoids in the specimen are correspondingly attached to the two inclined planes in the other fixture. Among them, lubricating grease or lubricating oil is applied between the contact surfaces of the waist and the inclined plane. The cylinder in the specimen is located in the groove of the fixture and does not contact the bottom surface of the groove, thus forming the specimen assembly 4. For the partial enlarged view of the specimen assembly 4, see Figure 3 the figure;

[0037] (4) Place the specimen assembly 4 between the incident bar 2 and the transmission bar 6 of the Hopkinson bar experimental device. The end faces of the two fixtures without the processed grooves are respectively in contact with the transmission bar 6 and the incident bar 2. By changing the length and loading rate of the bullet 1, different strain rate loadings on the specimen assembly 4 are achieved. Combine the ultra-high-speed digital camera 8 to monitor the dynamic loading and its failure process;

[0038] As Figure 3 shown, the Hopkinson bar experimental device includes a bullet 1, an incident bar 2, a strain gauge I 3, a strain gauge II 5, a transmission bar 6, a Wheatstone bridge II 7, an ultra-high-speed digital camera 8, a Wheatstone bridge I 9, an optoelectronic switch 10, an ultra-dynamic strain gauge 12, an oscilloscope 13, a computer I 14, and a computer II 15;

[0039] The strain signals (incident strain and reflected strain) of the incident bar 2 are collected by the strain gauge I 3 attached to the incident bar 2, and the strain signals (transmitted strain) of the transmitted bar 6 are collected by the strain gauge II 5 attached to the transmitted bar 6. The information collected by the strain gauge I 3 passes through the Wheatstone bridge I 9, and the information collected by the strain gauge II 5 passes through the Wheatstone bridge II 7, and then successively passes through the ultra-dynamic strain gauge 12 and the oscilloscope 13 and is recorded on the computer I 14; the impact velocity of the bullet 1 can be estimated by the distance between the two photoelectric switches 10 and the time difference of the bullet 1 passing through the two photoelectric switches 10; the computer I 14 is used to record and store the incident and transmitted signals and control the synchronous trigger of the ultra-high-speed digital camera 8 to facilitate recording the failure process of the specimen, and the computer II 15 is used to control the ultra-high-speed digital camera 8; the camera of the ultra-high-speed digital camera 8 corresponds to the cylindrical section in the specimen and is used to record the failure process of the specimen;

[0040] The test data collected by the Split Hopkinson Pressure Bar test device and the data of the dynamic change process monitored by the ultra-high-speed digital camera 8 are processed subsequently, so that the force-displacement curve, displacement field, strain field and their failure change process of the small-size specimen in the dynamic compression and tension process can be obtained;

[0041] (5) Alternatively, the specimen assembly 4 is tested for its quasi-static compression and tension performance in a compression manner under a material testing machine by the same assembly method. Figure 4 The test results of the force-displacement curve of 943 armor steel are given in [reference]. It can be seen from the figure that in the static compression and tension test, the specimen experienced three stages: elastic deformation stage, plastic deformation stage, and finally fracture.

[0042] Observing the specimen after fracture in the static / dynamic compression and tension test, it is found that the fracture occurs in the test section area of the specimen, indicating that the specimen assembly 4 designed in the present invention can realize the static / dynamic compression and tension performance test of small-size specimens.

[0043] In summary, the above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A specimen assembly for testing static / dynamic compression and tensile mechanical properties based on small-sized specimens, characterized in that: The specimen assembly includes a specimen and fixtures; The specimen includes two loading sections, two transition sections and a test section. Among them, the loading section is an isosceles trapezoid, the transition section is a frustum of a cone, and the test section is a cylinder. The two ends of the test section are correspondingly connected to the two loading sections through the two transition sections to form an I-shaped structure; The fixture is a cylinder with a radial groove penetrating through its end face, and the two ends of the bottom surface of the groove are respectively processed into inclined surfaces that match the waists of the isosceles trapezoid in the specimen. The width of the groove is equal to the thickness of the isosceles trapezoid in the specimen; The specimen is assembled with the two fixtures. The two waists on one side of the two isosceles trapezoids in the specimen are correspondingly attached to the two inclined surfaces in one fixture, and the two waists on the other side of the two isosceles trapezoids in the specimen are correspondingly attached to the two inclined surfaces in the other fixture. The cylinder in the specimen is located in the groove of the fixture and does not contact the bottom surface of the groove.

2. The specimen assembly for testing static / dynamic compression-tension mechanical properties based on small-sized specimens according to claim 1, wherein: The outer circumferential surface of the transition section is processed by filleting at the connection with the loading section and the test section.

3. The specimen assembly for testing static / dynamic compression and tensile mechanical properties based on small-sized specimens according to claim 1, wherein: The included angle between the waist and the lower base of the isosceles trapezoid in the specimen is 45°, and at the same time, the slope of the inclined surface of the groove in the fixture is 45°.

4. The specimen assembly for testing static / dynamic compression-tension mechanical properties based on small-sized specimens according to claim 1, wherein: The distance between the large end of the inclined surface of the groove in the fixture and the other end face of the fixture without the processed groove is not less than 2 mm, and the wall thickness of the groove in the fixture is not less than 2 mm.

5. The specimen assembly for testing static / dynamic compression-tension mechanical properties based on small-sized specimens according to claim 1, characterized in that: The length of the bottom surface of the groove in the fixture is 0.7 - 0.8 times the diameter of the fixture.

6. The specimen assembly for testing static / dynamic compression-tension mechanical properties based on small-sized specimens according to claim 1, wherein: Lubricating grease or lubricating oil is applied to the contact surface between the waist of the isosceles trapezoid in the specimen and the inclined surface in the fixture.

7. The specimen assembly for testing static / dynamic compression and tensile mechanical properties based on small-sized specimens according to claim 1, characterized in that: The material strength of the fixture should be greater than or equal to the material strength of the Hopkinson bar.

8. The specimen assembly for testing static / dynamic compression and tensile mechanical properties based on small-sized specimens according to claim 1, characterized in that: The absolute value of the difference between the diameter of the fixture and the diameter of the Hopkinson bar is less than or equal to 5 mm.

9. The specimen assembly for testing static / dynamic compression-tension mechanical properties based on small-sized specimens according to any one of claims 1 to 8, characterized in that: The length of the cylinder in the specimen is 0.4 - 0.5 times the diameter of the fixture.

10. The specimen assembly for testing static / dynamic compression-tension mechanical properties based on small-sized specimens according to claim 9, characterized in that: The diameter of the cylinder in the specimen is 2 - 4 mm.

Images