Composite material fatigue layering extension microscopic damage evolution SEM in-situ test method

Abstract

The invention provides a composite material fatigue layering extension microscopic damage evolution SEM in-situ test method, and specifically belongs to the technical field of composite material fatigue behavior test characterization. Microscopic test characterization of the fatigue layering behavior of the composite material can be realized through two groups of test methods including a quasi-static in-situ tensile test and an in-situ fatigue layering test, clear observation of composite material fibers and a matrix can be realized through a preparation method of an in-situ test piece, and the problem that a single fiber cannot be observed in a microscopic view is solved. The device comprises an in-situ clamp and an in-situ test piece, and further comprises preparation of the in-situ test piece, quasi-static in-situ tensile test and in-situ fatigue layering test. The number of the in-situ clamps is two, one end of each in-situ clamp is connected with an eccentric connector which is of an L-shaped structure, the in-situ clamps are connected with in-situ test pieces through the eccentric connectors, and pins are arranged at the joints of the in-situ clamps and the in-situ test pieces.

Description

Technical Field

[0001] The invention relates to a SEM in-situ test method for composite material fatigue delamination extension microscopic damage evolution, and specifically belongs to the technical field of composite material fatigue behavior test characterization. Background Art

[0002] Composite materials have become key structural materials in the aerospace field due to their superior mechanical properties. Composite materials have excellent in-plane performance, but weak interlayer performance;

[0003] In engineering applications, it is found that more than 50% of composite material structure failures are closely related to delamination damage. Especially under fatigue loads, delamination damage will lead to strength and stiffness degradation of composite material structures, and even catastrophic accidents.

[0004] In recent years, the experimental characterization of fatigue delamination behavior of composite materials has been focused on macroscopic tests. It is undeniable that macroscopic tests have made certain contributions to the overall understanding of fatigue delamination behavior of composite materials, but they are limited in characterizing the microscopic damage mechanism of fatigue delamination. In the fatigue delamination process, microscopic factors such as the damage relationship between fibers and matrix, the path of microcrack propagation, and the role of bridging fibers are crucial and cannot be ignored in characterizing the fatigue delamination behavior of composite materials. Therefore, it is necessary to provide an in-situ SEM test method for the microscopic damage evolution of fatigue delamination expansion of composite materials. Summary of the invention

[0005] The purpose of the present invention is to provide a SEM in-situ test method for microscopic damage evolution of fatigue delamination and extension of composite materials, which can realize microscopic test characterization of fatigue delamination and extension behavior of composite materials.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: the invention includes an in-situ fixture and an in-situ specimen, and also includes the preparation of the in-situ specimen, a quasi-static in-situ tensile test and an in-situ fatigue delamination test;

[0007] Two in-situ fixtures are provided, one end of the in-situ fixture is fixedly connected with an eccentric connector, the eccentric connector is an "L"-shaped structure, the in-situ fixture is connected to the in-situ specimen via the eccentric connector, and a pin is provided at the connection between the in-situ fixture and the in-situ specimen.

[0008] Furthermore, by setting up an "L"-shaped structure of the eccentric connecting head, the effective observation range of the in-situ specimen under the scanning electron microscope can be expanded. The in-situ specimen can be prepared to meet the requirements of scanning electron microscope observation. The load value can be recorded through a quasi-static in-situ tensile test. The load displacement information and cycle number information can be collected through an in-situ fatigue delamination test, thereby realizing the microscopic experimental characterization of the fatigue delamination behavior of the composite material, providing an experimental basis for further exploring the damage mechanism and mechanism.

[0009] The preparation steps of in-situ specimens include:

[0010] 201: Observe and mark the crack tip position of the macroscopic in-situ specimen with delamination cracks;

[0011] 202: Determine the cutting line of the quasi-in-situ specimen according to the crack tip position and perform cutting;

[0012] 203: Manual grinding of the in-situ specimen;

[0013] 204: drilling holes into the in-situ specimen;

[0014] 205: Manual polishing of the in-situ specimen after drilling;

[0015] 206: performing gold spraying on the in-situ test piece.

[0016] The quasi-in-situ specimens have a dimensional margin, and the ratio of the delamination crack length of the in-situ specimens to the intact part is 2:8;

[0017] Silk polishing cloth was used for manual polishing, and the total manual polishing time was 40 minutes, including 10 minutes of water polishing, 10 minutes of dry polishing with polishing agent, and 20 minutes of water polishing;

[0018] Furthermore, the in-situ specimen preparation method can achieve clear observation of the composite material fibers and matrix, solving the problem of being unable to observe single fibers under a microscopic field of view.

[0019] The quasi-static in-situ tensile test steps include:

[0020] 301: Connect the two in-situ specimens and the in-situ fixture together through pins and install them on the test equipment;

[0021] 302: The equipment is evacuated, and the force and displacement are adjusted to zero, the equipment is adjusted to the tensile test mode, and the quasi-static in-situ tensile test is started;

[0022] 303: Observe the opening change of the crack front edge of the in-situ specimen. Once a microcrack occurs, stop the test immediately and record the load value at this time;

[0023] The in-situ fatigue delamination test steps include:

[0024] 401: Determine the loading method, load ratio and maximum load at which crack propagation occurs in fatigue test;

[0025] 402: Adjust the equipment to fatigue test mode and start the in-situ fatigue delamination test;

[0026] 403: During the test, when the crack expands and reaches an integer multiple of 500 cycles, the test is suspended and the microscopic crack expansion image is collected. The test is then continued until the in-situ specimen fails completely. The load displacement information and cycle number information are collected throughout the test;

[0027] Furthermore, through two sets of test methods, namely quasi-static in-situ tensile test and in-situ fatigue delamination test, clear observation of composite materials fibers and matrix was achieved, which solved the problem of being unable to observe single fibers under microscopic field of view, and proved the effectiveness and reliability of the invented method.

[0028] The beneficial effects of the present invention are:

[0029] 1. Through the two sets of experimental methods of quasi-static in-situ tensile test and in-situ fatigue delamination test, the microscopic experimental characterization of the fatigue delamination behavior of composite materials can be achieved, providing an experimental basis for further exploring the damage mechanism and mechanism.

[0030] 2. The setting of the "L"-shaped structure of the eccentric connector can expand the effective observation range of the in-situ specimen under the scanning electron microscope.

[0031] 3. The in-situ specimen preparation method can achieve clear observation of the composite material fibers and matrix, solving the problem of being unable to observe single fibers under a microscopic field of view. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the overall flow chart of the structure of the present invention;

[0033] Figure 2 It is a schematic diagram of the three-dimensional structure of the in-situ fixture of the present invention;

[0034] Figure 3 It is a schematic diagram of the three-dimensional structure of the in-situ specimen of the present invention;

[0035] Figure 4 It is a schematic diagram of the assembly structure of the in-situ test piece and the in-situ fixture of the present invention;

[0036] Figure 5 It is a diagram showing the observation effect of the structural test of the present invention.

[0037] 1. In-situ fixture; 2. In-situ specimen; 3. Pin. DETAILED DESCRIPTION

[0038] The following will be combined with the attached Figure 1-5 , clearly and completely describe the technical solutions in the embodiments.

[0039] Specific implementation method 1: Figure 2-4As shown, two in-situ fixtures 1 are provided, and adjacent ends of the two in-situ fixtures 1 are fixedly connected with eccentric connectors, and the two eccentric connectors are arranged in an "L"-shaped structure, so as to expand the effective observation range of the in-situ specimen 2 under the scanning electron microscope, and the two in-situ fixtures 1 are connected with the in-situ specimen 2 through the eccentric connectors, and the eccentric connectors are connected to the in-situ specimen 2 through the pins 3, so as to facilitate the subsequent quasi-static in-situ tensile test and in-situ fatigue delamination test on the in-situ specimen 2, and can realize the microscopic experimental characterization of the fatigue delamination behavior of the composite material, and provide an experimental basis for further exploring the damage mechanism and mechanism;

[0040] Specific implementation method 2: Figure 1 As shown, the preparation steps of the in-situ specimen 2 include:

[0041] 201: Observe and mark the crack tip position of the macroscopic in-situ specimen 2 having delamination cracks;

[0042] 202: Determine a cutting line of the quasi-in-situ specimen 2 according to the crack tip position and perform cutting;

[0043] The quasi-in-situ specimen 2 has a size margin, so as to ensure that the quasi-in-situ specimen 2 has prefabricated delamination, and the ratio of the delamination crack length of the in-situ specimen 2 to the intact part is 2:8;

[0044] 203: Manually polish the in-situ specimen 2;

[0045] This satisfies the dimensional requirements of the in-situ specimen 2, ensures that the in-situ specimen 2 has prefabricated delamination, and the ratio of the delamination crack length to the intact part is 2:8;

[0046] 204: drilling holes into the in-situ specimen 2;

[0047] The in-situ specimen 2 can be connected to the in-situ fixture through the pins;

[0048] 205: manually polishing the in-situ specimen 2 after the drilling;

[0049] Silk polishing cloth was used in manual polishing, and the total manual polishing time was 40 minutes, including 10 minutes of water polishing, 10 minutes of dry polishing with polishing agent, and 20 minutes of water polishing, so that the surface of the in-situ specimen 2 was as bright as a mirror;

[0050] 206: performing gold spraying on the in-situ specimen 2;

[0051] Make the in-situ specimen 2 meet the requirements of scanning electron microscope observation.

[0052] Specific implementation method three: Figure 5 As shown in the figure, the quasi-static in-situ tensile test steps include:

[0053] 301: Connect two in-situ specimens 2 and the in-situ fixture 1 together through pins 3 and install them on the test equipment;

[0054] 302: The equipment is evacuated, and the force and displacement are adjusted to zero, the equipment is adjusted to the tensile test mode, and the quasi-static in-situ tensile test is started;

[0055] 303: Observe the opening change of the crack front edge of the in-situ specimen 2. Once a microcrack is generated, stop the test immediately and record the load value at this time;

[0056] The in-situ fatigue delamination test steps include:

[0057] 401: Determine the loading method, load ratio and maximum load at which crack propagation occurs in fatigue test;

[0058] 402: Adjust the equipment to fatigue test mode and start the in-situ fatigue delamination test;

[0059] 403: During the test, when the crack propagates and reaches an integer multiple of 500 cycles, the test is suspended, and the microscopic crack propagation image is collected. The test is then continued until the in-situ specimen 2 completely fails. The load displacement information and cycle number information are collected throughout the test;

[0060] The two test methods of quasi-static in-situ tensile test and in-situ fatigue delamination test can realize the microscopic test characterization of fatigue delamination behavior of composite materials, providing an experimental basis for further exploration of damage mechanism and mechanism;

[0061] At the same time, it can achieve clear observation of composite materials fibers and matrices, solving the problem of being unable to observe single fibers under a microscopic field of view, and proving the effectiveness and reliability of the test method.

[0062] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A SEM in-situ test method for fatigue delamination extension micro-damage evolution of composite materials, comprising an in-situ fixture (1) and an in-situ specimen (2), characterized in that: It also includes the preparation of in-situ specimens (2), quasi-static in-situ tensile tests and in-situ fatigue delamination tests; Two in-situ clamps (1) are provided, one end of the in-situ clamp (1) is connected to an eccentric connector, the eccentric connector is an "L"-shaped structure, the in-situ clamp (1) is connected to an in-situ test piece (2) via the eccentric connector, and a pin (3) is provided at the connection between the in-situ clamp (1) and the in-situ test piece (2).

2. The SEM in-situ test method for composite material fatigue delamination extension micro damage evolution according to claim 1, characterized in that: The preparation steps of the in-situ specimen (2) include: 201: Observe and mark the crack tip position of the macroscopic in-situ specimen (2) having delamination cracks; 202: Determine a cutting line of the quasi-in-situ specimen (2) according to the crack tip position and perform cutting; 203: Manually polishing the in-situ test piece (2); 204: drilling holes in the in-situ test piece (2); 205: manually polishing the in-situ test piece (2) after the drilling; 206: Spray gold onto the in-situ test piece (2).

3. The SEM in-situ test method for composite material fatigue delamination extension micro damage evolution according to claim 2, characterized in that: The quasi-in-situ specimen (2) has a dimensional margin, and the ratio of the delamination crack length of the in-situ specimen (2) to the intact part is 2:

8.

4. The SEM in-situ test method for composite material fatigue delamination extension micro damage evolution according to claim 2, characterized in that: Silk polishing cloth was used for manual polishing, and the total manual polishing time was 40 minutes, including 10 minutes of water polishing, 10 minutes of dry polishing with polishing agent, and 20 minutes of water polishing.

5. The SEM in-situ test method for composite material fatigue delamination extension micro damage evolution according to claim 1, characterized in that: The quasi-static in-situ tensile test steps include: 301: Connect two in-situ test pieces (2) and the in-situ fixture (1) together through a pin (3) and install them on the test equipment; 302: The equipment is evacuated, and the force and displacement are adjusted to zero, the equipment is adjusted to the tensile test mode, and the quasi-static in-situ tensile test is started; 303: Observe the opening change of the crack front edge of the in-situ specimen (2). Once microcracks are generated, stop the test immediately and record the load value at this time.

6. The SEM in-situ test method for composite material fatigue delamination extension micro damage evolution according to claim 1, characterized in that: The in-situ fatigue delamination test steps include: 401: Determine the loading method, load ratio and maximum load at which crack propagation occurs in fatigue test; 402: Adjust the equipment to fatigue test mode and start the in-situ fatigue delamination test; 403: During the test, when the crack expands and reaches an integer multiple of 500 cycles, the test is suspended to collect microscopic crack expansion images, and then the test is continued until the in-situ specimen (2) completely fails. Load displacement information and cycle number information are collected throughout the test.

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