A device and method for forming a composite biaxial tensile test specimen

Abstract

The application relates to the technical field of tensile test, in particular to a forming device and method of a composite biaxial tensile test piece. In use, a co-cured test piece and a secondary cemented test piece can be obtained respectively. Since the upper cover plate and the lower bottom plate are detachably connected with the center area chamfer slope forming piece of the reinforcing sheet, when the device is used to manufacture the test piece by adopting the secondary cementing method, the center area chamfer slope forming piece of the reinforcing sheet is prevented from glue overflow and glue blocking during the secondary adhesion and solidification of the test piece and the reinforcing sheet. After the first solidification of the reinforcing sheet, the center area chamfer slope forming piece of the reinforcing sheet is demoulded without the need of demoulding, and the purpose of glue blocking is achieved after the secondary adhesion of the test piece, so that the problem of glue overflow and glue blocking during the secondary adhesion is solved. Meanwhile, the center area chamfer slope direction through hole of the co-cured test piece reinforcing sheet area can be directly solidified and formed under the action of the center area chamfer slope forming piece of the reinforcing sheet, so that the machining step is saved, and the problems of interlaminar delamination and splitting of the reinforcing sheet fiber layer can be avoided.

Description

Technical Field

[0001] This invention relates to the field of tensile testing technology, and in particular to a molding apparatus and method for biaxial tensile test specimens of composite materials. Background Technology

[0002] Carbon fiber reinforced composites are increasingly widely used in aerospace, rail transportation, and other fields. With the development of advanced composite molding technology, the application of carbon fiber composites in load-bearing structures is also increasing, leading to more complex stress states. Many structures, such as composite fuselage sections and composite high-pressure gas cylinders, face loads in two directions. Single-direction mechanical property testing is insufficient to evaluate structural safety; simultaneous biaxial loading is required for verification. Therefore, the biaxial tensile test of carbon fiber composite laminates is an important testing method for verifying the biaxial load-bearing capacity of structures.

[0003] In existing technologies, composite material parts are mostly obtained through two methods: secondary bonding and co-curing. However, secondary bonding requires controlling adhesive overflow. If the overflow cannot be controlled, not only is the bonding quality affected, but the central area of ​​the test piece becomes covered by the adhesive film and cannot be removed. This makes it impossible to accurately judge the trend of damage in the central area of ​​the test piece during testing, resulting in inaccurate test data. Furthermore, after co-curing, the central area of ​​the reinforcing sheets on both sides of the test piece needs to be machined with chamfered and beveled square through holes, which leads to delamination and splitting of the reinforcing sheet fibers.

[0004] Therefore, there is an urgent need for a molding device for biaxial tensile test specimens of composite materials to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a molding device and method for biaxial tensile test specimens of composite materials, which can manufacture biaxial tensile test specimens for different processes.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, a molding apparatus for a biaxial tensile test specimen of a composite material includes:

[0008] A molding frame, comprising an upper cover plate, a lower bottom plate, and a sealing plate, wherein at least the lower bottom plate is used to lay a reinforcing sheet with carbon fiber prepreg, and the lower bottom plate and the upper cover plate are disposed within the space enclosed by the sealing plate;

[0009] A circular forming limiting component is disposed on the inner wall of the lower base plate or the upper cover plate. There are four circular forming limiting components, and the reinforcing sheet of the carbon fiber prepreg is laid between the four circular forming limiting components. The circular forming limiting components are in contact with the lower base plate and the upper cover plate respectively.

[0010] A reinforced sheet with a chamfered slope forming component in the center area, wherein the upper cover plate and the lower base plate are detachably connected to the reinforced sheet with a chamfered slope forming component in the center area;

[0011] The test specimen is loaded with an end forming limiter, which is disposed between adjacent circular forming limiters to abut against the reinforcing sheet of the carbon fiber prepreg.

[0012] As a preferred technical solution for the molding device of the above-mentioned composite biaxial tensile test specimen, the center of the upper cover plate and the center of the lower base plate are both provided with assembly holes for installing the chamfered slope molding part of the central area of ​​the reinforcing sheet.

[0013] As a preferred technical solution for the molding device of the above-mentioned biaxial tensile test specimen of composite material, both the upper cover plate and the lower base plate are provided with positioning pin holes, and the upper cover plate and the lower base plate are connected and positioned by positioning pins passing through the positioning pin holes.

[0014] As a preferred technical solution for the molding device of the above-mentioned composite material biaxial tensile test specimen, one of the four test specimen loading end molding limiting members is provided with a mounting groove for installing a thermocouple, and the sealing plate has a through hole, which is arranged opposite to the mounting groove.

[0015] Secondly, a method for forming a biaxial tensile test specimen of composite materials is provided, applied to the forming apparatus for biaxial tensile test specimens of composite materials described in any of the above embodiments, comprising the following steps:

[0016] Install a reinforced plate with a chamfered beveled center area at the center of the bottom plate and / or top cover plate;

[0017] At least one of the body sheet and the reinforcing sheet is laid on the bottom plate and the top cover plate, wherein the body sheet and the reinforcing sheet are not in contact with the chamfered beveled part in the center area;

[0018] The test piece is loaded with end forming limiters and round forming limiters, which are then installed on the bottom plate and the top cover.

[0019] The lower base plate and the upper cover plate are placed in an autoclave and pressurized to complete the curing process.

[0020] After curing, allow the pressure to be released and the material to cool before demolding and removing the biaxial tensile test specimen.

[0021] As a preferred technical solution for the molding device of the above-mentioned composite material biaxial tensile test specimen, at least one of the body sheet and the reinforcing sheet is laid on the lower base plate and the upper cover plate, wherein the body sheet and the reinforcing sheet do not contact the beveled central area of ​​the molding part, including:

[0022] The body sheet and reinforcing sheet are laid on the bottom plate and the top plate, with the body sheet above the reinforcing sheet and the body sheet not in contact with the chamfered beveled part in the center area of ​​the reinforcing sheet. After laying, the top plate is rotated 180° so that the body sheet is horizontally facing the bottom plate. The mold is closed by passing the positioning pin through the top plate and the bottom plate to obtain the composite biaxial tensile test specimen.

[0023] As a preferred technical solution for the molding device of the above-mentioned composite biaxial tensile test specimen, at least one of the body sheet and the reinforcing sheet is laid on the lower base plate and the upper cover plate, wherein the body sheet and the reinforcing sheet do not contact the chamfered beveled molding part in the central area, including:

[0024] The reinforcing sheet is laid on the bottom plate with the chamfered slope forming part in the center area of ​​the reinforcing sheet and the top cover plate with the chamfered slope forming part in the center area of ​​the reinforcing sheet, and the body sheet is laid on another bottom plate without the chamfered slope forming part in the center area of ​​the reinforcing sheet or another top cover plate without the chamfered slope forming part in the center area of ​​the reinforcing sheet.

[0025] The upper cover plate and the lower bottom plate are placed in an autoclave for curing to obtain a reinforcing part and a body part. A chamfered slope forming part is retained in the center area of ​​the reinforcing plate on the reinforcing part, and the two sides of the obtained body part are bonded to the reinforcing part to obtain a preformed part.

[0026] The preform is cured a second time to obtain a biaxial tensile test specimen.

[0027] As a preferred technical solution for the molding method of the above-mentioned composite material biaxial tensile test specimen, the method is characterized in that, before laying the reinforcing sheet and the body sheet, laser projection targets are inserted into the positioning pin holes of the upper cover plate and the lower base plate respectively, and the laser projector projects the plane of the reinforcing sheet to complete the laying of the reinforcing sheet. After the laying is completed, the laser projection targets are removed.

[0028] As a preferred technical solution for the molding method of the above-mentioned composite material biaxial tensile test specimen, the bottom plate and the top cover plate are put into the autoclave, the autoclave is pressurized to 600kPa-650kPa, the heating temperature is 120℃-180℃, and the heating time is not less than 2 hours.

[0029] As a preferred technical solution for the molding method of the above-mentioned composite biaxial tensile test specimen, one of the molding limiting parts at the loading end of the test specimen has a mounting groove for installing thermocouples. The leading thermocouple is placed in the mounting groove and, after contacting the carbon fiber prepreg, the thermocouple is fixed on the outside of the sealing plate using pressure-sensitive tape. After the sealing plate is placed around the bottom plate, the hysteresis thermocouple is arranged on the surface of the device and fixed using pressure-sensitive tape.

[0030] The present invention has at least the following beneficial effects:

[0031] The molding apparatus for biaxial tensile test specimens of composite materials provided by this invention can obtain co-cured test specimens and secondary bonded test specimens separately. Since both the upper cover plate and the lower base plate are detachably connected to the chamfered slope molding component in the central area of ​​the reinforcing sheet, when the apparatus manufactures test specimens using the secondary bonding method, during the secondary bonding and curing process of the test specimen and the reinforcing sheet, the excess adhesive film in the center of the reinforcing sheet is blocked. After the first curing of the reinforcing sheet, there is no need to demold the chamfered slope molding component in the central area of ​​the reinforcing sheet; demolding after secondary bonding with the test specimen achieves the purpose of blocking adhesive, thus solving the problem of difficulty in blocking excess adhesive during secondary bonding. Simultaneously, the through holes in the chamfered slope direction of the reinforcing sheet area of ​​the co-cured test specimen can be directly cured and formed under the action of the chamfered slope molding component in the central area of ​​the reinforcing sheet, eliminating machining steps and avoiding problems such as delamination and splitting between the reinforcing sheet fiber layers. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the content of the embodiments of the present invention and these drawings without creative effort.

[0033] Figure 1 A schematic diagram of the molding device for a biaxial tensile test specimen of composite materials provided in an embodiment of the present invention;

[0034] Figure 2 An exploded view of the molding apparatus for a biaxial tensile test specimen of composite materials provided in an embodiment of the present invention;

[0035] Figure 3 This is a top view of the molding apparatus for a biaxial tensile test specimen of composite materials provided in an embodiment of the present invention;

[0036] Figure 4 A first flowchart of the molding method for a composite biaxial tensile test specimen provided in an embodiment of the present invention;

[0037] Figure 5 This is a second flowchart of the molding method for a composite biaxial tensile test specimen provided in an embodiment of the present invention.

[0038] In the picture:

[0039] 1. Molded frame; 11. Top cover plate; 12. Bottom plate; 13. Sealing plate; 131. Perforation; 14. Assembly hole; 15. Locating pin hole; 16. Locating pin; 2. Round molded limiting part; 21. Clearance groove; 3. Chamfered slope molding part in the center area of ​​the reinforcing plate; 4. Molded limiting part at the loading end of the test piece; 100. Biaxial tensile test piece; 41. Mounting groove. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0041] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0042] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0043] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0044] To address the problems in the prior art, this invention provides a molding apparatus for biaxial tensile test specimens of composite materials, thereby solving the problem of obtaining biaxial tensile test specimens through different processes in the prior art.

[0045] like Figures 1 to 3As shown, the molding device for a composite biaxial tensile test specimen includes a molding frame 1, a circular molding limiting member 2, a chamfered slope molding member 3 for the central area of ​​the reinforcing sheet, and a molding limiting member 4 for the loaded end of the test specimen. The molding frame 1 includes an upper cover plate 11, a lower base plate 12, and a sealing plate 13. At least the lower base plate 12 is used to lay the reinforcing sheet with carbon fiber prepreg. The lower base plate 12 and the upper cover plate 11 are disposed within the space enclosed by the sealing plate 13. Furthermore, the upper cover plate 1... Both the bottom plate 1 and the bottom plate 12 are detachably connected to the chamfered slope forming part 3 of the center area of ​​the reinforcing sheet; the circular forming limiting part 2 is set on the side of the bottom plate 12 facing the top cover plate 11, and there are four circular forming limiting parts 2. The reinforcing sheet of the carbon fiber prepreg is laid between the four circular forming limiting parts 2, and the circular forming limiting parts 2 are in contact with the bottom plate 12 and the top cover plate 11 respectively; the forming limiting part 4 of the loading end of the test piece is set with the adjacent circular forming limiting part 2 to abut against the reinforcing sheet of the carbon fiber prepreg.

[0046] The molding apparatus for biaxial tensile test specimens of composite materials provided by this invention can obtain co-cured test specimens and secondary bonded test specimens respectively. Since both the upper cover plate 11 and the lower base plate 12 are detachably connected to the chamfered slope molding component 3 in the central area of ​​the reinforcing sheet, when the apparatus manufactures test specimens using the secondary bonding method, during the secondary bonding and curing process of the test specimen and the reinforcing sheet, the excess adhesive film in the center of the reinforcing sheet is blocked. After the first curing of the reinforcing sheet, there is no need to demold the chamfered slope molding component 3 in the central area of ​​the reinforcing sheet. Demolding after secondary bonding with the test specimen can achieve the purpose of blocking adhesive, thus solving the problem of difficulty in blocking excess adhesive during secondary bonding. At the same time, the through holes in the chamfered slope direction of the reinforcing sheet area of ​​the co-cured test specimen can be directly cured and formed under the action of the chamfered slope molding component 3 in the central area of ​​the reinforcing sheet, eliminating the machining steps and avoiding the problems of delamination and splitting between the reinforcing sheet fibers.

[0047] In some embodiments, the center of the upper cover plate 11 and the center of the lower base plate 12 are both provided with mounting holes 14 for mounting the chamfered slope forming part 3 of the center area of ​​the reinforcing sheet. The mounting holes 14 and the chamfered slope forming part 3 of the center area of ​​the reinforcing sheet are provided with an interference fit, which can prevent the adhesive film from flowing out from the gap between the mounting holes 14 and the chamfered slope forming part 3 of the center area of ​​the reinforcing sheet. In addition, it can also prevent the chamfered slope forming part 3 of the center area of ​​the reinforcing sheet from detaching from the mounting holes 14 after the mold is opened.

[0048] In some embodiments, both the upper cover plate 11 and the lower base plate 12 are provided with positioning pin holes 15. The upper cover plate 11 and the lower base plate 12 are connected and positioned by positioning pins 16 passing through the positioning pin holes 15. Specifically, a positioning pin hole 15 is provided at each of the four corners of the upper cover plate 11 and the lower base plate 12. Before laying the reinforcing sheet, a laser projection target can be inserted into the positioning pin hole 15. The laser projection target and the laser projector work together to obtain the laying plane, which can improve the laying efficiency. The positioning pin hole 15 can not only position the positioning pins 16 of the upper cover plate 11 and the lower base plate 12 when they are molded together, but also insert the laser projector target point for laser layer positioning in the laying process, ensuring the laying accuracy of the cross contour and the central inverted slope contour of each layer of reinforcing sheet.

[0049] The round forming limiting part 2 is provided with a relief groove 21 at the corner facing the upper cover plate 11. The relief groove 21 can avoid the positioning pin 16. Compared with the hole in the round forming limiting part 2, the relief groove 21 is easier to process.

[0050] Furthermore, in order to obtain the internal temperature of the molding apparatus for the biaxial tensile test specimen of the composite material during operation, in some embodiments, one of the four test specimen loading end molding limiting members 4 is provided with a mounting groove 41 for mounting a thermocouple, and the sealing plate 13 has a through hole 131, which is arranged opposite to the mounting groove 41. The thermocouple installed in the mounting groove 41 can detect and obtain the internal temperature to ensure that the temperature reaches the standard during the test specimen preparation process.

[0051] Furthermore, the present invention also provides a method for forming a biaxial tensile test specimen of composite materials, applicable to the forming apparatus for biaxial tensile test specimens of composite materials provided in the embodiments of the present invention, such as... Figure 4 As shown, it includes the following steps:

[0052] S101. Install the reinforcing plate center area chamfered slope forming part 3 at the center position of the lower base plate 12 and / or upper cover plate 11;

[0053] S102, At least one of the body sheet and the reinforcing sheet is laid on the lower base plate 12 and the upper cover plate 11, wherein the body sheet and the chamfered slope forming part 3 in the center area of ​​the reinforcing sheet do not contact each other;

[0054] S103. Install the test piece loading end forming limiter 4 and the round forming limiter 2 onto the lower base plate 12 and the upper cover plate 11;

[0055] The test specimen loading end forming limiter 4 can ensure that the end sidewall of the obtained test specimen is set vertically, while the round forming limiter 2 can ensure that the chamfer of the test specimen can be formed directly without the need for machining to obtain a round chamfer.

[0056] S105. Place the lower base plate 12 and the upper cover plate 11 in a hot autoclave and pressurize to complete the curing process.

[0057] S106. After curing, wait for the pressure to be released and the material to cool before demolding and removing the biaxial tensile test specimen 100.

[0058] The molding method for biaxial tensile test specimens of composite materials provided by this invention can obtain co-cured test specimens and secondary bonded test specimens respectively. Since both the upper cover plate 11 and the lower base plate 12 are detachably connected to the chamfered slope molding part 3 in the central area of ​​the reinforcing sheet, when the device uses the secondary bonding method to manufacture the test specimen, during the secondary bonding and curing process of the main body and the reinforcing part, the adhesive film at the center of the reinforcing part can be treated by the chamfered slope molding part 3 in the central area of ​​the reinforcing sheet to prevent overflow. After the first curing of the reinforcing sheet, there is no need to demold the chamfered slope molding part 3 in the central area of ​​the reinforcing sheet. Demolding after secondary bonding with the main body can achieve the purpose of preventing overflow, thus solving the problem of difficulty in preventing overflow during secondary bonding. At the same time, when manufacturing test specimens through co-curing, the through holes in the chamfered slope direction of the reinforcing sheet area can be directly cured and formed under the action of the chamfered slope molding part 3 in the central area of ​​the reinforcing sheet, eliminating the machining steps and avoiding the problems of delamination and splitting between the fiber layers of the reinforcing sheet.

[0059] In some embodiments, when the test specimen is a co-cured specimen, at least one of a body sheet and a reinforcing sheet is laid on the lower base plate 12 and the upper cover plate 11, wherein the body sheet and the chamfered beveled forming element 3 in the central area of ​​the reinforcing sheet do not contact each other. This includes laying the body sheet and the reinforcing sheet on the lower base plate 12 and the upper cover plate 11, with the body sheet positioned above the reinforcing sheet, and the body sheet not contacting the chamfered beveled forming element 3 in the central area of ​​the reinforcing sheet. At this time, it is necessary to lay the reinforcing sheet and the body sheet on the upper cover plate 11, with the body sheet directly above the reinforcing sheet, and lay the reinforcing sheet and the body sheet on the lower base plate 12, with the body sheet directly above the reinforcing sheet. The already laid upper cover plate 11 is rotated 180° so that the reinforcing sheet is horizontally facing the lower base plate 12. The mold is closed by passing the positioning pin 16 through the positioning pin holes 15 of the upper cover plate 11 and the lower base plate 12 to obtain a composite biaxial tensile test specimen. This ensures the thickness of the obtained test specimen.

[0060] In some other embodiments, when the test specimen is a secondary adhesive bonding test specimen, at least one of the body sheet and the reinforcing sheet is laid on the lower base plate 12 and the upper cover plate 11, wherein the body sheet and the chamfered beveled forming part 3 in the central area of ​​the reinforcing sheet do not contact each other, including:

[0061] A reinforcing sheet is laid on a lower base plate 12 with a reinforcing sheet center area chamfered slope forming part 3 and an upper cover plate 11 with a reinforcing sheet center area chamfered slope forming part 3, and a body sheet is laid on another lower base plate 12 without a reinforcing sheet center area chamfered slope forming part 3 or another upper cover plate 11 without a reinforcing sheet center area chamfered slope forming part 3.

[0062] The upper cover plate 11 and the lower bottom plate 12 are placed in a hot autoclave for curing to obtain a reinforcing part and a body part. A chamfered slope forming part 3 is retained in the center area of ​​the reinforcing plate on the reinforcing part, and the two sides of the obtained body part are bonded to the reinforcing part to obtain a preformed part.

[0063] The preform is cured a second time to obtain biaxial tensile test specimen 100.

[0064] That is, the upper cover plate 11 and the lower bottom plate 12 are directly put into the autoclave without being molded. In this way, the reinforcing part and the main body can be obtained through the upper cover plate 11 and the lower bottom plate 12. After obtaining the reinforcing part, the chamfered slope forming part 3 of the central area of ​​the reinforcing plate is retained on the reinforcing part. The obtained reinforcing parts and the main body are bonded with adhesive and then cured for a second time to obtain the biaxial tensile test piece 100. At this time, the chamfered slope forming part 3 of the central area of ​​the reinforcing plate is removed.

[0065] It should be noted that before the secondary curing of the reinforcing component and the main body component after bonding with adhesive, the surfaces of the reinforcing component and the main body component to be bonded should be sanded with sandpaper until smooth, without abrading the fibers. After sanding, wipe away the dust with a cloth and cleaning agent. After sanding, bond the reinforcing component and the main body component with adhesive.

[0066] After the top surface of the main body is coated with adhesive film, the reinforcing member located on the upper cover plate 11 is coated with adhesive film and then rotated horizontally 180°. The main body of the upper cover plate 11 is then bonded using the positioning pin 16. After the adhesive film is firmly bonded to the main body, tools are used to press the chamfered beveled forming part 3 in the center area of ​​the reinforcing sheet from the lower base plate 12 and the upper cover plate 11 respectively, and then the lower base plate 12 and the upper cover plate 11 are removed. The four loading ends are fixed with pressure-sensitive adhesive tape, and thermocouples are arranged to contact the adhesive film at the loading ends to meet the curing requirements.

[0067] Specifically, before laying the reinforcing sheet, laser projection targets are inserted into the positioning pin holes 15 of the upper cover plate 11 and the lower base plate 12, respectively. The laser projector projects the plane on which the reinforcing sheet and the body sheet are laid, so that the reinforcing sheet and the body sheet can be laid. After the laying is completed, the laser projection targets are removed. The plane on which the reinforcing sheet is laid by the laser projector is existing technology and will not be described in detail here.

[0068] In some embodiments, after the bonded preform is placed in an autoclave, the autoclave is pressurized to 600 kPa-650 kPa. For example, the autoclave is pressurized to 600 kPa, 610 kPa, 620 kPa, 630 kPa, 640 kPa, or 650 kPa; no specific limitation is made in this embodiment. The heating temperature is 180°C, and the heating time is not less than 2 hours.

[0069] It should be noted that one of the test piece loading end molding limiting parts 4 has a mounting groove 41 for installing thermocouples. The leading thermocouple is placed in the mounting groove 41 and after contacting the carbon fiber prepreg, the hysteresis thermocouple is fixed on the outside of the sealing plate 13 using pressure-sensitive tape. After the sealing plate 13 is placed around the bottom plate 12, the hysteresis thermocouple is arranged on the surface of the device and fixed using pressure-sensitive tape.

[0070] One of the sealing plates 13 has a through hole 131 through which a thermocouple is inserted. The test piece loading end forming limiting member 4 has a mounting groove 41 through which a thermocouple is inserted. The mounting groove 41 corresponds to the through hole 131 and is inserted to place the leading thermocouple. After contacting the material, the thermocouple is fixed on the outside of the sealing plate 13 using pressure-sensitive tape.

[0071] Specifically, such as Figure 5 As shown, when the biaxial tensile test specimen 100 is obtained through secondary bonding, the following steps are included:

[0072] S201. Obtain the carbon fiber prepreg. After thawing, use an automatic feeder to feed the reinforcing sheets of the test pieces using the layer-dropping sheet program designed by fibersim.

[0073] S202. Apply one to two layers of release agent evenly to each surface of the lower base plate 12, upper cover plate 11, round forming limiter 2, test piece loading end forming limiter 4, and the chamfered slope forming part 3 in the center area of ​​the reinforcing sheet, and let them air dry for more than 30 minutes.

[0074] S203, the chamfered slope forming part 3 of the central area of ​​the reinforcing plate is placed in the center of the lower base plate 12 and the upper cover plate 11 respectively and is fixed to the lower base plate 12 and the upper cover plate 11.

[0075] S204. Insert laser projection targets into the lower base plate 12 and the upper cover plate 11 respectively. The body sheet and reinforcing sheet on the lower base plate 12 and the upper cover plate 11 are laid according to the laser projection. After the laying is completed, remove the laser projection targets.

[0076] S205. Fix the round forming limiting member 2 and the test piece loading end forming limiting member 4 to the lower base plate 12 and clamp the body piece and reinforcing piece of the lower base plate 12 together.

[0077] S206, The sealing plate 13 is placed between the upper cover plate 11 and the lower bottom plate 12, and the area enclosed by the upper cover plate 11 and the lower bottom plate 12 is sealed off.

[0078] S207. Rotate the upper cover plate 11, which has been laid with the main body and reinforcing sheet, 180°. Use the positioning pin 16 through the positioning pin hole 15 of the upper cover plate 11 and the positioning pin hole 15 of the lower base plate 12 to close the mold. The sealing plate 13 is clamped around the closed and adjusted device and fixed with bolts to close the area enclosed by the upper cover plate 11 and the lower base plate 12.

[0079] S208. Arrange the hysteresis thermocouple on the surface of the sealing plate 13 and fix it with pressure-sensitive tape.

[0080] S209. Prepare a vacuum bag, place a breathable felt and a non-porous isolation membrane inside the vacuum bag, and evacuate the vacuum bag to -80kPa for side leakage.

[0081] S210, the molding device for the biaxial tensile test specimen of composite material is placed in an autoclave and pressurized to 600kPa-650kPa, and heated at 180℃ for 2 hours to complete the curing.

[0082] S211. After depressurization and cooling, demold the biaxial tensile test piece 100.

[0083] Furthermore, the method for performing biaxial tensile secondary adhesive bonding test specimens includes the following steps:

[0084] Before performing this method, two sets of molding devices for biaxial tensile test specimens of composite materials provided in the embodiments of the present invention need to be prepared.

[0085] S301. Collect the carbon fiber prepreg. After thawing, use an automatic feeder to feed the reinforcing sheets of the test pieces using the layer-dropping sheet program designed by fibersim.

[0086] S302. Apply one to two layers of release agent evenly to each surface of the lower base plate 12, upper cover plate 11, round forming limiter 2, test piece loading end forming limiter 4, and the chamfered slope forming part 3 in the center area of ​​the reinforcing plate, and let them air dry for more than 30 minutes.

[0087] S303, the chamfered slope forming part 3 of the center area of ​​the reinforcing plate is installed in the positioning pin hole 15 of the lower base plate 12 and the upper cover plate 11 respectively.

[0088] S304, the upper cover plate 11 and the other reinforcing plate with a chamfered slope forming part 3 in the center area are connected through the assembly hole 14 of the upper cover plate 11.

[0089] S305. Insert laser projection targets into the lower base plate 12 and the upper cover plate 11 respectively. The reinforcing sheets of the lower base plate 12 and the upper cover plate 11 are laid according to the projection program. The test piece body sheet is laid on the flat fixture. Remove the laser projection targets.

[0090] S306, the circular forming limiting member 2 and the test piece loading end forming limiting member 4 respectively clamp the reinforcing pieces of the lower base plate 12 and the upper cover plate 11.

[0091] S307. Place the four sealing plates 13 on the upper cover plate 11 and the lower base plate 12 respectively, and fix the four sealing plates 13 with bolts. One of the sealing plates 13 has a through hole 131. The through hole 131 and the mounting groove 41 are inserted into the leading thermocouple and the leading thermocouple is brought into contact with the material to be fixed. Then, pressure-sensitive tape is used to fix the sealing plate 13 on the outside. The hysteresis thermocouple is arranged on the surface of the molding device of the composite biaxial tensile test specimen and fixed with pressure-sensitive tape.

[0092] S308. Prepare a vacuum bag, and place the molding device for the biaxial tensile test specimen of the composite material inside the vacuum bag after covering it with a breathable felt and a non-porous isolation membrane. Vacuum the bag to -80 kPa to check for leaks.

[0093] S309, pressurize in an autoclave at 600kPa-650kPa, and heat at 180℃ for 2 hours to complete curing.

[0094] S310. After depressurization and cooling, demold and remove the reinforcing sheet and body that constitute the biaxial tensile test specimen 100. The chamfered slope forming part in the center area of ​​the reinforcing sheet on the two reinforcing parts shall be retained without demolding.

[0095] S311. Obtain the film-like adhesive, and after thawing, cut it into pieces according to the bonding dimensions using a feeding machine.

[0096] S312. Use sandpaper to sand the surfaces of the main body and reinforcement parts to be bonded. Sand until smooth, but do not abrade the fibers. After sanding, wipe away the dust with a cloth and cleaning agent.

[0097] S313. Place the reinforcing parts and the main body parts to be bonded into an oven for drying. Drying conditions: dry at 102℃-112℃ for at least 6 hours.

[0098] S314. Connect the reinforcing member to the mating clearance hole assembly hole 14 of the lower base plate 12 and the upper cover plate 11 respectively according to the chamfered slope forming part 3 of the center area of ​​the reinforcing piece.

[0099] S315. The reinforcing member, body part, and reinforcing member bonding are installed sequentially from top to bottom. The bonding process is completed manually. Note that after the test piece is bonded to the reinforcing sheet on the bottom plate 12, the reinforcing member obtained from the top cover plate 11, after applying the adhesive film, should be rotated horizontally 180°. The reinforcing sheet on the top cover plate 11 is then bonded using the positioning pin 16. After the adhesive film is firmly applied to the body part and the reinforcing member to obtain a pre-formed part, tools are used to press against the chamfered slope forming part 3 in the center area of ​​the reinforcing sheet from the bottom plate 12 and the top cover plate 11 respectively, and then the bottom plate 12 and the top cover plate 11 are removed. The four loading ends are fixed with pressure-sensitive tape, and the adhesive film is arranged to contact the thermocouples at the loading ends.

[0100] S316. Prepare a vacuum bag, place a breathable felt and a non-porous isolation membrane inside the vacuum bag, and evacuate the vacuum bag to -80kPa for side leakage.

[0101] S317. The preformed part is placed in an autoclave and pressurized to 600kPa-650kPa, then heated at 180℃ for 2 hours to complete the curing.

[0102] S318. After depressurization and cooling, demold and remove the chamfered slope forming part 3 in the center area of ​​the reinforcing sheet to obtain the biaxial tensile test piece 100.

[0103] In step S308, the molding device for the biaxial tensile test specimen of the composite material is in an unclosed state, and the lower base plate 12 with reinforcing sheet, the upper cover plate 11 with reinforcing sheet and the upper cover plate 11 with body sheet are simultaneously placed in the same vacuum bag, or the lower base plate 12 with reinforcing sheet, the upper cover plate 11 with reinforcing sheet and the upper cover plate 11 with body sheet are placed in different vacuum bags respectively.

[0104] Furthermore, the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A molding apparatus for biaxial tensile test specimens of composite materials, characterized in that, include: A molding frame (1) includes an upper cover plate (11), a lower bottom plate (12), and a sealing plate (13). At least the lower bottom plate (12) is used to lay a reinforcing sheet with carbon fiber prepreg. The lower bottom plate (12) and the upper cover plate (11) are disposed within the space enclosed by the sealing plate (13). A circular forming limiting member (2) is disposed on the inner wall of the lower base plate (12) or the upper cover plate (11). There are four circular forming limiting members (2), and the reinforcing sheet of the carbon fiber prepreg is laid between the four circular forming limiting members (2). The circular forming limiting members (2) are in contact with the lower base plate (12) and the upper cover plate (11) respectively. The reinforced sheet has a chamfered slope forming part (3) in the center area. The upper cover plate (11) and the lower bottom plate (12) are both detachably connected to the reinforced sheet has a chamfered slope forming part (3) in the center area. The test specimen loading end forming limiting member (4) is disposed between adjacent circular forming limiting members (2) to abut against the reinforcing sheet of the carbon fiber prepreg; When manufacturing test pieces using a secondary bonding method, the reinforcing sheet does not need to be demolded after the first curing. The chamfered slope forming part (3) in the center area of ​​the reinforcing sheet can be demolded after secondary bonding with the test piece to achieve the purpose of sealing the adhesive. The through holes in the chamfered slope direction of the reinforcing plate of the co-cured test specimen can be directly cured and formed under the action of the chamfered slope forming part (3) in the center area of ​​the reinforcing plate.

2. The molding apparatus for biaxial tensile test specimens of composite materials according to claim 1, characterized in that, The center of the upper cover plate (11) and the center of the lower base plate (12) are both provided with assembly holes (14) for installing the chamfered slope forming part (3) of the central area of ​​the reinforcing sheet.

3. The molding apparatus for biaxial tensile test specimens of composite materials according to claim 1, characterized in that, Both the upper cover plate (11) and the lower base plate (12) are provided with positioning pin holes (15). The upper cover plate (11) and the lower base plate (12) are connected and positioned by positioning pins (16) passing through the positioning pin holes (15).

4. The molding apparatus for biaxial tensile test specimens of composite materials according to claim 1, characterized in that, One of the four test specimen loading end forming limiting members (4) is provided with a mounting groove (41) for installing a thermocouple, and the sealing plate (13) has a through hole (131) which is disposed opposite to the mounting groove (41).

5. A method for forming a biaxial tensile test specimen of a composite material, characterized in that, A molding apparatus for a composite material biaxial tensile test specimen according to any one of claims 1-4, comprising the following steps: Install a reinforced plate with a chamfered slope forming part (3) in the center of the lower base plate (12) and / or upper cover plate (11); At least one of the body sheet and the reinforcing sheet is laid on the bottom plate (12) and the top cover plate (11), wherein the body sheet and the chamfered slope forming part (3) in the center area of ​​the reinforcing sheet do not contact each other; The test specimen loading end forming limiter (4) and round forming limiter (2) are installed on the lower base plate (12) and the upper cover plate (11); The lower base plate (12) and the upper cover plate (11) are placed in an autoclave and pressurized to complete the curing process; After curing, allow the pressure to be released and the material to cool before demolding and removing the biaxial tensile test specimen.

6. The molding method for a biaxial tensile test specimen of composite materials according to claim 5, characterized in that, At least one of the body sheet and the reinforcing sheet is laid on the lower base plate (12) and the upper cover plate (11), wherein the body sheet and the chamfered beveled part (3) in the center area of ​​the reinforcing sheet do not contact each other, including: The body sheet and the reinforcing sheet are laid on the bottom plate (12) and the top plate (11), with the body sheet positioned above the reinforcing sheet and the body sheet not in contact with the chamfered slope forming part (3) in the center area of ​​the reinforcing sheet. After laying, the top plate (11) is rotated 180° so that the body sheet is horizontally facing the bottom plate (12). The mold is closed by passing the positioning pin (16) through the top plate (11) and the bottom plate (12) to obtain the composite biaxial tensile test specimen.

7. The method for forming a biaxial tensile test specimen of composite materials according to claim 5, characterized in that, At least one of the body sheet and the reinforcing sheet is laid on the lower base plate (12) and the upper cover plate (11), wherein the body sheet and the chamfered beveled part (3) in the center area of ​​the reinforcing sheet do not contact each other, including: By laying reinforcing plates on the bottom plate (12) with the reinforcing plate center area chamfered slope forming part (3) and the top plate (11) with the reinforcing plate center area chamfered slope forming part (3), and laying body plates on another bottom plate (12) without the reinforcing plate center area chamfered slope forming part (3) or another top plate (11) without the reinforcing plate center area chamfered slope forming part (3); The upper cover plate (11) and the lower bottom plate (12) are placed into a hot autoclave for curing to obtain a reinforcing part and a body part. A chamfered slope forming part (3) is retained in the center area of ​​the reinforcing plate on the reinforcing part, and the two sides of the obtained body part are bonded to the reinforcing part to obtain a preformed part. The preform is cured a second time to obtain a biaxial tensile test specimen.

8. The method for forming a biaxial tensile test specimen of composite material according to claim 5, characterized in that, Before laying the reinforcing sheet and the main body sheet, laser projection targets are inserted into the positioning pin holes (15) of the upper cover plate (11) and the lower base plate (12) respectively. The laser projector projects the plane of the reinforcing sheet so that the reinforcing sheet can be laid. After the laying is completed, the laser projection targets are removed.

9. The method for forming a biaxial tensile test specimen of composite materials according to claim 5, characterized in that, The bottom plate (12) and the top cover plate (11) are inserted into the autoclave, pressurizing the autoclave to 600kPa-650kPa, heating at 120℃-180℃, and heating for no less than 2 hours.

10. The molding method for a composite biaxial tensile test specimen according to claim 5, characterized in that, One of the test specimen loading end molding limiters (4) has a mounting groove (41) for mounting thermocouples. The leading thermocouple is placed in the mounting groove (41), and after contacting the carbon fiber prepreg, the thermocouple is fixed on the outside of the sealing plate (13) using pressure-sensitive tape. After the sealing plate (13) is placed around the bottom plate (12), the hysteresis thermocouple is arranged on the surface of the device and fixed using pressure-sensitive tape.

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