Variable-stiffness high-temperature test composite material tensile test piece and forming mold

Abstract

The utility model discloses a variable-rigidity high-temperature test composite material tensile test piece and a forming mold, relates to the technical field of composite material forming, and solves the problems that the test quality is influenced and even a reinforcing sheet is separated from a test piece body due to necking when the reinforcing sheet is adhered to the existing test piece in a tensile test. According to the utility model, a plurality of main fiber layer middle sections are continuously stacked together to form a tensile test piece main body; a plurality of thickening fiber layers are arranged at the two ends of the tensile test piece main body, and are alternately laid among the plurality of main fiber layers to form a dumbbell-shaped structure; sawtooth structure layers are arranged on the inner sides of the upper surface first main fiber layer and the lower surface first main fiber layer at the two ends of the tensile test piece main body. According to the utility model, the condition that the tensile test piece is locally compressed or extruded to damage the test piece under a clamping load is effectively avoided; the sawtooth structure layer is additionally arranged to be matched with sawteeth of the clamping tool to form mutual meshing of structures, so that good transfer of loads between the clamping tool and the test piece is ensured.

Description

Technical Field

[0001] The utility model relates to the technical field of composite material molding, in particular to a variable stiffness high temperature test composite material tensile test piece and a molding die. Background Art

[0002] Heat resistance is an important indicator in the design and use of resin-based fiber-reinforced composite materials. With the rapid development of my country's aerospace technology, the application of composite materials is becoming more and more extensive, and the requirements for their application environment are becoming more and more stringent, especially for heat resistance and strength retention after high temperature testing.

[0003] Composite materials are composed of multiple components. When the thermal expansion coefficients of the components differ greatly, even if the temperature changes slightly, large microscopic thermal stresses will be generated in the matrix. When the temperature rises, thermal expansion and certain internal stresses will be generated first. When the temperature rises further, the component materials of the composite material will gradually soften, melt, decompose, and even burn, causing a series of changes, which will sharply reduce the mechanical properties of the composite material. Therefore, it is necessary to characterize and evaluate the mechanical properties of composite materials at high temperatures.

[0004] Conventional testing methods are generally applicable to mechanical tests and sample preparation at ambient temperatures below 200°C. The main reasons are: first, when conventional high-temperature adhesives are used to paste reinforcement sheets, the shear strength drops below 10MPa after the use temperature exceeds 200°C, which cannot meet the shear force required for sample destruction; second, the operating temperature range of the conventional imported (INSTRON) resistive electronic extensometer for strain acquisition is -70°C to 200°C. Moreover, the working conditions under high-temperature test environments are complex, and matrix expansion, fiber resin peeling, matrix microcracks, reinforcement sheet cracking, etc. may occur. There are no corresponding method standards to guide testing in China or even internationally. Therefore, the mechanical property testing of composite materials above 200°C has always been a difficult problem for mechanical testing of composite materials.

[0005] However, bonding the reinforcing sheets on both sides of the specimen will form a stiffness mutation area. Due to the difference in modulus between the reinforcing sheet and the specimen, there is only a shear interface of the resin at the interface between the continuous layer and the discontinuous layer in the thickened area, and there is no continuous fiber transition. When subjected to a large tensile load, the shear stress of the interface is likely to exceed the shear strength of the material and crack first, making it impossible to accurately characterize the tensile strength of the material under high temperature conditions. During the tensile test, necking is likely to occur in the variable stiffness area, affecting the test quality, and even the reinforcing sheet may detach from the specimen body, making it impossible to accurately characterize the high-temperature mechanical properties of the material. Utility Model Content

[0006] In order to solve the above-mentioned problem that the existing specimens with adhesive reinforcement sheets will shrink during tensile testing, affecting the test quality, or even the reinforcement sheet will be separated from the specimen body and unable to accurately characterize the high-temperature mechanical properties of the material, the utility model proposes a variable stiffness high-temperature test composite material tensile specimen and molding mold. The utility model effectively avoids the situation where the specimen is partially compressed or squeezed under the support load and damaged by the support load by alternately laying thickened fiber layers at both ends of several main fiber layers; by adding a serrated structure layer to cooperate with the serrations of the support tooling, a structure is formed to bite each other, ensuring good load transfer between the support tooling and the specimen.

[0007] The utility model proposes a variable stiffness high-temperature test composite material tensile specimen, which specifically comprises a plurality of main fiber layers, a plurality of thickened fiber layers and four serrated structure layers, wherein the middle sections of the plurality of main fiber layers are continuously stacked together to form a tensile specimen body; a plurality of thickened fiber layers are arranged at both ends of the tensile specimen body, and the plurality of thickened fiber layers are alternately laid between the plurality of main fiber layers to form a dumbbell-shaped structure; a serrated structure layer is arranged on the inner side of the first main fiber layer on the upper surface of both ends of the tensile specimen body and on the inner side of the first main fiber layer on the lower surface.

[0008] Furthermore, the length of the thickened fiber layer gradually decreases from the center of the tensile specimen to the upper and lower surfaces of the tensile specimen.

[0009] Furthermore, the sawtooth structure layer is made of sheet molding compound.

[0010] A mold for preparing the above-mentioned tensile specimen, characterized in that it includes an upper mold, a middle mold and a lower mold, the upper mold and the lower mold have the same structure, both are provided with a boss structure at the middle position of one side, and a plurality of serration structures are provided on both sides of the boss structure; an upper mold is provided at the upper end of the middle mold, and a lower mold is provided at the lower end, the boss structures of the upper mold and the lower mold are opposite, and a dumbbell-shaped cavity is formed inside the middle mold.

[0011] The beneficial effects of the variable stiffness high temperature test composite material tensile test piece and the forming die described in the utility model are:

[0012] (1) The variable stiffness high-temperature test composite material tensile test specimen and molding die described in the utility model overcome the problem that the existing specimen adhesive reinforcement sheet will shrink during the tensile test, affecting the test quality or even separating the reinforcement sheet from the specimen body. By alternately laying thickened fiber layers at both ends of several main fiber layers, the situation where the specimen is locally compressed or squeezed and damaged by the applied load is effectively avoided. The continuous fiber and non-continuous fiber layers are spliced ​​and laid in an offset manner, which increases the interface between the middle and end of the specimen, ensuring that the tensile load is transmitted from the end of the specimen to the middle measurement area of ​​the specimen, which can better characterize the high-temperature mechanical properties of the material;

[0013] (2) The variable stiffness high temperature test composite material tensile test piece and forming mold described in the utility model, by adding a sawtooth structure layer to cooperate with the sawtooth of the supporting tooling, form a structure that bites each other, and ensure good load transfer between the supporting tooling and the test piece;

[0014] (3) The variable stiffness high-temperature test composite material tensile test specimen and forming mold described in the utility model form a transition zone between the middle part and the thickened area of ​​the specimen by changing the length of the thickened fiber layer, thereby avoiding the abnormal specimen damage caused by the necking phenomenon at the root of the specimen due to a sudden change in stiffness. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and the description thereof are used to explain the present invention and do not constitute an improper limitation on the present invention.

[0016] In the attached picture:

[0017] Figure 1 It is a structural schematic diagram of a variable stiffness high temperature test composite material tensile test piece described in the utility model;

[0018] Figure 2 It is a schematic diagram of the laying structure of the serrated structure layer on the lower surface of the end of a variable stiffness high temperature test composite material tensile test piece described in the utility model;

[0019] Figure 3 It is a structural schematic diagram of a variable stiffness high temperature test composite material tensile test piece of the utility model, in which the main fiber layer and the thickened fiber layer are alternately laid at the end;

[0020] Figure 4 It is a schematic diagram of the laying structure of the serrated structure layer on the upper surface of the end of a composite material tensile test piece for variable stiffness high temperature testing according to the utility model;

[0021] Figure 5 It is a structural schematic diagram of an upper mold of a molding mold for a composite material tensile specimen with variable stiffness and high temperature testing according to the utility model;

[0022] Figure 6 It is a structural schematic diagram of a middle mold of a molding mold for a composite material tensile specimen with variable stiffness and high temperature testing according to the utility model;

[0023] Figure 7 It is a structural schematic diagram of a lower mold of a molding mold for a composite material tensile specimen with variable stiffness and high temperature testing according to the utility model;

[0024] Figure 8 It is a schematic structural diagram of a variable stiffness high temperature test composite material tensile test piece forming mold after mold closing;

[0025] Fig. 9 This is a schematic diagram of the size division of a variable stiffness high temperature test composite material tensile test piece described in the utility model;

[0026] Among them: 1-upper mold, 2-middle mold, 3-lower mold, 4-tensile specimen. DETAILED DESCRIPTION

[0027] The specific implementation of the utility model is further described in detail below with reference to the accompanying drawings:

[0028] Specific implementation method 1: See Figure 1-Figure 9 The present embodiment is described in detail. The variable stiffness high temperature test composite material tensile specimen described in the present embodiment specifically comprises a plurality of main fiber layers, a plurality of thickened fiber layers and four serrated structure layers, wherein the middle sections of the plurality of main fiber layers are continuously stacked together to form the tensile specimen body; a plurality of thickened fiber layers are arranged at both ends of the tensile specimen body, and the plurality of thickened fiber layers are alternately laid between the plurality of main fiber layers to form a dumbbell-shaped structure; a serrated structure layer is arranged on the inner side of the first main fiber layer on the upper surface of both ends of the tensile specimen body and on the inner side of the first main fiber layer on the lower surface.

[0029] The length of the thickened fiber layer is gradually shortened from the center of the tensile specimen to the upper and lower surfaces of the tensile specimen, so that the transition zone between the middle area of ​​the tensile specimen and the thickened areas at both ends is gradually laid in a transitional manner. In this way, the shear area can be increased in the thickened area, thereby greatly improving the bearing capacity of the thickened area, and the material properties can be accurately characterized.

[0030] The sawtooth structure layer is made of sheet molding compound (SMC), and the sawtooth structure layer cooperates with the saw teeth of the supporting tooling to form a structure that bites each other, ensuring good load transmission between the supporting tooling and the specimen; the tooth groove direction of the sawtooth structure layer is parallel to the width direction of the tensile specimen.

[0031] A mold for preparing the above-mentioned tensile test piece includes an upper mold 1, a middle mold 2 and a lower mold 3. The upper mold 1 and the lower mold 3 have the same structure, and both are provided with a boss structure at the middle position of one side, and a plurality of serration structures are provided on both sides of the boss structure; the upper mold 1 is provided at the upper end of the middle mold 2, and the lower mold 3 is provided at the lower end, the boss structures of the upper mold 1 and the lower mold 3 are opposite, and a dumbbell-shaped cavity is formed inside the middle mold 2; the upper mold 1, the middle mold 2 and the lower mold 3 are connected by bolts.

[0032] A method for preparing the above-mentioned variable stiffness high temperature test composite material tensile specimen comprises the following steps:

[0033] Firstly lay the first main fiber layer in the molding mold, and place a serrated structure layer at both ends of the main fiber layer; above the serrated structure layer, the main fiber layer and the thickened fiber layer are alternately laid several times by adopting the interlaced staggered laying method, and the thickened fiber layer is laid at both ends of the main fiber layer; place a serrated structure layer at both ends of the second to last main fiber layer, and lay the last main fiber layer above the serrated structure layer; close the mold and perform pressure molding.

[0034] The specific preparation process of the variable stiffness high temperature test composite material tensile test piece described in the utility model is as follows:

[0035] 1. Cutting

[0036] The length of the specimen is L, the thickness of the thickened area at both ends of the tensile specimen is T, the thickness of the middle section of the specimen is t, the length of the transition zone is l, and the length of the middle section of the specimen is l0. Fig. 9 shown.

[0037] The starting length of the transition zone is (L-l0-2l) / 2 and [(L-l0-2l) / 2+l]. When laying, first lay the lower thickened area, then the middle area, and then the upper thickened area.

[0038] The thickness of the single layer of prepreg used in the specimen is h, and the number of prepreg layers required in the middle of the specimen is n:

[0039] n=t / h

[0040] The length of the main fiber layer at the center of the tensile specimen is L.

[0041] Then the number of prepreg layers N required for the thickened areas on both sides is:

[0042] N=(Tt) / h

[0043] Then the number of prepreg layers N1 required for the single-sided thickening area is:

[0044] N1=(Tt) / 2h

[0045] The length of the transition zone is l, and the length of the thickened fiber layer at one end of the tensile specimen is:

[0046] Layer 1: (L-l0-2l) / 2;

[0047] Layer 2: (L-l0-2l) / 2+l / (Tt) / 2h;

[0048] Layer 3: (L-l0-2l) / 2+l / (Tt) / 2h×2; ......

[0050] The (Tt) / 2h layer: [(L-l0-2l) / 2+l].

[0051] The cutting lengths of the main fiber layers are:

[0052] Layer 1: (L+2l);

[0053] Layer 2: [L+2l-l / (Tt) / 2h×2];

[0054] Layer 3: [L+2l-l / (Tt) / 2h×4]; ......

[0056] Layer t / 2h: L.

[0057] 2. Process molding

[0058] Lay out the lower half first.

[0059] First, lay the first main fiber layer, and then place the sawtooth structure layer of sheet molding compound (SMC) at both ends of the first main fiber layer, and lay the second main fiber layer on the sawtooth structure layer. Figure 2 shown.

[0060] Afterwards, the thickening fiber layer and the main fiber layer are laid alternately on top of the second main fiber layer, and the thickening fiber layer is only laid at both ends of the main fiber layer, such as Figure 3 As shown. During this process, the length of the thickened fiber layer gradually increases, reaching the maximum at the [(Tt) / 2h]th layer, completing the laying of the lower half of the tensile specimen. Then, the laying of the upper half of the tensile specimen begins. The laying process is similar to that of the lower half, and the thickened fiber layer and the main fiber layer are laid alternately. During this process, the length of the thickened fiber layer gradually decreases. A sawtooth structure layer is placed above the second-to-last main fiber layer, and the last main fiber layer is laid above the sawtooth structure layer, as shown in FIG. Figure 4 After the laying is completed, the forming mold is closed and pressed into shape, as shown in FIG. Figure 1 The upper and lower surfaces of the molded product are both continuous main fiber layers. The two ends of the tensile test piece are laid in staggered layers through splicing to increase the load-bearing capacity of the thickened fiber layer, which can accurately characterize the tensile strength of the material under high temperature conditions.

[0061] Summarizing the above implementation cases, the variable stiffness high-temperature test composite material tensile test specimen and forming mold described in the utility model overcome the problem that the existing specimen adhesive reinforcement sheet will shrink during the tensile test, affecting the test quality and even the separation of the reinforcement sheet from the specimen body. By alternately laying thickened fiber layers at both ends of several main fiber layers, the situation in which the specimen is locally compressed or squeezed and damaged under the applied load is effectively avoided. The continuous fiber and non-continuous fiber layers are spliced ​​and laid in an offset manner, which increases the interface between the middle and end of the specimen, ensuring that the tensile load is transmitted from the end of the specimen to the middle measurement area of ​​the specimen. domain, which can better characterize the high-temperature mechanical properties of the material; the variable stiffness high-temperature test composite material tensile specimen and forming mold described in the utility model, by adding a serrated structure layer and cooperating with the serrations of the supporting tooling, form a structure that bites each other, thereby ensuring good load transmission between the supporting tooling and the specimen; the variable stiffness high-temperature test composite material tensile specimen and forming mold described in the utility model, by changing the length of the thickened fiber layer, form a transition zone in the middle of the specimen and the thickened area, thereby avoiding the sudden change of stiffness and causing the necking phenomenon at the root of the specimen, resulting in abnormal specimen damage.

[0062] The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the utility model in detail. It should be understood that the above description is only a specific embodiment of the utility model and is not intended to limit the utility model. It can also be a reasonable combination of the features recorded in the above implementation methods. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

Claims

1. A variable stiffness high temperature test composite material tensile specimen, characterized in that: It includes several main fiber layers, several thickened fiber layers and four serrated structure layers. The middle sections of the several main fiber layers are continuously stacked together to form a main body of the tensile specimen; several thickened fiber layers are arranged at both ends of the main body of the tensile specimen, and the several thickened fiber layers are alternately laid between the several main fiber layers to form a dumbbell-shaped structure; the serrated structure layer is arranged on the inner side of the first main fiber layer on the upper surface of both ends of the main body of the tensile specimen and on the inner side of the first main fiber layer on the lower surface.

2. The variable stiffness high temperature test composite material tensile specimen according to claim 1, characterized in that: The length of the thickened fiber layer gradually decreases from the center of the tensile specimen to the upper and lower surfaces of the tensile specimen.

3. The variable stiffness high temperature test composite material tensile specimen according to claim 1, characterized in that: The sawtooth structure layer is made of sheet molding compound.

4. A forming die for preparing the tensile test piece according to claim 1, 2 or 3, characterized in that: The invention comprises an upper mold (1), a middle mold (2) and a lower mold (3); the upper mold (1) and the lower mold (3) have the same structure, and both are provided with a boss structure at the middle section of one side, and a plurality of sawtooth structures are provided on both sides of the boss structure; the upper mold (1) is provided at the upper end of the middle mold (2), and the lower mold (3) is provided at the lower end; the boss structures of the upper mold (1) and the lower mold (3) are opposite to each other, and a dumbbell-shaped cavity is formed inside the middle mold (2).

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