Clamp for stretching of testing machine

Abstract

The invention discloses a clamp for stretching of a testing machine, and relates to the technical field of material stretching testing. According to the technical scheme, the device is characterized by comprising two clamping blocks which are mounted in a jaw of a testing machine and are used for clamping a sample; main anti-skid teeth and auxiliary anti-skid teeth are respectively arranged on the clamping surfaces of the clamping blocks; the tooth tops of the main anti-skid teeth are provided with biting tips, the tooth tops of the auxiliary anti-skid teeth are provided with anti-skid contact planes, and the tooth height of the main anti-skid teeth is larger than that of the auxiliary anti-skid teeth. Compared with the mode that only one kind of anti-skid teeth is arranged on the clamping face, the main anti-skid teeth and the auxiliary anti-skid teeth which are different in tooth height are combined, the main anti-skid teeth are used for biting a sample, the auxiliary anti-skid teeth are used for increasing friction force, and therefore the maximum stress borne by the main anti-skid teeth can be reduced while the biting depth of the main anti-skid teeth is increased; therefore, the anti-slip teeth can be prevented from being broken and slipping, the service life is prolonged, and the anti-slip teeth can be suitable for tensile testing of a sample with the tensile strength of 1250-2200 MPa.

Description

Technical Field

[0001] The invention relates to the technical field of material tensile testing, and more particularly to a clamp for tensile testing machines. Background Art

[0002] Universal testing machines are widely used in tensile, bending, shear and other mechanical property tests of various metal and non-metal materials. Universal testing machines have two upper and lower jaws, each with a pair of clamps for clamping the specimen during tensile tests. For example, the Chinese patent with the authorization announcement number CN201222026Y discloses a universal testing machine pipe tensile test fixture.

[0003] In order to clamp the specimen, anti-slip teeth are usually provided on the clamping surface of the clamping block. For example, the existing Chinese patent with publication number CN104550400A discloses an anti-slip tooth design suitable for stretching and straightening of high-hardness metal profiles, wherein the anti-slip teeth are straight teeth or barbed teeth with isosceles triangle cross-sections, the extension direction of the teeth is perpendicular to the stretching direction, and the width of the platform between the teeth is 0 to 50 mm.

[0004] However, when the anti-skid teeth in the above patent are used to perform tensile tests on samples with a tensile strength of 1250 to 2200 MPa, since the hardness of the sample is 46 to 52 HRC, which is relatively high, the anti-skid teeth are difficult to bite into the sample or the biting depth is insufficient, and as the tensile test proceeds, the stress on the anti-skid teeth gradually increases, which can easily lead to the anti-skid teeth breaking, causing the clamp to slip after a certain number of tests, and then the clamp needs to be replaced, resulting in increased costs.

[0005] Therefore, how to prevent the anti-skid teeth from breaking and extend the use times and life of the clamp block is an urgent problem to be solved. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a clamp for tensile testing machine, which adopts main anti-slip teeth in combination with auxiliary anti-slip teeth, and uses the auxiliary anti-slip teeth to increase friction. In this way, when performing tensile tests on samples with a tensile strength of 1250 to 2200 MPa, the number of tests of the clamp block can be increased and the test cost can be reduced.

[0007] To achieve the above object, the present invention provides the following technical solutions: A clamp for tensile testing machine, the clamp comprising two clamping blocks installed in the jaws of the testing machine and used for clamping a sample; main anti-skid teeth and auxiliary anti-skid teeth are respectively arranged on the clamping surfaces of the clamping blocks; a biting tip is arranged at the tooth top of the main anti-skid teeth, an anti-skid contact plane is arranged at the tooth top of the auxiliary anti-skid teeth, and the tooth height of the main anti-skid teeth is greater than the tooth height of the auxiliary anti-skid teeth.

[0008] Furthermore, when a tensile test is performed on a sample, the biting tip of the main anti-skid tooth contacts the sample first, and as the test tensile force increases, the anti-skid contact plane of the auxiliary anti-skid tooth contacts the sample later.

[0009] Furthermore, the main anti-skid teeth and the auxiliary anti-skid teeth are integrally formed, so that the anti-skid contact plane is connected to the side wall of the main anti-skid teeth.

[0010] Furthermore, the tensile strength of the sample is 1500-2000 MPa.

[0011] Furthermore, the cross section of the main anti-skid teeth is triangular, and the cross section of the auxiliary anti-skid teeth is isosceles trapezoidal.

[0012] Furthermore, the main anti-skid teeth and the auxiliary anti-skid teeth are alternately arranged on the clamping surface of the clamping block.

[0013] Furthermore, an inter-tooth platform is provided between adjacent main anti-skid teeth and auxiliary anti-skid teeth, and the width of the inter-tooth platform is 0-1 mm.

[0014] Furthermore, the difference in tooth height between the main anti-skid teeth and the auxiliary anti-skid teeth is no more than 0.2 mm.

[0015] Furthermore, the tooth top angle of the main anti-skid teeth is 40° to 60°, and the tooth height is 0.3 to 0.8 mm.

[0016] Furthermore, the auxiliary anti-skid teeth have a tooth height of 0.2-0.7 mm, a tooth top width of 0.2-0.4 mm, and a tooth bottom angle of 60°-80°.

[0017] In summary, the present invention has the following beneficial effects: Compared with only arranging one anti-skid tooth on the clamping surface, the present invention combines main anti-skid teeth with different tooth heights with auxiliary anti-skid teeth, uses the main anti-skid teeth to bite into the sample, and uses the auxiliary anti-skid teeth to increase the friction force. In this way, while increasing the biting depth of the main anti-skid teeth, the maximum stress on the main anti-skid teeth can be reduced, thereby avoiding the occurrence of anti-skid tooth breakage and slipping, extending the service life, and being suitable for tensile testing of samples with a tensile strength of 1250 to 2200 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of the clamp used for stretching in the testing machine in Example 1; Figure 2 This is a schematic diagram of the structure of the clamp used for stretching in the testing machine in Example 2; Figure 3 This is a schematic diagram of the structure of the clamp used for stretching in the testing machine in Example 3; Figure 4 This is a test simulation diagram of the clamp used for stretching in the testing machine in Example 4; Figure 5 Experimental simulation of a single anti-slip tooth Figure 1 ; Figure 6 Experimental simulation of a single anti-slip tooth Figure 2 .

[0019] In the figure: 1. Clamping block; 2. Main anti-skid teeth; 3. Auxiliary anti-skid teeth. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0021] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law. Embodiment 1:

[0022] A clamp for tensile testing machine, refer to Figure 1 The clamp includes two clamping blocks 1 installed in the jaws of the testing machine and used for clamping the sample; the clamping surfaces of the clamping blocks 1 are respectively provided with main anti-skid teeth 2 and auxiliary anti-skid teeth 3; in this embodiment, the main anti-skid teeth 2 are provided with biting tips at the tooth tops, the auxiliary anti-skid teeth 3 are provided with anti-skid contact planes at the tooth tops, and the tooth height of the main anti-skid teeth 2 is greater than the tooth height of the auxiliary anti-skid teeth 3; and, in this embodiment, the main anti-skid teeth 2 are used to bite into the sample, and the auxiliary anti-skid teeth 3 are used to increase the friction between the sample and the sample, thereby reducing the stress on the main anti-skid teeth and improving the fracture resistance of the main anti-skid teeth, thereby extending the service life of the clamping block and reducing the test cost.

[0023] Reference Figure 1 Specifically, at the beginning of the tensile test, only the main anti-skid teeth 2 are in contact with the sample, and the total contact area is small, so the main anti-skid teeth 2 generate a large compressive stress on the sample, so that they can bite into the sample smoothly and increase the biting depth; as the tensile test proceeds, the test tension increases, and the two clamping blocks 1 gradually approach each other, so that the clamping force increases. The greater the test tension, the greater the clamping force generated; as the test tension increases, the tensile stress on the biting part of the main anti-skid teeth 2 becomes greater and greater, because the two clamping blocks 1 gradually approach each other, so the auxiliary anti-skid teeth 3 begin to contact the sample; the anti-skid contact plane of the auxiliary anti-skid teeth 3 can be used to increase the contact area with the sample, generate friction, and prevent the sample from slipping; the pressure on the anti-skid contact plane gradually increases, and the friction generated continues to increase, then the auxiliary anti-skid teeth 3 share the tensile stress on the main anti-skid teeth 2, thereby reducing the tensile stress on the main anti-skid teeth 2, slowing down the deformation and fracture of the main anti-skid teeth 2, and thus increasing the number of uses and extending the service life.

[0024] Specifically, the tensile strength of the sample in this embodiment is 1250-2200 MPa; that is, when performing a tensile test on a sample with a tensile strength of 1250-2200 MPa, using the clamp in this embodiment can effectively avoid slipping of the sample, increase the number of tests of the clamp, and extend its service life.

[0025] Reference Figure 1 Preferably, in this embodiment, the main anti-skid teeth 2 and the auxiliary anti-skid teeth 3 are alternately arranged on the clamping surface of the clamping block 1; that is, the auxiliary anti-skid teeth 3 are arranged between two adjacent main anti-skid teeth 2; an inter-tooth platform is provided between adjacent main anti-skid teeth 2 and auxiliary anti-skid teeth 3, that is, a spacing is formed between the main anti-skid teeth 2 and the auxiliary anti-skid teeth 3; preferably, the width d of the inter-tooth platform is greater than 0 and less than or equal to 1 mm; the main anti-skid teeth 2 and the auxiliary anti-skid teeth 3 are alternately arranged, so that the force on the teeth is more uniform, preventing local stress concentration.

[0026] Reference Figure 1 In this embodiment, the main anti-skid teeth 2 and the auxiliary anti-skid teeth 3 extend perpendicular to the tensile direction and are rack-shaped; the cross-section of the main anti-skid teeth 2 is an isosceles triangle, and the cross-section of the auxiliary anti-skid teeth 3 is an isosceles trapezoid; wherein the cross-section is perpendicular to the clamping surface and passes through the tooth tip of the main anti-skid teeth; preferably, in this embodiment, the tooth top angle α of the main anti-skid teeth 2 is 40° to 60°; in the initial stage of the tensile test, only the main anti-skid teeth 2 bite into the sample, and the contact area is small. In order to avoid excessive stress on the main anti-skid teeth 2, the tooth top angle α is not less than 40°, which can increase the contact area and reduce the stress of the main anti-skid teeth; if the tooth top angle α is greater than 60°, although the stress on the main anti-skid teeth 2 is small, the biting depth is insufficient.

[0027] Reference Figure 1 If the tooth height of the main anti-skid teeth 2 is too small, the processing will be more difficult and the depth of the main anti-skid teeth biting into the sample will be limited; if the tooth height is too large, the risk of deformation will increase during the quenching of the clamp block, and during the tensile test, the larger tooth height will cause the tooth root to be subjected to greater stress, which is easy to break the tooth; therefore, preferably, in this embodiment, the tooth height H of the main anti-skid teeth 2 is 0.3-0.8 mm.

[0028] Reference Figure 1Preferably, in this embodiment, the tooth height h of the auxiliary anti-skid teeth is 0.2-0.7 mm, the tooth top width b is 0.2-0.4 mm, and the tooth bottom angle γ is 60°-80°; the cross section of the auxiliary anti-skid teeth 3 is an isosceles trapezoid, and the anti-skid contact plane at the top is used to provide friction, so the tooth top width should not be too small to provide sufficient friction; but too large a tooth top width will reduce the number of main anti-skid teeth, increase the stress of the main anti-skid teeth, and make the main anti-skid teeth easy to break; therefore, in this embodiment, the tooth top width of the auxiliary anti-skid teeth is preferably 0. 2~0.4mm; preferably, in order to ensure that the auxiliary anti-skid teeth 3 can smoothly contact the sample and generate friction, and facilitate processing, the tooth height of the auxiliary anti-skid teeth 3 in this embodiment is 0.2~0.7mm; when the tooth height and the tooth top width are within the preferred range, if the tooth bottom angle of the auxiliary anti-skid teeth is too small, the area occupied by the auxiliary anti-skid teeth is large, which reduces the number of main anti-skid teeth, increases stress, and is prone to breakage; if the tooth bottom angle of the auxiliary anti-skid teeth is too large, it is not conducive to processing; therefore, the tooth bottom angle γ of the auxiliary anti-skid teeth is preferably 60°~80°.

[0029] Reference Figure 1 In this embodiment, the auxiliary anti-skid teeth 3 are used to increase the friction force, which is beneficial to avoid the main anti-skid teeth 2 from breaking; preferably, the tooth height difference between the main anti-skid teeth and the auxiliary anti-skid teeth is not more than 0.2mm; when a tensile test is performed on a sample with a tensile strength of 1250-2200MPa, in order to avoid the main anti-skid teeth 2 from breaking, when the stress on the main anti-skid teeth 2 is 70%-85% of its breaking strength, the auxiliary anti-skid teeth 3 start to contact with the sample and then provide friction; therefore, the tooth height difference between the main anti-skid teeth and the auxiliary anti-skid teeth is not more than 0.2mm; that is, in this embodiment, the tooth height difference between the main anti-skid teeth and the auxiliary anti-skid teeth is related to the timing of the auxiliary anti-skid teeth contacting the sample, and the timing of the auxiliary anti-skid teeth contacting the sample is related to the stress on the main anti-skid teeth, and the purpose is to avoid the main anti-skid teeth from breaking. Embodiment 2:

[0030] A clamp for tensile testing machine, refer to Figure 2 Compared with Example 1, the difference between this embodiment and Example 1 is that: in this embodiment, the main anti-skid teeth 2 and the auxiliary anti-skid teeth 3 are integrally formed, so that the anti-skid contact plane is connected with the side wall of the main anti-skid teeth; the main anti-skid teeth 2 and the auxiliary anti-skid teeth 3 are integrally formed, which can increase the rigidity of the main anti-skid teeth and further improve the deformation and fracture resistance of the main anti-skid teeth, thereby extending the service life. Embodiment 3:

[0031] A clamp for tensile testing machine, refer to Figure 3 Compared with Example 1, the difference between this embodiment and Example 1 is that the cross-section of the auxiliary anti-skid teeth 3 in this embodiment is rectangular; of course, in other optional embodiments, the auxiliary anti-skid teeth can also adopt other shapes as long as they can provide an anti-skid contact plane. Embodiment 4:

[0032] Based on Example 1, the difference between this embodiment and Example 1 is that: in this embodiment, the main anti-skid teeth 2 are pyramidal, and the auxiliary anti-skid teeth 3 are prism-shaped; specifically, the clamping surface of the clamping block is provided with anti-skid teeth arranged horizontally and vertically; in each horizontal row, the main anti-skid teeth 2 and the auxiliary anti-skid teeth 3 are arranged alternately; in each vertical row, the main anti-skid teeth 2 and the auxiliary anti-skid teeth 3 are arranged alternately.

[0033] Reference Figure 4 The fixture in this embodiment is used to carry out simulation tests. From the simulation results, it can be seen that during the tensile test of the fixture in this embodiment, the maximum stress on the main anti-skid teeth 2 is 1500MPa, which is less than the fracture strength of the main anti-skid teeth (usually 2000MPa); therefore, the main anti-skid teeth 2 will not break; in addition, the bite depth of the main anti-skid teeth 2 is 0.12mm, and the auxiliary anti-skid teeth 3 provide sufficient friction, which avoids the occurrence of slipping and increases the service life of the fixture.

[0034] Reference Figure 5 and Figure 6 , only one type of pyramidal anti-slip teeth is arranged on the clamping surface of the clamping block for simulation test, among which, Figure 5 The interdental platform is larger. Figure 6 The interdental platform is small; see Figure 5 When the inter-tooth platform is large, although the anti-slip teeth have a large bite depth of 0.19 mm, the maximum stress on the anti-slip teeth is 5700 MPa, which is much greater than the fracture strength of the anti-slip teeth (usually 2000 MPa). Therefore, the anti-slip teeth will break, and then slip, which will reduce the service life; Figure 6 When the platform between teeth is small, although the stress on the anti-slip teeth is small, only 1167MPa, and no fracture will occur, the depth of the anti-slip teeth biting into the specimen is shallow, only 0.08mm, and the friction force provided is smaller than the test tensile force, which will cause slippage and affect the test.

[0035] Therefore, compared to arranging only one anti-skid tooth on the clamping surface, the present invention combines main anti-skid teeth with different tooth heights with auxiliary anti-skid teeth, uses the main anti-skid teeth to bite into the sample, and uses the auxiliary anti-skid teeth to increase the friction force. In this way, while increasing the biting depth of the main anti-skid teeth, the maximum stress on the main anti-skid teeth can be reduced, thereby avoiding the occurrence of anti-skid tooth breakage and slipping, extending the service life, and being suitable for tensile testing of samples with a tensile strength of 1250 to 2200 MPa.

Claims

1. A clamp for tensile testing machine, the clamp comprising two clamping blocks installed in the jaws of the testing machine and used to clamp the sample; characterized in that: The clamping surface of the clamping block is respectively provided with a main anti-skid tooth and an auxiliary anti-skid tooth; the tooth top of the main anti-skid tooth is provided with a biting tip, the tooth top of the auxiliary anti-skid tooth is provided with an anti-skid contact plane, and the tooth height of the main anti-skid tooth is greater than the tooth height of the auxiliary anti-skid tooth.

2. The clamp for tensile testing machine according to claim 1, characterized in that: When a tensile test is performed on a sample, the biting tip of the main anti-skid tooth contacts the sample first, and as the test tensile force increases, the anti-skid contact plane of the auxiliary anti-skid tooth contacts the sample later.

3. The clamp for tensile testing machine according to claim 1, characterized in that: The main anti-skid teeth and the auxiliary anti-skid teeth are integrally formed, so that the anti-skid contact plane is connected with the side wall of the main anti-skid teeth.

4. The clamp for tensile testing machine according to claim 1, characterized in that: The tensile strength of the sample is 1250-2200 MPa.

5. The clamp for tensile testing machine according to claim 1, characterized in that: The cross section of the main anti-skid teeth is triangular, and the cross section of the auxiliary anti-skid teeth is isosceles trapezoidal.

6. The clamp for tensile testing machine according to claim 1, characterized in that: The main anti-skid teeth and the auxiliary anti-skid teeth are alternately arranged on the clamping surface of the clamping block.

7. The clamp for tensile testing machine according to claim 6, characterized in that: An inter-tooth platform is arranged between adjacent main anti-skid teeth and auxiliary anti-skid teeth, and the width of the inter-tooth platform is 0-1 mm.

8. The clamp for tensile testing machine according to claim 1, characterized in that: The difference in tooth height between the main anti-skid teeth and the auxiliary anti-skid teeth is no more than 0.2 mm.

9. The clamp for tensile testing machine according to claim 5, characterized in that: The tooth top angle of the main anti-skid teeth is 40° to 60°, and the tooth height is 0.3 to 0.8 mm.

10. The clamp for tensile testing machine according to claim 5, characterized in that: The auxiliary anti-skid teeth have a tooth height of 0.2-0.7 mm, a tooth top width of 0.2-0.4 mm, and a tooth bottom angle of 60°-80°.

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