A bending test fixture for measuring carbon fiber composite material large curvature test

Abstract

The present application relates to a kind of for measuring carbon fiber composite material big curvature test bending test fixture, belong to composite material mechanical property testing technical field.It includes the upper and lower clamps of independent each other, test piece clamping component, testing machine connecting piece, connecting rod;Clamp arm and test piece clamping component are connected by four screws, and then test piece is fixed, ensure that test piece realizes firm clamping when bending load starts;Clamp center of gravity and pivot coincide, ensure that the torque caused by gravity in bending test does not affect test result.The advantage is that the structure is simple, clamping is convenient, can be adapted to a variety of testing machines, and has good application prospect in carbon fiber composite material bending test.

Description

Technical Field

[0001] This invention relates to a bending test fixture for measuring the large curvature of carbon fiber composite materials, and relates to the field of mechanical property testing of composite materials. Background Technology

[0002] High-strain composites are a class of fiber-reinforced composite materials designed to operate under bending strain greater than 1%. Structures made from these materials are housed through a mechanism that relies on the materials to fold at large curvatures. Due to their ability to withstand large strains, lightweight nature, and autonomous deployment capabilities without the need for external mechanical components, high-strain composites hold great potential for applications in the aerospace field, such as large deployable antennas and deployable solar cell arrays. Since high-strain composites rely on bending as their primary deformation mode, testing their bending performance is a crucial requirement for various deployable structures.

[0003] However, there are some problems with the bending test fixtures used to measure the bending response of carbon fiber composites: simple vertical test fixtures cannot avoid the influence of horizontal lateral loads caused by gravity, which causes shear strain in the specimen at large angles; pressure plate test fixtures cannot guarantee that the pure bending moment acts at the transition point between the plane and the curved surface; and large deformation four-point bending test fixtures, in some cases, clamping the edge of the test piece can cause stress concentration in certain areas, leading to failure.

[0004] The column bending test fixture combines the features of the pressure plate test fixture and the large deformation four-point bending test fixture. It can provide pure bending stress conditions to determine the bending stiffness and failure parameters of ultrathin carbon fiber laminates, and can also evaluate the nonlinear and progressive failure behavior of materials. However, the influence of fixture weight and the length ratio of the fixture to the test specimen on the results still exists. Therefore, it is still necessary to design the test fixture to minimize the impact on the test results. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the aforementioned technologies by proposing a bending test fixture for measuring the large curvature of carbon fiber composite materials. This fixture is used for the effective clamping of specimens in column bending tests, enabling the study of the bending stiffness and failure parameters of the material under pure bending conditions, and for evaluating the nonlinear and progressive failure behavior of the material.

[0006] To achieve the above technical content, the present invention is implemented through the following technical solution:

[0007] A bending test fixture for measuring the large curvature of carbon fiber composite materials includes an upper fixture, a lower fixture, a test piece clamping component, a testing machine connector, and a connecting rod. Both the upper and lower fixtures have intermediate machined holes for the connecting rod to enter. The upper and lower fixtures are connected to the testing machine connector via the connecting rod. To ensure that the unidirectional displacement load of the testing machine is converted into rotation, a bearing is installed in the intermediate machined hole. The test sample is placed between the upper and lower fixtures, which are connected to the test piece clamping component. During the clamping process, positioning blocks are used to position the test sample, ensuring that the test sample is centered along the axis after clamping.

[0008] Furthermore, the upper and lower clamps are spindle-shaped; both the upper and lower clamps are machined with four threaded holes, which can be connected to the test piece clamping component by bolts to fix the test piece.

[0009] Furthermore, the bearings in the intermediate machining holes of the upper and lower clamps are ball bearings of the same size to reduce the frictional force when longitudinal displacement is converted into rotation; the radial dimension of the connecting rod is the same as the inner diameter of the ball bearing; the upper and lower clamps are made of polylactic acid (PLA) plastic.

[0010] Furthermore, the test piece clamping component is spindle-shaped after being connected to the upper and lower clamps; the test piece clamping component provides a non-zero initial angle for the test piece after being connected to the clamp arm; the overall center of gravity of the clamp is aligned with the axis of rotation after the test piece clamping component is connected; the test piece clamping part is also made of the same polylactic acid (PLA) plastic material as the clamp.

[0011] Furthermore, the testing machine connector is connected to the uniaxial testing machine via screws. The upper part of the testing machine connector is connected to the moving end of the testing machine, and the lower part of the testing machine connector is connected to the fixed end of the testing machine. The testing machine connector has reserved space to ensure that the fixture can rotate 90° without interference. The testing machine connector can be replaced with a suitable connection method according to different uniaxial testing machines. The material of the testing machine connector can be aluminum alloy or polylactic acid (PLA) plastic.

[0012] Furthermore, the test specimen is made of resin-based carbon fiber composite material, with an overall rectangular shape, and different layup angles can be designed according to requirements.

[0013] Compared with the prior art, the present invention has the following advantages: 1. The fixture is designed to coincide the center of gravity with the axis of rotation, thereby minimizing the shear deformation of the sample caused by gravity and ensuring the accuracy of the test results; 2. The structure is simple and the clamping is convenient; 3. It can be adapted to various testing machines by changing the connecting parts of the testing machine. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is an overall connection diagram of the present invention in a bending test.

[0016] Figure 2 This is a schematic diagram of the assembly of the present invention.

[0017] Figure 3 This is the positioning of the test piece during the bending test according to the present invention.

[0018] Figure 4 This is a schematic cross-sectional view of the assembly of the present invention.

[0019] In the diagram: 1. Upper clamp; 2. Lower clamp; 3. Test piece clamping component; 4. Testing machine connector; 5. Connecting rod; 6. Test piece; 7. Positioning block. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] 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 embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. 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.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0024] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0025] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0026] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0027] like Figures 1-4As shown in the figure, this invention discloses a bending test fixture for measuring the curvature of carbon fiber composite materials, including an upper fixture 1, a lower fixture 2, a test piece clamping component 3, a testing machine connecting component 4, and a connecting rod 5. The upper fixture 1 and the lower fixture 2 are connected to the testing machine connecting component 4 via a connecting rod and a centrally machined hole. To ensure that the unidirectional displacement load of the testing machine is converted into a rotation angle, a bearing is installed in the centrally machined hole between the upper fixture 1 and the lower fixture 2. The upper fixture 1, the lower fixture 2, and the test piece clamping component 3 are connected by four screws, thereby applying pressure to the test piece and ensuring that the test piece can be firmly clamped before the bending test loading begins. During the clamping process between the upper fixture 1, the lower fixture 2, and the test piece, a positioning block 7 is used for positioning to achieve axial centering of the test piece after clamping. In this embodiment, the sample is installed in the middle of the upper clamp 1 and the lower clamp 2, and the centering and positioning operation is performed by the positioning block. The screw holes of the upper clamp 1 and the lower clamp 2 are set at the edge of the upper clamp 1 and the lower clamp 2 to ensure that the sample is not in contact with the clamp while it is being clamped, thus preventing experimental errors.

[0028] like Figure 2-3 As shown, the upper clamp 1 and lower clamp 2 are spindle-shaped, specifically, the cross-sectional area is largest at the middle connecting rod 5, and gradually decreases towards both ends; both the upper clamp 1 and lower clamp 2 are machined with four threaded holes, which can be connected to the test piece clamping component 3 by bolts to fix the test piece; the upper clamp 1 and lower clamp 2 have a middle machined hole, and ball bearings of the same size are selected to reduce the friction when longitudinal displacement is converted into rotation; the radial dimension of the connecting rod 5 is the same as the inner diameter of the ball bearing, connecting the upper clamp 1 and lower clamp 2 to the testing machine connecting component 4; the upper clamp 1 and lower clamp 2 are made of polylactic acid (PLA) plastic.

[0029] like Figure 4 As shown, the test specimen clamping component 3, after being connected to the upper clamp 1 and the lower clamp 2, forms a complete spindle shape; after being connected to the clamp arm, the test specimen clamping component 3 provides an initial angle of 5° for the test specimen; the test specimen clamping component 3 provides pressure to fully clamp the sample under the action of four screws; after the test specimen clamping component 3 is connected, the center of gravity of the entire clamp is aligned with the axis of rotation; the test specimen clamping part 3 is also made of the same polylactic acid (PLA) plastic material as the clamp.

[0030] like Figure 4As shown, the testing machine connector 4 is connected to the uniaxial testing machine. The upper half of the connector is connected to the moving end of the testing machine, and the lower half is connected to the fixed end. In this embodiment, the uniaxial testing machine is a universal testing machine, i.e., one end is fixed and the other end is moving. The moving end can only move up and down. The moving end is connected to the testing machine connector via a thread. When the moving end moves downward, pressure is applied. During the test, because there is a bearing at the connection between the testing machine connector and the clamp arm, the pressure is converted into the rotation angle of the clamp arm, thus achieving a bending effect. The testing machine connector 4 has reserved space to ensure that the clamp arm can rotate 90° without interference. The testing machine connector 4 can be replaced with a suitable connection method according to different uniaxial testing machines. The material of the testing machine connector 4 can be aluminum alloy or polylactic acid (PLA) plastic.

[0031] The test specimen is made of resin-based carbon fiber composite material, and its overall shape is rectangular. Different layup angles can be designed according to requirements.

[0032] In summary, once the fixture and specimen are fully installed and fixed, a column bending test can be performed. A pure bending load is applied to the specimen, and data such as curvature and strain of the specimen are acquired in real time using digital image correlation technology to achieve test data measurement. This method has the advantages of low cost and lightweight design, and the testing machine connectors can be replaced to allow testing on different testing machines.

[0033] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. The present invention is not limited to the above embodiments; the embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its essence and scope, and all such changes and modifications fall within the scope of the claims, which are defined by the appended claims and their equivalents.

Claims

1. A bending test fixture for measuring the large curvature of carbon fiber composite materials, characterized in that: The system includes an upper clamp (1), a lower clamp (2), a test piece clamping component (3), a testing machine connector (4), and a connecting rod (5). Both the upper clamp (1) and the lower clamp (2) have intermediate machining holes for the connecting rod (5) to enter. The upper clamp (1) and the lower clamp (2) are connected to the testing machine connector via the connecting rod. A bearing is installed in the intermediate machining hole between the upper clamp (1) and the lower clamp (2). The test piece is placed between the upper clamp (1) and the lower clamp (2). The upper clamp (1) and the lower clamp (2) are connected to the test piece clamping component (3). During the clamping process, the upper clamp (1) and the lower clamp (2) use a positioning block (7) for positioning, achieving axial centering of the clamped test piece. The test piece clamping component (3) is spindle-shaped after being connected to the upper clamp (1) and the lower clamp (2); the test piece clamping component (3) provides the test piece with an initial angle that is not zero after being connected to the clamp arm; the test piece clamping component (3) makes the center of gravity of the entire clamp coincide with the axis of rotation after being connected. The upper clamp (1) and lower clamp (2) are made of polylactic acid (PLA) plastic; the test piece clamping component (3) is also made of the same polylactic acid (PLA) plastic as the clamp.

2. The bending test fixture for measuring the large curvature of carbon fiber composite materials according to claim 1, characterized in that: The upper clamp (1) and lower clamp (2) are spindle-shaped. Both the upper clamp (1) and lower clamp (2) are machined with four threaded holes, which can be connected to the test piece clamping component (3) by bolts to fix the test piece.

3. The bending test fixture for measuring the large curvature of carbon fiber composite materials according to claim 1, characterized in that: The bearings in the intermediate machining holes of the upper clamp (1) and lower clamp (2) are ball bearings of the same size to reduce the friction when the longitudinal displacement is converted into the rotation angle; the radial dimension of the connecting rod (5) is the same as the inner diameter of the ball bearing.

4. The bending test fixture for measuring the large curvature of carbon fiber composite materials according to claim 1, characterized in that: The testing machine connector (4) is connected to the uniaxial testing machine by screws. The upper part of the testing machine connector is connected to the moving end of the testing machine, and the lower part of the testing machine connector (4) is connected to the fixed end of the testing machine. The testing machine connector (4) has reserved space to ensure that the clamp arm can rotate 90° without interference. The testing machine connector (4) can be replaced with a suitable connection method according to different uniaxial testing machines. The material of the testing machine connector (4) can be aluminum alloy or polylactic acid (PLA) plastic.

5. A bending test fixture for measuring the large curvature of carbon fiber composite materials according to claim 1, characterized in that: The material of the connecting parts (4) of the testing machine can be aluminum alloy or polylactic acid (PLA) plastic.

6. A bending test fixture for measuring the large curvature of carbon fiber composite materials according to claim 1, characterized in that: The test specimen is made of resin-based carbon fiber composite material, with an overall rectangular shape and different layup angles designed according to requirements.

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