Tensile test clamp for high-strength round bar sample

Abstract

The invention discloses a tensile test fixture for a high-strength round bar sample, the tensile test fixture comprises two symmetrical clamping units with consistent structures, and each clamping unit comprises a clamping bar, an inner sleeve, two clamping blocks and an outer sleeve; a through hole is formed in one end of the inner sleeve, the clamping rod is divided into a clamping section and a shaft shoulder end, and the clamping section of the clamping rod penetrates through the through hole and abuts against the shaft shoulder end. A through hole is formed in the outer sleeve, so that the round bar sample can penetrate through the through hole; the two clamping blocks are combined to form a groove for clamping a round bar sample; the inner side surface of the other end of the inner sleeve is a conical surface; the outer sides of the two combined clamping blocks are conical surface sides, and the conical surfaces of the two combined clamping blocks are attached to the conical surface of the inner sleeve; an internal thread is arranged on the inner side surface of the outer sleeve and is matched and screwed with the external thread of the inner sleeve; during a tensile test, the clamping blocks cannot move outwards in the radial direction under the constraint of the inner sleeve and the outer sleeve, so that the frictional wear between a sample and the clamping blocks is weakened, the service life of the clamp is prolonged, and the test precision is also improved.

Description

Technical Field

[0001] This invention relates to the field of mechanical testing, and more specifically to a tensile testing fixture for high-strength round bar specimens. Background Technology

[0002] With the advancement of technology, high-strength steel is increasingly widely used in aerospace, defense equipment, automotive lightweighting, and high-end molds. Against this backdrop, accurately characterizing the mechanical properties of high-strength materials is crucial, and tensile testing, as an important method for obtaining fundamental mechanical property indicators, plays an irreplaceable role.

[0003] For tensile test specimens of round bars, V-groove clamps are typically used to directly hold the specimen at both ends during tensile testing until the specimen breaks. However, for high-strength material performance testing, because the material's hardness (e.g., CALDIE steel, HRC 58-61) is similar to or higher than the hardness of the testing machine clamps (HRC 56), the clamps may not effectively hold the specimen during clamping. This causes severe wear on the clamp teeth during the test, leading to slippage between the clamps and the sample, making the test impossible to conduct normally and ultimately resulting in test failure.

[0004] To address the aforementioned issues, CN216669515U discloses a tensile specimen clamping device for ultra-high strength steel round bars. This device employs a symmetrical clamping head structure, with the clamping head featuring a circular hole and a square slot with side openings. The specimen can be directly inserted into the large end from the side, and the tensile force is transmitted to the clamping part through a stepped connection structure. It has the advantages of easy clamping and preventing the specimen from slipping out. However, this clamping device requires modifications to the original testing machine clamping device, and the clamping and disassembling process is relatively cumbersome. CN116288059B discloses a high-strength tensile testing machine fixture steel and its preparation method. Through optimized composition (C: 0.35-0.45%, Si: 0.20-0.40%, Mn: 0.50-0.80%, Cu: 0.10-0.30%, Ni: 0.10-0.35%, Cr: 3.00-3.50%, Mo: 1.0-1.5%, V: 0.10-0.30%, balance Fe and impurities) and a specific heat treatment process (quenching at 900-950℃ + tempering at 180-250℃), a high-strength fixture steel with a hardness of HRC65-67 and significantly improved service life is obtained. However, this material has high requirements for rolling and heat treatment processes; improper rolling or heat treatment processes will significantly reduce the material's hardness. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a tensile testing fixture for high-strength round bar specimens. This fixture solves problems such as slippage and wear and deformation of the fixture when holding high-strength round bar specimens in a V-groove fixture for tensile testing. Compared with existing technologies, it does not require modification of the original tensile testing machine fixture, is easy to clamp, uses materials with mature manufacturing processes, and has low manufacturing costs.

[0006] The objective of this invention is achieved through the following technical solution: A tensile testing fixture for high-strength round bar specimens, comprising two identical and symmetrical clamping units. Each clamping unit includes a clamping rod, an inner sleeve, two clamping blocks, and an outer sleeve. One end of the inner sleeve has a through hole. The clamping rod is divided into a clamping section and a shoulder end. The clamping section of the clamping rod passes through the through hole, and the shoulder end abuts against it. The outer sleeve has a through hole to allow the round bar specimen to pass through. The two clamping blocks combine to form a groove for clamping the round bar specimen. The other end of the inner sleeve... The sides are conical, and the outer sides are provided with external threads; the outer sides of the two combined clamping blocks are conical, and the conical surfaces of the two combined clamping blocks fit into the conical surface of the inner sleeve; the inner side of the outer sleeve is provided with internal threads, which fit into the external threads of the inner sleeve and are tightened, so that the inner bottom surface of the outer sleeve is in close contact with the bottom surface of the two clamping blocks and a preload is generated between the threads. Under the action of the preload, the conical surface of the inner sleeve exerts a pressure perpendicular to the conical surface formed by the two clamping blocks. The radial pressure decomposed from this pressure will cause the two clamping blocks to have a radial tightening tendency, thereby clamping the round bar sample.

[0007] Furthermore, a blind hole is provided at the shoulder end of the clamping bar to reserve axial movement space for the round bar sample.

[0008] Furthermore, the groove surface formed by the combination of the two clamping blocks is the clamping surface, and the contact surface between the clamping surface and the round bar sample is a clearance fit.

[0009] Furthermore, the groove mates with the transition section of the round bar sample, including: designing a corresponding groove based on the outer surface of the transition section of the round bar sample to clamp the round bar sample.

[0010] Furthermore, the diameter of the through hole of the inner sleeve is larger than the outer diameter of the clamping section of the clamping rod, but smaller than the outer diameter of the shoulder end of the clamping rod.

[0011] Furthermore, the inner diameter of the inner sleeve is larger than the outer diameter of the shoulder end of the clamping rod.

[0012] Furthermore, the clamping rod is made of 45 steel.

[0013] Furthermore, the clamping block, inner sleeve, and outer sleeve are made of SKD11 material. Preferably, the SKD11 is quenched and then tempered at low temperature. SKD11 is a cold work die steel. Suppliers typically provide annealed SKD11, which has low hardness and does not meet the requirements. Therefore, quenching and low-temperature tempering are necessary to meet these requirements (quenching and low-temperature tempering are standard heat treatment procedures for this material). The specific heat treatment method is as follows: first, preheat the material to 700℃-800℃ to ensure uniform heating; then heat the material to 1030℃ and hold for 30 minutes, followed by air cooling to room temperature to complete quenching; finally, heat the material to 180℃ and hold for 2 hours, then air cool to room temperature to complete low-temperature tempering.

[0014] Furthermore, the conical surfaces of the two combined clamping blocks have the same angle of inclination as the conical surface of the inner sleeve.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: the tensile testing machine fixture is easy to install, requiring only the clamping bar part of the original testing machine's V-groove fixture to be clamped, without the need to adjust the original testing machine fixture; the clamping block is designed with a conical side, and due to the characteristics of the conical structure, when the outer sleeve and inner sleeve are threaded together, the pushing action of the outer sleeve on the clamping block will cause the conical side of the clamping block and the conical surface of the inner wall of the inner sleeve to fit tightly together, and the bottom surface of the clamping block and the top bottom surface of the outer sleeve to fit tightly together. During the tensile test, under the constraint of the inner sleeve and the outer sleeve, the clamping block cannot move radially outward, which reduces the friction and wear between the specimen and the clamping block, improves the service life of the fixture, and also improves the test accuracy; in most cases, only the clamping blocks with different grooves need to be replaced to adapt to tensile specimens of different sizes. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a cross-sectional schematic diagram of the tensile testing fixture provided in an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the clamping rod structure according to a specific embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the inner sleeve structure according to a specific embodiment of the present invention.

[0020] Figure 4 This is a schematic diagram of the clamping block structure according to a specific embodiment of the present invention.

[0021] Figure 5 This is a schematic diagram of the outer sleeve structure according to a specific embodiment of the present invention.

[0022] In the diagram, 1 is the upper clamping rod; 2 is the lower clamping rod; 3 is the upper inner sleeve; 4 is the lower inner sleeve; 5 is the upper clamping block; 6 is the lower clamping block; 7 is the upper outer sleeve; 8 is the lower outer sleeve; and 9 is the tensile specimen. The upper clamping rod 1 and the lower clamping rod 2 have the same structure, the upper inner sleeve 3 and the lower inner sleeve 4 have the same structure, there are two upper clamping blocks 5 and two lower clamping blocks 6, all with the same structure, and the upper outer sleeve 7 and the lower outer sleeve 8 have the same structure. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings. Unless otherwise specified, the features of the following embodiments and implementations can be combined with each other.

[0024] The present invention provides a tensile testing fixture for high-strength round bar specimens, such as... Figures 1-5 As shown, it includes an upper clamping unit and a lower clamping unit with the same structure and arranged symmetrically; the upper clamping unit includes an upper clamping rod 1, an upper inner sleeve 3, an upper clamping block 5 and an upper outer sleeve 7, and the lower clamping unit includes a lower clamping rod 2, a lower inner sleeve 4, a lower clamping block 6 and a lower outer sleeve 8.

[0025] In this embodiment, the specimen is a "dog bone" shaped round bar specimen 9. The larger diameter parts at both ends of the specimen are the clamping loading section, and the smaller diameter part in the middle is the parallel test section. The clamping loading section and the parallel test section are connected by an arc section, which is the transition section.

[0026] The fixture provided in this embodiment includes an upper clamping unit and a lower clamping unit. The upper clamping unit and the lower clamping unit have the same structure and are symmetrically installed. The structure of the clamping unit is described below using the upper clamping unit as an example.

[0027] The upper clamping rod 1 consists of a clamping section and a shoulder end; the upper inner sleeve 3 consists of a threaded connection end and a shoulder end; the upper clamping block 5 comprises two clamping blocks with identical structures, each including a clamping surface, a conical side, and a bottom surface; and the upper outer sleeve 7 consists of a threaded connection end and a bottom surface. The clamping surface of the upper clamping block 5 is connected to the round bar sample 9; the conical side of the upper clamping block 5 is in contact with the inner wall of the threaded connection end of the upper inner sleeve 3; the threaded connection end of the upper inner sleeve 3 is connected to the threaded connection end of the upper outer sleeve 7; the shoulder end of the upper inner sleeve 3 is connected to the shoulder end of the upper clamping rod 1; and the clamping section of the upper clamping rod 1 is directly clamped by the original V-groove clamp of the tensile testing machine.

[0028] The shoulder end of the upper clamping rod 1 refers to the end with the larger diameter of the upper clamping rod 1, and the shoulder end of the upper inner sleeve 3 refers to the end of the upper inner sleeve 3 that mates with the shoulder end of the upper clamping rod 1. The shoulder end of the upper inner sleeve 3 has a circular hole, the diameter of which is slightly larger than the diameter of the clamping section of the upper clamping rod 1, but smaller than the diameter of the shoulder end of the upper clamping rod 1. The clamping section of the upper clamping rod 1 can freely pass through the circular hole at the shoulder end of the upper inner sleeve 3, but the shoulder end cannot pass through, thus preventing force transmission.

[0029] The connection between the shoulder end of the upper inner sleeve 3 and the shoulder end of the upper clamping rod 1 means that after the clamping section of the upper clamping rod 1 passes through the circular hole of the shoulder end of the upper inner sleeve 3 from the threaded connection end, the outer contact surface of the shoulder end of the upper clamping rod 1 and the inner contact surface of the shoulder end of the upper inner sleeve 3 are connected in a positive and negative stepped shape. During the tensile test, the upward tensile force on the upper clamping rod 1 will become the interaction force between the positive and negative stepped shapes. The tensile force is transmitted to the upper clamping block 5 through other connecting parts. The upper clamping block 5 clamps the round bar sample 9 and stretches it upward. The other end of the round bar sample 9 is clamped by the clamping block 6 in the lower clamping section unit. The force applied by the lower clamping block 6 to the round bar sample 9 is equal in magnitude and opposite in direction to that of the upper clamping block 5. The tensile test of the round bar sample 9 is completed under the simultaneous action of the upper and lower clamping units.

[0030] A blind hole is opened at the center of the shoulder end face of the upper clamping bar 1. The diameter of the blind hole is slightly larger than the diameter of the clamping section of the round bar sample 9, and the depth is preferably sufficient to allow axial movement space for the round bar sample 9, so as to facilitate the installation of the round bar sample 9.

[0031] The clamping surfaces of the two clamping blocks included in the upper clamping block 5 form a groove that matches the transition section of the round bar specimen 9. The transition section of the round bar specimen 9 is placed in the groove, and the two clamping blocks included in the upper clamping block 5 are combined to clamp the round bar specimen 9. The groove on the clamping surface of the upper clamping block 5 and the transition section of the specimen are in clearance fit.

[0032] The conical side of the upper clamping block 5 fits against the inner wall of the threaded connection end of the upper inner sleeve 3, meaning the contour of the inner wall of the threaded connection end of the upper inner sleeve 3 matches the conical side of the upper clamping block 5. In other words, the inner wall contour of the threaded connection end of the upper inner sleeve 3 is conical, and the conical angle is not limited. The threaded connection end of the upper inner sleeve 3 is connected to the threaded connection end of the upper outer sleeve 7 via threads. Tightening the outer sleeve 7 causes the inner bottom surface of the upper outer sleeve 7 to fit against the outer bottom surface of the upper clamping block 5, generating a preload force between the threads. Under the action of the preload force, the conical surface of the inner wall of the threaded connection end of the upper inner sleeve 3 will exert a pressure perpendicular to the conical surface of the upper clamping block 5. This pressure can be decomposed into radial pressure and axial pressure. The radial pressure will cause the upper clamping block 5 to tend to tighten radially, thereby clamping the round bar sample. During the tensile test, the radial pressure can inhibit the radial outward movement of the two clamping blocks, thereby improving experimental accuracy and extending the clamp life.

[0033] A circular hole is opened at the center of the bottom surface of the upper outer sleeve 7. The diameter of the circular hole should be slightly larger than the diameter of the clamping section of the round bar sample 9 so that the sample can pass through the circular hole smoothly. When clamping the round bar sample 9, the round bar sample 9 needs to pass through the circular hole at the center of the bottom surface of the upper outer sleeve 7.

[0034] In this embodiment, the upper clamping bar 1 and the lower clamping bar 2 in the fixture are held by the original V-groove fixture of the tensile testing equipment. The tensile testing equipment and the V-groove fixture are not the end point of the description in this application embodiment, and will not be specifically explained here. This embodiment provides a tensile testing fixture for high-strength round bar specimens. The specimens have high strength, and the tensile testing equipment should be able to provide the tensile force required for the tensile test.

[0035] This embodiment describes a tensile test using a high-strength round bar specimen tensile testing fixture, specifically including the following steps: Step 1: Pass the clamping section of the upper clamping rod 1 through the threaded connection end of the upper inner sleeve 3 and through the round hole at the shoulder end of the upper inner sleeve 3 on one side, so that the outer contact surface of the shoulder end of the upper clamping rod 1 contacts the inner contact surface of the shoulder end of the upper inner sleeve 3.

[0036] Step 2: Place the transition section at one end of the round bar sample 9 into the clamping surface groove of the two clamping blocks included in the upper clamping block 5, and the clamping surfaces of the two clamping blocks included in the upper clamping block 5 are in contact to clamp the round bar sample 9.

[0037] Step 3: Place the upper clamping block 5 along with the round bar sample 9 on the conical inner wall of the threaded connection end of the upper inner sleeve 3, with the conical side of the upper clamping block 5 in contact with the conical surface of the conical inner wall of the threaded connection end of the upper inner sleeve 3.

[0038] Step 4: Pass the bottom circular hole of the upper outer sleeve 7 through the free end of the round bar sample 9, and screw the threaded connection end of the upper outer sleeve 7 to the threaded connection end of the upper inner sleeve 3 through the thread and apply a certain preload.

[0039] Step 5: Pass the bottom circular hole of the lower outer sleeve 8 through the free end of the round bar sample 9.

[0040] Step 6: Pass the clamping section of the lower clamping rod 2 through the threaded connection end of the lower inner sleeve 4 and through the round hole at the shoulder end of the lower inner sleeve 4 on one side, so that the outer contact surface of the shoulder end of the lower clamping rod 2 contacts the inner contact surface of the shoulder end of the lower inner sleeve 4.

[0041] Step 7: Use the two clamps included in the lower clamp 6 to clamp the transition section of the free end of the round bar sample 9.

[0042] Step 8: Fit the inner wall conical surface of the threaded connection end of the lower inner sleeve 4 against the conical side of the lower clamping block 6.

[0043] Step 9: Connect the lower outer sleeve 8 and the lower inner sleeve 4 by threading and apply a certain preload. Through the above steps, both ends of the round bar sample 9 are clamped by the upper clamping unit and the lower clamping unit of the fixture, respectively.

[0044] Step 10: Leave a certain distance between the upper V-groove clamp and the lower V-groove clamp of the tensile testing equipment in order to install the clamp provided in this embodiment.

[0045] Step 11: Clamp the clamping section of the upper clamping bar 1 with the upper V-groove clamp of the tensile testing equipment, adjust the distance between the V-groove clamp and the lower V-groove clamp on the tensile testing equipment so that the lower clamping bar 2 is in a suitable position in the lower V-groove clamp, and then clamp the lower clamping bar 2.

[0046] Step 12: After the fixture and round bar specimen provided in this embodiment are installed, a tensile test is performed to obtain test data.

[0047] The above embodiments are only used to illustrate the design concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A tensile testing fixture for high-strength round bar specimens, characterized in that, The device comprises two identical and symmetrical clamping units, each including a clamping rod, an inner sleeve, two clamping blocks, and an outer sleeve. One end of the inner sleeve has a through hole. The clamping rod is divided into a clamping section and a shoulder end; the clamping section passes through the through hole, and the shoulder end abuts against it. The outer sleeve has a through hole for the round bar sample to pass through. The two clamping blocks combine to form a groove for clamping the round bar sample. The inner surface of the other end of the inner sleeve is conical, and the outer surface has external threads. The outer sides of the combined two clamping blocks are conical, and their conical surfaces fit against the conical surface of the inner sleeve. The inner surface of the outer sleeve has internal threads, which engage with the external threads of the inner sleeve to tighten it, causing the inner bottom surface of the outer sleeve to fit tightly against the bottom surfaces of the two clamping blocks and generating a preload force between the threads. Under the action of the preload force, the conical surface of the inner sleeve exerts a pressure perpendicular to the conical surface formed by the two clamping blocks. The radial pressure resulting from this pressure decomposes into a radial tightening tendency between the two clamping blocks, thereby clamping the round bar sample.

2. The tensile testing fixture for high-strength round bar specimens according to claim 1, characterized in that, The shoulder end of the clamping bar is provided with a blind hole to allow axial movement space for the round bar sample.

3. A tensile testing fixture for high-strength round bar specimens according to claim 1, characterized in that, The groove surface formed by the combination of the two clamping blocks is the clamping surface, and the contact surface between the clamping surface and the round bar sample is a clearance fit.

4. A tensile testing fixture for high-strength round bar specimens according to claim 1, characterized in that, The groove engages with the transition section of the round bar sample, including: designing a corresponding groove based on the outer surface of the transition section of the round bar sample to clamp the round bar sample.

5. A tensile testing fixture for high-strength round bar specimens according to claim 1, characterized in that, The diameter of the through hole of the inner sleeve is larger than the outer diameter of the clamping section of the clamping rod, but smaller than the outer diameter of the shoulder end of the clamping rod.

6. A tensile testing fixture for high-strength round bar specimens according to claim 1, characterized in that, The inner diameter of the inner sleeve is larger than the outer diameter of the shoulder end of the clamping rod.

7. A tensile testing fixture for high-strength round bar specimens according to claim 1, characterized in that, The clamping rod is made of 45 steel.

8. A tensile testing fixture for high-strength round bar specimens according to claim 1, characterized in that, The clamping block, inner sleeve, and outer sleeve are made of SKD11 material.

9. A tensile testing fixture for high-strength round bar specimens according to claim 1, characterized in that, The conical surfaces of the two clamping blocks are at the same angle as the conical surface of the inner sleeve.

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