Specimens, fixtures, and methods for testing the interlaminar shear properties of fiber-reinforced composites

Abstract

This application discloses a specimen, fixture, and method for testing the interlaminar shear properties of fiber-reinforced composite materials. The specimen is integrally molded, generally strip-shaped and flat, with multiple stacked fiber layers inside. The thickness plane of the specimen is approximately parallel to the plane of the fiber layers. The specimen has a force-bearing portion at its center. Along its length, the specimen has a first clamping and fixing portion and a second clamping and fixing portion at each end. A first connecting portion is formed between the first clamping and fixing portion and the force-bearing portion, and a second connecting portion is formed between the second clamping and fixing portion and the force-bearing portion. The specimen is clamped and fixed to the testing equipment using the fixture, and then the testing equipment applies a tensile force to the specimen to perform a tensile test, resulting in good test accuracy. Furthermore, the specimen has a simple and compact structure, is easy to manufacture, and the fixture provides flexible and convenient assembly for the specimen.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new materials, in particular to a sample, clamp and method for testing interlaminar shear performance of fiber reinforced composite material. BACKGROUND

[0002] Fiber reinforced composite materials, such as carbon fiber reinforced ceramic matrix composite (C / SiC), have been widely used in aerospace power systems, thermal protection fields, and fields of automobiles, airplanes and high-speed trains, etc. due to their excellent mechanical properties. Since the fiber preform is laid and woven during the preparation of the fiber reinforced composite material, the interlaminar shear performance of the material is lower than the axial tensile and compressive performance, so the fiber reinforced composite material is prone to interlaminar debonding separation under extreme conditions, resulting in loss of performance. Therefore, it is necessary to study and test the interlaminar shear performance of the fiber reinforced composite material. The existing test methods mainly include double-notch compression method, short beam shear method, four-point bending method, etc. The double-notch compression method needs an additional fixed plate to fix the sample to prevent the sample from turning over during the test, but the actual operation is difficult to assemble and fix the sample. Moreover, the double-notch compression method is cracked by compression, which is not directly consistent with the tearing in the actual use of the material, so the test result is not very accurate. The short beam shear method and the four-point bending method load the force perpendicular to the material layer direction, and the deflection difference changes in the thickness direction of different layers, which is more inconsistent with the tearing in the actual use of the material, and cannot directly and accurately obtain the bonding strength between the layers. In addition, the sample size used in these test methods is generally large, which can easily cause material waste, and the accuracy of the material performance test under large size is not high. SUMMARY

[0003] The purpose of the present application is to provide a sample, clamp and method for testing interlaminar shear performance of fiber reinforced composite material, which has better test accuracy.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical solutions.

[0005] The present application provides a sample for testing interlaminar shear performance of fiber reinforced composite material, which is integrally formed and substantially in the shape of a strip, has a plurality of fiber layers stacked and arranged inside, and the thickness plane of the sample is substantially parallel to the plane where the fiber layers are located. The central part of the sample has a stress part, and the sample has a first clamping and fixing part and a second clamping and fixing part at both ends in the length direction, respectively. The first clamping and fixing part and the stress part have a first connecting part therebetween, and the second clamping and fixing part and the stress part have a second connecting part therebetween.

[0006] In an embodiment, the first clamping and fixing part and the second clamping and fixing part are both in the shape of a dovetail.

[0007] In an embodiment, the first connecting part has a first end connected with the force receiving part and a second end connected with the first clamping fixing part, and the width of the first connecting part gradually increases from the first end to the second end; the second connecting part has a first end connected with the force receiving part and a second end connected with the second clamping fixing part, and the width of the second connecting part gradually increases from the first end to the second end.

[0008] In an embodiment, the first connecting part has a first groove at the connection with the force receiving part, and the second connecting part has a second groove at the connection with the force receiving part; the sample has a first face and a second face in the thickness direction, the first groove is recessed from the first face to the second face, and the second groove is recessed from the second face to the first face; the sample is mirror-symmetric in the length direction and inversion-symmetric in the width direction.

[0009] In an embodiment, the depth of the first groove and the depth of the second groove are both greater than half the thickness of the sample.

[0010] In an embodiment, the vertical distance between the bottom of the first groove and the bottom of the second groove is equivalent to the thickness of one or two fiber layers.

[0011] The embodiments of the present application also provide another kind of clamp for testing the interlaminar shear performance of a fiber-reinforced composite material, which is used for clamping and fixing a sample to test the interlaminar shear performance of the sample. The clamp is generally columnar, has a threaded outer surface at the first end, and has a clamping and fixing groove recessed inwardly at the outer surface of the second end. The two sides of the clamping and fixing groove are provided with pin holes, and the vertical distance between the connecting line of the two pin holes and the bottom surface of the clamping and fixing groove is equivalent to the thickness of the sample. The pin holes are matched with pin shafts to fix the sample in the clamping and fixing groove.

[0012] In an embodiment, the clamping and fixing groove is dovetail-shaped and matches the shape of the sample.

[0013] The embodiments of the present application also provide a method for testing the interlaminar shear performance of a fiber-reinforced composite material. Two clamps are used to fix a sample in a mechanical performance testing machine. The clamps are the clamps for testing the interlaminar shear performance of a fiber-reinforced composite material as described above, and the sample is the sample for testing the interlaminar shear performance of a fiber-reinforced composite material as described above. The sample is subjected to a tensile test by using the mechanical performance testing machine.

[0014] In an embodiment, the sample is subjected to high-temperature oxidation in advance.

[0015] In summary, the beneficial effects of the present application are: the sample, clamp and method for testing the interlaminar shear performance of the fiber-reinforced composite material disclosed in the present application, the sample is clamped and fixed on the testing equipment by the clamp, and then the testing equipment applies a tensile force to the sample for tensile testing. The tensile force is parallel to the plane of the thickness of the sample and the plane of the fiber lay-up in the sample, so that at the end of the test process, the stress part of the center part of the sample will tear, which is consistent with the natural tearing of the material in the actual use process. The test accuracy is better. Moreover, the structure of the sample is simple and small, easy to manufacture, and the clamp is flexible and convenient for assembling the sample. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the following embodiment description will be briefly introduced. It is obvious that the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0017] Figure 1 A perspective structural schematic view of a sample for testing the interlaminar shear performance of a fiber-reinforced composite material is provided for the first embodiment of the present application.

[0018] Figure 2 A perspective structural schematic view of a clamp for testing the interlaminar shear performance of a fiber-reinforced composite material is provided for the second embodiment of the present application.

[0019] Figure 3 An assembly schematic view of the sample and the clamp in a method for testing the interlaminar shear performance of a fiber-reinforced composite material is provided for the third embodiment of the present application.

[0020] Figure 4 A load-displacement curve diagram obtained by testing a C / SiC material by the method for testing the interlaminar shear performance of a fiber-reinforced composite material provided in the third embodiment of the present application.

[0021] Figure 5 A load-displacement curve diagram obtained by testing a C / SiC material by a prior art testing method.

[0022] Main reference signs:

[0023] Sample 1, stress part 10,

[0024] First clamping and fixing part 11, second clamping and fixing part 12,

[0025] First engaging part 13, second engaging part 14,

[0026] First groove 15, second groove 16,

[0027] First face 17, second face 18,

[0028] Clamp 2, thread 20,

[0029] Clamping groove 21, pin hole 22,

[0030] Pin shaft 23, first inflection point K1,

[0031] First inflection point K2, third inflection point K3. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, the orientation words such as "upper", "lower", "left" and "right" can be the direction of the actual use or working state of the device, or the direction of the drawing surface in the reference drawings, or the direction of the two relative directions; and "inner" and "outer" are relative to the profile of the device.

[0033] Please refer to Figure 1 As shown in the drawings, the first embodiment of the present application provides a sample 1 for testing the interlaminar shear performance of a fiber-reinforced composite material. The sample 1 is integrally formed and has a generally strip-shaped flat shape, and has a plurality of fiber plies arranged in layers inside. The thickness plane of the sample 1 is substantially parallel to the plane where the fiber plies are located. The central part of the sample 1 has a stress part 10. In the length direction of the sample 1, the two ends respectively have a first clamping fixing part 11 and a second clamping fixing part 12. The first clamping fixing part 11 and the stress part 10 have a first connecting part 13 therebetween. The second clamping fixing part 12 and the stress part 10 have a second connecting part 14 therebetween.

[0034] The sample 1 can be clamped and fixed on a testing device through the first clamping fixing part 11 and the second clamping fixing part 12. Then the testing device applies a tensile force to the sample 1 to perform a tensile test. The tensile force is parallel to the plane where the thickness of the sample 1 is located and the plane where the fiber plies of the sample 1 are located. Therefore, at the end of the test process, the stress part 10 at the central part of the sample 1 will tear, which is consistent with the natural tearing of the material in the general actual use process, and the accuracy of the test is good.

[0035] In an embodiment, the first clamping fixing part 11 and the second clamping fixing part 12 are dovetail-shaped. In this way, the clamping and fixing of the test sample 1 in the testing equipment is facilitated.

[0036] In an embodiment, the first connecting part 13 has a first end connected with the force receiving part 10 and a second end connected with the first clamping fixing part 11, and the width of the first connecting part 13 gradually increases from the first end to the second end; the second connecting part 14 has a first end connected with the force receiving part 10 and a second end connected with the second clamping fixing part 12, and the width of the second connecting part 14 gradually increases from the first end to the second end. In this way, on the one hand, the clamping and fixing of the test sample 1 in the testing equipment is facilitated, and on the other hand, the force applied by the testing equipment is conducted to the force receiving part 10 at the center of the test sample 1 as much as possible.

[0037] In an embodiment, the first connecting part 13 has a first groove 15 at the connection with the force receiving part 10, and the second connecting part 14 has a second groove 16 at the connection with the force receiving part 10; the test sample 1 has a first face 17 and a second face 18 opposite in the thickness direction, the first groove 15 is recessed from the first face 17 to the second face 18, and the second groove 16 is recessed from the second face 18 to the first face 17; the test sample 1 is mirror-symmetric in the length direction and flip-symmetric in the width direction. In this way, when the testing equipment applies a tensile force through the two ends of the test sample 1 for testing, the force applied by the testing equipment can be concentrated on the force receiving part 10 at the center of the test sample 1.

[0038] In an embodiment, the depth of the first groove 15 and the second groove 16 is greater than half the thickness of the test sample 1. In this way, the force applied by the testing equipment can be more concentrated on the center of the force receiving part 10 at the center of the test sample 1.

[0039] In an embodiment, the vertical distance between the bottom of the first groove 15 and the bottom of the second groove 16 is equivalent to the thickness of one or two fiber plies. In this way, the force applied by the testing equipment can be concentrated on the fiber plies at the center of the force receiving part 10 at the center of the test sample 1 as much as possible, so that the fiber plies are torn, and the state of tearing of the fiber-reinforced composite material in the actual use is better approached.

[0040] The test sample 1 can be directly and integrally formed; or a cubic block in a strip-shaped flat shape can be first made, and then a diamond tool is used for low-speed grinding to make it into the above shape, so as to ensure the size accuracy while avoiding material damage. The test sample 1 described in the present application has a simple and compact structure and is easy to make.

[0041] Please refer to Figure 2As shown, the second embodiment of the present application provides a fixture 2 for testing the interlaminar shear performance of a fiber-reinforced composite material, which is used to clamp and fix a sample 1 to test the interlaminar shear performance of the sample 1. The fixture 2 is generally columnar, the first end outer surface is provided with a thread 20, and the second end outer surface is inwardly recessed to form a clamping and fixing groove 21. The clamping and fixing groove 21 is provided with pin holes 22 on both sides, and the perpendicular distance between the connecting line of the two pin holes 22 and the bottom surface of the clamping and fixing groove 21 is equivalent to the thickness of the sample 1. The pin holes 22 are matched with pin shafts 23 (see Figure 3 The sample 1 is fixed in the clamping and fixing groove 21.

[0042] The fixture 2 can be easily matched with a testing device through the thread 20 of the first end, so as to clamp and fix the sample 1 through the clamping and fixing groove 21 of the second end, and then fix the sample 1 on the testing device. Then, the testing device applies a tensile force to the sample 1 to perform a tensile test. The tensile force is parallel to the plane where the thickness of the sample 1 is located and the plane where the fiber lay-up of the sample 1 is located. Therefore, at the end of the test process, the stress part 10 at the center of the sample 1 will be torn, which is consistent with the natural tearing of the material in the actual use process, and the accuracy of the test is better. Moreover, the centering during assembly is better guaranteed to ensure the accuracy of the test.

[0043] In an embodiment, the clamping and fixing groove 21 is dovetail-shaped, which is matched with the shape of the sample 1. In this way, the sample 1 is more easily fixed.

[0044] Please refer to Figure 3 As shown, the third embodiment of the present application provides a method for testing the interlaminar shear performance of a fiber-reinforced composite material, which uses two fixtures 2 to fix a sample 1 on a mechanical property testing machine (not shown). The fixture 2 is the fixture 2 for testing the interlaminar shear performance of a fiber-reinforced composite material as described above, and the sample 1 is the sample 1 for testing the interlaminar shear performance of a fiber-reinforced composite material as described above. The mechanical property testing machine is used to perform a tensile test on the sample 1.

[0045] The mechanical property testing machine can be an MTS universal testing machine, which has multiple test modes. The present application uses a tensile mode to perform a tensile test on the sample 1. The applicant tests a carbon fiber-reinforced ceramic matrix composite material (C / SiC), and obtains a load-displacement curve as shown in Figure 4The load-displacement curve is shown in FIG. 6. There are three inflection points from left to right. When the force of the testing equipment is just applied, the displacement of the sample 1 is not obvious, but the load continues to rise rapidly, and the slope of the load-displacement curve is large. The first inflection point K1, which is about 65N of the load, the matrix of the fiber layer of the sample 1 begins to crack, the displacement begins to be obvious, and the slope of the load-displacement curve obviously becomes smaller. The second inflection point K2, which is about 110N of the load, the interface of the fiber layer of the sample 1 cracks and shear slip occurs, the load-displacement curve appears a horizontal section of the displacement increasing without the load changing, and then the load and the displacement increase synchronously, and the slope after the second inflection point K2 (1.488KN / mm) obtained by linear fitting of origin is greater than the slope before the second inflection point K2 (0.828KN / mm), which is consistent with the change of the load-displacement curve obtained by Liu Wei in the study of the strengthening effect of the interlaminar shear strength of C / SiC composite material (as shown in FIG. 7). Figure 5 The third inflection point K3, which is about 321N of the load, the material occurs cliff-like separation failure, and there is no several secondary peak values of tensile failure, mainly because the interface is broken when the fiber is sheared and fractured, which causes the transverse fiber to be debonded and pulled out, and loses the bridging load bearing effect. At this time, it is the maximum load of the tensile test, and the interlaminar shear strength is calculated according to the interlaminar shear strength formula (σ t is the interlaminar shear strength, F max is the maximum load, W and B are the width and length of the force receiving part 10, respectively) is 11.46MPa, which is of the same order of magnitude as the test results of 16-18MPa of Dong Shibo, 5-8MPa of Cao Xiaoyu, and 18MPa of Zhang Chengyu, and the difference in specific values is caused by the slight difference in the specific process of the sample 1 in the test method of each person. Therefore, the method for testing the interlaminar shear performance of the fiber reinforced composite material described in the application can be used to test the interlaminar shear performance of the fiber reinforced composite material, and the test result is more accurate.

[0046] In an embodiment, the method for testing the interlaminar shear performance of the fiber reinforced composite material described in the application further comprises pre-oxidizing the sample 1 at high temperature. After the sample 1 is oxidized at high temperature, the method for testing the interlaminar shear performance of the fiber reinforced composite material described in the application is used for tensile test, and the test result obtained is also more accurate, the fracture of the sample 1 is flat, the fiber is not debonded, the internal matrix texture is obvious, and the interlaminar shear fracture characteristics are obviously met.

[0047] In summary, the beneficial effects of the present application are: the sample, clamp and method for testing the interlaminar shear performance of the fiber-reinforced composite material disclosed in the present application, the sample is clamped and fixed on the testing equipment by the clamp, then the testing equipment applies a tensile force to the sample for tensile testing, and the tensile force is parallel to the plane of the thickness of the sample and the plane of the fiber lay-up in the sample, so that at the end of the test process, the stress part 10 in the center part of the sample will tear, which is consistent with the natural tearing of the material in the actual use process, and the accuracy of the test is better. Moreover, the structure of the sample is simple and small, easy to manufacture, and the assembly of the clamp on the sample is flexible and convenient.

[0048] In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0049] The technical solutions provided by the embodiments of the present application are described in detail above, and the principles and implementation modes of the present application are described by applying specific examples; the above description of the embodiments is only used to help understand the method of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed, and the above description should not be understood as a limitation of the present application.

Claims

1. A test specimen for testing interlaminar shear properties of a fiber reinforced composite material, characterized by, The sample is integrally formed and substantially in the shape of a flat strip, has a plurality of fiber plies arranged in layers inside, and the plane where the thickness of the sample is located is substantially parallel to the plane where the fiber plies are located; the central part of the sample has a force receiving part, the two ends of the sample in the length direction respectively have a first clamping fixed part and a second clamping fixed part, the first clamping fixed part and the force receiving part have a first connecting part therebetween, the second clamping fixed part and the force receiving part have a second connecting part therebetween, the first clamping fixed part and the second clamping fixed part are both in the shape of a swallowtail; the first connecting part and the force receiving part have a first groove at the connecting position, the second connecting part and the force receiving part have a second groove at the connecting position; the sample has opposite first and second faces in the thickness direction, the first groove is recessed from the first face to the second face, the second groove is recessed from the second face to the first face, the sample is mirror-symmetric in the length direction and is flip-symmetric in the width direction, the depth of the first groove and the second groove is both greater than half the thickness of the sample, the vertical distance between the bottom of the first groove and the bottom of the second groove is equivalent to the thickness of one or two fiber plies; the sample is clamped and fixed on a testing device through the first clamping fixed part and the second clamping fixed part, then the testing device applies a tensile force to the sample to perform a tensile test, the tensile force is parallel to the plane where the thickness of the sample is located, which is also the plane where the fiber plies are located in the sample, so that at the end of the test process, the fiber plies at the center of the force receiving part of the central part of the sample are torn, which is consistent with the natural tearing of the material in the actual use process.

2. The test specimen for interlaminar shear properties of fiber reinforced composites of claim 1, wherein, The first connecting part has a first end connected with the force receiving part and a second end connected with the first clamping fixed part, and the width of the first connecting part gradually increases from the first end to the second end; the second connecting part has a first end connected with the force receiving part and a second end connected with the second clamping fixed part, and the width of the second connecting part gradually increases from the first end to the second end.

3. A method of testing the interlaminar shear performance of a fiber reinforced composite material, characterized by, Two clamps are used to fix the sample on a mechanical property testing machine, the sample is a sample for testing the interlaminar shear performance of a fiber-reinforced composite material according to any one of claims 1-2, the clamps are in the shape of a column, the outer surface of the first end has threads, the outer surface of the second end is recessed inward to form a clamping and fixing groove, the two sides of the clamping and fixing groove are provided with pin holes, the vertical distance between the connecting line of the two pin holes and the bottom surface of the clamping and fixing groove is equivalent to the thickness of the sample, the pin holes are matched with pin shafts to fix the sample in the clamping and fixing groove, the clamping and fixing groove is in the shape of a swallowtail and matches the shape of the sample, the clamps are matched with the testing device through the threads, the sample is clamped and fixed in the clamping and fixing groove to be fixed on the testing device; the sample is subjected to a tensile test by using the mechanical property testing machine to obtain a load-displacement curve, and the interlaminar shear strength is calculated according to the interlaminar shear strength formula: ； σ t F is the interlaminar shear strength, F max W is the maximum load, and W and B are the width and length of the force receiving portion, respectively.

4. The method of testing the interlaminar shear properties of a fiber reinforced composite material according to claim 3, wherein, Also included is pre-oxidizing the sample at high temperature.

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