Fiber reinforced composite material fretting fatigue test clamp suitable for uniaxial testing machine

Abstract

The invention discloses a fiber reinforced composite material fretting fatigue test clamp suitable for a uniaxial testing machine. The clamp and a test device comprise an upper clamp assembly with a fretting pad limiting device, a lower clamp assembly, a fretting pad, an upper gasket, a lower gasket, a test piece and a stress ring assembly. Wherein the upper clamp assembly and the lower clamp assembly are clamped through a hydraulic chuck and are used for fixing a test piece and transmitting an axial load. The test pieces are arranged in the limiting grooves of the upper and lower clamps, and the upper and lower gaskets are arranged between the two test pieces. The clamp is tightened through the fastening bolt to fix the test piece and prevent slipping; the set screw penetrates through the clamp, the test piece and the gasket to further fix the test piece. The micro-motion pad is arranged in the micro-motion pad limiting groove of the upper clamp, centering is guaranteed, and normal loads are transmitted. The device solves the problem that a fiber reinforced composite material is not matched with a metal material clamp, and has the advantages that the parallelism of a test piece and the centering degree of a micro-motion pad can be ensured, the test piece is prevented from slipping, the test precision is ensured, and the experiment success rate is improved.

Description

Technical Field

[0001] This invention relates to the field of materials testing technology, and specifically to a fretting fatigue testing fixture device for fiber-reinforced composite materials suitable for uniaxial testing machines. Background Technology

[0002] Fretting fatigue is a common form of fatigue failure. It refers to the physical phenomenon where, under cyclic loading, two contacting structural units experience contact loads and simultaneously undergo minute displacements and relative sliding, resulting in complex wear. This significantly reduces the fatigue strength of the structure and accelerates the failure process. Fretting fatigue is present in a considerable number of components, especially some critical components, in aero-engines and aircraft.

[0003] In recent years, composite materials have been widely used in various fields, especially in aerospace, due to their excellent mechanical properties. However, the harm of fretting fatigue to composite material connection structures has become increasingly prominent. Therefore, it is of great significance to conduct fretting fatigue experiments on the interface between composite materials and metal materials.

[0004] However, existing fretting fatigue tests mainly focus on metallic materials. The testing fixtures for metallic materials are not suitable for fiber-reinforced composite materials. Metal specimens are typically connected by drilling holes and bolts, but drilling holes in composite materials significantly degrades their performance, often leading to stress concentration fractures around the holes, which contradicts the testing objectives. Existing fretting fatigue testing devices add fretting pads and limiting grooves to ordinary fatigue testing equipment to accommodate fretting conditions. This results in a complex structure, and the fretting is easily slipped due to the reliance on bolt tightening for fixation. Summary of the Invention

[0005] Purpose of the invention: In view of the above-mentioned prior art, a fretting fatigue test fixture for fiber-reinforced composite materials suitable for uniaxial testing machines is proposed to solve the problem of slippage in fretting fatigue testing of composite materials and improve the accuracy and success rate of the test.

[0006] Technical solution: A fiber-reinforced composite material fretting fatigue test fixture suitable for a uniaxial testing machine, comprising an upper fixture assembly with a fretting pad limiting device, an upper pad, a lower pad, a lower fixture assembly, and a fretting pad; Both the upper clamping assembly and the lower clamping assembly adopt a flat plate clamping structure, and the inner side of the flat plate clamping structure is provided with a rectangular groove; The upper parts of the two test pieces arranged opposite each other and the upper pad located between the upper parts of the two test pieces are clamped in the rectangular groove of the upper clamping assembly; The lower parts of the two test pieces and the lower pad located between the lower parts of the two test pieces are clamped in the rectangular groove of the lower clamping assembly; The upper part of the upper clamping assembly is clamped by a hydraulic upper chuck, and the lower part of the lower clamping assembly is clamped by a hydraulic lower chuck. The hydraulic upper chuck and the hydraulic lower chuck are used to provide clamping force and transmit axial load. A gap is left between the upper clamping assembly and the lower clamping assembly. The micro-motion pad limiting device includes a boss located on the outside of the upper clamping assembly away from the clamping end, and a through hole located on the boss. The through hole is a combination through hole with a square hole outline and an additional circular hole at the center. Two micro-motion pads are respectively embedded into the through hole from both sides of the upper clamping assembly. The circular hole is used to connect the stress application rod of the stress ring assembly that provides normal load.

[0007] Furthermore, the upper clamp assembly and the lower clamp assembly are each provided with a boss for connecting a fastening bolt. The fastening bolt passes through the boss and is connected to a nut to further fix the two test pieces and the upper and lower shims located between the two test pieces.

[0008] Furthermore, the upper clamp assembly and the lower clamp assembly are respectively provided with set screws that pass through the clamp assembly, the two test pieces and the spacer between them.

[0009] Furthermore, the boss used for connecting the fastening bolts has four connecting through holes arranged in a rectangular array.

[0010] Furthermore, the set screw is located near the clamping end, and the end face of the set screw is lower than the surface of the clamping assembly.

[0011] Furthermore, the height of the boss on the outer side of the upper clamping assembly, away from the clamping end, is such that the micro-motion pad is fully embedded in the through hole.

[0012] Beneficial Effects: This invention discloses a fretting fatigue testing fixture for fiber-reinforced composite materials suitable for a uniaxial testing machine. The fixture and testing apparatus include: an upper fixture assembly with a fretting pad limiting device, a lower fixture assembly, a fretting pad, upper and lower gaskets, a test piece, and a stress ring assembly. The upper and lower fixture assemblies are clamped by hydraulic clamps to fix the test piece and transmit axial loads. The test piece is placed in the limiting grooves of the upper and lower fixtures, and the upper and lower gaskets are placed between the two test pieces. Fastening bolts on both sides of the fixture are tightened to fix the test piece and prevent slippage; set screws pass through the fixture, test piece, and gaskets to further fix the test piece and prevent slippage. The fretting pad is placed in the limiting groove of the upper fixture's fretting pad to ensure alignment and transmit normal loads.

[0013] This invention solves the problem of mismatch between fiber-reinforced composite materials and metal material clamps, and has the advantages of ensuring the parallelism of the test specimen, the centering of the micro-movement pad, avoiding slippage of the test specimen, ensuring test accuracy, and improving the success rate of the experiment. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the overall structure of the clamp of the present invention; Figure 2 This is an assembly diagram of the fixture of the present invention; Figure 3 This is a schematic diagram of the upper clamp of the fixture of the present invention; Figure 4 A schematic diagram of the lower clamp of the invention fixture; Figure 5 This is a schematic diagram of the test loading of the fixture of the present invention; Explanation of reference numerals in the attached figures: 1-Upper clamp assembly; 2-Upper gasket; 3-Lower gasket; 4-Lower clamp assembly; 5-Micro-motion pad; 6-Test specimen; 7-Set screw; 8- Bolt and nut assembly; 801-Fastening Bolts; 802-Flat Washer; 803 - Spring Pad; 804-nut; 13-Stress ring; 14-Stress ring bolt; 15-Hydraulic upper chuck; 16-Hydraulic lower chuck. Detailed Implementation

[0015] The invention will now be further explained with reference to the accompanying drawings. Example

[0016] like Figures 1 to 5 As shown, a fiber-reinforced composite material fretting fatigue testing fixture suitable for a uniaxial testing machine is disclosed. The fixture employs a flat plate clamping structure and includes: an upper clamping assembly 1, an upper washer 2, a lower washer 3, a lower clamping assembly 4, a fretting washer 5, a set screw 7, and a bolt and nut assembly 8. The bolt and nut assembly 8 includes a fastening bolt 801, a flat washer 802, a spring washer 803, and a nut 804, all of which are 12.9 grade standard parts, facilitating maintenance and replacement.

[0017] The upper clamp assembly 1, clamped by the hydraulic upper chuck 15, is used to fix the upper part of the test piece 6 and transmit axial load. The hydraulic upper chuck 15 directly clamps the upper part of the upper clamp assembly 1 to fix the test piece 6, which can provide greater clamping force and prevent the test piece 6 from slipping compared to the traditional bolt tightening method.

[0018] A rectangular groove is machined on the inner side of the upper clamping assembly 1 for assembling the test piece 6, defining the position of the test piece 6, and ensuring that the test piece 6 is vertical. Two rectangular bosses are machined on the outer side of the upper clamping assembly 1. Four through holes are machined in a rectangular array on the bosses near the clamping end for inserting a set of fastening bolts 801. The test piece 6 is further fixed by nuts 804 to increase the clamping force and prevent the test piece from slipping.

[0019] A through hole is machined on the boss away from the clamping end. The through hole is a combination through hole with a square hole outline and a circular hole added to the center. The square hole is the same size as the micro-motion pad 5 and is used to limit the position of the micro-motion pad 5 to ensure that the micro-motion pads 5 on both sides of the test piece 6 are aligned. The boss is raised to ensure that the micro-motion pad 5 is completely fixed in the vertical direction and does not slide with the test piece 6. The circular hole is used to insert stress ring bolts 14 from both sides, so that the ends of the stress ring bolts 14 abut against the micro-motion pads 5 on both sides of the test piece 6 to provide normal load.

[0020] The lower clamp assembly 4, clamped by the hydraulic lower chuck 16, is used to fix the lower part of the test piece 6 and transmit axial load. Similarly, the hydraulic lower chuck 16 directly clamps the lower part of the lower clamp assembly 4 to fix the test piece 6. The inner side of the lower clamp assembly 4 is machined with a rectangular groove for assembling the test piece 6, defining the position of the test piece 6, and ensuring that the test piece 6 is vertical; the outer side is machined with a rectangular boss, on which four through holes are machined in a rectangular array for inserting another set of fastening bolts 801, and further fixing the test piece 6 by nuts 804.

[0021] A gap is left between the upper clamp assembly 1 and the lower clamp assembly 4 for observation during the test, while avoiding additional friction or constraints and ensuring the accuracy of the stress state of the test section.

[0022] The upper shim 2 and the lower shim 3 are both placed between two opposing test pieces 6 to isolate the two test pieces 6, prevent friction between the test pieces 6, increase the gap between the two micro-movement pads 5, and prevent interference of normal load.

[0023] One set screw 7 passes through the upper clamp assembly 1, the test piece 6, and the upper washer 2; another set screw 7 passes through the lower clamp assembly 4, the test piece 6, and the lower washer 3, further securing the test piece 6 and ensuring the fixed position between the assemblies, further preventing the test piece 6 from slipping. The end faces of the set screws 7 are all below the surface of the clamp assembly and do not contact the hydraulic upper chuck 15 or the hydraulic lower chuck 16.

[0024] The specific installation steps for this fixture are as follows: S1: Place the upper shim 2 and the lower shim 3 between the two test pieces 6 to form a sandwich structure; S2: Place the entire sandwich structure into the rectangular groove of the upper clamping assembly 1, insert the fastening bolt 801 into the flat washer 802, and then pass it through the through hole of the boss of the upper clamping assembly 1. From the other side of the upper clamping assembly 1, put on another flat washer 802 and a spring washer 803. Finally, tighten the fastening bolt 801 and nut 804 with a torque wrench to fix the upper part of the sandwich structure. S3: Align the rectangular groove of the lower clamp assembly 4 with the lower part of the sandwich structure and install it. Similarly, insert the fastening bolt 801 into the flat washer 802, and then pass it through the through hole of the boss of the lower clamp assembly 4. From the other side of the lower clamp assembly 4, put on another flat washer 802 and a spring washer 803. Tighten the fastening bolt 801 and nut 804 with a torque wrench to fix the lower part of the sandwich structure. S4: Screw in one of the upper set screws 7 to secure the upper clamp assembly 1, test piece 6, and upper washer 2; screw in one of the lower set screws 7 to secure the lower clamp assembly 4, test piece 6, and lower washer 3; S5: Insert the two micro-motion pads 5 into the micro-motion pad limiting grooves of the upper clamping assembly 1 from both sides, that is, into the square holes away from the clamping end boss.

[0025] By using the above installation method, the requirements for fretting fatigue testing of fiber-reinforced composite materials are met, ensuring the parallelism of the test specimen, the centering of the fretting pad, and providing sufficient clamping force. This can effectively prevent the test specimen from slipping, ensure test accuracy, and improve the success rate of the experiment.

[0026] Reference Figure 5 As shown, the specific loading method for the fretting fatigue test of fiber-reinforced composite materials using this fixture on a uniaxial testing machine is as follows: the upper part of the upper fixture assembly 1 is directly hydraulically clamped by the upper hydraulic chuck 15 of the uniaxial testing machine, and the lower hydraulic chuck 16 is directly hydraulically clamped by the lower part of the lower fixture assembly 4, providing a periodic axial load for the test. A stress ring is fitted onto the outside of the fixture, and the ends of two opposing stress ring bolts 14 are inserted into the through holes of the bosses on the upper fixture assembly 1 away from the clamping end, pressing against the fretting pad 5 to provide a normal load. The stress ring bolts 14 are tightened with a wrench, while the deformation of the stress ring 13 is monitored until the strain value reaches the corresponding normal stress load magnitude; at this point, the normal load meets the test conditions.

[0027] This invention solves the problem of mismatch between fiber-reinforced composite materials and metal material clamps, and has the advantages of ensuring the parallelism of the test specimen, the centering of the micro-movement pad, avoiding slippage of the test specimen, ensuring test accuracy, and improving the success rate of the experiment. Example

[0028] like Figures 1 to 5As shown, a fiber-reinforced composite material fretting fatigue testing fixture suitable for a uniaxial testing machine is disclosed. The fixture employs a flat plate clamping structure and includes: an upper clamping assembly 1, an upper washer 2, a lower washer 3, a lower clamping assembly 4, a fretting washer 5, and a bolt and nut assembly 8. The bolt and nut assembly 8 includes a fastening bolt 801, a flat washer 802, a spring washer 803, and a nut 804, all of which are 12.9 grade standard parts, facilitating maintenance and replacement.

[0029] The upper clamp assembly 1, clamped by the hydraulic upper chuck 15, is used to fix the upper part of the test piece 6 and transmit axial load. The hydraulic upper chuck 15 directly clamps the upper part of the upper clamp assembly 1 to fix the test piece 6, which can provide greater clamping force and prevent the test piece 6 from slipping compared to the traditional bolt tightening method.

[0030] A rectangular groove is machined on the inner side of the upper clamping assembly 1 for assembling the test piece 6, defining the position of the test piece 6, and ensuring that the test piece 6 is vertical. Two rectangular bosses are machined on the outer side of the upper clamping assembly 1. Four through holes are machined in a rectangular array on the bosses near the clamping end for inserting a set of fastening bolts 801. The test piece 6 is further fixed by nuts 804 to increase the clamping force and prevent the test piece from slipping.

[0031] A through hole is machined on the boss away from the clamping end. The through hole is a combination through hole with a square hole outline and a circular hole added to the center. The square hole is the same size as the micro-motion pad 5 and is used to limit the position of the micro-motion pad 5 to ensure that the micro-motion pads 5 on both sides of the test piece 6 are aligned. The boss is raised to ensure that the micro-motion pad 5 is completely fixed in the vertical direction and does not slide with the test piece 6. The circular hole is used to insert stress ring bolts 14 from both sides, so that the ends of the stress ring bolts 14 abut against the micro-motion pads 5 on both sides of the test piece 6 to provide normal load.

[0032] The lower clamp assembly 4, clamped by the hydraulic lower chuck 16, is used to fix the lower part of the test piece 6 and transmit axial load. Similarly, the hydraulic lower chuck 16 directly clamps the lower part of the lower clamp assembly 4 to fix the test piece 6. The inner side of the lower clamp assembly 4 is machined with a rectangular groove for assembling the test piece 6, defining the position of the test piece 6, and ensuring that the test piece 6 is vertical; the outer side is machined with a rectangular boss, on which four through holes are machined in a rectangular array for inserting another set of fastening bolts 801, and further fixing the test piece 6 by nuts 804.

[0033] A gap is left between the upper clamp assembly 1 and the lower clamp assembly 4 for observation during the test, while avoiding additional friction or constraints and ensuring the accuracy of the stress state of the test section.

[0034] The upper shim 2 and the lower shim 3 are both placed between two opposing test pieces 6 to isolate the two test pieces 6, prevent friction between the test pieces 6, increase the gap between the two micro-movement pads 5, and prevent interference of normal load.

[0035] The specific installation steps for this fixture are as follows: S1: Place the upper shim 2 and the lower shim 3 between the two test pieces 6 to form a sandwich structure; S2: Place the entire sandwich structure into the rectangular groove of the upper clamping assembly 1, insert the fastening bolt 801 into the flat washer 802, and then pass it through the through hole of the boss of the upper clamping assembly 1. From the other side of the upper clamping assembly 1, put on another flat washer 802 and a spring washer 803. Finally, tighten the fastening bolt 801 and nut 804 with a torque wrench to fix the upper part of the sandwich structure. S3: Align the rectangular groove of the lower clamp assembly 4 with the lower part of the sandwich structure and install it. Similarly, insert the fastening bolt 801 into the flat washer 802, and then pass it through the through hole of the boss of the lower clamp assembly 4. From the other side of the lower clamp assembly 4, put on another flat washer 802 and a spring washer 803. Tighten the fastening bolt 801 and nut 804 with a torque wrench to fix the lower part of the sandwich structure. S4: Insert the two micro-motion pads 5 into the micro-motion pad limiting grooves of the upper clamping assembly 1 from both sides, that is, into the square holes away from the clamping end boss.

[0036] By using the above installation method, the requirements for fretting fatigue testing of fiber-reinforced composite materials are met, ensuring the parallelism of the test specimen, the centering of the fretting pad, and providing sufficient clamping force. This can effectively prevent the test specimen from slipping, ensure test accuracy, and improve the success rate of the experiment.

[0037] Reference Figure 5 As shown, the specific loading method for the fretting fatigue test of fiber-reinforced composite materials using this fixture on a uniaxial testing machine is as follows: the upper part of the upper fixture assembly 1 is directly hydraulically clamped by the upper hydraulic chuck 15 of the uniaxial testing machine, and the lower hydraulic chuck 16 is directly hydraulically clamped by the lower part of the lower fixture assembly 4, providing a periodic axial load for the test. A stress ring is fitted onto the outside of the fixture, and the ends of two opposing stress ring bolts 14 are inserted into the through holes of the bosses on the upper fixture assembly 1 away from the clamping end, pressing against the fretting pad 5 to provide a normal load. The stress ring bolts 14 are tightened with a wrench, while the deformation of the stress ring 13 is monitored until the strain value reaches the corresponding normal stress load magnitude; at this point, the normal load meets the test conditions.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fretting fatigue testing fixture for fiber-reinforced composite materials suitable for a uniaxial testing machine, characterized in that, Includes an upper clamping assembly (1) with a micro-motion pad limiting device, an upper pad (2), a lower pad (3), a lower clamping assembly (4), and a micro-motion pad (5); Both the upper clamping assembly (1) and the lower clamping assembly (4) adopt a flat plate clamping structure, and the inner side of the flat plate clamping structure is provided with a rectangular groove; The upper parts of the two test pieces (6) arranged opposite to each other and the upper pad (2) located between the upper parts of the two test pieces (6) are clamped in the rectangular groove of the upper clamping assembly (1); The lower parts of the two test pieces (6) and the lower pad (3) located between the lower parts of the two test pieces (6) are clamped in the rectangular groove of the lower clamp assembly (4); The upper part of the upper clamping assembly (1) is clamped by a hydraulic upper chuck (15), and the lower part of the lower clamping assembly (4) is clamped by a hydraulic lower chuck (16). The hydraulic upper chuck (15) and the hydraulic lower chuck (16) are used to provide clamping force and transmit axial load. There is a gap between the upper clamping assembly (1) and the lower clamping assembly (4). The micro-motion pad limiting device includes a boss located on the outside of the upper clamping assembly (1) away from the clamping end, and a through hole located on the boss. The through hole is a combination through hole with a square hole outline and an added circular hole at the center. Two micro-motion pads (5) are respectively embedded into the through hole from both sides of the upper clamping assembly (1). The circular hole is used to connect the stress application rod of the stress ring assembly that provides normal load.

2. The fiber-reinforced composite material fretting fatigue test fixture according to claim 1, characterized in that, The upper clamp assembly (1) and the lower clamp assembly (4) are each provided with a boss for connecting a fastening bolt. The fastening bolt passes through the boss and is connected to a nut to further fix the two test pieces (6) and the upper shim (2) and lower shim (3) located between the two test pieces (6).

3. The fiber-reinforced composite material fretting fatigue test fixture according to claim 1, characterized in that, The upper clamp assembly (1) and the lower clamp assembly (4) are respectively provided with set screws (7) that pass through the clamp assembly, the two test pieces (6) and the gasket between them.

4. The fiber-reinforced composite material fretting fatigue test fixture according to claim 2, characterized in that, The boss used for connecting and fastening bolts has four connecting through holes arranged in a rectangular array.

5. The fiber-reinforced composite material fretting fatigue test fixture according to claim 3, characterized in that, The set screw (7) is located near the clamping end, and the end face of the set screw (7) is lower than the surface of the clamping assembly.

6. The fiber-reinforced composite material fretting fatigue test fixture according to any one of claims 1-5, characterized in that, The height of the boss on the outer side of the upper clamping assembly (1) away from the clamping end is such that the micro-motion pad (5) is fully embedded in the through hole.

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