Test fixture and determination method for shear performance of flexible skin

Abstract

The invention discloses a test fixture and a determination method for the shearing performance of a flexible skin, and belongs to the technical field of material mechanical property testing. The test fixture comprises a cylindrical adapter chuck, a pre-tightening ring, a threaded connecting shaft, a fastening nut, a double-lug U-shaped connecting piece, a frame strip, a clamping strip and a fastening bolt. The cylindrical adapter chuck is connected with a testing machine through a pin, a threaded connection shaft and a fastening nut are used for carrying out load transmission, and a bearing is used at a frame strip lug piece to reduce friction loss in a test. According to the measuring method, a load-displacement curve measured by a test is converted into a shear modulus-shear strain curve based on geometric and stress analysis of a sample, and accurate material performance data is provided for structural design and optimization of the flexible skin. According to the test fixture and the determination method for the shearing performance of the flexible skin, the use is convenient, the operation is simple, the manufacturing cost is low, the precision is high, and a reasonable and effective technical means is provided for testing the shearing performance of the flexible skin.

Description

Technical Field

[0001] The invention belongs to the technical field of flexible material mechanical property testing, and in particular relates to a testing fixture and a measuring method for shearing properties of a flexible composite material skin of a variant wing. Background Art

[0002] Flexible skin has been widely used in the fields of variant wings because it can realize large deformation function, withstand certain aerodynamic loads and maintain aerodynamic shape. At present, most of the research on the basic mechanical properties of flexible skin is focused on the test of axial tensile performance. However, when the variant wing implements tasks such as changing the wing sweep angle and changing the airfoil curvature, the flexible skin must not only withstand tensile loads, but also withstand considerable shear loads. Therefore, it is far from enough to only test the axial tensile performance of the flexible skin. Due to the low stiffness of the flexible skin, its shear mechanical properties cannot be measured by traditional shear performance test methods, which greatly limits the practical application and development of flexible skin on variant wings. To this end, the present invention proposes a test fixture and a measurement method for the shear performance of a flexible skin, which provides technical means for the shear performance test of the flexible skin. Summary of the invention

[0003] 1. Purpose: The purpose of the present invention is to provide a test fixture and a method for measuring the shear performance of a flexible skin. The method is simple to operate and has low cost.

[0004] 2. Technical solution: A test fixture and measurement method for the shear performance of a flexible skin.

[0005] The test fixture for the shear performance of the flexible skin is characterized by being composed of a cylindrical adapter chuck, a preload ring, a threaded connection shaft, a fastening nut, a double-ear U-shaped connector, a frame bar, a clamping bar and a fastening bolt. The connection relationship between the various components is as follows: (1) The cylindrical adapter chuck is connected to the testing machine through a pin, and is used for the transfer and load transfer between the testing machine and the shear performance test fixture; (2) The cylindrical adapter chuck is locked with the testing machine by using the preload ring to prevent relative movement between the fixture and the testing machine during the test, thereby ensuring the stability of load transfer; (3) The other end of the cylindrical adapter chuck is connected and fixed to the upper double-ear U-shaped connector by using the threaded connection shaft and the fastening nut, so as to transfer the tensile load on the testing machine to the clamping mechanism, thereby driving the cross-shaped specimen to undergo shear deformation; (4) The single-ear ear piece of the frame bar and the double-ear ear piece of the adjacent frame bar are hinged by fastening bolts, nuts and bearings; (5) The clamping bar is fixed to the frame bar by fastening bolts, and plays the role of clamping the cross-shaped specimen. The four load arms of the cross-shaped specimen are clamped between the frame bar and the clamping bar respectively, and the load arms of the specimen are fixed to the frame bar through the clamping bar by fastening bolts, thereby achieving the function of fixing the cross-shaped specimen and driving the cross-shaped specimen to undergo shear deformation.

[0006] The method for determining the shear performance of the flexible skin comprises the following specific steps:

[0007] Step 1: Prepare the flexible skin test piece. Cut the flexible fabric into Figure 3 For a test piece of the shape and size shown in the figure, the entire test piece can be divided into a test effective area and a clamping area, and the clamping area is the area clamped by the clamping fixture.

[0008] Step 2. Install the chuck of the test fixture. Use fastening bolts, nuts, bearings and other parts to connect the four frame strips and the double-ear U-shaped connector, and check the tightness of the joints to avoid obvious gaps between adjacent parts. At the same time, ensure that the diamond clamping mechanism can perform smooth deformation movement. Connect the cylindrical adapter chuck to the double-ear U-shaped connector through a threaded shaft, adjust the adapter chuck to a suitable angle, tighten the fastening nut, and ensure a tight connection between the adapter joint and the double-ear U-shaped connector. Turn on the electric tensile testing machine, and adjust the testing machine chuck to a suitable position. Fix the upper and lower cylindrical adapter chucks of the shear fixture to the testing machine with pins, and tighten the preload ring to ensure that there is no relative movement between the testing machine and the cylindrical adapter chuck.

[0009] Step 3. Clamp the test piece and start the test. By changing the tensile displacement of the testing machine, adjust the angle between the two adjacent frame bars of the shear fixture to 90°. Place the cross-shaped flexible skin specimen on the frame bar of the shear fixture, adjust the load arm to the appropriate position, and then use the fastening bolts to fix the clamping bar of the shear fixture to the frame bar. At the same time, fix the cross-shaped flexible skin specimen in the middle of the clamping bar and the frame bar to complete the clamping of the shear specimen. When fixing the clamping bar, always pay attention to the position of the load arm of the cross-shaped flexible skin specimen and adjust it continuously to ensure that the clamped skin specimen is in the center of the shear fixture and the surface is flat to avoid affecting the test results. Enter the necessary dimensional data, apply a displacement load to the shear specimen at a tensile rate of 15mm / min, and use a camera and a testing machine to record the deformation phenomenon and load-displacement data respectively.

[0010] Step 4: Processing of flexible skin shear performance test data.

[0011] From the analysis of the flexible skin geometry, we know that the shear strain of the flexible skin can be expressed as

[0012]

[0013] Where θ is half of the fixture / deformation zone vertex angle, and γ is the shear strain in the deformation zone.

[0014] The shear stress of the flexible skin can be defined as

[0015]

[0016] Where P is the tensile load measured by the testing machine, l is the side length of the deformation zone in the center of the specimen, and τ is the shear stress in the deformation zone.

[0017] According to the geometric relationship of the flexible skin, we can get

[0018]

[0019]

[0020] Where L is the side length of the fixture and δ is the tensile displacement measured by the testing machine.

[0021] According to the definition of shear modulus, we get

[0022]

[0023] in,

[0024]

[0025] Substituting equations (3), (4), (6) and (7) into equation (5), we get the shear modulus expression:

[0026]

[0027] 3. Advantages and effects: The test fixture of the shear modulus of the flexible skin of the present invention solves the clamping and clamping problems of the shear test of the flexible skin, and provides a stable and reliable clamping device for its shear performance test. The test fixture of the present invention has the advantages of simple operation and low cost. The method for measuring the shear modulus of the flexible skin of the present invention transforms the load-displacement curve measured in the test into a shear modulus-shear strain curve, and further obtains the shear modulus based on the load-displacement curve. The method for measuring the shear modulus of the flexible skin of the present invention is simple, practical and highly accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the test fixture structure for the shear performance of the flexible skin;

[0029] Figure 1 Middle: Component 1 is a cylindrical adapter chuck, Component 2 is a threaded connection shaft, Component 3 is a double-ear U-shaped connector, Component 4 is a frame bar, Component 5 is a clamping bar, Component 6 is a solid nut, Component 7 is a preload ring, and Component 8 is a fastening bolt;

[0030] Figure 2 This is a physical picture of the test fixture for the shear performance of the flexible skin;

[0031] Figure 3 This is the geometrical dimension diagram of the flexible skin shear specimen;

[0032] Figure 4 This is the geometric analysis diagram of the flexible skin shear specimen;

[0033] Figure 4 Middle: l is the side length of the deformation zone, L is the side length of the fixture, and θ is half of the vertex angle between the fixture and the deformation zone;

[0034] Figure 5 This is the force analysis diagram of the flexible skin shear specimen. DETAILED DESCRIPTION

[0035] The specific implementation modes of the present invention are further described in detail with reference to the accompanying drawings and embodiments.

[0036] Embodiment 1:

[0037] Shear properties test of 1100dtex polyester plain fabric / 3L rubber composites.

[0038] Step 1: Prepare the shear performance test specimen

[0039] All samples were made of 1100dtex polyester plain fabric / 3L rubber composite materials, with both fiber reinforcement and matrix made of flexible materials and a thickness of 0.12mm. Figure 1 The flexible skin is cut into the geometric shape and size shown, and finally a cross shear specimen is obtained.

[0040] Step 2: Install the shear performance test fixture

[0041] Use fastening bolts, nuts, bearings and other parts to connect the four frame strips and the double-ear U-shaped connector, and check the tightness of the connection to avoid obvious gaps between adjacent parts. At the same time, ensure that the diamond clamping mechanism can perform smooth deformation movement. Connect the cylindrical adapter chuck to the double-ear U-shaped connector through the threaded connecting shaft, adjust the adapter chuck to the appropriate angle, tighten the fastening nut to ensure a tight connection between the adapter and the double-ear U-shaped connector. Turn on the MTS-100kN electronic tensile testing machine, adjust the testing machine chuck to the appropriate position, fix the upper and lower cylindrical adapter chucks of the shear fixture to the testing machine with pins, and tighten the preload ring to ensure that there is no relative movement between the testing machine and the cylindrical adapter chuck.

[0042] Step 3: Clamp the sample and start the test

[0043] By changing the tensile displacement of the testing machine, the angle between the two adjacent frame bars of the shear fixture is adjusted to 90°. Place the specimen on the frame bar of the shear fixture, adjust the load arm to the appropriate position, and then use the fastening bolts to fix the clamping bar of the shear fixture to the frame bar, and fix the specimen between the clamping bar and the frame bar to complete the clamping of the specimen. When fixing the clamping bar, always pay attention to the position of the specimen load arm and adjust it continuously to ensure that the clamped specimen is in the center of the shear fixture and the surface is flat to avoid affecting the test results. Enter the necessary dimensional data, apply the displacement load at a tensile rate of 15mm / min, and use the camera and testing machine to record the deformation phenomenon and load-displacement data respectively.

[0044] Step 4: Geometry and force analysis

[0045] From the analysis of the flexible skin geometry, we know that the shear strain of the flexible skin can be expressed as

[0046]

[0047] Where θ is half of the fixture / deformation zone vertex angle, and γ is the shear strain in the deformation zone.

[0048] The shear stress of the flexible skin can be defined as

[0049]

[0050] Where P is the tensile load measured by the testing machine, l is the side length of the deformation zone in the center of the specimen, and τ is the shear stress in the deformation zone.

[0051] According to the geometric relationship of the flexible skin, we can get

[0052]

[0053] Where L is the side length of the fixture and δ is the tensile displacement measured by the testing machine.

[0054] Step 5: Solve for the shear modulus

[0055] According to the definition of shear modulus, we get

[0056]

[0057] in,

[0058]

[0059] Substituting equations (3), (4), (6) and (7) into equation (5), we get the shear modulus expression:

[0060]

[0061] According to the method, the load-displacement curve obtained from the shear performance test of the 1100 dtex polyester fiber plain fabric / 3L rubber composite material can be converted into a shear modulus-shear strain curve.

Claims

1. A test fixture for the shear performance of a flexible skin, characterized in that: The utility model is composed of a cylindrical adapter chuck, a preload ring, a threaded connection shaft, a fastening nut, a double-ear U-shaped connecting piece, a frame strip, a clamping strip and a fastening bolt. The connection relationship between the various components of the test fixture is as follows: (1) The cylindrical adapter chuck is connected to the testing machine through a pin and is used for the connection and load transfer between the testing machine and the shear performance test fixture; (2) The cylindrical adapter chuck is locked with the testing machine using a preload ring to prevent relative movement between the fixture and the testing machine during the test, thereby ensuring the stability of load transfer; (3) Use a threaded connecting shaft and a fastening nut to connect and fix the other end of the cylindrical adapter chuck to the upper double-ear U-shaped connector, so as to transfer the tensile load on the testing machine to the clamping mechanism, thereby driving the cross-shaped specimen to undergo shear deformation; (4) The single-ear ear piece of the frame bar and the double-ear ear piece of the adjacent frame bar are hinged by fastening bolts, nuts and bearings; (5) The clamping bar is fixed to the frame bar by fastening bolts to play the role of clamping the cross-shaped specimen. The four load arms of the cross-shaped specimen are clamped between the frame bar and the clamping bar respectively, and the load arms of the specimen are fixed to the frame bar through the clamping bar by fastening bolts, thereby achieving the function of fixing the cross-shaped specimen and driving the cross-shaped specimen to undergo shear deformation.

2. The method for measuring the shear performance of the flexible skin according to claim 1, characterized in that: The following steps are involved: 1) Prepare the flexible skin test piece. Cut the flexible fabric into a test piece of fixed size. The entire test piece can be divided into an effective test area and a clamping area. The clamping area is the area clamped by the clamping fixture. 2) Install the chuck of the test fixture. Use fastening bolts, nuts, bearings and other parts to connect the four frame strips and the double-ear U-shaped connector, and check the tightness of the joints to avoid obvious gaps between adjacent parts. At the same time, ensure that the diamond clamping mechanism can perform smooth deformation movement. Connect the cylindrical adapter chuck to the double-ear U-shaped connector through a threaded shaft, adjust the adapter chuck to a suitable angle, tighten the fastening nut, and ensure a tight connection between the adapter joint and the double-ear U-shaped connector. Turn on the electric tensile testing machine, and adjust the chuck of the testing machine to a suitable position. Fix the upper and lower cylindrical adapter chucks of the shear fixture to the testing machine with pins, and tighten the preload ring to ensure that there is no relative movement between the testing machine and the cylindrical adapter chuck. 3) Clamp the test piece and start the test. By changing the tensile displacement of the testing machine, adjust the angle between the two adjacent frame bars of the shear fixture to 90°. Place the cross-shaped flexible skin specimen on the frame bar of the shear fixture, adjust the load arm to the appropriate position, and then use the fastening bolts to fix the clamping bar of the shear fixture to the frame bar. At the same time, fix the cross-shaped flexible skin specimen in the middle of the clamping bar and the frame bar to complete the clamping of the shear specimen. When fixing the clamping bar, always pay attention to the position of the load arm of the cross-shaped flexible skin specimen and adjust it continuously to ensure that the clamped skin specimen is in the center of the shear fixture and the surface is flat to avoid affecting the test results. Enter the necessary dimensional data, apply a displacement load to the shear specimen at a tensile rate of 15mm / min, and use a camera and a testing machine to record the deformation phenomenon and load-displacement data respectively. 4) Flexible skin shear performance test data processing. From the analysis of the flexible skin geometry, we know that the shear strain of the flexible skin can be expressed as Where θ is half of the fixture / deformation zone vertex angle, and γ is the shear strain in the deformation zone. The shear stress of the flexible skin can be defined as Where P is the tensile load measured by the testing machine, l is the side length of the deformation zone in the center of the specimen, and τ is the shear stress in the deformation zone. According to the geometric relationship of the flexible skin, we can get Where L is the side length of the fixture and δ is the tensile displacement measured by the testing machine. According to the definition of shear modulus, we get in, Substituting equations (3), (4), (6) and (7) into equation (5), we get the shear modulus expression: 。

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