Method for forming a meridional tensile test specimen and meridional tensile test specimen produced thereby

Abstract

The application relates to the technical field of composite material forming, and discloses a method for forming a longitudinal tensile test plate, which comprises the following steps: S1, main material preparation; S2, mold preparation; S3, laying and pasting; S4, packaging; S5, curing; and S6, demolding.

Description

Technical Field

[0001] This application relates to the field of composite material molding technology, and in particular to a method for molding a meridional tensile test specimen and the meridional tensile test specimen prepared therefrom. Background Technology

[0002] Existing warp tensile test specimens are mostly prepared using oven curing processes, but the steps of laying, compacting and sealing lack systematic standards, which makes it easy for bubbles, wrinkles and fiber orientation deviations to be generated inside the specimens, making it difficult to ensure the accuracy and consistency of tensile performance testing. Summary of the Invention

[0003] The purpose of this application is to provide a method for forming a longitudinal tensile test specimen, including the following steps: S1: Main material preparation steps: Take the prepreg material out of the frozen environment, check the material's storage expiration date, remaining operating life, and remaining mechanical property life, and ensure that the remaining operating life is >0h and the remaining mechanical property life is >0h; Thaw the material for no less than 8 hours, and it is considered thawed when no water droplets or moisture condense after wiping the outer packaging dry; Cut the prepreg material using an automatic fabric cutter, aligning the roll length edge line with the machine's 0° line during cutting, controlling the fiber direction angle deviation of unidirectional prepreg within ±2°, controlling the fiber direction angle deviation of fabric prepreg within ±3°, and controlling the sheet size deviation within ±2.5mm; S2: Mold preparation steps: Use a glass mold, clean the mold surface, and lay adhesive-backed fluorine-containing release cloth in the laying area. The size of the adhesive-backed release cloth is larger than the size of the test plate. S3: Laying Steps: Mark the 0° and 90° coordinate systems on the mold. Using the mold edges parallel to the 0° and 90° directions as a reference, place the laying reference baffle parallel to the mold laying area. Lay the prepreg layer by layer according to the layup table at the laying position. After laying each layer of prepreg, check whether the fiber direction is consistent with the angle in the layup table. Use a scraper and blower to assist heating along the fiber direction to remove air bubbles and smooth out wrinkles. During the laying process, retain the backing release paper and release film. After laying, count and check to ensure that there are no foreign objects. Perform vacuum pre-compaction according to the layer sequence required in the layup table. The vacuum degree of vacuum pre-compaction is -100KPa to -80KPa, and the holding time is not less than 15 minutes. After the last layer is laid, remove the laying reference baffle and perform final vacuum compaction. The compaction vacuum degree is -100KPa to -85KPa, and the holding time is not less than 1 hour. S4: Packaging Steps: Apply a layer of high-temperature tape to the bottom edge of the topmost sheet as the reference edge of the test plate; use a curing auxiliary material group to make a vacuum bag for packaging. The order of laying the auxiliary materials is: release cloth, non-porous release film, pressure equalizing plate, breathable felt, vacuum bag film. The pressure equalizing plate is slightly smaller than the sheet size and placed in the center; arrange the vacuum tube at the vacuum detection point and arrange the thermocouple at the thermocouple embedding position; evacuate to a pressure value of -100KPa to -85KPa at each detection point, requiring that the vacuum degree decay value of all detection points is not greater than 5KPa within 15 minutes; S5: Curing step: Send the packaged mold into the oven, connect the vacuum pipeline and thermocouple, and after the vacuum degree is qualified, set the curing parameters for curing. After curing, the product temperature drops to below 60℃ and is taken out of the oven. S6: Demolding step: After the product temperature drops to room temperature, remove the auxiliary materials and separate the test plate from the mold.

[0004] Optionally, during the main material preparation step, the outer packaging must not be opened or damaged during the thawing of the material. If the packaging bag is found to be damaged during transportation, it must be sealed immediately with tape, and the start and end times of thawing must be recorded.

[0005] Optionally, in the main material preparation step, the cut material pieces are packaged with the part name and drawing number marked and then transferred to the laying station; if laying does not start within 48 hours, the cut material pieces are bagged and stored back in the freezer, and then thawed before the laying process begins.

[0006] Optionally, in the mold preparation step, a white cotton cloth, cleaning agent, plastic scraper and vacuum cleaner are used to clean the dust and glue stains on the surface of the mold and tooling, and to confirm that the mold markings and engravings are complete and clear.

[0007] Optionally, the process may include an auxiliary material preparation step before the laying step: cutting a set of auxiliary materials for vacuum pre-compression and a set of auxiliary materials for vacuum curing. The set of auxiliary materials for vacuum pre-compression includes a porous release film, a release cloth, a breathable felt, and a vacuum bag film. The set of auxiliary materials for vacuum curing includes a release cloth, a non-porous release film, a breathable felt, and a vacuum bag film. The vacuum bag film is cut to size according to the mold size, ensuring complete coverage of the product and the mold edges while leaving room for pleating.

[0008] Optionally, the laying step may include a pre-laying inspection step: checking whether the ambient temperature is 22±4℃ and the humidity is ≤60% and recording it; checking whether the measuring instruments are within the calibration validity period; checking whether the remaining operating life and mechanical property life of the raw materials meet the requirements; checking whether the mold information is correct and whether the bolts and movable parts are complete.

[0009] Optionally, in the laying step, during the prepreg laying process, the edge of the sheet in the 0° direction and the right edge of the sheet in the 90° direction coincide with two laying reference baffles, and ensure that there is no sheet stacking at the bottom of the baffles.

[0010] Optionally, in the laying step, scissors and a utility knife are used to remove the prepreg outside the laying area; the orientation tolerance of the fabric prepreg is controlled within ±3° of the fabric radial direction specified in the engineering drawing.

[0011] Optionally, in the packaging step, a part label is placed horizontally in the upper left corner of each test plate.

[0012] Optionally, during the vacuum degree test in the packaging step, if the vacuum degree decay value is greater than 5 kPa, it is necessary to check whether there is any air leakage at the vacuum bag film, vacuum pipeline, vacuum quick-connect suction cup and mold. After filling the air leakage point with sealing strip, the vacuum degree test operation is repeated.

[0013] Optionally, in the curing step, the remaining working life of the material is ensured to be >0h before the laying process is completed, and the remaining mechanical property life of the material is ensured to be >0h before the heating equipment is turned on for curing; the curing parameters are 2h@80℃+2h@120℃.

[0014] Optionally, in the demolding step, a nylon demolding wedge is gradually inserted along the joint between the edge of the part and the mold, and gently pried to separate the part from the mold, and the residual adhesive on the mold surface is cleaned.

[0015] Optionally, the demolding step is followed by an appearance quality inspection step: visually inspect the test plate for areas with low resin content, fiber wrinkles, creases, cracks or scratches, damaged release cloth, dry spots or surface pores, areas with high resin content, and areas with deformed or twisted fibers. If any defects are found, circle them on the product surface with a white paint pen and record them.

[0016] Optionally, the apparent quality inspection step may be followed by a quality inspection step: requesting the quality department to conduct a quality inspection, and transferring qualified test plates to the strip cutting process.

[0017] This application also provides a warp tensile test specimen, which is prepared by the warp tensile test specimen molding method described in the above scheme. The specimen is a carbon fiber composite laminate, comprising multiple layers of laid carbon fiber fabric prepreg, each layer having a thickness of 0.22 mm and a layup structure of 0f°~5s~. Attached Figure Description

[0018] Figure 1 The diagram shows a flow chart of a method for forming a meridional tensile test specimen according to this application. Figure 2This is another flowchart illustrating a method for forming a meridional tensile test specimen according to this application. Figure 3 This is another flowchart illustrating a method for forming a meridional tensile test specimen according to this application. Figure 4 This is another flowchart illustrating a method for forming a meridional tensile test specimen according to this application. Figure 5 This is another schematic diagram of a method for forming a meridional tensile test specimen according to this application. Detailed Implementation

[0019] The following embodiments further illustrate the technical solutions of this application. It should be understood that the specific embodiments described herein are merely for explaining this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not all of them.

[0020] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0021] In this application, unless otherwise expressly 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 being 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 being 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.

[0022] The term "aircraft" is defined as an air transport system of any size having at least one lift propeller as its propulsion source. The term "aircraft" can include both "manned" and "unmanned" air transport systems. A manned aircraft can mean an air transport system carrying one or more human passengers, none of whom have control over the aircraft. A manned aircraft can also mean an air transport system carrying one or more human passengers, some of whom, or one of whom, has partial or full control over the aircraft. An unmanned aircraft can mean an air transport system that does not carry any human passengers and flies autonomously or is remotely controlled by someone at a distance.

[0023] In this specification, "aircraft" includes manned aircraft and any unmanned vehicle, such as unmanned aerial vehicles (UAVs), unmanned aircraft, remote-controlled aircraft, unmanned aircraft systems, any aircraft classified by the International Civil Aviation Organization (ICAO) under cycle 328AN / 190, and so on. As an example, a drone can take the form of a single- or multi-rotor helicopter (such as a quadcopter) or a fixed-wing aircraft. Furthermore, certain portions of this disclosure can be used in conjunction with drones in the form of other types of unmanned vehicles (e.g., wheeled, tracked, and / or watercraft).

[0024] The embodiments of this application are described below with reference to the accompanying drawings. These embodiments detail the specific implementation of a method for forming a meridional tensile test specimen and the meridional tensile test specimen prepared therefrom.

[0025] I. Preparation of main ingredients Raw material preparation is a fundamental step in ensuring the quality of test panels. The raw material used in this invention is carbon fiber prepreg, including carbon fiber fabric prepreg and unidirectional carbon fiber prepreg. Prepregs typically need to be stored in a frozen environment during transportation and storage to extend their service life and maintain the processing properties of the resin system.

[0026] In the main material preparation step, the required materials are first removed from the frozen environment (usually below -18°C), and the material's storage expiration date, remaining operational life, and remaining mechanical property life are checked. Operational life refers to the time window during which the prepreg maintains good tiling performance at room temperature. Beyond this window, the prepreg's tackiness decreases significantly, making normal tiling difficult. Mechanical property life refers to the time period during which the prepreg maintains its cured mechanical properties at room temperature. It is essential to ensure that the material's remaining operational life is greater than 0 hours to guarantee sufficient tackiness during tiling and good bonding with adjacent layers. Simultaneously, it is crucial to ensure that the material's remaining mechanical property life is greater than 0 hours to guarantee that the final cured test panel meets the design requirements for mechanical properties. If the remaining life is insufficient, the batch of material should be discarded and replaced with new material.

[0027] After removal from the packaging, the materials need to be thawed. The thawing time should be no less than 8 hours, but may be adjusted according to the packaging specifications and ambient temperature. Thawing is complete when no more water droplets or moisture condense on the outer packaging after wiping it dry. Do not open or damage the outer packaging during thawing to maintain uniform internal temperature and prevent moisture from condensing on the material surface. If the packaging is found to be damaged during handling, immediately seal it with tape and record the start and end times of thawing for tracing the material's condition history.

[0028] After the materials have thawed, an automatic fabric cutter is used to prepare them according to a preset cutting program. The automatic cutter precisely controls the cutting size and fiber direction, reducing errors caused by manual cutting. When cutting prepreg, the length edge of the roll must coincide with the machine's 0° line to ensure the fiber direction of the cut sheets is consistent with the design direction. For unidirectional prepreg, the fiber direction angle deviation is controlled within ±2°; for woven prepreg, the fiber direction angle deviation is controlled within ±3°. The allowable dimensional deviation of the sheets is ±2.5mm to ensure accurate alignment during installation.

[0029] After cutting, the quantity and markings of the sheet materials need to be checked. The sheet material packaging should clearly indicate the part name, drawing number, and other information before being transferred to the installation station. If installation is not planned to begin within 48 hours, the cut sheet materials need to be individually bagged and returned to the freezer to prevent excessive depletion of operational and mechanical lifespan due to prolonged exposure to room temperature. Before the installation process begins, these sheet materials should be removed from the freezer and thawed.

[0030] II. Mold Preparation This invention uses glass molds to form test panels. Glass molds have advantages such as high surface smoothness, low coefficient of thermal expansion, and ease of cleaning, which are beneficial for obtaining test panels with excellent surface quality. First, the mold number is recorded to facilitate traceability of the production process for each batch of test panels.

[0031] Ensure the mold markings and scribe lines are complete and clear. The markings and scribe lines on the mold are used for positioning and alignment during installation, and their clarity directly affects the installation accuracy, so they must be checked before each use.

[0032] Clean the mold and tooling surfaces of dust and adhesive residue using a white cotton cloth, cleaning agent, plastic scraper, and vacuum cleaner. Specifically: first, gently scrape away larger adhesive residue residues from the mold surface with the plastic scraper; then wipe the mold surface with a white cotton cloth dampened with cleaning agent; finally, vacuum up fine dust particles. The cleaned mold surface should be free of any residue to ensure the release cloth can adhere smoothly.

[0033] Apply a fluorinated release cloth with adhesive backing to the application area. The fluorinated release cloth has excellent release properties, ensuring that the cured test panel can be easily separated from the mold without damaging the surface. The size of the release cloth should be larger than the test panel size, generally with an allowance of 30-50mm on each side, to ensure that the edge areas of the test panel are also adequately protected during release.

[0034] III. Preparation of Auxiliary Materials The preparation of auxiliary materials is a crucial step in the vacuum bag forming process. This invention relates to two types of auxiliary material sets: practical auxiliary materials for vacuum pre-compression and auxiliary materials for vacuum curing.

[0035] The practical auxiliary materials for vacuum preloading include a porous release liner, a release cloth, a breathable felt, and a vacuum bag film. The porous release liner has tiny pores that allow interlayer gas to escape smoothly during vacuuming; the release cloth is laid on the surface of the prepreg to prevent the prepreg from sticking to the release liner; the breathable felt has good air permeability, ensuring that the vacuum negative pressure is evenly transmitted to the entire laying area.

[0036] The auxiliary materials for vacuum curing include a release cloth, a non-porous release membrane, a breathable felt, and a vacuum bag film. Unlike the auxiliary materials for pre-compression, the curing auxiliary materials use a non-porous release membrane to prevent resin from seeping out and contaminating the breathable felt and vacuum bag film during the curing process.

[0037] Cut the auxiliary material according to the area of ​​the part to be covered. The size of the auxiliary material should be slightly larger than the size of the test plate, generally with an allowance of 50-100mm on each side. Cut the vacuum bag film according to the mold size, ensuring that it can completely cover the product and the edge of the mold, and leaving a margin for pleating. Generally, an allowance of 100-150mm on each side is allowed to form enough pleats during the vacuuming process to absorb excess bag film material.

[0038] IV. Pre-laying inspection Pre-layout inspection is a necessary step to ensure a smooth laying process and the quality of the final test panel.

[0039] Check the ambient temperature and humidity. The application of composite materials has strict requirements for environmental conditions. Too low a temperature will cause a decrease in the viscosity of the prepreg and make application difficult, while too high a temperature may accelerate the resin reaction process and shorten its service life. This invention requires the ambient temperature to be controlled at 22±4℃ and the humidity at ≤60%, and the actual temperature and humidity values ​​should be recorded.

[0040] Check whether the measuring instruments meet the usability requirements and are within their calibration validity period. The measuring instruments involved include thermometers, hygrometers, vacuum gauges, thermocouples, etc. The accuracy of these instruments is directly related to the control precision of process parameters, and it must be ensured that they are within their validity period and in good calibration condition.

[0041] Check whether the remaining operational life and mechanical property life of the raw materials meet the requirements. Since it takes a certain amount of time from the preparation of the main material to the completion of the installation, the remaining life of the material will continue to decrease as it is left at room temperature. Therefore, it is necessary to confirm again before installation that the remaining life of the material meets the requirements.

[0042] Check that the mold information is correct and that all accessories such as bolts and adjustable parts are complete. Ensure the mold is in good condition and all accessories are present to avoid interruptions during installation due to missing parts.

[0043] V. Laying Laying is the core step that determines the fiber orientation accuracy and internal quality of the test board.

[0044] First, mark a coordinate system on the mold, with the 0° and 90° directions parallel to the mold edge. Using the mold edges parallel to the 0° and 90° directions as a reference, place a laying reference baffle parallel to the mold's laying area. The purpose of the laying reference baffle is to provide a precise positioning reference for the placement of each layer of material, ensuring that the fiber orientation of each layer of material is consistent.

[0045] Lay the prepreg layer by layer according to the layup schedule. The layup schedule specifies in detail the material type, fiber orientation, and placement position for each layer. During the prepreg laying process, the edge of the prepreg at 0° and the right edge of the prepreg at 90° must coincide with two laying reference baffles, and it must be ensured that there is no prepreg stacking at the bottom of the baffles—if there is prepreg stacking at the bottom of the baffles, it will cause the baffles to lift and the positioning to fail.

[0046] After each layer of prepreg is laid, it is necessary to visually check whether the fiber direction is consistent with the angle inside the layup. For fabric prepreg, its orientation tolerance should be controlled within ±3° of the fabric radial direction specified in the engineering drawings. Use a scraper to smooth the prepreg along the fiber direction, and use a blower to assist in heating to reduce resin viscosity and improve the layup properties of the prepreg, thereby removing air bubbles and smoothing wrinkles generated during the laying process. Use scissors and a utility knife to remove excess prepreg outside the laying area.

[0047] During the installation process, the backing release paper and release film should be retained. These backing materials should not be removed until the installation is complete to protect the prepreg surface from contamination and prevent accidental adhesion between adjacent layers. After installation, count and verify all backing materials to ensure that the quantity matches the number of layers, thus confirming that no backing material has been trapped between layers to form inclusions. At the same time, visually inspect to confirm that there are no other foreign objects (such as hair, debris, etc.) remaining.

[0048] Vacuum pre-compacting is performed according to the layer sequence required in the layup table. The purpose of vacuum pre-compacting is to remove air between layers and ensure a tight bond between them. A vacuum bag is fabricated using vacuum pre-compacting auxiliary materials, and a porous release film, release cloth, breathable felt, and vacuum bag film are laid out sequentially. A vacuum is then drawn to a level of -100 kPa to -80 kPa and maintained for at least 15 minutes. After vacuum pre-compacting, the interlayer gas is effectively expelled, and preliminary adhesion is formed between the prepreg layers.

[0049] After the final layer is applied, remove the base plate and, following the sealing procedure, use vacuum compaction auxiliary materials to create a vacuum bag for final compaction. The vacuum bag should have evenly and symmetrically arranged pleats to accommodate the shrinkage of the bag film during vacuuming. The final compaction vacuum level should be -100 kPa to -85 kPa, and maintained for at least 1 hour. The longer final compaction time is to ensure thorough adhesion between layers, reduce interlayer gas residue, and establish a good interfacial bond for subsequent curing.

[0050] In one specific implementation, the reference layup scheme is as follows: carbon fiber fabric prepreg is used, with a single layer thickness of 0.22 mm and a layup structure of 0f°0f°~5s~, that is, 5 layers of fabric prepreg are laid in the 0° direction, and the fiber direction is arranged entirely along the warp direction (0° direction), which is used to prepare the test plate required for the warp tensile test.

[0051] VI. Packaging Encapsulation is a crucial step in isolating the prepreg layer from the outside environment, creating a vacuum environment, and preparing it for curing.

[0052] First, place the part labels. Place one part label in the upper left corner of each test plate (with the text horizontally aligned as the reference direction). The label should include the part name, drawing number, layup information, operator, and date for traceability. The label should be placed on the edge of the test plate so that it does not affect the effective testing area of ​​the tensile specimen after curing.

[0053] Apply a layer of high-temperature adhesive tape to the bottom edge of the topmost sheet as a reference edge for the test plate. This reference edge will serve as a positioning reference during subsequent strip cutting to ensure that the cut tensile specimens are dimensionally accurate and that the fiber direction is consistent with the specimen axis.

[0054] Vacuum bags are fabricated using a curing auxiliary material set for sealing. The auxiliary materials are laid out in the following order: release cloth, non-porous release film, pressure equalizing plate, breathable felt, and vacuum bag film. The release cloth is laid directly on the surface of the top layer of prepreg to ensure that the auxiliary materials can be easily peeled off after curing; the non-porous release film is laid on top of the release cloth to prevent resin leakage; the pressure equalizing plate is slightly smaller than the material sheet size and is placed in the center on top of the non-porous release film. The pressure equalizing plate and the vacuum bag enter the curing process together. Its function is to provide uniform pressure distribution during curing and reduce ripples and uneven thickness on the surface of the test plate; the breathable felt is laid on top of the pressure equalizing plate to ensure uniform transmission of vacuum negative pressure; the outermost layer is the vacuum bag film, which is adhered to the mold by sealing strips to form a sealed vacuum system.

[0055] During the encapsulation process, vacuum tubes are embedded at pre-arranged vacuum detection points, and thermocouples are embedded at their respective locations. Multiple vacuum detection points monitor the pressure distribution at different locations within the vacuum bag, ensuring uniform overall vacuum. Thermocouples are used to monitor the temperature at different locations on the test plate in real time during the curing process, ensuring a uniform temperature field.

[0056] Vacuum degree testing is a core control step in packaging quality. The vacuum pump is turned on to remove air from the vacuum bag film. Vacuuming is stopped when the pressure at all testing points reaches -100 kPa to -85 kPa. The vacuum degree decay at all testing points should not exceed 5 kPa within 15 minutes. Vacuum degree decay reflects the sealing performance of the vacuum bag system—minor damage to the vacuum bag film, loose vacuum line joints, or poor sealing between the sealing strip and the mold will cause air to slowly seep into the vacuum bag, resulting in a gradual decrease in vacuum degree. If the decay value exceeds 5 kPa, it is necessary to check for leaks in the vacuum bag film, vacuum lines, vacuum quick-connect suction cups, and mold. Troubleshooting methods include: visually inspecting the vacuum bag film for damage, checking the tightness of all line joints, and checking the tightness of the sealing strip's fit with the mold. If leaks are found, they can be filled with yellow sealing strips, and the vacuum degree testing operation should be repeated until the requirements are met.

[0057] VII. Curing Curing is a key step that causes the resin matrix in the prepreg to undergo a cross-linking reaction and form the final composite material part.

[0058] Before curing begins, the material's remaining operational life must be reconfirmed. For prepreg materials, the remaining operational life must be greater than 0 hours before the installation process is completed; and the remaining mechanical life must be greater than 0 hours before turning on the heating equipment for curing. This is because the installation process is carried out at room temperature, and the material's operational and mechanical lifespans are continuously consumed. Even if the remaining lifespan meets the requirements when installation is completed, if the material is left to cure for too long, its mechanical lifespan may still be exhausted.

[0059] The molds that have undergone the above operations are then placed into an oven. The oven should have precise temperature control and a uniform temperature field to ensure that the temperature of all parts of the test panel is consistent during the curing process.

[0060] Connecting the vacuum line and thermocouples facilitates subsequent temperature data acquisition and curing process control. The vacuum line should be continuously evacuated during curing to maintain the test plate under vacuum conditions. Temperature data collected by the thermocouples is used to monitor whether the curing process follows the set temperature curve.

[0061] Perform a vacuum test again inside the oven. Stop vacuuming when the pressure at the vacuum test point reaches -100 kPa to -85 kPa. The vacuum decay at the test point should not exceed 5 kPa within 15 minutes. Because the coefficient of thermal expansion of the vacuum bag film and sealing strip differs from that of the mold during oven heating, new leakage channels may appear at high temperatures. Therefore, the vacuum must be retested inside the oven before curing begins. If the decay value exceeds 5 kPa, check for leaks in the vacuum bag film, vacuum lines, vacuum quick-connect suction cups, and mold. Fill any leaks with sealing strips and repeat the vacuum test.

[0062] The curing parameters are set as follows: 2h@80℃ + 2h@120℃. First, the resin system is held at 80℃ for 2 hours to allow initial cross-linking and viscosity reduction, followed by gradual curing. Then, the temperature is increased to 120℃ and held for 2 hours to ensure complete cross-linking and achieve the designed degree of curing. This two-stage curing process helps control the reaction rate, reduces thermal stress caused by concentrated heat release during curing, and improves the internal quality of the test specimen.

[0063] After curing, the product temperature must drop below 60℃ before it can be removed from the oven. The cooling process should not be too rapid to avoid thermal stress causing warping or internal micro-cracks in the test panel. Typically, the oven is cooled in-flight or allowed to cool naturally after the heating power is turned off. The mold is then removed from the oven when the temperature drops below 60℃.

[0064] 8. Demolding Demolding is the process of separating the cured test panel from the mold. It must be done carefully to avoid damaging the test panel.

[0065] Wait for the product temperature to drop naturally to room temperature. Although it can be removed from the oven at below 60°C, the demolding operation should be carried out after the product has completely cooled to room temperature. This is because the difference in thermal expansion between the test plate and the mold at high temperatures may cause demolding difficulties, and forcibly demolding when the temperature is not uniform can easily cause the test plate to deform.

[0066] Remove auxiliary materials such as vacuum bag film, breathable felt, non-porous release film, release cloth, and sealing strips from the surface of the parts. When removing these materials, start from the edges and peel them off gradually to avoid breaking or leaving residue. Remove the vacuum connector and thermocouple, clean them thoroughly, and place them in designated locations for reuse.

[0067] Use a nylon release wedge to gradually insert it along the gap between the part and the mold edge, and gently pry to separate the part from the mold. Nylon is less hard than glass molds and carbon fiber test plates, and will not scratch the mold or test plate surface. When prying, apply force gradually from multiple points to avoid excessive force at a single point, which could lead to localized stress concentration and cracking of the test plate.

[0068] Clean any residual resin from the mold surface. After demolding, a small amount of resin or sealant residue may remain on the mold surface. Use a plastic scraper and cleaning agent to clean it and keep the mold clean for the next use.

[0069] IX. Appearance Quality Inspection After demolding, the test plates need to undergo an appearance quality inspection to confirm whether there are any defects that could affect the tensile performance test.

[0070] Visually inspect the parts for areas lacking resin. Areas lacking resin are characterized by exposed fibers and a lack of resin coverage. The load transfer capacity between fibers in these areas is reduced, making them weak points in tensile tests.

[0071] Visually inspect the parts for defects such as fiber wrinkles, creases, cracks, or scratches that damage the fibers. Fiber wrinkles and creases can alter the local fiber orientation, causing tensile property test results to deviate from the true values; cracks and scratches are obvious structural damage that will significantly reduce the load-bearing capacity of the test plate. If any of the above defects are found, circle them on the product surface with a white paint pen and record them.

[0072] Visually inspect the release cloth for integrity. Damage to the release cloth during curing may cause direct contact between the release film or breathable felt and the test panel surface, resulting in surface contamination or abnormal resin exudation. Record the location and extent of any damage.

[0073] Visually inspect for dry spots or surface pores. Dry spots refer to areas where the resin has not fully impregnated the fibers, appearing as gaps between fibers; surface pores refer to tiny holes on the surface of the test panel. These defects will affect the compactness and mechanical properties of the test panel. If any are found, circle them on the product surface with a white paint pen.

[0074] Visually inspect for areas rich in resin. Areas rich in resin are characterized by localized resin buildup and low fiber content. The mechanical properties of these areas differ from normal areas, and they may become stress concentration points during tensile testing. If any are found, circle them on the product surface with a white paint pen.

[0075] Visually inspect the product for areas of fiber deformation or twisting. Fiber deformation or twisting usually occurs due to improper handling during installation or poor prepreg coverage, which can alter the local fiber orientation. If any such areas are found, circle them on the product surface with a white paint pen.

[0076] 10. Quality Inspection and Handover After passing the appearance quality inspection, the test panel is submitted to the Quality Department for quality inspection. The Quality Department conducts a comprehensive inspection of the dimensions, thickness, surface quality, fiber orientation, etc., of the test panel in accordance with relevant standards and specifications to confirm that the test panel meets the requirements of the warp tensile test.

[0077] The qualified carbon fiber test plates are then transferred to the strip cutting process. Strip cutting is performed according to the warp tensile test standard, cutting tensile specimens of specified dimensions from a specific area of ​​the test plate, followed by tensile property testing.

[0078] The above embodiments are merely illustrative of the principles and effects of this application. Any person skilled in the art can modify or alter the above embodiments without departing from the purpose of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the purpose disclosed in this application should still be covered by the claims of this application.

Claims

1. A method for forming a test plate for a radial tensile test, characterized in that, Includes the following steps: S1: Main material preparation: Remove the prepreg material from the frozen environment and check the material's storage expiration date, remaining operating life, and remaining mechanical property life to ensure that the remaining operating life is >0h and the remaining mechanical property life is >0h; Thaw the material for no less than 8 hours, and it is considered thawed when no more water droplets or moisture condense after wiping the outer packaging dry; Cut the prepreg using an automatic fabric cutter, ensuring that the edge line of the roll length coincides with the 0° line of the machine during cutting, and control the fiber direction angle deviation of unidirectional prepreg within ±2°, the fiber direction angle deviation of fabric prepreg within ±3°, and the sheet size deviation within ±2.5mm; S2: Mold preparation: Use a glass mold, clean the mold surface, and lay an adhesive-backed fluorine-containing release cloth in the laying area. The size of the adhesive-backed release cloth is larger than the size of the test plate. S3: Laying: Mark the 0° and 90° coordinate systems on the mold. Using the mold edges parallel to the 0° and 90° directions as a reference, place the laying reference baffle parallel to the mold laying area. Lay the prepreg layer by layer according to the layup table at the laying position. After laying each layer of prepreg, check whether the fiber direction is consistent with the angle in the layup table. Use a scraper and blower to assist heating along the fiber direction to remove air bubbles and smooth out wrinkles. During the laying process, retain the backing release paper and release film. After laying, count and check to ensure that there are no foreign objects. Perform vacuum pre-compaction according to the layer sequence required in the layup table. The vacuum degree of vacuum pre-compaction is -100KPa to -80KPa, and the holding time is not less than 15 minutes. After the last layer is laid, remove the laying reference baffle and perform final vacuum compaction. The compaction vacuum degree is -100KPa to -85KPa, and the holding time is not less than 1 hour. S4: Encapsulation: Apply a layer of high-temperature tape to the bottom edge of the topmost sheet as the reference edge of the test plate; use a curing auxiliary material group to make a vacuum bag for encapsulation. The order of laying the auxiliary materials is: release cloth, non-porous release film, pressure equalizing plate, breathable felt, vacuum bag film. The pressure equalizing plate is slightly smaller than the sheet size and placed in the center; arrange the vacuum tube at the vacuum detection point and arrange the thermocouple at the thermocouple embedding position; evacuate to a pressure value of -100KPa to -85KPa at each detection point. It is required that the vacuum degree decay value of all detection points is not greater than 5KPa within 15 minutes. S5: Curing: Send the packaged mold into the oven, connect the vacuum pipeline and thermocouple, and after the vacuum degree is qualified, set the curing parameters for curing. After curing, the product temperature drops to below 60℃ and is taken out of the oven. S6: Demolding: After the product temperature drops to room temperature, remove the auxiliary materials and separate the test plate from the mold.

2. The method for forming a warp tensile test specimen according to claim 1, characterized in that, In step S1, the outer packaging must not be opened or damaged during the material thawing process. If the packaging bag is found to be damaged during handling, it must be sealed immediately with tape, and the start and end times of thawing must be recorded.

3. The method for forming a warp tensile test specimen according to claim 1, characterized in that, In step S1, the cut material pieces are packaged with the part name and drawing number marked on them and then transferred to the installation station. If installation does not begin within 48 hours, the cut material pieces are bagged and stored back in the freezer. They are then thawed before the installation process begins.

4. The method for forming a warp tensile test specimen according to claim 1, characterized in that, In step S2, a white cotton cloth, cleaning agent, plastic scraper, and vacuum cleaner are used to clean the dust and adhesive residue on the surface of the mold and tooling, and to confirm that the mold markings and engravings are complete and clear.

5. The method for forming a warp tensile test specimen according to claim 1, characterized in that, Before S3, there is also S21: auxiliary material preparation step: cutting the practical auxiliary material group for vacuum pre-compression and the auxiliary material group for vacuum curing. The practical auxiliary material group for vacuum pre-compression includes a porous release film, a release cloth, a breathable felt, and a vacuum bag film. The auxiliary material group for vacuum curing includes a release cloth, a non-porous release film, a breathable felt, and a vacuum bag film. The vacuum bag film is cut according to the mold size after being scaled up, ensuring that it completely covers the product and the edge of the mold and leaves room for pleating.

6. The method for forming a warp tensile test specimen according to claim 1, characterized in that, Before S, there is also S22: Pre-laying inspection steps: check whether the ambient temperature is 22±4℃ and the humidity is ≤60% and record it; check whether the measuring instruments are within the calibration validity period; check whether the remaining operating life and mechanical property life of the raw materials meet the requirements; check whether the mold information is correct and whether the bolts and loose parts are complete.

7. The method for forming a warp tensile test specimen according to claim 1, characterized in that, In step S3, during the prepreg laying process, the edge of the sheet in the 0° direction and the right edge of the sheet in the 90° direction coincide with two laying reference baffles, and ensure that there is no sheet stacking at the bottom of the baffles.

8. The method for forming a warp tensile test specimen according to claim 1, characterized in that, In step S3, scissors and a utility knife are used to remove the prepreg outside the laying area; the orientation tolerance of the fabric prepreg is controlled within ±3° of the fabric radial direction specified in the engineering drawing.

9. The method for forming a radial tensile test specimen according to claim 1, characterized in that, In step S4, a part label is placed horizontally in the upper left corner of each test board.

10. The method for forming a warp tensile test specimen according to claim 1, characterized in that, In the vacuum degree test of S4, if the vacuum degree decay value is greater than 5 kPa, it is necessary to check whether there is any air leakage in the vacuum bag film, vacuum pipeline, vacuum quick-connect suction cup and mold. After filling the air leakage point with sealing strip, repeat the vacuum degree test operation.

11. The method for forming a warp tensile test specimen according to claim 1, characterized in that, In step S5, the remaining working life of the material is ensured to be greater than 0h before the laying process is completed, and the remaining mechanical property life of the material is ensured to be greater than 0h before the heating equipment is turned on for curing; the curing parameters are 2h@80℃+2h@120℃.

12. The method for forming a warp tensile test specimen according to claim 1, characterized in that, In step S6, a nylon release wedge is gradually inserted along the gap between the edge of the part and the mold, and gently pried to separate the part from the mold, and the residual adhesive on the mold surface is cleaned.

13. The method for forming a warp tensile test specimen according to claim 1, characterized in that, The S6 is followed by S7: Appearance quality inspection: Visually inspect the test plate for areas with low resin content, fiber wrinkles, creases, cracks or scratches, damaged release cloth, dry spots or surface pores, areas with high resin content, and areas with deformed or twisted fibers. If there are any defects, circle them on the product surface with a white paint pen and record them.

14. The method for forming a radial tensile test specimen according to claim 1, characterized in that, S7 is followed by S8: Quality Inspection: Report to the Quality Department for quality inspection, and transfer qualified test plates to the strip cutting.

15. A test plate for a radial tensile test, characterized in that, The test plate is prepared by the warp tensile test plate forming method as described in any one of claims 1-14. The test plate is a carbon fiber composite laminate, comprising multiple layers of laid carbon fiber fabric prepreg, each layer having a thickness of 0.22 mm and a layup structure of 0f°~5s~.

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