Test method and test system

Abstract

The invention belongs to the technical field of material performance testing, and discloses a testing method and a testing system. The testing method is used for testing the tensile property of the prepreg. The method specifically comprises the following steps: film covering: covering two side surfaces of a prepreg with films; sealing: sealing the double-layer diaphragm; vacuumizing, namely vacuumizing a coating space formed by the double-layer membrane, so that the prepreg is attached to the membrane; stretching, namely applying stretching force to two ends of a complex formed by the prepreg and the double-layer membrane at a preset temperature and a preset pressure; and measuring, namely measuring a shear angle and a shear force in the stretching process. By means of the prepreg tensile property testing device, tensile property testing of the prepreg under the dual effects of a certain temperature and a certain pressure can be achieved, meanwhile, it can be guaranteed that the prepreg is stably clamped in the tensile process, and the accuracy of the prepreg tensile test is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of material performance testing, and in particular to a testing method and a testing system. Background Art

[0002] In-plane shear performance is generally considered to be the main deformation mechanism of prepregs. Good shear performance prevents the material from wrinkling or buckling during the process of transforming from a flat structure to a three-dimensional structure, especially during the molding process of double-curvature structural parts.

[0003] The shear performance data of prepregs is a necessary input for simulating the prepreg preforming process using simulation methods. In addition, testing the forming performance of prepregs is also beneficial for understanding the deformation behavior of the material during the forming process and making reasonable selection based on the deformation performance of the material, thereby improving the quality of the formed structural parts.

[0004] At present, the shear performance of prepregs under a certain molding temperature and a certain pressure is relatively different from the shear performance under room temperature and normal pressure mode. Moreover, the data measured at room temperature and normal pressure does not have sufficient reference value for the simulation analysis of the preforming process and the analysis of the deformation mechanism of the preforming process. In addition, the viscosity of the prepreg resin is low at high temperature, and the thickness of the clamping end of the prepreg is easily changed under the action of pressure, which causes the sample to slip.

[0005] Therefore, there is an urgent need for a testing method and a testing system to solve the above-mentioned problem of testing the forming performance of prepregs under the dual effects of temperature and pressure. Summary of the Invention

[0006] The purpose of the present invention is to provide a testing method and testing system for realizing the tensile performance test of prepreg under the dual action of a certain temperature and a certain pressure, while ensuring that the prepreg is stably clamped during the stretching process, thereby improving the accuracy of the prepreg tensile test.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] The test method for tensile testing of prepregs comprises the following steps:

[0009] Laminating, covering the surfaces of both sides of the prepreg with membranes;

[0010] Sealing, sealing the double-layer diaphragm;

[0011] Vacuuming the enclosed space formed by the double-layer membrane to laminate the prepreg to the membrane;

[0012] Stretching, applying a tensile force to a composite body formed by the prepreg and the double-layered membrane at a preset temperature and a preset pressure;

[0013] Measure the shear angle and shear force during stretching.

[0014] As an optional solution of the testing method, before the vacuuming step, the composite body is pre-pressed at a first preset temperature for a first preset time.

[0015] A test system, based on the test method described in any of the above schemes, includes the diaphragm, and,

[0016] a sealing strip, sealing the composite body along the outer periphery of the double-layered membrane;

[0017] an upper clamp, clamping one end of the complex;

[0018] a lower clamp, clamping the other end of the complex;

[0019] An environmental chamber, wherein the upper fixture, the lower fixture, and the composite body are all disposed in the environmental chamber, and the environmental chamber is capable of changing the temperature within the chamber;

[0020] One end of the vacuum tube is inserted into the complex body, and the other end is connected to the vacuum pump.

[0021] As an optional solution for a testing system, the upper clamp includes a first clamping plate and a second clamping plate; the first clamping plate and the second clamping plate are respectively provided with a plurality of first mounting holes, one end of the composite body is placed between the first clamping plate and the second clamping plate, and a threaded fastener passes through the first mounting hole so that the first clamping plate and the second clamping plate clamp one end of the composite body.

[0022] As an optional solution of the testing system, one of the first clamping plate and the second clamping plate is connected to one end of a traction rod, and the other end of the traction rod is connected to the traction end of the mechanical testing machine.

[0023] As an optional solution of the test system, a through hole is provided on the composite body at a position corresponding to the first mounting hole, and the threaded fastener can pass through the through hole.

[0024] As an optional solution for the testing system, the lower clamp includes a third clamping plate and a fourth clamping plate; the third clamping plate and the fourth clamping plate are respectively provided with a plurality of second mounting holes, the other end of the complex is placed between the third clamping plate and the fourth clamping plate, and threaded fasteners pass through the second mounting holes so that the third clamping plate and the fourth clamping plate clamp the other end of the complex.

[0025] As an optional solution of the testing system, one of the third clamping plate and the fourth clamping plate is connected to one end of a mounting rod, and the other end of the mounting rod is connected to a fixed end of a mechanical testing machine.

[0026] As an optional solution of the testing system, the testing system further includes a camera, which is located outside the environmental chamber. An observation window is provided on the door of the environmental chamber, and the camera is used to photograph the tensile state of the composite through the observation window.

[0027] As an optional solution of a test system, the diaphragm is a silicone rubber membrane.

[0028] Beneficial effects:

[0029] In the first aspect, the method first covers the two sides of the prepreg with a diaphragm. When the two are bonded, the outer periphery of the diaphragm can cover the prepreg, and the gap formed by the double-layer diaphragm is sealed at the outer periphery of the diaphragm, so that the prepreg is completely coated. At this time, there is no sufficient bonding pressure between the prepreg and the diaphragm. The coating space formed by the double-layer diaphragm is vacuumed, and the double-layer diaphragm is tightly bonded to the prepreg by air pressure. Further, the test temperature and pressure are adjusted to a preset temperature and a preset pressure respectively, and a tensile test is performed on both ends of the composite formed by the prepreg and the double-layer diaphragm. The shear force and shear angle as well as the change process of the prepreg tensile process are obtained through the test. This test method can realize the tensile performance test of the prepreg under the dual action of a certain temperature and a certain pressure. Compared with the data measured at room temperature and normal pressure, it has more reference value for the simulation analysis of the preforming process and the analysis of the deformation mechanism of the preforming process. At the same time, the composite can ensure that the prepreg is stably clamped during the stretching process, thereby improving the accuracy and stability of the prepreg tensile test.

[0030] Secondly, the testing system based on this method can ensure that the tensile test of the prepreg is stably completed under a certain temperature and pressure. At the same time, the composition of this testing system is relatively simple, which saves testing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flow chart of a testing method provided by an embodiment of the present invention;

[0032] Figure 2 2 is a schematic structural diagram of an upper clamp provided by an embodiment of the present invention;

[0033] Figure 3 1 is a schematic structural diagram of a lower clamp provided by an embodiment of the present invention;

[0034] Figure 4 Schematic diagram of structural parameters of the prepreg before denaturation provided by an embodiment of the present invention;

[0035] Figure 5 Schematic diagram of structural parameters of the prepreg after modification provided by an embodiment of the present invention.

[0036] In the picture:

[0037] 1. Upper clamp; 11. First clamping plate; 12. Second clamping plate;

[0038] 2. Lower clamp; 21. Third clamping plate; 22. Fourth clamping plate;

[0039] 3. Traction rod; 4. Mounting rod. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0041] In the description of the present invention, unless otherwise expressly specified or limited, the terms "connected," "connected," and "fixed" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific circumstances.

[0042] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0043] In the description of this embodiment, the terms "upper," "lower," "right," and other orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely for ease of description and simplified operation. They do not indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used solely for descriptive purposes and have no special meanings.

[0044] Please see the attached Figure 1 The first aspect of this embodiment relates to a testing method for performing a tensile property test on a prepreg. Specifically, the method comprises the following steps:

[0045] S1, laminating, covering the surfaces of both sides of the prepreg with a film;

[0046] S2, sealing, sealing the double-layer diaphragm;

[0047] S3. Vacuuming the covering space formed by the double-layer diaphragm to make the prepreg and the diaphragm fit together;

[0048] S4, stretching, applying a tensile force to the composite formed by the prepreg and the double-layer membrane at a preset temperature and a preset pressure;

[0049] S5. Measure the shear angle and shear force.

[0050] Prepregs are a composite of continuous fibers or fabrics impregnated with a resin matrix under strictly controlled temperature conditions. They serve as an intermediate material in the preparation of composite materials. Because prepreg resin has low viscosity at high temperatures, the thickness of the prepreg clamping end can easily change under pressure, causing specimen slippage during tensile testing.

[0051] This method first covers the two side surfaces of the prepreg with a diaphragm. The diaphragm can be a thin silicone rubber diaphragm. Since the prepreg needs to be completely covered by the diaphragm, the area of ​​the diaphragm actually used is larger than the surface area of ​​the prepreg. When the two are bonded, the outer periphery of the diaphragm can completely cover the outer periphery of the prepreg, and the gap formed by the double-layer diaphragm is sealed at the outer periphery of the diaphragm to completely wrap the prepreg. At this time, there is not enough bonding pressure between the prepreg and the diaphragm. By vacuuming the covering space formed by the double-layer diaphragm, the double-layer diaphragm is tightly bonded to the prepreg using air pressure. Further, the test temperature and pressure are adjusted to the preset temperature and preset pressure respectively, and a tensile test is performed on both ends of the composite formed by the prepreg and the double-layer diaphragm. The shear force and shear angle of the prepreg stretching process and the change process are obtained through the test.

[0052] In this embodiment, since the friction coefficient between the surfaces of the diaphragm and the prepreg is very small, during the tensile test, the effect of the friction force introduced into the diaphragm on the tensile force value of the prepreg is relatively small. Therefore, the tensile test of the composite can relatively truly reflect the tensile properties of the prepreg itself. On the other hand, even under certain temperature and pressure conditions, the viscosity of the prepreg decreases under the action of high temperature, and the thickness changes under the action of pressure. However, the clamping end acts on the diaphragm, and the diaphragm and prepreg have become a complete composite, which can effectively prevent the entire composite from slipping and ensure the stable progress of the tensile test.

[0053] In summary, this test method can realize the tensile performance test of prepreg under the dual action of a certain temperature and a certain pressure. Compared with the data measured at room temperature and normal pressure, the test data obtained by this method has more sufficient reference value for the simulation analysis of the preforming process and the analysis of the deformation mechanism of the preforming process. At the same time, the composite can ensure that the prepreg is stably clamped during the stretching process, thereby improving the accuracy and stability of the prepreg tensile test.

[0054] Optionally, before the vacuuming step, the composite body is pre-pressed at a first preset temperature for a first preset time.

[0055] In this embodiment, when the vacuum degree reaches 1 atmosphere, the pressure is maintained at 40° C. for 10 minutes to pre-compact the prepreg laminate, which can improve the overall stiffness of the prepreg laminate and facilitate subsequent operations.

[0056] Please see the attached Figure 2 and attached Figure 3 The second aspect of this embodiment also relates to a testing system based on the above-mentioned testing method, specifically comprising a diaphragm, a sealing strip, an upper fixture 1, a lower fixture 2, an environmental chamber, and a vacuum tube. The sealing strip seals the composite along the periphery of the double-layered diaphragm; the upper fixture 1 clamps one end of the composite; the lower fixture 2 clamps the other end of the composite; the upper fixture 1, the lower fixture 2, and the composite are all placed in the environmental chamber, which can change the temperature within the chamber; one end of the vacuum tube is inserted into the composite, and the other end is connected to a vacuum pump.

[0057] In this embodiment, the prepreg is first cut to the required size. For prepreg with a 45° layup, the non-supported section is at least twice the width. Space is reserved on both sides of the diaphragm for sealant. The two ends of the diaphragm and prepreg composite are clamped by an upper clamp 1 and a lower clamp 2, respectively. The upper clamp 1 is the stretching end, and the lower clamp 2 is the fixed end. The upper clamp 1 pulls the composite upward. The upper clamp 1, the lower clamp 2, and the composite are completely placed inside the environmental chamber, which is used to set the temperature and pressure of the composite's stretching environment. At the same time, vacuum tubes are introduced on both sides of the composite, and the interior of the composite is evacuated by a vacuum pump. After reaching the predetermined pressure, the vacuum pump is turned off and the pressure is maintained for 15 minutes without air leakage to ensure the sealing between the diaphragms.

[0058] Based on the above test method, this system can ensure that the tensile test of prepreg is stably completed under a certain temperature and pressure. At the same time, the composition structure of this test system is relatively simple, saving test costs.

[0059] Optionally, the upper clamp 1 includes a first clamping plate 11 and a second clamping plate 12; a plurality of first mounting holes are respectively opened on the first clamping plate 11 and the second clamping plate 12, one end of the complex is placed between the first clamping plate 11 and the second clamping plate 12, and the threaded fastener passes through the first mounting hole so that the first clamping plate 11 and the second clamping plate 12 clamp one end of the complex.

[0060] Furthermore, the lower clamp 2 includes a third clamping plate 21 and a fourth clamping plate 22; a plurality of second mounting holes are respectively opened on the third clamping plate 21 and the fourth clamping plate 22, and the other end of the complex is placed between the third clamping plate 21 and the fourth clamping plate 22, and the threaded fasteners pass through the second mounting holes so that the third clamping plate 21 and the fourth clamping plate 22 clamp the other end of the complex.

[0061] In this embodiment, the structures of the upper clamp 1 and the lower clamp 2 are basically the same, and the two ends of the complex are stably clamped by double-plate pressure clamping. The structures of the upper clamp 1 and the lower clamp 2 are simple, and the locking method using multiple sets of threaded fasteners is simple and easy to operate.

[0062] Optionally, one of the first clamping plate 11 and the second clamping plate 12 is connected to one end of the traction rod 3 , and the other end of the traction rod 3 is connected to the traction end of the mechanical testing machine.

[0063] In this embodiment, the traction end of the mechanical testing machine acts on the traction rod 3, which is screwed to the first clamping plate 11 or the second clamping plate 12, so that the traction rod 3 drives the entire upper clamp 1 to pull the complex upward.

[0064] Optionally, one of the third clamping plate 21 and the fourth clamping plate 22 is connected to one end of the mounting rod 4 , and the other end of the mounting rod 4 is connected to a fixed end of the mechanical testing machine.

[0065] In this embodiment, the fixed end of the mechanical testing machine is connected to the mounting rod 4 , and the mounting rod 4 is used to fix the lower clamp 2 .

[0066] Optionally, a through hole is provided on the composite body at a position corresponding to the first mounting hole, and the threaded fastener can pass through the through hole.

[0067] In this embodiment, by providing a through hole at a position of the composite body corresponding to the first mounting hole and allowing the threaded fastener to pass through the through hole, the composite body can be stably positioned relative to the upper fixture 1, thereby improving operability.

[0068] Optionally, the test system further comprises a camera, which is located outside the environmental chamber. An observation window is provided on the door of the environmental chamber, and the camera is used to photograph the tensile state of the composite through the observation window.

[0069] To further monitor the changes in the prepreg fibers during testing, a camera installed outside the environmental chamber records the entire stretching process of the prepreg stack. This camera is connected to the processor signal, and the relevant software of the computing platform is used to process and record the data.

[0070] The following content is used to introduce the calculation principle of the prepreg tensile performance test model.

[0071] In the case of double diaphragm pressure, the diaphragm material and prepreg deform together during the test without sliding against each other. Therefore, the friction between the two is not considered. The force to stretch the prepreg stack can be calculated using the following formula:

[0072] F be =F t -F d (1)

[0073] Where F t is the force value recorded by the mechanical testing machine, F d F is the force value obtained by stretching the diaphragm material under the same conditions; be is the force to stretch the prepreg laminate.

[0074] For fabric materials, according to the PJN theory, the specimen can be divided into three regions: A, B and C, such as Figure 4 and Figure 5 As shown. If there is no intralayer slip in the specimen, region C is a pure shear region, and the shear angle can be extracted from this region. The shear angle of region B is always half of that of region C, while the shear angle of region A remains unchanged during deformation. Figure 4 In the equation (2), Lc is the side length of the square in region C and remains constant during deformation. Assuming that the fiber angle of the prepreg is ±45° before deformation, the fiber angle during deformation can be calculated using formula (2).

[0075]

[0076] Where H0 is the initial effective length, W0 is the initial width of the specimen, and d is the displacement during the test.

[0077] The shear angle γ during the eccentric tensile test can be calculated using formula (3).

[0078]

[0079] Since there is no shear limit restriction of fabric materials during the shearing process of unidirectional prepreg, its shearing behavior is quite different from that of fabric, that is, formula (2) does not hold. At the same time, in the actual material forming process, the shearing behavior of the prepreg laminate is affected by pressure, temperature and stretching rate. Therefore, the present invention proposes an improved off-axis stretching shear angle analysis model. The calculation formula for the off-axis stretching shear angle of unidirectional prepreg under pressure, temperature and stretching rate can be defined as:

[0080] γ=90°-2θ=90°-2(K1d+K2d 2 ) (4)

[0081] Where K1 and K2 are model parameters. K1 and K2 are obtained by nonlinear fitting of the shear angle-displacement curve of the specimen at different temperatures, pressures, and stretching rates. K1 and K2 are functions related to temperature T (K), stretching rate V (mm / min), and pressure P (MPa):

[0082] K1=a1+a2T+a3V+a4P (5)

[0083] K2=b1+b2T+b3V+b4P (6)

[0084] Wherein a1, a2, a3, a4, b1, b2, b3 and b4 are model parameters, among which a1, a2, a3 and a4 can be obtained by linear fitting of K1 and temperature / stretching rate / pressure curve, and b1, b2, b3 and b4 can be obtained by linear fitting of K2 and temperature / stretching rate / pressure curve.

[0085] Since the data directly obtained from the test is axial force, not shear force, it is necessary to extract the shear force first. From formula (4), we can know that:

[0086]

[0087] Where, is the shear rate, is the stretching rate.

[0088] During the test, F be Acting on the specimen, it causes deformation in areas B and C. Therefore, the following formula can be obtained:

[0089]

[0090]

[0091]

[0092] Where A γ is the initial area of ​​area C, Aγ is the initial area of ​​area B, C s (γ) is the torque required to produce γ shear deformation per unit area. To produce per unit area The torque required for shear deformation. Substituting formula (9) and formula (10) into formula (8), we can obtain:

[0093]

[0094] Unit area torque C s and shear force F nor The relationship is:

[0095] C s (γ)=F nor (γ)·cos(γ) (12)

[0096]

[0097] therefore,

[0098]

[0099] It can be found from formula (13) that (13) depends on its own value at γ / 2, that is, In addition, the lack of a boundary condition makes it difficult to solve these equations. In order to obtain a more accurate shear force, an analytical expression for the relationship between shear force and shear angle is proposed, assuming that there is a power function relationship between the normalized shear force and the shear angle:

[0100] F nor (γ)=Aγ B +C (15)

[0101] Substituting formula (15) into formula (14), we can obtain the following formula:

[0102]

[0103] Because F nor (0) = 0, so the parameter C in formula (15) is 0. From formula (4)

[0104] You can get:

[0105]

[0106] Therefore, formula (16) can be transformed into:

[0107]

[0108] The shear angle γ obtained from the test is compared with its corresponding F beSubstituting the values ​​into formula (18) can obtain the parameter values ​​of the model.

[0109] Shear stress F sh (γ) can be obtained by normalizing the shear force F nor (γ) divided by the initial thickness of the specimen (h) yields:

[0110]

[0111] The shear modulus G(γ) is determined by the derivative of the shear stress with respect to the shear angle:

[0112]

[0113] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. A person skilled in the art would be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A test method for testing the tensile properties of prepregs, characterized in that: The following steps are involved: Laminating, covering the surfaces of both sides of the prepreg with membranes; Sealing, sealing the double-layer diaphragm; Vacuuming the enclosed space formed by the double-layer membrane to laminate the prepreg to the membrane; Stretching, applying a tensile force to a composite body formed by the prepreg and the double-layered membrane at a preset temperature and a preset pressure; Measure the shear angle and shear force during stretching.

2. The testing method according to claim 1, wherein: Before the vacuuming step, the composite body is pre-pressed at a first preset temperature for a first preset time.

3. The test system is characterized in that The test method according to any one of claims 1 and 2, comprising the diaphragm, and a sealing strip, sealing the composite body along the outer periphery of the double-layered membrane; an upper clamp (1) for clamping one end of the composite body; a lower clamp (2) for clamping the other end of the complex; An environmental box, wherein the upper fixture (1), the lower fixture (2) and the composite body are all arranged in the environmental box, and the environmental box can change the temperature inside the box; One end of the vacuum tube is inserted into the complex body, and the other end is connected to the vacuum pump.

4. The test system according to claim 3, characterized in that: The upper clamp (1) includes a first clamping plate (11) and a second clamping plate (12); a plurality of first mounting holes are respectively opened on the first clamping plate (11) and the second clamping plate (12); one end of the composite body is placed between the first clamping plate (11) and the second clamping plate (12), and a threaded fastener passes through the first mounting hole so that the first clamping plate (11) and the second clamping plate (12) clamp one end of the composite body.

5. The test system according to claim 4, characterized in that: One of the first clamping plate (11) and the second clamping plate (12) is connected to one end of the traction rod (3), and the other end of the traction rod (3) is connected to the traction end of the mechanical testing machine.

6. The test system according to claim 4, characterized in that: A through hole is provided on the composite body at a position corresponding to the first mounting hole, and the threaded fastener can pass through the through hole.

7. The test system according to claim 3, wherein: The lower clamp (2) includes a third clamping plate (21) and a fourth clamping plate (22); a plurality of second mounting holes are respectively provided on the third clamping plate (21) and the fourth clamping plate (22); the other end of the composite body is placed between the third clamping plate (21) and the fourth clamping plate (22), and a threaded fastener passes through the second mounting hole so that the third clamping plate (21) and the fourth clamping plate (22) clamp the other end of the composite body.

8. The test system according to claim 7, characterized in that: One of the third clamping plate (21) and the fourth clamping plate (22) is connected to one end of the mounting rod (4), and the other end of the mounting rod (4) is connected to the fixed end of the mechanical testing machine.

9. The test system according to claim 3, wherein: The testing system further includes a camera, which is located outside the environmental chamber. An observation window is provided on the door of the environmental chamber. The camera is used to photograph the tensile state of the composite through the observation window.

10. The test system according to claim 3, wherein: The diaphragm is a silicone rubber membrane.

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