Test specimen, biaxial mechanical testing method, method of preparing test specimen

Abstract

The application discloses a sample, a biaxial mechanical test method and a sample preparation method. The sample is used for biaxial mechanical test, and the sample comprises a flat plate. The periphery of the flat plate is used for fixation. The middle part of the flat plate is a working section. The working section is used for bearing loading force and generating upward or downward displacement. By using the sample, biaxial mechanical test can be completed by using a single-axis loading device, thereby avoiding the use of a special biaxial loading device for mechanical test. The application not only reduces the cost, but also simplifies the operation and improves the test efficiency. In addition, compared with a cross-shaped cross sample, the flat plate sample can effectively reduce the waste generated by mechanical processing, has lower manufacturing cost and simpler process.

Description

Technical Field

[0001] This invention relates to the field of complex load testing of composite materials, and particularly to a specimen, a biaxial mechanical testing method, and a specimen preparation method. Background Technology

[0002] For composite laminates used in actual structures, they often bear biaxial loads rather than simply uniaxial stress loads. This is because structures in actual service environments experience complex load conditions, and the forms of stress are not singular. Therefore, the material and structural strength obtained through uniaxial loading tests in strength testing is usually insufficient to fully meet design requirements. To address this technical need, biaxial mechanical testing is required to obtain the structural strength performance under biaxial stress states.

[0003] However, for biaxial mechanical testing, whether for composite or metallic structures, the mainstream method currently involves directly applying tensile and compressive loads using specialized biaxial loading testing machines. These biaxial loading devices are bulky, few in number, and have complex control systems, resulting in high costs and limited testing resources for biaxial mechanical testing.

[0004] Furthermore, for biaxial equal load mechanical tests, cross-shaped cross specimens are usually used. Regardless of whether such specimens are in the form of simple composite laminates or composite sandwich structures, the manufacturing cost is very high and the manufacturing process is complicated due to the complexity of the cross-shaped cross specimen configuration and the large amount of waste generated after machining. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects in the prior art and provide a solution.

[0006] The present invention solves the above-mentioned technical problems through the following technical solution: This embodiment provides a specimen for biaxial mechanical testing. The specimen includes a plate, the periphery of which is used for fixing, and the middle part of which is a working section, which is used to bear the loading force and generate upward or downward displacement.

[0007] In this scheme, by using the aforementioned specimens, biaxial mechanical testing can be performed using a uniaxial loading device, thus avoiding the need for specialized biaxial loading equipment. This not only reduces costs but also simplifies operation and improves testing efficiency. Furthermore, compared to cross-shaped intersecting specimens, flat plate specimens effectively reduce waste generated during machining, resulting in lower manufacturing costs and a simpler process.

[0008] Preferably, the surface of the plate is provided with a skin, the skin including an assessment skin and a non-assessment skin, the assessment skin being thinner than the non-assessment skin.

[0009] In this design, the test skin is made thinner than the non-test skin, which helps the test skin obtain the effective laminate failure mode located in the working section of the specimen during the test.

[0010] Preferably, the periphery of the flat plate is encapsulated with core material.

[0011] In this scheme, core material is potted around the perimeter of the plate to enhance the strength of the core material and prevent premature damage to the core material during the test.

[0012] Preferably, the working section includes openings or impact damage.

[0013] In this scheme, by implementing a drop hammer impact test at the center of the working section or opening a through hole of the required size, the test requirements for the strength of the laminate are improved to take into account the defects and damage that are difficult to be detected during the service life of the composite laminate structure.

[0014] Preferably, the periphery of the flat plate is provided with a gasket.

[0015] In this scheme, by setting shims to distribute the applied load more evenly, the premature failure of the sample due to localized crushing of the sandwich structure caused by excessive concentration of contact force from the loading fixture is avoided during the test.

[0016] The present invention also provides a biaxial mechanical testing method, which is applied to the specimen as described above, and the biaxial mechanical testing method includes the following steps:

[0017] S1. Fix the periphery of the plate and continuously apply force to the middle of the plate to produce an upward or downward displacement, causing the plate to undergo symmetrical bending deformation, and collect the strain data of the working section.

[0018] In this solution, by adopting the above testing method, the use of specially designed biaxial loading equipment for biaxial mechanical testing can be avoided, which not only reduces costs but also simplifies operation and improves testing efficiency.

[0019] The present invention also provides a method for preparing a sample, the method being used to prepare the sample as described above, the method comprising the following steps:

[0020] S10. Design and manufacture a flat plate.

[0021] In this scheme, the preparation method described above is simple and low-cost.

[0022] Preferably, the surface of the plate is provided with a skin, the skin including an assessment skin and a non-assessment skin. In S10, a skin is provided on the surface of the plate, and the assessment skin is thinner than the non-assessment skin.

[0023] Preferably, the periphery of the flat plate is encapsulated with core material, and the preparation method includes the following steps:

[0024] S11. The periphery of the flat plate is filled with core material using potting compound.

[0025] Preferably, the working section includes openings or impact damage, and the preparation method further includes the following steps:

[0026] S12. Select the central position on the plate to perform a drop hammer impact or open a through hole.

[0027] Preferably, the plate has a gasket around its perimeter, and the preparation method further includes the following steps:

[0028] S13. A gasket is provided around the perimeter of the flat plate.

[0029] The positive and progressive effects of this invention are as follows: The specimen provided by this invention is used for biaxial mechanical testing. The specimen includes a flat plate, the periphery of which is used for fixation, and the middle part of the plate is a working section used to withstand the loading force and generate upward or downward displacement. By using the above specimen, biaxial mechanical testing can be performed using a uniaxial loading device, thereby avoiding the use of specially designed biaxial loading equipment for mechanical testing. This not only reduces costs but also simplifies operation and improves testing efficiency. Furthermore, compared to cross-shaped intersecting specimens, flat plate specimens can effectively reduce waste generated during machining, resulting in lower manufacturing costs and a simpler process. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the sample in an embodiment of the present invention during biaxial mechanical testing.

[0031] Figure 2 This is a schematic diagram of the sample in an embodiment of the present invention during biaxial mechanical testing.

[0032] Figure 3 This is a schematic diagram of the structure of the sample according to an embodiment of the present invention.

[0033] Figure 4 This is a schematic diagram of the steps of the biaxial mechanical testing method according to an embodiment of the present invention.

[0034] Figure 5 This is a schematic diagram of the steps in the sample preparation method according to an embodiment of the present invention.

[0035] Explanation of reference numerals in the attached figures:

[0036] Sample 1

[0037] Work Section 11

[0038] Test skin 111

[0039] Non-test skin 112

[0040] Core material potting 113

[0041] 114 openings

[0042] Simple stand 2

[0043] Loading tool 3 Detailed Implementation

[0044] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the following embodiments.

[0045] like Figures 1-3 As shown, this embodiment provides a specimen 1 for biaxial mechanical testing. Specimen 1 includes a flat plate, with its periphery for fixation and its center as a working section 11. The working section 11 is used to withstand the loading force and generate upward or downward displacement. Specimen 1 is used to measure the strength performance of laminates under biaxial loads, and its overall design is a composite sandwich structure. Specifically, the in-plane shape of specimen 1 is designed as a simple square to facilitate manufacturing. The central part of this square specimen 1 is the working section 11, and the effective failure mode occurs within this working section 11. During biaxial mechanical testing, the four sides of the flat plate specimen 1 are simply supported and fixed. Simultaneously, upward or downward displacement is applied to the center of specimen 1, causing the center of the flat plate specimen 1 to bend upward or downward. Due to the bending stress of the plate, and because the bending of the square plate center is a completely symmetrical biaxial bending deformation, a biaxial equal load stress state will be exhibited on the laminate in the central working area of ​​specimen 1, achieving a biaxial equal load mechanical test on the laminate. By using the aforementioned specimen 1, biaxial mechanical testing can be performed using a uniaxial loading device, thus avoiding the need for specialized biaxial loading equipment. This not only reduces costs but also simplifies operation and improves testing efficiency. Furthermore, compared to the cross-shaped intersecting specimen 1, the flat plate specimen 1 effectively reduces waste generated during machining, resulting in lower manufacturing costs and a simpler process. In this embodiment, the aforementioned flat plate specimen 1 is completely symmetrical; in other embodiments, the flat plate specimen 1 can also be non-completely symmetrical, i.e., rectangular.

[0046] like Figure 2As shown, the surface of the plate is further provided with a skin, which includes a test skin 111 and a non-test skin 112, with the test skin 111 being thinner than the non-test skin 112. The test skin 111 and the non-test skin 112 are respectively attached to the upper and lower surfaces of the plate. During the test, an extensometer or strain gauge is attached to the test skin 111 to measure the in-plane strain or displacement data of the specimen 1, allowing for intuitive and timely data acquisition. Furthermore, designing the test skin 111 to be thinner than the non-test skin 112 helps the test skin 111 obtain the effective laminate failure mode located in the working section 11 of the specimen 1 during the test.

[0047] Furthermore, core material potting 113 is provided around the perimeter of the plate. Specifically, during the processing, the core material in the sandwich structure of the plate is filled with potting material at the weakest points and in the area around the perimeter of the plate that will be used to contact the loading fixture 3 in the future, in order to strengthen the core material and prevent premature damage to the core material during the test.

[0048] like Figure 3 As shown, the working section 11 further includes an opening 114 or impact damage. Specifically, a drop hammer impact test or a through hole of the required size is performed at the center of the working section 11 to introduce impact damage or through opening 114 features into the biaxial mechanical test specimen 1. This is to account for the defects and damage that are difficult to detect in actual composite laminate structures during their service life, thereby increasing the testing requirements for laminate strength. The side length of this square sandwich structure plate specimen 1 should be designed to be long enough to ensure that the central opening 114 or impact damage has sufficient edge distance. In addition, sufficient side length is also a necessary design to ensure that the working section 11 is far enough from the boundary of the specimen 1 to avoid boundary effects. It is generally recommended that the side length of this type of specimen 1 be more than 4 times the diameter of the central working section 11.

[0049] Furthermore, gaskets are provided around the perimeter of the plate. Specifically, gaskets are attached to the contact surfaces between the plate and the loading fixture 3 to distribute the applied load more evenly, thereby preventing premature failure of the specimen 1 due to excessive concentration of contact force from the loading fixture 3 during the test, which could lead to localized crushing of the sandwich structure.

[0050] like Figure 1 , Figure 2 , Figure 4 As shown, this embodiment also provides a biaxial mechanical testing method, which is applied to the sample 1 described above. The biaxial mechanical testing method includes the following steps:

[0051] S1. Fix the periphery of the plate and continuously apply force to the middle of the plate to produce upward or downward displacement, so that the plate undergoes symmetrical bending deformation, and collect the strain data of the working section 11.

[0052] Specifically, the specimen 1 also includes a skin, which is located on the upper and lower surfaces of the plate. The skin includes a test skin 111 and a non-test skin 112, with the test skin 111 being thinner than the non-test skin 112. During testing, a simple support 2 is used to fix the four sides of the plate specimen 1. Simultaneously, an upward or downward displacement is applied to the center of the specimen 1, causing the center of the plate specimen 1 to bend upward or downward. Due to the bending stress of the plate, and because the bending of the square plate at the center is a biaxially symmetrical bending deformation, a biaxially equal load stress state will be presented on the laminate in the central working area of ​​the specimen 1, realizing a biaxial equal load mechanical test on the laminate. Continuing to apply greater displacement and bending deformation to the specimen 1 until the test skin 111 in the working section 11 finally fails, at which point the test ends and the failure strength under biaxial stress is obtained. The loading fixture 3 is a ring-shaped cylindrical structure, the diameter of which is the diameter range of the working section 11. During loading, it presses on the skin in the central working area and applies an upward or downward displacement. By adopting the above testing method, biaxial mechanical testing can be performed using a single-axis loading device, thereby avoiding the need for specially designed biaxial loading devices for mechanical testing. This not only reduces costs but also simplifies operation and improves testing efficiency.

[0053] like Figure 5As shown, this embodiment also provides a method for preparing sample 1. This method is used to prepare sample 1 as described above, and includes the following steps: In S10, a flat plate is designed and processed. Specifically, the flat plate is a composite sandwich structure, and the upper and lower surfaces of the plate are provided with skins. One side is the test skin 111, and the other side is the non-test skin 112. The test skin 111 is specially designed to be thinner than the non-test skin, which helps the test skin 111 to obtain the effective laminate failure mode located in the working section 11 of sample 1 during the test. In S11, the periphery of the flat plate is filled with core material using potting compound. Specifically, the core material is filled with potting compound in the direction where the core material strength of the sandwich structure is weak and in the area near the periphery of the sandwich plate that will be used to contact the loading fixture 3, in order to strengthen the core material strength in these areas and avoid premature damage to the core material during the test. In S12, a drop hammer impact or a through hole is opened at the central position on the flat plate. Specifically, a drop hammer impact test is performed at an appropriate central position on the aforementioned sandwich structure plate, or a through hole of the required size is opened. This is to account for the defects and damage that are difficult to detect during the service life of the composite laminate structure, thereby increasing the testing requirements for the strength of the laminate. The side length of the square sandwich structure plate specimen 1 should be designed to be long enough to ensure sufficient edge distance for the central opening 114 or impact damage. In addition, sufficient side length is also a necessary design to ensure that the working section 11 is far enough from the boundary of the specimen 1 to avoid boundary effects. It is generally recommended that the side length of this type of specimen 1 be more than 4 times the diameter of the central working section 11. In S13, shims are placed around the perimeter of the plate. Specifically, metal or glass fiber composite material shims are attached to the tooling contact positions on the specimen 1 to distribute the contact force applied to the specimen 1 by the tooling more evenly during the test, avoiding premature failure of the local sandwich structure due to excessive concentration of contact force. By adopting the above preparation method, the manufacturing is simple and low-cost.

[0054] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A specimen for biaxial mechanical testing, characterized in that, The sample includes a flat plate, the four sides of which are used for fixing, and the middle part of the flat plate is a working section. The working section is used to bear the loading force and generate upward or downward displacement, so that the working section undergoes symmetrical bending deformation. The flat plate is square; The specimen was subjected to biaxial mechanical testing using a uniaxial loading device. The surface of the plate is provided with a skin, which includes a test skin and a non-test skin, and the test skin is thinner than the non-test skin. The side length of the sample is more than four times the diameter of the central working section.

2. The sample as described in claim 1, characterized in that, The periphery of the flat plate is encapsulated with core material.

3. The sample as described in claim 1, characterized in that, The working section includes openings or impact damage.

4. The sample as described in claim 1, characterized in that, The plate is provided with pads around its perimeter.

5. A biaxial mechanical testing method, characterized in that, The biaxial mechanical testing method is applied to the specimen as described in claim 1, and the biaxial mechanical testing method includes the following steps: S1. Fix the periphery of the plate and continuously apply force to the middle of the plate to produce an upward or downward displacement, causing the plate to undergo symmetrical bending deformation, and collect the strain data of the working section.

6. A method for preparing a sample, characterized in that, The preparation method is used to prepare the sample as described in claim 1, and the preparation method includes the following steps: S10. Design and fabricate a square flat plate.

7. The preparation method according to claim 6, characterized in that, The surface of the plate is provided with a skin, which includes an assessment skin and a non-assessment skin. In S10, a skin is provided on the surface of the plate, and the assessment skin is thinner than the non-assessment skin.

8. The preparation method according to claim 6, characterized in that, The periphery of the flat plate is encapsulated with core material, and the preparation method includes the following steps: S11. The periphery of the flat plate is filled with core material using potting compound.

9. The preparation method according to claim 6, characterized in that, The working section includes openings or impact damage, and the preparation method further includes the following steps: S12. Select the central position on the plate to perform a drop hammer impact or open a through hole.

10. The preparation method according to claim 6, characterized in that, The plate is provided with a gasket around its perimeter, and the preparation method further includes the following steps: S13. A gasket is provided around the perimeter of the flat plate.

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