Self-tightening fixture and test method for V-notch shear test of composite materials

Abstract

The present application discloses a self-tightening fixture for a V-notch shear test of a composite material, which includes two oppositely arranged clamping members; each clamping member includes a body, the body includes a clamping portion and a stretching portion connected together, both ends of the clamping portion are formed as a connecting end and a clamping end, and the stretching portion is connected to the connecting end; a stretching rod is installed on the stretching portion, and the side surface of the stretching portion facing the clamping end is formed as a positioning surface; a wedge-shaped groove is provided on the clamping portion, and two wedge-shaped clamping blocks are movably installed in the wedge-shaped groove, and a clamping groove is formed between the two wedge-shaped clamping blocks; a clamping groove is formed at one end of each wedge-shaped clamping block facing the stretching portion, an adjusting plate is inserted into the clamping groove, and an adjusting screw rod is connected to the adjusting plate. The present application also discloses a test method using the self-tightening fixture. By using the present application, the requirement of the coincidence of the central axis of the V-notch cross-section of the V-notch specimen and the load line can be effectively guaranteed, the test efficiency can be improved, and the specimen installation time and labor can be saved.

Description

Technical Field

[0001] The present invention relates to a self-tightening fixture and a test method for a V-notch shear test of a composite material, which can be used for testing the V-notch shear performance of composite materials in engineering fields such as aviation, aerospace, wind power, and rail transit. Background Art

[0002] At present, the main methods for testing the in-plane shear performance of composite materials are: torsion method, off-axis tension method, and shear method. The torsion method is a method based on the shear performance test of metal materials. It mainly generates pure shear stress on a thin-walled cylinder by applying torque to both ends of the thin-walled cylinder. However, due to the complex specimen preparation of this method, the shear force caused by the torque at the clamping end during the test process makes it difficult for the specimen to fail at the gauge length, resulting in large deviations in the test results. Moreover, an additional torsion testing machine is required. Therefore, this method is not the preferred method for testing the in-plane shear performance of composite materials. Although the off-axis tension method has simple specimen preparation process and test method, since it does not generate pure shear stress during the test process and there is a complex stress field at the boundary surface, the test results are often on the low side.

[0003] The shear method mainly generates shear loading on the specimen through a pair of non-collinear coplanar loads. Currently, there are mainly rail shear method, Iosipescu shear method, and V-notch shear method.

[0004] ASTM D4255 specifies a rail shear method. This method generates shear load through double-rail tension or triple-rail compression to measure the in-plane shear performance, but the shear stress generated is not uniform. ASTM D5379 specifies an Iosipescu shear method. This method applies a pair of loads with opposite directions and equal magnitudes to both ends of the specimen notch in a compression manner to generate shear stress at the gauge length of the specimen. However, due to the small working area of this method, it is difficult to apply to some thick fibers or large-spacing fibers. ASTM D7078 specifies a V-notch shear method. This method generates shear stress at the gauge length of the specimen by applying tensile loads to both sides of the V-notch of the specimen. Currently, this method is the most main and common method for testing the shear performance of composite materials at home and abroad. However, when testing according to the fixture recommended by ASTM D7078, the following problems are likely to occur: (1) The specimen is fixed by screws on both sides of the fixture. Due to the problem of human operation differences, it is easy for the specimen (9) to twist or misalign in the fixture, resulting in the non-coincidence of the central axis of the V-notch cross-section and the load line. Especially for specimens about 2 mm, the influence on the results is greater; (2) The whole set of fixtures has 12 screws. To ensure the clamping of the specimen, each screw needs to be tightened slowly with a torque wrench to increase the torque. Therefore, the specimen installation is time-consuming and laborious, and the efficiency is low. Summary of the Invention

[0005] To solve the above problems, the present invention first proposes a self-tightening fixture for V-notch shear test of composite materials, which includes two clamping parts arranged opposite to each other;

[0006] Each clamping member includes an L-shaped body, the body including a clamping portion and a stretching portion connected together, wherein the clamping portion extends along a first axis and the stretching portion extends along a second axis, the first axis being perpendicular to the second axis; the two ends of the clamping portion in the first axis direction are respectively formed as a connecting end and a clamping end, and the stretching portion is connected to the connecting end;

[0007] A stretching rod is installed on the side of the stretching portion facing away from the clamping end, and the side of the stretching portion facing the clamping end is formed as a positioning surface;

[0008] A wedge-shaped groove is provided on the clamping portion, and the wedge-shaped groove is formed by the inner side surface of the clamping portion being recessed along the second axis. The small end of the wedge-shaped groove faces away from the connecting end, and the small end of the wedge-shaped groove is open. Two wedge-shaped clamping blocks are movably installed in the wedge-shaped groove. The side surface of each wedge-shaped clamping block facing the other wedge-shaped clamping block is formed as a clamping surface, and a clamping groove is formed between the two clamping surfaces. The clamping surfaces extend along the first axis direction, and the side surface of each wedge-shaped clamping block facing away from the other wedge-shaped clamping block is formed as a pressing surface, and the pressing surface is parallel to the inner side surface of the wedge-shaped groove.

[0009] A slot is provided at one end of each wedge-shaped clamping block facing the stretching portion, and both ends of an adjustment plate are respectively inserted into the slots of a wedge-shaped clamping block. An adjustment bolt passes through the stretching portion along the first axis and is connected to the adjustment plate. The adjustment bolt engages with an adjustment threaded hole in the stretching portion.

[0010] When both ends of the V-notch specimen are clamped in the clamping grooves respectively, the tensile rods on the two clamping pieces are coaxial.

[0011] When this application is working, follow the steps below:

[0012] (1) Insert one end of the V-notch specimen into the clamping groove of a clamp and adjust the position of the V-notch specimen;

[0013] (2) Tighten the adjusting bolt to push the wedge clamp toward the small end of the wedge groove and tighten the V-notch specimen;

[0014] (3) Insert the other end of the V-notch specimen into the clamping groove of another clamping piece and adjust the position of the V-notch specimen;

[0015] (4) Tighten the other adjusting bolt to tighten the V-notch specimen;

[0016] (5) Connect the tensile rod to the tensile testing machine, perform testing and record the data.

[0017] By using the present application, it is possible to effectively ensure the coincidence requirement between the central axis of the V-notch cross-section of the V-notch specimen and the load line, while ensuring the effective clamping of the V-notch specimen, preventing slipping, improving the test efficiency, and saving the specimen installation time and labor.

[0018] Furthermore, to increase the clamping force, the clamping surface is a rough surface.

[0019] Furthermore, corresponding to each wedge-shaped clamping block, a tensioning device is provided, and a sliding groove penetrating the clamping part along the second direction is formed on the clamping part. Each tensioning device includes a tension spring and a synchronizing rod. The tension spring is located outside the clamping part. One end of the tension spring is fixed to the end of the clamping end of the clamping part, and the other end of the tension spring extends towards the connecting end and is connected to one end of the synchronizing rod. The other end of the synchronizing rod passes through the sliding groove and is fixed to the corresponding wedge-shaped clamping block.

[0020] The tension spring can be used to clamp the wedge-shaped clamping block on the V-notch specimen, keeping the V-notch specimen in the clamping groove, which is convenient for clamping and positioning the V-notch specimen.

[0021] Furthermore, to improve the synchronism when the two wedge-shaped clamping blocks move, a synchronizing plate is freely arranged on the outer side surface of the clamping part. Corresponding to each synchronizing rod, a swinging groove extending along the third axis direction is formed on the synchronizing plate. One end of the synchronizing rod passes through the swinging groove and is connected to the tension spring; the third axis is perpendicular to both the first axis and the second axis. By using the swinging groove, the movements of the two synchronizing rods are kept consistent, so that the movements of the two wedge-shaped clamping blocks are kept consistent.

[0022] Specifically, each tension rod includes a connecting rod and a joint. One end of the connecting rod is fixed to the tension part, and one end of the joint is detachably connected to the other end of the connecting rod. One end of the joint is used to connect to the tensile testing machine. This design can enable the direction adjustment of the self-tightening fixture.

[0023] Furthermore, to prevent the wedge-shaped clamping block from disengaging from the wedge-shaped groove, corresponding to each wedge-shaped clamping block, a clamping strip is installed on the inner side surface of the clamping part, and the clamping strip presses against the corresponding wedge-shaped clamping block.

[0024] Furthermore, to facilitate the positioning of the V-notch specimen, a positioning block is further included, which is used to be placed between the V-notch of the V-notch specimen and the positioning surface;

[0025] When the two ends of a V-notch specimen are respectively clamped to a clamping member, a positioning block is placed between each V-notch of the V-notch specimen and the opposite positioning surface, and the structures of the two positioning blocks are the same;

[0026] Each positioning block includes a rectangular block, one end of which is provided with a V-shaped wedge-shaped portion, which can be inserted into the V-shaped notch; when the wedge-shaped portion is inserted into the V-shaped notch, the outer surface of the wedge-shaped portion fits into the inner surface of the V-shaped notch, and the end of the rectangular block facing away from the wedge-shaped portion extends outward beyond the V-shaped notch.

[0027] Since the two V-notches of the V-notch specimen are of the same shape and size, a positioning block is placed between each V-notch and the corresponding positioning surface when the V-notch specimen is clamped on the clamping piece, so that the positions of the two ends of the V-notch specimen on the two clamping pieces are the same. Therefore, during the clamping process, the clamping forces exerted on the two ends of the V-notch specimen are the same, so that the two ends of the V-notch specimen produce the same deformation due to the same clamping force, so that during the test, the experimental data will not be adversely affected by the different clamping forces at the two ends of the V-notch specimen.

[0028] During the research process, the inventors of this application found that when the clamping force at both ends of the specimen is different, the fracture point will often deviate from the preset position during the test, and the test data will also fluctuate. The reason may be that when the clamping force is different, the two ends of the specimen will produce different deformations and different internal stresses inside the two ends of the specimen. These internal stresses will produce a superimposed effect with the loading force during the test, resulting in deviations and fluctuations in the test data.

[0029] By using the positioning block, the sample is clamped in the same position on the two clamps, thereby generating the same pressure and internal stress at both ends of the sample, thereby ensuring that the interference of internal stress on the test data is reduced during the test.

[0030] Secondly, the present application also proposes a test method for a V-notch shear test of a composite material, which uses any of the above-mentioned self-tightening fixtures, and the test method includes the following steps:

[0031] (1) The two clamping members are respectively referred to as the first clamping member and the second clamping member;

[0032] Insert one end of the V-notch specimen into the clamping groove of the first clamping member, and adjust the V-notch specimen to a first set position on the first clamping member;

[0033] (2) Tighten the adjusting bolt on the first clamping piece to push the wedge-shaped clamping block of the first clamping piece toward the small end of the wedge-shaped groove of the first clamping piece, and tightly clamp one end of the V-notch specimen on the first clamping piece;

[0034] (3) Insert the other end of the V-notch specimen into the clamping groove of the second clamping member, and adjust the V-notch specimen to the second set position on the second clamping member;

[0035] (4) Turn the adjusting bolt on the second clamping member, push the wedge block of the second clamping member towards the small end direction of the wedge groove of the second clamping member, and tightly clamp the other end of the V-notch specimen on the second clamping member; the tensile rods on the two clamping members and the cross-sectional central axis of the V-notch are all located on the same axis;

[0036] (5) Fix the tensile rods on the two clamping members to a clamping head of the tensile testing machine respectively, conduct the test and record the data.

[0037] In this test method, the two clamping members are respectively clamped at both ends of the specimen, and the two tensile rods and the cross-sectional central axis of the V-notch are all located on the same axis. During the test process, the external forces applied to the two clamping members are on the same axis, avoiding torsion or misalignment of the specimen and ensuring the accuracy of the test.

[0038] Further, the two V-shaped notches of the V-notch specimen are respectively called the first V-shaped notch and the second V-shaped notch. When clamping the V-notch specimen on the first clamping member and the second clamping member, the first V-shaped notch faces the positioning surface of the first clamping member, and the second V-shaped notch faces the positioning surface of the second clamping member;

[0039] In step (1), a first positioning block is inserted between the first V-shaped notch of the V-notch specimen and the positioning surface of the first clamping member, and the V-notch specimen abuts against the positioning surface of the first clamping member through the first positioning block;

[0040] In step (3), a second positioning block is inserted between the second V-shaped notch of the V-notch specimen and the positioning surface of the second clamping member, and the V-notch specimen abuts against the positioning surface of the second clamping member through the second positioning block;

[0041] In step (4), after tightly clamping the other end of the V-notch specimen on the second clamping member, the first positioning block and the second positioning block are pulled out.

[0042] During the research process, the inventors of this application found that when the clamping forces at both ends of the specimen are different, during the test, the fracture location often deviates from the preset position, and the test data also fluctuates. The reason may be that when the clamping forces are different, different deformations are generated at both ends of the specimen, and different internal stresses are generated inside both ends of the specimen. These internal stresses will produce a superimposed effect with the loading force during the test process, resulting in deviation and fluctuation of the test data.

[0043] By using the positioning block, the specimen has the same clamping position on the two clamping members, so as to generate the same pressure on both ends of the specimen and generate the same internal stress, thereby ensuring that during the test process, the interference caused by the internal stress to the test data is reduced.

[0044] Furthermore, the first and second positioning blocks have the same structure, each comprising a rectangular block with a V-shaped wedge-shaped portion at one end. This wedge-shaped portion can be inserted into the V-shaped notch. When the wedge-shaped portion is inserted into the V-shaped notch, the outer surface of the wedge-shaped portion abuts the inner surface of the V-shaped notch, and the end of the rectangular block facing away from the wedge-shaped portion extends outward from the V-shaped notch. When the positioning block is inserted into the V-shaped notch, the positioning block and the inner surface of the V-shaped notch are in surface contact, which prevents the positioning block from damaging the specimen. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a structural schematic diagram of an embodiment of a self-tightening clamp.

[0046] Figure 2 It is a bottom view of the first clamping member.

[0047] Figure 3 It is a structural diagram of the first positioning block.

[0048] Figure 4 This is a diagram of the state when the self-tightening fixture is clamping the specimen.

[0049] Figure 5 This is a state diagram of the self-tightening clamp when working. DETAILED DESCRIPTION

[0050] See also Figure 1 and Figure 2 In the accompanying drawings, the direction of the first axis X represents the direction of the first axis, the direction of the second axis Y represents the direction of the second axis, and the direction of the third axis Z represents the direction of the third axis.

[0051] A self-tightening fixture for V-notch shear test of composite materials includes two clamping members arranged opposite to each other, namely a first clamping member 10 and a second clamping member 30. The first clamping member 10 and the second clamping member 30 have the same structure.

[0052] The first clamping member includes an L-shaped body 11, which comprises a clamping portion 111 and a stretching portion 112 connected together. The clamping portion 111 extends along a first axis, and the stretching portion 112 extends along a second axis, the first axis being perpendicular to the second axis. The two ends of the clamping portion 111 along the first axis are formed as a connecting end 113 and a clamping end 114, respectively. The stretching portion 112 is connected to the connecting end 113. In this embodiment, the body 11 is a monolithic structural member.

[0053] A stretching rod 20 is mounted on a side of the stretching portion 112 facing away from the clamping end 114 , and a side surface of the stretching portion 112 facing the clamping end 114 is formed as a positioning surface 116 .

[0054] In this embodiment, each stretching rod 20 includes a connecting rod 21 and a joint 26. One end of the connecting rod 21 is fixed on the stretching part 112, and a slot 22 is formed at the other end of the connecting rod 21. One end of the joint 26 is formed with a plug 27, and the other end of the joint 26 is used to be clamped to a tensile testing machine. After inserting the plug 27 into the slot 22, the plug 27 is detachably connected to the slot 22 with a pin 29.

[0055] A wedge-shaped groove 16 is provided on the clamping part 111. The wedge-shaped groove is formed by the inner side surface of the clamping part being recessed along the second axis direction. The small end of the wedge-shaped groove faces away from the connecting end, and the small end of the wedge-shaped groove is open. Two wedge-shaped clamping blocks 17 are movably installed in the wedge-shaped groove. Each side of each wedge-shaped clamping block facing the other wedge-shaped clamping block is formed as a clamping surface 171, and a clamping groove 40 is formed between the two clamping surfaces. The clamping surface extends along the first axis direction. Each side of each wedge-shaped clamping block facing away from the other wedge-shaped clamping block is formed as a pressing surface, and the pressing surface is parallel to the inner side surface of the wedge-shaped groove. In this embodiment, when observed along the second axis direction, the wedge-shaped groove 16 is an isosceles trapezoid, and the wedge-shaped clamping block 17 is a right trapezoid. Both clamping surfaces are rough surfaces. Specifically, in this embodiment, diamond patterns are pressed on the clamping surfaces.

[0056] A clamping groove 172 is provided at one end of each wedge-shaped clamping block 17 facing the stretching part 112. Two ends of an adjusting plate 191 are respectively inserted into the clamping grooves of one wedge-shaped clamping block, and an adjusting bolt 19 passes through the stretching part 112 along the first axis direction and is connected to the adjusting plate. The adjusting bolt 19 is engaged in an adjusting threaded hole inside the stretching part;

[0057] Please refer to Figure 4 , when the two ends of the V-notch specimen 90 are respectively clamped in the clamping groove 40, the stretching rods 20 on the two clamping members are coaxial.

[0058] In this embodiment, a tensioning device is provided corresponding to each wedge-shaped clamping block 17, and a sliding groove 15 is formed on the clamping part 111 and penetrates through the clamping part along the second direction. Each tensioning device includes a tension spring 12 and a synchronizing rod 14. The tension spring 12 is located outside the clamping part. In this application, the side of the clamping part facing the other clamping part is called the inner side, and the side opposite to the inner side is called the outer side.

[0059] One end of the tension spring 12 is fixed at the end of the clamping end of the clamping part, and the other end of the tension spring extends towards the connecting end 113 and is connected to one end of the synchronizing rod 14. The other end of the synchronizing rod passes through the sliding groove 15 and is fixed to the corresponding wedge-shaped clamping block 17.

[0060] A synchronization plate 13 is freely provided on the outer surface of the clamping portion 111. Corresponding to each synchronization rod 14, a swing groove 131 extending along the third axis direction is opened on the synchronization plate 13. One end of the synchronization rod passes through the swing groove and is connected to the tension spring.

[0061] Corresponding to each wedge-shaped clamping block, a clamping strip 18 is installed on the inner side surface of the clamping portion. The clamping strip 18 presses against the corresponding wedge-shaped clamping block to prevent the wedge-shaped clamping block from falling out of the wedge-shaped groove 16.

[0062] This embodiment also includes a positioning block, which is positioned between the V-notch of the V-notch specimen and the positioning surface. When the two ends of a V-notch specimen are clamped to a clamping member, a positioning block is placed between each V-notch of the V-notch specimen and the corresponding positioning surface. The two positioning blocks have the same structure. For ease of description, the two positioning blocks are referred to as the first positioning block 51 and the second positioning block 52, respectively.

[0063] See also Figure 3 The first positioning block 51 includes a rectangular block 511, and a V-shaped wedge-shaped portion 512 is provided at one end of the rectangular block. The wedge-shaped portion 512 can be inserted into the V-shaped notch; when the wedge-shaped portion is inserted into the V-shaped notch, the outer surface 513 of the wedge-shaped portion 512 fits into the inner surface of the V-shaped notch, and the end of the rectangular block away from the wedge-shaped portion extends outward from the V-shaped notch.

[0064] The following describes the test method for V-notch shear test of composite materials. Figure 4 and Figure 5 The test method uses the self-tightening fixture mentioned above. For the convenience of description, the two V-notches of the V-notch specimen 90 are respectively referred to as the first V-notch 91 and the second V-notch 92. Figure 5 The letter F in the diagram indicates the direction of tension during the test.

[0065] The specific steps of the test method are as follows:

[0066] (1) Insert one end of the V-notch specimen 90 into the clamping groove of the first clamping member 10, with the first V-notch 91 facing the positioning surface of the first clamping member. Insert the first positioning block 51 between the first V-notch of the V-notch specimen and the positioning surface of the first clamping member. The V-notch specimen rests on the positioning surface of the first clamping member via the first positioning block. Adjust the V-notch specimen to the first set position on the first clamping member 10.

[0067] (2) Tighten the adjusting bolt 19 on the first clamping member to push the wedge-shaped clamping block of the first clamping member toward the small end of the wedge-shaped groove of the first clamping member, and tightly clamp one end of the V-notch specimen on the first clamping member.

[0068] (3) Then insert the other end of the V-notch specimen 90 into the clamping groove of the second clamping member 30. A second positioning block 52 is inserted between the second V-notch of the V-notch specimen and the positioning surface of the second clamping member. The V-notch specimen abuts against the positioning surface of the second clamping member via the second positioning block; adjust the V-notch specimen to the second set position on the second clamping member.

[0069] (4) Rotate the adjusting bolt 19 on the second clamping member to push the wedge-shaped clamping block of the second clamping member to move towards the small end of the wedge-shaped groove of the second clamping member, and tightly clamp the other end of the V-notch specimen on the second clamping member; the tensile rods on the two clamping members and the cross-sectional central axis of the V-notch are all on the same axis. Withdraw the first positioning block and the second positioning block.

[0070] (5) Fix the tensile rods on the two clamping members to a clamping head of a tensile testing machine respectively, conduct the test and record the data.

Claims

1. A self-tightening fixture for the V-notch shear test of composite materials, characterized in that It includes two clamping members arranged opposite to each other; Each clamping member includes an L-shaped body, the body including a clamping portion and a stretching portion connected together, wherein the clamping portion extends along a first axis and the stretching portion extends along a second axis, the first axis being perpendicular to the second axis; the two ends of the clamping portion in the first axis direction are respectively formed as a connecting end and a clamping end, and the stretching portion is connected to the connecting end; A stretching rod is installed on the side of the stretching portion facing away from the clamping end, and the side of the stretching portion facing the clamping end is formed as a positioning surface; A wedge-shaped groove is provided on the clamping portion, and the wedge-shaped groove is formed by the inner side surface of the clamping portion being recessed along the second axis. The small end of the wedge-shaped groove faces away from the connecting end, and the small end of the wedge-shaped groove is open. Two wedge-shaped clamping blocks are movably installed in the wedge-shaped groove. The side surface of each wedge-shaped clamping block facing the other wedge-shaped clamping block is formed as a clamping surface, and a clamping groove is formed between the two clamping surfaces. The clamping surfaces extend along the first axis direction, and the side surface of each wedge-shaped clamping block facing away from the other wedge-shaped clamping block is formed as a pressing surface, and the pressing surface is parallel to the inner side surface of the wedge-shaped groove. A slot is provided at one end of each wedge-shaped clamping block facing the stretching portion, and both ends of an adjustment plate are respectively inserted into the slots of a wedge-shaped clamping block. An adjustment bolt passes through the stretching portion along the first axis and is connected to the adjustment plate. The adjustment bolt engages with an adjustment threaded hole in the stretching portion. When the two ends of the V-notch specimen are clamped in the clamping grooves respectively, the tensile rods on the two clamping pieces are coaxial; Corresponding to each wedge-shaped clamping block, a tensioning device is provided, and a sliding groove is provided on the clamping portion and passes through the clamping portion along the second direction. Each tensioning device includes a tension spring and a synchronization rod.

2. The self-tightening clamp according to claim 1, characterized in that, The clamping surface is rough.

3. The self-tightening clamp according to claim 1, characterized in that: The tension spring is located on the outside of the clamping part, one end of the tension spring is fixed to the end of the clamping end of the clamping part, the other end of the tension spring extends toward the connecting end and is connected to one end of the synchronization rod, and the other end of the synchronization rod is fixed to the corresponding wedge-shaped clamping block after passing through the slide slot.

4. The self-tightening clamp according to claim 3, characterized in that: A synchronization plate is freely provided on the outer surface of the clamping portion. Corresponding to each synchronization rod, a swing groove extending along the third axis is opened on the synchronization plate. One end of the synchronization rod passes through the swing groove and is connected to the tension spring; the third axis is perpendicular to the first axis and the second axis.

5. The self-tightening clamp according to claim 1, characterized in that: Each stretching rod includes a connecting rod and a joint, one end of the connecting rod is fixed on the stretching part, one end of the joint is detachably connected to the other end of the connecting rod, and one end of the joint is used to be connected to the tensile machine.

6. The self-tightening clamp according to claim 1, characterized in that: Corresponding to each wedge-shaped clamping block, a clamping strip is installed on the inner side surface of the clamping portion, and the clamping strip presses against the corresponding wedge-shaped clamping block.

7. The self-tightening clamp according to claim 1, characterized in that: Also included is a positioning block, which is used to be placed between the V-notch of the V-notch specimen and the positioning surface; When both ends of a V-notch specimen are clamped on a clamping piece, a positioning block is placed between each V-notch of the V-notch specimen and the corresponding positioning surface, and the two positioning blocks have the same structure; Each positioning block includes a rectangular block, one end of which is provided with a V-shaped wedge-shaped portion, which can be inserted into the V-shaped notch; when the wedge-shaped portion is inserted into the V-shaped notch, the outer surface of the wedge-shaped portion fits into the inner surface of the V-shaped notch, and the end of the rectangular block facing away from the wedge-shaped portion extends outward beyond the V-shaped notch.

8. Test method for V-notch shear test of composite materials, characterized in that, Using the self-tightening fixture according to any one of claims 1 to 7, the test method comprises the following steps: (1) The two clamping members are respectively referred to as the first clamping member and the second clamping member; Insert one end of the V-notch specimen into the clamping groove of the first clamping member, and adjust the V-notch specimen to a first set position on the first clamping member; (2) Tighten the adjusting bolt on the first clamping piece to push the wedge-shaped clamping block of the first clamping piece toward the small end of the wedge-shaped groove of the first clamping piece, and tightly clamp one end of the V-notch specimen on the first clamping piece; (3) Insert the other end of the V-notch specimen into the clamping groove of the second clamping member, and adjust the V-notch specimen to the second set position on the second clamping member; (4) Tighten the adjusting bolt on the second clamping piece, push the wedge-shaped clamping block of the second clamping piece toward the small end of the wedge-shaped groove of the second clamping piece, and tightly clamp the other end of the V-notch specimen on the second clamping piece; the tensile rods on the two clamping pieces and the center axis of the V-notch section are all located on the same axis; (5) Fix the tensile rods on the two clamps to a clamping head of the tensile testing machine respectively, perform testing and record the data.

9. The test method according to claim 8, characterized in that The two V-notches of the V-notch specimen are respectively referred to as the first V-notch and the second V-notch. When the V-notch specimen is clamped on the first clamping member and the second clamping member, the first V-notch faces the positioning surface of the first clamping member, and the second V-notch faces the positioning surface of the second clamping member. In step (1), a first positioning block is inserted between the first V-notch of the V-notch specimen and the positioning surface of the first clamping member, and the V-notch specimen rests on the positioning surface of the first clamping member via the first positioning block; In step (3), a second positioning block is inserted between the second V-notch of the V-notch specimen and the positioning surface of the second clamping member, and the V-notch specimen rests on the positioning surface of the second clamping member via the second positioning block; In step (4), after the other end of the V-notch specimen is tightly clamped on the second clamping member, the first positioning block and the second positioning block are pulled out.

10. The test method according to claim 8, characterized in that The first positioning block and the second positioning block have the same structure. The first positioning block and the second positioning block both include a rectangular block. A V-shaped wedge-shaped portion is provided at one end of the rectangular block, and the wedge-shaped portion can be inserted into the V-shaped notch. When the wedge-shaped portion is inserted into the V-shaped notch, the outer surface of the wedge-shaped portion fits into the inner surface of the V-shaped notch, and the end of the rectangular block facing away from the wedge-shaped portion extends outward beyond the V-shaped notch.

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