Sample, clamp and method for testing shear performance of composite material in thickness direction

Abstract

The invention discloses a sample, a clamp and a method for testing the shear performance of a composite material in the thickness direction, the sample is butterfly-shaped and comprises a left side wing and a right side wing which are symmetrically arranged, and a working section is arranged between the left side wing and the right side wing; the two ends, away from the working section, of the left side wing and the right side wing are each provided with a fixing hole. The clamp comprises a first upper clamping plate, a second upper clamping plate, a first lower clamping plate and a second lower clamping plate, and the sample is clamped and fixed between the first upper clamping plate and the second upper clamping plate and between the first supporting table and the second lower clamping plate; an avoiding space allowing the sample working section to freely deform when the sample working section is subjected to shearing force is formed among the first upper clamping plate, the second upper clamping plate, the first supporting table and the second lower clamping plate. Through the configuration of the specific sample piece and the clamp, when the sample is subjected to a shear test on test equipment, the working section of the sample can freely deform in the vertical direction, and other parts of the sample piece are restrained and prevented from deforming through the clamp, so that the shear performance of the composite material in the thickness direction is accurately tested.

Description

Technical Field

[0001] The invention belongs to the field of composite material testing, and in particular relates to a sample, a fixture and a method for testing the shear performance of a composite material in a thickness direction. Background Art

[0002] Fiber-reinforced composite materials are widely used in aerospace, rail transit, automobile and other fields due to their high specific stiffness, light weight, and strong designability. Composite panels generally use the traditional ABD theory, which only requires testing the in-plane performance of the material. However, in some cases, such as engineering design and simulation, it is necessary to know the tensile, compression, and shear properties in the thickness direction. The shear properties in the thickness direction include the strength and modulus of the material. There is no suitable test method in the current standard to measure the shear properties in the thickness direction, especially the shear modulus, so a test method that can measure the shear properties in the thickness direction is developed. Summary of the invention

[0003] Based on the above-mentioned technical problems, the present invention aims to provide a specimen, a fixture and a method for testing the shear properties of a composite material in the thickness direction.

[0004] The present application provides a specimen for shear performance testing in the thickness direction of a composite material, wherein the specimen is butterfly-shaped and comprises a symmetrically arranged left wing and right wing, wherein a working section is arranged between the left wing and the right wing, and the working section is 5-10 mm wide; a fixing hole is arranged on each of the two ends of the left wing and the right wing away from the working section.

[0005] The present application provides a fixture for testing the shear properties of a composite material in the thickness direction, comprising a first upper clamp, a second upper clamp, a first lower clamp, and a second lower clamp; the first lower clamp comprises a first support platform and a second support platform, a first positioning column and a bolt hole are arranged on the first support platform, and a second positioning column is arranged on the second support platform; a bolt hole and a positioning hole corresponding to the position of the positioning column of the second support platform are arranged on the second lower clamp, and the second lower clamp is sleeved on the second support platform of the first lower clamp through the positioning hole and the positioning column of the second support platform; the first upper clamp is provided with bolt holes corresponding to the positions of the bolt holes of the first support platform of the first lower clamp , and a positioning hole corresponding to the position of the positioning column; the first upper clamping plate is sleeved on the positioning column of the first support platform through the positioning hole in cooperation with the positioning column of the first support platform, and is connected and fixed to the first support platform of the first lower clamping plate by bolts; the second upper clamping plate is provided with bolt holes corresponding to the positions of the bolt holes of the second lower clamping plate, and a positioning hole matching the positioning column of the second support platform of the first lower clamping plate; the second upper clamping plate is sleeved on the positioning column of the second support platform through the positioning hole in cooperation with the positioning column of the first support platform and is connected to the second lower clamping plate by bolts; the sample is clamped between the first upper clamping plate, the second upper clamping plate and the first support platform, the second lower clamping plate, and is fixed by bolts.

[0006] In another embodiment, a clearance space is provided between the first upper clamping plate, the second upper clamping plate, the first support platform, and the second lower clamping plate to allow the sample to deform freely when subjected to shear force.

[0007] In another embodiment, the fixture further comprises a support plate, which is movably arranged between the second lower clamping plate and the second support platform. When the fixture and the sample are installed, the support plate provides support for the second lower clamping plate, the sample, and the first upper clamping plate, and can be horizontally withdrawn after the fixture and the sample are installed.

[0008] The present application also provides a method for testing the shear properties of a composite material in the thickness direction.

[0009] In shear deformation, the change in the angle between orthogonal line segments in the solid deformation is called shear strain or angular strain. The physical relationship of shear deformation is: , Where: : Shear stress, unit: MPa; G: shear modulus, unit: GPa; : Shear strain, unit: rad.

[0010] Therefore, to obtain the shear modulus, it is necessary to test the proportional relationship between shear stress and shear strain.

[0011] See attached Figure 1 , assuming that the micro-unit is subjected to shear deformation: The shear strain generated is α, then tanα=c / l, Where: c: displacement value of the micro-unit deformation; l: working length of the micro unit; According to Taylor's formula: tanx=x+x^3 / 3+2x^5 / 15+17x^7 / 315+62x^9 / 2835+...+[2^(2n)*(2^(2n)-1)*B(2n-1)*x^(2n-1)] / (2n)! When x is a very small value (in this invention, x is defined as being within 50000με, which is considered to be a very small value), tanx=x, then α = tanα = c / l; Therefore, it is necessary to measure c and l in order to calculate the shear strain α.

[0012] (2) Calculation formula of shear stress: , Where: is shear stress, unit: MPa; P is the loading force, in N. When P takes the maximum value during the loading process, we get The value is the shear strength; w is the working width of the micro unit, in mm; h is the working thickness of the micro unit, in mm.

[0013] (3) The shear modulus of the micro-unit when the loading force is P can be calculated using the following formula: ,

[0014] Where: G: shear modulus, unit: GPa; In order to make the shear modulus calculation more accurate, the increment of τ and γ within a certain period of time can be taken, so, ,

[0015] Where: : Select a shear strain point in the lower shear strain range (1500-2500με) as the starting point, select a shear strain point in the higher shear strain range (3500-4500με) as the end point, and the shear strain difference between the two shear strain points; : The difference between the shear stress corresponding to the shear strain at the starting point and the shear stress corresponding to the shear strain at the end point.

[0016] Based on the above theory, the present application provides a method for testing the shear properties of a composite material in the thickness direction, including using a universal testing machine, a displacement meter and the fixture, and the specific steps include: S1. Cut out 3-5 butterfly-shaped specimens from the composite material plate. The specimens should avoid defects such as cuts, delamination, and grooves. The working section length of the specimen is recorded as L, the working section width is recorded as W, and the working section thickness is recorded as H. S2, clamping and fixing the sample between the first upper clamping plate, the second upper clamping plate and the first support platform, the second lower clamping plate, and fixing them by bolts; S3. In the universal testing machine, enter the working section length, working section width and working section thickness of the sample currently to be tested, and set the following calculation formula: Shear stress calculation formula: ; Shear strain calculation formula: ; Where: C is the displacement value of the deformation of the working section of the specimen; S4. Place the fixture that holds the sample in the universal testing machine, so that the axis of the testing machine force passes through the centroid of the loading head and is perpendicular to the second upper clamping plate, and apply a certain preload to eliminate the gap between the fixture and the test piece, then pull out the support table, install the displacement meter and reset it to zero; S5. Load the loading head at a speed of 0.5 mm / min, so that the sample, the second upper clamping plate, and the second lower clamping plate are displaced vertically along the positioning column. Stop loading when the shear strain on the testing machine reaches 50,000 με or the sample is damaged; S6. Obtain the shear properties of the composite material in the thickness direction from the testing machine; S7. Calculation of shear modulus, the formula is as follows:

[0017] in: : Select a shear strain point in the lower shear strain range (1500-2500με) as the starting point, select a shear strain point in the higher shear strain range (3500-4500με) as the end point, and the shear strain difference between the two shear strain points; : The difference between the shear stress corresponding to the shear strain at the starting point and the shear stress corresponding to the shear strain at the end point.

[0018] The beneficial effects of the present invention are: (1) This test method designs the working section and the fixed part through the configuration of a specific specimen, and clamps and constrains the specimen through a specific specimen fixture, so that when the specimen is shear tested on the test equipment, the working section of the composite material can deform freely in the vertical direction and the displacement value can be accurately obtained, while the fixed part of the specimen is constrained by the fixture to prevent deformation; (2) Using trigonometric functions and Taylor series theorem, we can calculate the change in angle and thus find the shear strain. (3) In the prior art, the performance test of composite materials is mainly to test the shear performance in the in-plane direction of the composite materials. Since it is impossible to attach strain gauges in the thickness direction, only the destructive strength of the material can be tested. The test method disclosed in the present invention can test the shear strength of the composite material in the thickness direction and the shear modulus in the thickness direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0020] Attached Figure 1 It is a schematic diagram of the deformation of a tiny unit body when it is subjected to shear; Attached Figure 2 It is a schematic diagram of the three-dimensional structure of the sample; Attached Figure 3 It is a schematic diagram of the top view of the specimen; Attached Figure 4 It is a schematic diagram of the three-dimensional structure of the fixture; Attached Figure 5 It is a schematic diagram of the three-dimensional structure of the lower splint; Attached Figure 6 is a schematic diagram of the support plate structure; Attached Figure 7 This is a schematic diagram of the specimen clamping structure; Attached Figure 8 This is a schematic diagram of the structure of the sample after shear deformation; Attached Fig. 9 This is a schematic diagram of vertical displacement of shear deformation; Among them: 1-first upper clamping plate; 2-second upper clamping plate; 3-first lower clamping plate; 31-first supporting platform; 32-second supporting platform; 33-first positioning column; 34-second positioning column; 4-second lower clamping plate; 5-supporting plate; 51-slot; 6-positioning hole; 7-bolt hole; 8-sample; 81-left wing; 82-right wing; 83-working section. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application. In addition, it should be understood that the specific implementation methods 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, unless otherwise stated, the directional words used, such as "up", "down", "left" and "right", can be the direction of the actual use or working state of the device, can also be the direction of the drawing with reference to the accompanying drawings, and can also refer to two relative directions; while "inside" and "outside" refer to the outline of the device. Example 1

[0022] This embodiment provides a specimen for testing the shear properties of a composite material in the thickness direction.

[0023] Combined with Figure 2 The sample 8 is butterfly-shaped, including a symmetrically arranged left wing 81 and right wing 82, a working section 83 is arranged between the left wing 81 and the right wing 82; a bolt hole 7 is arranged on each of the four ends of the left wing 81 and the right wing 82 away from the working section 83; the thickness of the sample 8 is 5mm, the width b of the working section 83 is 5mm, and the length L of the working section 83 is 20mm. The sample can be a continuous fiber laminate or a SMC composite board, and the sample ply angle can be [0] n or [0 / 90] n Lamination, other forms of symmetrical lamination can also be used. Example 2

[0024] This embodiment provides a fixture for testing the shear properties of a composite material in the thickness direction.

[0025] Combined with Figure 3-5The clamp comprises a first upper clamping plate 1, a second upper clamping plate 2, a first lower clamping plate 3, a second lower clamping plate 4, and a support plate 5; the first lower clamping plate 3 comprises a first support platform 31 and a second support platform 32, the first support platform 31 is provided with a first positioning column 33 and a bolt hole 7, and the second support platform 32 is provided with a second positioning column 34; the second lower clamping plate 4 is provided with a bolt hole 7 and a positioning hole 6 matched with the second positioning column 34, and the second lower clamping plate 4 is sleeved on the second positioning column 34 through the positioning hole; the first upper clamping plate 1 is provided with a bolt hole 7 and a positioning hole 6, the position of the bolt hole 7 corresponds to the position of the bolt hole 7 on the first support platform 31, and the positioning hole 6 is matched with the first positioning column 33; the first upper clamping plate 1 is sleeved on the first positioning column 33 through the positioning hole 6, and is connected and fixed by bolts; the second upper clamping plate 2 A positioning hole 6 and a bolt hole 7 are provided, the positioning hole 6 cooperates with the second positioning column 34 on the second support platform 32, the position of the bolt hole 7 corresponds to the position of the bolt hole 7 of the second lower clamping plate 4, the second upper clamping plate 2 is sleeved on the second positioning column 34 of the second support platform 32 through the positioning hole 6, and is connected to the second lower clamping plate 3 thereunder by bolts; the support plate 5 is movably arranged between the second lower clamping plate 4 and the second support platform 32; the left side wing 81 of the sample 8 is clamped between the first upper clamping plate 1 and the first support platform 31 and fixed by bolts, and the right side wing 82 of the sample 8 is clamped between the second upper clamping plate 2 and the second lower clamping plate 4 and fixed by bolts; a clearance space is provided between the first upper clamping plate 1, the second upper clamping plate 2, the first support platform 31 and the second lower clamping plate 4 to allow the working section 83 of the sample 8 to deform freely when subjected to shear force.

[0026] The edges of the first support platform 31 and the second upper clamping plate 2 in the length direction close to the working section 83 of the sample 8 are chamfered to form a clearance space that allows the working section of the sample to deform freely when subjected to shear force.

[0027] The fixture can be used in conjunction with a universal testing machine to perform shear performance testing on a sample. Example 3

[0028] Based on the sample of Example 1 and the fixture of Example 2, a method for testing the shear performance of a composite material in the thickness direction is provided, including using a universal testing machine, a displacement meter and the fixture. The connection between the displacement meter and the universal testing machine is a prior art in the art. The displacement value of the sample when subjected to shear force can be detected in real time by the displacement meter, and the data can be fed back to the universal testing machine. The specific testing steps include: S1. Cut out 3-5 butterfly-shaped specimens from the composite material plate. The specimens should avoid defects such as cuts, delamination, and grooves. The working section length of the specimen is recorded as L, the working section width is recorded as W, and the working section thickness is recorded as H. S2, clamping and fixing the sample between the first upper clamping plate, the second upper clamping plate and the first support platform, the second lower clamping plate, and fixing them by bolts; S3. In the universal testing machine, enter the working section length, working section width and working section thickness of the sample currently to be tested, and set the following calculation formula: Shear stress calculation formula: ; Shear strain calculation formula: ; Where: C is the displacement value of the deformation of the working section of the specimen.

[0029] S4, placing the fixture for clamping and fixing the sample in the universal testing machine, making the axis of the testing machine force pass through the centroid of the loading head and be perpendicular to the second upper clamping plate, and applying a certain preload to eliminate the gap between the fixture and the test piece, then pulling out the support table, installing the displacement meter and clearing it to zero; the installation and connection between the displacement meter and the universal testing machine is a prior art, and the displacement meter in the present invention is mainly used to test the displacement value of the sample after being deformed by shear force, and feed back the data to the universal testing machine; S5. Load the loading head at a speed of 0.5 mm / min, so that the sample, the second upper clamping plate, and the second lower clamping plate are displaced vertically along the positioning column. Stop loading when the shear strain on the testing machine reaches 50,000 με or the sample is damaged; S6. Obtain the shear properties of the composite material in the thickness direction from the testing machine; S7. Calculation of shear modulus, the formula is as follows:

[0030] in: Δγ: Select a shear strain point as the starting point in the lower shear strain range (1500-2500με), select a shear strain point as the end point in the higher shear strain range (3500-4500με), and the shear strain difference between the two shear strain points; Δτ: The difference between the shear stress corresponding to the shear strain at the starting point and the shear stress corresponding to the shear strain at the end point.

[0031] The technical solutions provided by the embodiments of the present application are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A specimen for shear performance testing in the thickness direction of a composite material, characterized in that: The specimen is butterfly-shaped, including a symmetrically arranged left wing and right wing, with a working section arranged between the left wing and the right wing; a fixing hole is arranged on each of the two ends of the left wing and the right wing away from the working section; the thickness of the specimen is 5-10mm; and the width of the working section is 5-8mm.

2. A fixture for testing the shear performance of a composite material in the thickness direction, used for clamping and fixing the sample described in claim 1 to perform shear performance testing in the thickness direction, characterized in that: The invention comprises a first upper clamping plate, a second upper clamping plate, a first lower clamping plate and a second lower clamping plate; the first lower clamping plate comprises a first supporting platform and a second supporting platform, a first positioning column and a bolt hole are arranged on the first supporting platform, and a second positioning column is arranged on the second supporting platform; a bolt hole and a positioning hole matching with the second positioning column are arranged on the second lower clamping plate, and the second lower clamping plate is sleeved on the second positioning column through the positioning hole; a bolt hole corresponding to the position of the bolt hole of the first supporting platform of the first lower clamping plate and a positioning hole matching with the first positioning column are arranged on the first upper clamping plate through the positioning hole, and the first supporting platform of the first lower clamping plate is connected and fixed by bolts; the second upper clamping plate is provided with a bolt hole corresponding to the position of the bolt hole of the second lower clamping plate and a positioning hole matching with the second positioning column; the second upper clamping plate is sleeved on the second positioning column through the positioning hole, and is connected and fixed to the second lower clamping plate by bolts; the left side wing of the sample is clamped between the first upper clamping plate and the first supporting platform, and fixed by bolts; the right side wing of the sample is clamped between the second upper clamping plate and the second lower clamping plate, and fixed by bolts.

3. A fixture for testing shear properties of composite materials in the thickness direction according to claim 2, characterized in that: A clearance space is provided between the first upper clamping plate, the second upper clamping plate, the first supporting platform and the second lower clamping plate to allow the sample to deform freely when subjected to shear force.

4. A fixture for testing shear properties of composite materials in the thickness direction according to claim 2, characterized in that: It also includes a support plate, which is movably arranged between the second lower clamping plate and the second support platform.

5. A method for testing the shear properties of a composite material in the thickness direction, comprising using a universal testing machine, a displacement meter and the fixture, and the specific steps include: S1. Cut out 3-5 samples from the composite material plate. The samples should avoid defects such as cuts, delamination and grooves. The length of the working section of the sample is recorded as L, the width of the working section is recorded as W, and the thickness of the working section is recorded as H. S2, clamping and fixing the sample between the first upper clamping plate, the second upper clamping plate and the first support platform, the second lower clamping plate, and fixing them by bolts; S3. In the universal testing machine, enter the working section length, working section width, and working section thickness of the sample currently to be tested, and set the following calculation formula: Shear stress calculation formula: ; Shear strain calculation formula: ; in: C is the displacement value of the deformation in the working section of the specimen; S4. Place the fixture that holds the sample in the universal testing machine, so that the axis of the testing machine force passes through the centroid of the loading head and is perpendicular to the second upper clamping plate, and apply a certain preload to eliminate the gap between the fixture and the test piece, then pull out the support table, install the displacement meter and reset it to zero; S5. Load the loading head at a speed of 0.5 mm / min, so that the sample, the second upper clamping plate, and the second lower clamping plate are displaced vertically along the positioning column. Stop loading when the shear strain on the testing machine reaches 50,000 με or the sample is damaged; S6. Obtain the shear properties of the composite material in the thickness direction from the testing machine; S7. Calculate the shear modulus G using the following formula: Shear modulus calculation: ; in: : Select a shear strain point in the lower shear strain range (1500-2500με) as the starting point, select a shear strain point in the higher shear strain range (3500-4500με) as the end point, and the shear strain difference between the two shear strain points; : The difference between the shear stress corresponding to the shear strain at the starting point and the shear stress corresponding to the shear strain at the end point.

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