A device and method for testing the shear performance of composite materials in a heated environment

Abstract

The present application relates to a kind of device and method for testing the shear performance of composite material under heating environment, it is related to test equipment field, including clamp, cushion block, cover plate, heating device, heat insulation box, DIC camera and acoustic emission waveguide rod, two cushion blocks are clamped test piece one end, cover plate is fixed in clamp with cushion block by bolt to make clamp to test piece carry out longitudinal shear tensile;Heating device is erected in clamp to heat test piece, heat insulation box is covered in clamp and heating device to avoid heat loss, DIC camera is placed in the window of heat insulation box with the transparent material of filtering colored light wave, the strain state of the test piece with speckle side is observed, acoustic emission waveguide rod is abutted on the other side of test piece to measure acoustic emission signal, the present application has the advantages that the shear and longitudinal tensile strain results of effective area of test piece are compared and analyzed using DIC technology, to determine whether effective area is in shear state during loading process, and to determine the shear strength of test piece.

Description

Technical Field

[0001] This invention relates to the field of testing equipment technology, and in particular to an apparatus and method for testing the shear properties of composite materials under heating conditions. Background Technology

[0002] Currently, the standards for testing the shear properties of composite materials are mainly based on ASTM D5379 and ASTM D7078 published by the American Society for Testing and Materials (ASTM). The fixtures used in ASTM D5379 primarily employ end-face loading, which may damage the ends of the specimen and affect the experimental results. The fixtures used in ASTM D7078 primarily employ pure friction loading, which does not damage the ends of the specimen and is suitable for static shear tests. However, directly using them for fatigue tests can lead to bolt loosening and test failure. Furthermore, the lack of guide rails between the upper and lower shear blocks can affect the alignment of the fixtures during fatigue testing.

[0003] In addition, the commonly used standards for calculating the shear strength of composite materials are based on the shear stress corresponding to 50,000 microstrains. For some composite materials, such values ​​are too conservative and cannot truly characterize the shear strength of the composite material. Furthermore, most commonly used shear fixtures are used at room temperature. If a shear test is required in a heated environment, the fixture needs to be placed in an environmental temperature chamber. However, it is inconvenient to test the specimen by covering it with a temperature chamber.

[0004] Therefore, to address the above shortcomings, there is a need to provide an apparatus and method for testing the shear properties of composite materials under heating conditions. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] The technical problem to be solved by the present invention is how to conduct accurate tests and data detection on specimens under heating conditions.

[0007] (II) Technical Solution

[0008] To address the aforementioned technical problems, this invention provides an apparatus for testing the shear properties of composite materials under heating conditions, comprising a clamp, pads, a cover plate, a heating device, a heat insulation chamber, a DIC camera, and an acoustic emission waveguide. Two pads clamp one end of the specimen, and the cover plate fixes the pads inside the clamp so that the clamp can perform longitudinal shearing and tensile testing on the specimen. The heating device is mounted outside the clamp to heat the specimen, and the heat insulation chamber covers the clamp and heating device to prevent heat loss. The DIC camera is placed outside the window of the heat insulation chamber, which contains a transparent material that filters colored light waves, to observe the strain state of the speckled side of the specimen. The acoustic emission waveguide abuts against the other side of the specimen to measure the acoustic emission signal.

[0009] As a further explanation of the present invention, preferably, the transparent material for filtering colored light waves is high-temperature resistant glass with a filter attached, and the side of the glass away from the filter is fixed to the window of the heat insulation box.

[0010] As a further explanation of the present invention, preferably, the filter on the glass filters red light and retains blue-green light.

[0011] As a further explanation of the present invention, preferably, the clamp includes an upper shear body and a lower shear body, both of which are L-shaped structures with their protrusions interlocking vertically; clamping grooves are provided on the horizontally contacting sides of the protrusions of the upper and lower shear bodies, and the pad and the specimen are located in the clamping grooves.

[0012] As a further explanation of the present invention, preferably, the cover plate presses the pad and the specimen into the clamping groove, and a bolt is inserted into the cover plate. The bolt passes through one end of the clamp and is threaded with a nut so that the cover plate and the pad are in an interference fit.

[0013] As a further explanation of the present invention, preferably, the cover plate and the pad are fixed together by screws.

[0014] As a further explanation of the present invention, preferably, the contact surface between the pad and the test piece is provided with a plurality of rough block groups to roughen the surface of the pad.

[0015] As a further explanation of the present invention, preferably, cylindrical guide rods are fixedly connected to one side of both the upper and lower shear bodies, and linear bearings are fixedly connected to the other side of both the upper and lower shear bodies, with opposing guide rods inserted into the linear bearings to connect the upper and lower shear bodies.

[0016] As a further explanation of the present invention, preferably, the specimen adopts a standard V-shaped sheet structure made of composite material, and the pads are clamped at the ends of the specimen located on both sides of the V-shaped opening.

[0017] The present invention also provides a method for using a composite material shear performance testing device under heating conditions, comprising the following steps:

[0018] Ⅰ. Install the spacers in the clamping groove. After placing the specimen between the spacers, place the cover plate on top and tighten the bolts to clamp the specimen with the spacers.

[0019] II. Fix the heating device to the clamp, and then put the heat insulation box over the clamp and the heating device;

[0020] III. Set up the DIC camera on the glass, insert the acoustic emission waveguide into the heat insulation box, so that one end of the acoustic emission waveguide is attached to the surface of the specimen, and the other end of the acoustic emission waveguide is connected to the acoustic emission measuring device;

[0021] IV. Start the equipment to longitudinally stretch the specimen in the fixture; use a DIC camera to measure the strain in the effective area of ​​the specimen through the glass; use an acoustic emission measuring device to measure the acoustic emission signal during the test; based on the DIC measurement results, compare the magnitudes of the shear strain and the longitudinal tensile strain in the effective area of ​​the specimen. When the difference between the shear strain and the longitudinal tensile strain in the limited area of ​​the specimen is large, it is considered to be in the shear stage. When the longitudinal tensile strain increases instantaneously compared to the shear strain, it is considered to be shear failure, and the corresponding shear stress is the shear strength.

[0022] (III) Beneficial Effects

[0023] The above-described technical solution of the present invention has the following advantages:

[0024] This invention designs a novel testing device that can perform static and fatigue tests on standard V-groove composite material specimens under heating conditions. It utilizes a double-nut locking mechanism to prevent specimen loosening during fatigue, employs interlocking shear bodies to achieve a negative stress ratio shear fatigue condition, uses DIC measurement technology to measure the full-field strain of the specimen's effective area, and uses acoustic emission technology to characterize damage changes during static and fatigue tests. This allows for accurate determination of whether the effective area of ​​the specimen is in a shear state during loading, thereby determining the specimen's shear strength. Attached Figure Description

[0025] Figure 1 This is an exploded view of the present invention;

[0026] Figure 2 This is a front view of the fixture of the present invention;

[0027] Figure 3 This is a diagram showing the specimen clamping state of the present invention;

[0028] Figure 4 This is an exploded view of the mounting structure of the pad and cover plate of the present invention;

[0029] Figure 5 This is a structural diagram of the upper shear body of the present invention;

[0030] Figure 6 This is a structural diagram of the pad block of the present invention;

[0031] Figure 7 This is an assembly effect diagram of the present invention.

[0032] In the diagram: 1. Fixture; 11. Upper shear body; 12. Lower shear body; 13. Grip groove; 14. Guide rod; 15. Linear bearing; 16. Clamping rod; 2. Pad block; 21. Rough block group; 3. Cover plate; 4. Specimen; 5. Heating device; 51. Rod support; 52. Heating rod; 6. Insulation box; 61. Locking pair; 62. Glass; 7. DIC camera; 8. Acoustic emission waveguide rod. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] An apparatus for testing the shear properties of composite materials under heating conditions, combined with Figure 1 , Figure 6 The device includes a clamp 1, pads 2, cover plate 3, heating device 5, heat insulation box 6, DIC camera 7, and acoustic emission waveguide 8. Two pads 2 clamp one end of the specimen 4, and the cover plate 3 fixes the pads 2 inside the clamp 1. The heating device 5 is mounted outside the clamp 1, and the heat insulation box 6 covers the clamp 1 and the heating device 5. The DIC camera 7 abuts against one side of the heat insulation box 6, and the acoustic emission waveguide 8 abuts against the other side of the heat insulation box 6 located on the DIC camera 7.

[0035] Combination Figure 2 , Figure 5 The fixture 1 includes an upper shear body 11 and a lower shear body 12. Both the upper shear body 11 and the lower shear body 12 are L-shaped structures with their protrusions interlocking vertically. A clamping groove 13 is provided on the horizontally contacting sides of the protrusions of the upper shear body 11 and the lower shear body 12, allowing the specimen 4 to be placed within the groove 3. The specimen 4 is a standard V-shaped sheet structure made of composite material. Columnar clamping rods 16 are fixedly connected to both the upper shear body 11 and the lower shear body 12 for connection to the tensile testing machine.

[0036] Combination Figure 4 , Figure 5 The clamping groove 13 is a square groove, and the pad 2 is a square metal block. The length and width of the pad 2 are the same as the length and width of the clamping groove 13. Figure 6 The contact surface between the pad 2 and the specimen 4 is provided with several rough block groups 21 to roughen the surface of the pad 2. The side of the two pads 2 with the rough block groups 21 contacts the two sides of the specimen 4 located on the V-shaped opening side and is embedded in the clamping groove 13, so that both the pad 2 and the specimen 4 are located in the clamping groove 13, thereby achieving the initial clamping of the specimen 4.

[0037] Combination Figure 3 , Figure 4A bolt is inserted into the cover plate 3, and a nut is threaded onto one end of the bolt through the clamp 1. By tightening the nut, the cover plate 3 and the pad 2 are pressurized together, and the double nuts prevent loosening. This ensures that the pad 2 and the specimen 4 are pressurized together within the clamping groove 13, achieving stable clamping of the specimen 4. Furthermore, the cover plate 3 and the pad 2, as well as the pad 2 and the clamp 1, are all fixedly connected by screws to prevent the specimen 4 from pulling the pad 2 out of the clamping groove 13 during the test.

[0038] Combination Figure 3 , Figure 5 A cylindrical guide rod 14 is fixedly connected to one side of both the upper shear body 11 and the lower shear body 12, and a linear bearing 15 is fixedly connected to the other side of both. The guide rod of the upper shear body 11 is inserted into the linear bearing of the opposite lower shear body 12, and the guide rod of the lower shear body 12 is inserted into the linear bearing of the opposite upper shear body 11, so that the upper shear body 11 and the lower shear body 12 are connected and can slide longitudinally. The guide rod 14 and the linear bearing 15 not only allow the fixture 1 to move smoothly up and down during the experiment, but also limit the lateral misalignment of the fixture 1, ensuring that the fixture always has good centering and that the specimen 4 is only subjected to shear force.

[0039] Combination Figure 1 , Figure 2 The heating device 5 includes a rod support 51 and heating rods 52. The rod support 51 is fixed to the top of the upper shear body 11 located on both sides of the specimen 4. Several heating rods 52 are fixed to both ends of the rod support 51 along its length. The heating rods 52 are spiral heating wire structures. The heating rods 52 are close to the clamp 1 so that as much heat as possible is transferred to the specimen 4.

[0040] Combination Figure 1 , Figure 7 The heat insulation box 6 is divided into front and rear sections, both made of high-temperature resistant insulation board. The two sections of the heat insulation box 6 are connected by a locking joint 61. By enclosing the front and rear sections of the heat insulation box 6 around the clamp 1 and the heating device 5, heat loss can be prevented. The front section of the heat insulation box 6 has a window, and a high-temperature resistant transparent glass 62 is fixed to the window. A filter that can filter red light waves and retain blue-green light waves is affixed to the glass 62. The DIC camera is placed outside the glass 62 in the front section of the heat insulation box 6 to reduce the influence of the heating environment on the DIC measurement results. The rear section of the heat insulation box 6 has a hole, into which the acoustic emission waveguide rod 8 can be inserted to contact the specimen 4.

[0041] With the above structure, after the device is placed on the tensile testing machine, the upper shear body 11 and the lower shear body 12 are pulled to subject the two ends of the specimen 4 to pure frictional forces from different directions of the pads 2 inside the different shear bodies, thereby achieving the effect of applying shear force to the specimen 4, reducing the adverse effects of end loading on the specimen 4, and using a double nut locking method to prevent the specimen from loosening during shear fatigue; the interlocking shear bodies can realize the shear fatigue condition with negative stress ratio; the heating device, heat insulation device, shear fixture, and high-temperature resistant and light-filtering transparent material window are used to test the shear performance of composite materials under heating environment and measure the strain field using DIC technology.

[0042] The present invention also provides a method for using a composite material shear performance testing device under heating conditions, comprising the following steps:

[0043] I. First, place a pad 2 in the clamping groove 13 of both the upper shear body 11 and the lower shear body 12. After fixing them with screws, combine the upper shear body 11 and the lower shear body 12 together through the guide rod 14 and the linear bearing 15. Then, put the specimen 4 in. Then, put another pad 2, which is fixed to the cover plate 3 with screws, into the clamping groove 13. Do not tighten the bolts first. After adjusting the position of the specimen 4, tighten the bolts and nuts so that the pad 2 clamps the specimen 4.

[0044] II. Install the clamp 1 on the testing machine via the clamping rod 16, then fix the heating device 5 on the clamp 1, then put the heat insulation box 6 over the clamp 1 and the heating device 5, and fix the two parts of the heat insulation box 6 together through the locking pair 61. At this time, the heat insulation box 6 is hung on the rod support 51.

[0045] III. Set up the DIC camera 7 on the glass 62, insert the acoustic emission waveguide 8 into the hole of the heat insulation box 6, so that one end of the acoustic emission waveguide 8 is attached to the surface of the specimen 4, and the other end of the acoustic emission waveguide 8 is connected to the acoustic emission measuring device.

[0046] IV. Start the equipment to allow clamp 1 to shear specimen 4; DIC camera 7 measures the strain field of the effective area of ​​specimen 4 through glass 62; acoustic emission measuring device measures the acoustic emission signal during the test; based on the DIC measurement results, compare the magnitude of shear strain and longitudinal tensile strain in the effective area of ​​specimen 4. When the ratio of shear strain to longitudinal tensile strain in the effective area of ​​specimen 4 is large (when the shear strain is much greater than the longitudinal strain), it is considered to be in the shear stage. When the longitudinal tensile strain increases instantaneously compared with the shear strain or the shear load drops suddenly, it is considered to be shear failure, and the corresponding shear stress is the shear strength.

[0047] Conventional composite material shear test standards stipulate that if the test shear strain exceeds 50,000 microstrains, the stress value corresponding to 50,000 microstrains is taken as the shear strength. However, in practice, it has been found that some composite materials remain in a shear state after being loaded to 50,000 microstrains. Therefore, the shear strength value taken according to the standard may be too small. Using the method provided in this invention, even if the shear strain exceeds 50,000 during continued loading, the strain measured by DIC can be used to determine whether the specimen is still in a pure shear state. If the specimen fails in a pure shear state, the shear stress at failure is considered the shear strength. Compared to the shear strength corresponding to 50,000 microstrains specified in the standard, this method more accurately reflects the shear performance of specimen 4. Therefore, by comparing and analyzing the shear and longitudinal tensile strain results of the effective area of ​​specimen 4 using DIC technology, and combining the damage fracture information measured by acoustic wave data, it is determined whether the effective area is in a shear state during loading, and this is used to determine the shear strength of specimen 4. The resulting shear strength data is the most accurate.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for testing the shear properties of a composite material in a heated environment, characterized by: The device comprises a clamp (1), a cushion block (2), a cover plate (3), a heating device (5), a heat insulation box (6), a DIC camera (7) and an acoustic emission waveguide rod (8). Two cushion blocks (2) hold one end of a test piece (4), and the cover plate (3) fixes the cushion blocks (2) in the clamp (1) to make the clamp (1) longitudinally shear and stretch the test piece (4). The heating device (5) comprises a rod support (51) and a heating rod (52). The rod support (51) is fixed on the clamps (1) on both sides of the test piece (4), and several heating rods (52) are fixed on both ends of the length direction of the rod support (51). The heating rod (52) is a spiral heating wire structure, and is close to the clamp (1) to heat the test piece (4). The heat insulation box (6) covers the clamp (1) and the heating device (5) to avoid heat loss. The DIC camera (7) is placed outside the window of the heat insulation box (6) filled with transparent material filtering colored light waves to observe the strain state of the test piece (4) with a speckle surface. The acoustic emission waveguide rod (8) abuts against the other side of the test piece (4) to measure the acoustic emission signal.

2. The device for testing the shearing property of composite material in a heating environment according to claim 1, characterized in that: The transparent material filtering colored light waves is a high-temperature-resistant glass (62) with a filter. The glass (62) far from the filter is fixed on the window of the heat insulation box (6).

3. The apparatus for testing the shearing property of the composite material in a heated environment according to claim 2, wherein: The filter on the glass (62) filters red light and retains blue-green light.

4. The apparatus for testing the shearing property of the composite material in a heated environment according to claim 1, wherein: The clamp (1) comprises an upper shear body (11) and a lower shear body (12). Both the upper shear body (11) and the lower shear body (12) are L-shaped structures, and the protruding parts thereof are staggered and buckled in an up-down manner. A clamping groove (13) is formed on the side surface of the protruding part of the upper shear body (11) and the lower shear body (12) in contact with each other in the horizontal direction. The cushion block (2) and the test piece (4) are located in the clamping groove (13).

5. The apparatus for testing the shearing property of the composite material in a heated environment according to claim 4, wherein: The cover plate (3) presses the cushion block (2) and the test piece (4) into the clamping groove (13). A bolt is inserted into the cover plate (3), and a nut is threadedly connected to one end of the clamp (1) through the bolt to make the cover plate (3) and the cushion block (2) have an interference fit.

6. The apparatus for testing the shearing property of the composite material in a heated environment according to claim 5, wherein: The cover plate (3) and the cushion block (2) are fixed by a screw rod.

7. The apparatus for testing the shearing property of the composite material in a heated environment according to claim 5, wherein: A plurality of rough block groups are arranged on the interface between the cushion block (2) and the test piece (4) to make the surface of the cushion block (2) rough.

8. The apparatus for testing the shearing property of the composite material in a heated environment according to claim 7, wherein: A cylindrical guide rod (14) is fixed on one side of the upper shear body (11) and the lower shear body (12), and a linear bearing (15) is fixed on the other side of the upper shear body (11) and the lower shear body (12). The opposite guide rods (14) are inserted into the linear bearings (15) to connect the upper shear body (11) and the lower shear body (12).

9. The apparatus for testing the shearing property of the composite material in a heated environment according to claim 8, wherein: The test piece (4) is made of a standard V-shaped sheet structure of composite material, and the cushion block (2) is clamped at the end of the test piece (4) located on both sides of the V-shaped opening.

10. The method of using a device for testing the shear properties of a composite material in a heated environment according to claim 9, wherein: The device comprises the following steps, Ⅰ. Install the cushion block (2) in the clamping groove (13), and then place the cover plate (3) after the test piece (4) is placed between the cushion blocks (2) and tighten the bolt to make the cushion block (2) clamp the test piece (4); Ⅱ. Fix the heating device (5) on the clamp (1), and then cover the heat insulation box (6) outside the clamp (1) and the heating device (5); III. Set up the DIC camera at the glass (62), and insert the acoustic emission waveguide (8) into the heat insulation box (6) so that one end of the acoustic emission waveguide (8) is attached to the surface of the test piece (4) and the other end of the acoustic emission waveguide (8) is connected to the acoustic emission measuring device; IV. Start the equipment to longitudinally stretch the test piece (4); the DIC camera measures the strain of the effective area of the test piece (4) through the glass (62); the acoustic emission measuring device measures the acoustic emission signal in the test process; according to the DIC measurement result, the size of the shear strain and the longitudinal stretching strain at the effective area of the test piece (4) is compared, when the difference between the shear strain and the longitudinal stretching strain in the limited area of the test piece (4) is large, it is considered to be in the shear stage, when the longitudinal stretching strain instantaneously increases compared with the shear strain, it is considered to be shear failure, and the corresponding shear stress is the shear strength.

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