High-toughness carbon fiber epoxy resin prepreg and rocket engine shell prepared from same

Abstract

The invention relates to the technical field of carbon fiber materials, and provides a high-toughness carbon fiber prepreg and a rocket engine shell prepared from the same, the toughness of the carbon fiber epoxy resin prepreg is improved through an epoxy resin toughening method, and the Tg is not reduced and the viscosity is not increased while the resin toughness is improved. The rocket engine shell is prepared from the carbon fiber epoxy resin prepreg through the process of manual laying and autoclave curing, and the problems of too low axial pressure load and rough surface quality of a product caused by a fiber winding process are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber composite materials, and in particular to a high-toughness carbon fiber prepreg and a rocket engine casing prepared using the same. Background Art

[0002] The solid rocket motor casing is a key component of the engine and also part of the missile body. It must withstand not only the internal pressure of the engine during operation, but also various external forces during missile launch and flight. Carbon fiber composites can improve the engine's mass ratio. Currently, fiber winding molding is commonly used, which has the following problems: First, the engine casing is a rotating body such as a cylinder, and most of the fibers are wound in the circumferential direction, with only a small amount of longitudinal fiber winding layers at both ends. This reduces the axial compressive strength of the casing. Therefore, the winding molding process is widely used in large-diameter engines, but its application in small and medium-diameter engines is subject to certain restrictions. The fewer longitudinal fibers cannot meet the product's axial compressive load requirements.

[0003] Second, the outer surface of the solid rocket motor casing is an aerodynamic surface, requiring very high surface quality in actual use. Using the winding process, the outer surface of the casing is relatively rough after curing, requiring subsequent grinding and polishing to improve the surface quality. Grinding reduces the resin content, affecting the mechanical properties of the product, while also increasing construction costs.

[0004] Third, small and medium-sized engines have high axial compressive load requirements, necessitating a resin matrix with higher toughness. Introducing a second-phase modifier into the epoxy resin matrix is a relatively effective method for improving the toughness of epoxy cured products. Commonly used toughening agents include rubber elastomers, thermoplastic resins, inorganic rigid particles, and core-shell particles. Second-phase modifiers typically form small, micrometer-scale domains during the curing process, which can enhance the fracture toughness of epoxy resins through mechanisms such as crack bridging and deflection, internal cavitation, or shedding within these domains, thereby inducing voids or cavities within the epoxy matrix. However, controlling the size of the phase-separated particle domains during the curing process is difficult. If care is taken, the toughening agent may continue to dissolve in the matrix resin, resulting in incomplete phase separation, resulting in suboptimal toughening and a lowering of the material's glass transition temperature. Furthermore, to achieve optimal toughening, the added toughening agent content is typically relatively high, which not only reduces the strength and modulus of the epoxy matrix but also significantly increases the viscosity of the system, making subsequent processing difficult. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-toughness carbon fiber epoxy resin prepreg, which improves the toughness of the carbon fiber epoxy resin prepreg by an epoxy resin toughening method, and solves the problems of low axial compressive load and rough surface quality of the product caused by the fiber winding process.

[0006] Based on the above objectives, one aspect of the present invention provides a high-toughness carbon fiber epoxy resin prepreg, which is composed of carbon fiber tow and the following components by weight: 85-125 parts of epoxy resin, 5-10 parts of primary toughening agent, 3-5 parts of secondary toughening agent, 0.5-1.5 parts of accelerator, and 0.2-0.4 parts of filler; Among them, the epoxy resin is selected from one of MP24018 epoxy resin, 128 epoxy resin and 6101 epoxy resin or a mixture of any two of them, the primary toughening agent is PEEK thermoplastic particles, the secondary toughening agent is a product of the reaction of diphenylamine-formaldehyde and dicyandiamide, the accelerator is selected from one of acrylamide, polyvinyl butyral, organic urea and α-methacrylate passivated 2-ethyl-4-methylimidazole or a mixture of any two, the filler is asbestos powder or quartz powder, and the toughness of the carbon fiber epoxy resin prepreg is improved by the epoxy resin toughening method.

[0007] Optionally, the carbon fiber is prepared by dry-jet wet spinning, with a specification of T700 grade 12K and a linear density of 800±15 g / km.

[0008] Optionally, the high-toughness carbon fiber epoxy resin prepreg has an area density of 125±5 g / m2 and an epoxy resin mass content of 33±2%.

[0009] Optionally, the epoxy resin toughening method comprises the following steps: Step 1.1, prepare epoxy resin mixture: place epoxy resin and accelerator in a dry container and preheat until completely melted, the preheating temperature is 55-60°C, and the time is 65-75 minutes; Step 1.2, primary toughening: Add the epoxy resin mixture of step 1.1 to the primary toughening agent and stir thoroughly for 15-30 minutes.

[0010] Step 1.3: Then, place the preheated resin in a grinder and add the secondary toughening agent, then knead for 15-30 minutes, and cool it down to 40-50°C at room temperature; finally, place the ground resin mixture in a cold storage at ≤-18°C for use; Step 1.4: Place the kneaded resin mixture in a reactor at a temperature of 75-95°C, evacuate, add filler, turn on the high-speed shaft and dispersion disk to stir and disperse, and mix for 30-60 minutes before discharging; Step 1.5: Finally, cool the mixture to room temperature and store it in a cold storage at ≤-18°C until use.

[0011] Optionally, the method for preparing the prepreg comprises the following steps: Step 2.1, the epoxy resin mixture obtained in step 1.4 is subjected to a casting process to form a smooth and uniform epoxy resin film on a release paper; Step 2.2: Pull the carbon fiber tow onto the epoxy film in step 2.1, and impregnate the epoxy resin film into the carbon fiber tow to obtain a prepreg semi-finished product; Step 2.3, drying the prepreg semi-finished product; Step 2.4: Place the isolation film on the product dried in step 2.3; Step 2.5: Use a winding device to wind up the product in step 2.4 to obtain a carbon fiber prepreg.

[0012] Another aspect of the present invention provides a rocket engine casing prepared from high-toughness carbon fiber epoxy resin prepreg.

[0013] Furthermore, the method for preparing the rocket engine casing includes the following steps: Step 3.1, mold preparation: clean all surfaces except the bottom of the mold and the surfaces of fasteners and pins to remove oil and impurities; Step 3.2, cutting: cutting the prepreg into sheets, sealing the cut sheets in vacuum bags and storing them for future use; Step 3.3, laying: Lay the cut pieces on the mold according to the design requirements; Step 3.4: Make a vacuum bag: Lay a peelable cloth, a non-porous isolation film, and a layer of N4 breathable felt on the surface of the product in sequence. All auxiliary materials should be overlapped and laid. The height of the peelable cloth should be consistent with the height of the mold, and the bottom edge should be 40mm. Wrap the sealing strip with a non-porous isolation film and adhere it to the four sides of the mold. Place the bases of the two vacuum quick connectors on the forming mold. Pad the bottom surface of the vacuum quick connector with two layers of breathable felt. After vacuuming, perform an airtightness test. Step 3.5, curing: transfer the mold to the autoclave and conduct a vacuum leak test before curing. The autoclave door can be closed only after the airtightness meets the standard. The mold base selects the slowest mold temperature, the pressure increase rate is 0.30 bar / min, and the pressure reduction rate is 0.50 bar / min. The target temperature of the first section is set to 181°C, the heating rate is 2°C / min, and the holding time is 120 minutes. The air temperature of the second section is set to 50°C, the cooling rate does not exceed 3°C / min, and the target temperature is set to 59°C. Start pressurizing and start pressurizing to 6 bar. When the mold temperature drops below 60°C, release the pressure and open the autoclave.

[0014] Furthermore, the air tightness test requirements in step 3.4 are: the vacuum degree reaches above 950 mbar, and the pressure drop does not exceed 20 mbar within 5 minutes.

[0015] Beneficial effects of the present invention: The use of the lay-up process instead of the winding process increases the proportion of longitudinal carbon fiber layers, thereby increasing the engine casing's ability to withstand axial pressure loads.

[0016] Using negative mold molding, the outer surface of the product is the film surface, which provides surface quality.

[0017] The high-toughness epoxy resin prepared by the two-stage toughening method of the present invention improves the toughness of the resin while not reducing the Tg value and increasing the viscosity value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 A rocket engine composite material casing prepared by the present invention; Figure 2 The rocket engine composite material shell tooling (female mold) prepared by the present invention. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments. Example 1

[0021] A high-toughness carbon fiber epoxy resin prepreg is composed of carbon fiber tow and the following components in parts by weight: 90 parts of epoxy resin, 5 parts of a primary toughening agent, 5 parts of a secondary toughening agent, 0.5 parts of an accelerator, and 0.2 parts of a filler; Among them, the epoxy resin is MP24018 epoxy resin, the primary toughening agent is PEEK thermoplastic particles, the secondary toughening agent is a product of the reaction of diphenylamine-formaldehyde and dicyandiamide, the accelerator is acrylamide, and the filler is asbestos powder. The epoxy resin toughening method is used for toughening. The resin system adopts a composite multifunctional resin with a balanced rigid and tough main chain from the molecular structure design, and then uses a toughening curing agent to adjust the cross-linked network structure of the epoxy matrix; the thermoplastic resin is used to achieve the "primary toughening" of the matrix, and the in-situ interlayer reaction of reactive thermoplastic discrete particles is used to achieve the "secondary toughening" of the resin matrix. The specific steps are as follows: Step 1.1, prepare epoxy resin mixture: place epoxy resin and accelerator in a dry container and preheat until completely melted, the preheating temperature is 55°C, and the time is 65 minutes; Step 1.2, primary toughening: add the epoxy resin mixture of step 1.1 to the primary toughening agent and stir thoroughly for 20 minutes.

[0022] Step 1.3: Then, the preheated resin was placed in a grinder and a secondary toughening agent was added, followed by kneading for 15 minutes, and then cooled to 40°C at room temperature; finally, the ground resin mixture was placed in a cold storage at ≤-18°C for use; Step 1.4: Place the kneaded resin mixture in a reactor at 75°C, evacuate the mixture, add filler, turn on the high-speed shaft and dispersion disk to stir and disperse, and mix for 30 minutes before discharging. Step 1.5: Finally, cool the mixture to room temperature and store it in a cold storage at ≤-18°C until use.

[0023] The carbon fiber is prepared by dry-jet wet spinning, with specifications of T700 grade 12K and a linear density of 800g / km. The surface density of the carbon fiber prepreg is 125g / m2 and the epoxy resin mass content is 33%.

[0024] The preparation of high-toughness carbon fiber epoxy resin prepreg includes the following steps: Step 2.1, the epoxy resin mixture obtained in step 1.4 is subjected to a casting process to form a smooth and uniform epoxy resin film on a release paper; Step 2.2: Pull the carbon fiber tow onto the epoxy film in step 2.1, and impregnate the epoxy resin film into the carbon fiber tow to obtain a prepreg semi-finished product; Step 2.3, drying the product obtained in step 2.2; Step 2.4: Place the isolation film on the product dried in step 2.3; Step 2.5: Use a winding device to wind up the product in step 2.4 to obtain a carbon fiber prepreg. Example 2

[0025] High-toughness carbon fiber epoxy resin prepreg is composed of carbon fiber tow and the following components in parts by weight: 120 parts of epoxy resin, 10 parts of primary toughening agent, 3 parts of secondary toughening agent, 1.5 parts of accelerator, and 0.4 parts of filler. The epoxy resin is a mixture of 128 epoxy resin and 6101 epoxy resin, the accelerator is a mixture of polyvinyl butyral and organic urea, and the filler is quartz powder.

[0026] The method of toughening with epoxy resin includes the following steps: Step 1.1, prepare epoxy resin mixture: place epoxy resin and accelerator in a dry container and preheat until completely melted, the preheating temperature is 60°C, and the time is 70 minutes; Step 1.2, primary toughening: add the epoxy resin mixture of step 1.1 to the primary toughening agent and stir thoroughly for 30 minutes.

[0027] Step 1.3: Then, the preheated resin was placed in a grinder and a secondary toughening agent was added, followed by kneading for 30 minutes, and then cooled to 50°C at room temperature; finally, the ground resin mixture was placed in a cold storage at ≤-18°C for use; Step 1.4: Place the kneaded resin mixture in a reactor at 90°C, evacuate the mixture, add filler, turn on the high-speed shaft and dispersion disk to stir and disperse, and mix for 50 minutes before discharging. Step 1.5: Finally, cool the mixture to room temperature and store it in a cold storage at ≤-18°C. Example 3

[0028] The high-toughness carbon fiber epoxy resin prepreg is composed of carbon fiber tow and the following components in parts by weight: 100 parts of epoxy resin, 8 parts of primary toughening agent, 3 parts of secondary toughening agent, 1 part of accelerator, and 0.3 parts of filler. The epoxy resin is a mixture of MP24018 epoxy resin and 6101 epoxy resin, the accelerator is a mixture of polyvinyl butyral, organic urea and α-methacrylate passivated 2-ethyl-4-methylimidazole, and the filler is quartz powder.

[0029] The performance parameters of the high-toughness carbon fiber epoxy resin prepreg prepared by Examples 1-3 are shown in Table 1: Table 1

[0030] A method for manufacturing a rocket engine casing, wherein the rocket engine casing is as shown in the following Figure 1 As shown in the figure, the carbon fiber prepreg is cut into pieces of designed size and then Figure 2 ) and finally formed in an autoclave.

[0031] The steps include: Step 3.1, Mold Preparation: Disassemble the mold and arrange them by category. Use a clean white cloth to wipe all surfaces except the bottom of the mold, as well as the surfaces of fasteners and pins, to remove any visible oil stains. Use a spray bottle to drip detergent into the holes on the mold surface until the detergent overflows. Let it soak for 10 minutes, then use compressed air to blow the detergent away. Soak a clean rag with detergent until it drips, and wipe back and forth across the mold surface. To prevent oil stains from being transferred to the workpiece via the rag, wipe several times, then use another clean rag soaked in detergent and wipe again. After the final wipe, wipe until there is no visible residue on the rag. Cleaning is complete. Ensure the mold surface is smooth, free of oil and impurities. Allow the detergent to dry completely for half an hour before use.

[0032] Step 3.2, cutting: Cut the prepreg produced in step 2 according to the product design drawings, and seal the cut prepreg in a vacuum bag for storage; Step 3.3, laying: Lay the pieces cut in step 3.2 on the mold according to the design file.

[0033] Step 3.4, make vacuum bags: lay peelable cloth, non-porous isolation film, and a layer of N4 breathable felt on the surface of the product in sequence. All auxiliary materials are overlapped and laid. The height of the peelable cloth must be consistent with the height of the mold, and the bottom edge must be 40mm; wrap the sealing strip with non-porous isolation film and glue it around the mold. Place the bases of the two vacuum quick connectors on the forming mold, and pad the lower surface of the vacuum quick connector with two layers of breathable felt to improve the air conductivity. All connectors do not touch the product, and the two connectors are pulled out one side at a time. After the vacuum is drawn, perform an airtightness test. Vacuum test requirements: The vacuum degree reaches above 950mbar, and the pressure drop does not exceed 20mbar within 5 minutes; Step 3.5, Curing: Use a forklift to transfer the mold to the autoclave. Connect the vacuum line inside the autoclave to the vacuum connector. Perform a vacuum leak test before curing. Only close the autoclave door after the airtightness meets the requirements. For the mold base, select the slowest mold temperature, a pressure increase rate of 0.30 bar / min, and a pressure decrease rate of 0.50 bar / min. Set the target temperature for the first stage to 181°C, a temperature increase rate of 2°C / min, and a hold time of 120 minutes. Set the air temperature for the second stage to 50°C, a temperature decrease rate of no more than 3°C / min, and a target temperature of 59°C. Start pressurization and increase to 6 bar. Once the mold temperature drops below 60°C, release the pressure and open the autoclave.

[0034] It should be noted that, unless otherwise defined, the technical or scientific terms used in the present invention should have the usual meanings understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

Claims

1. A high-toughness carbon fiber epoxy resin prepreg, characterized in that: The invention is composed of carbon fiber tow and the following components in parts by weight: 85-125 parts of epoxy resin, 5-10 parts of primary toughening agent, 3-5 parts of secondary toughening agent, 0.5-1.5 parts of accelerator, and 0.2-0.4 parts of filler; Among them, the epoxy resin is selected from one of MP24018 epoxy resin, 128 epoxy resin and 6101 epoxy resin or a mixture of any two of them, the primary toughening agent is PEEK thermoplastic particles, the secondary toughening agent is a product of the reaction of diphenylamine-formaldehyde and dicyandiamide, the accelerator is selected from one of acrylamide, polyvinyl butyral, organic urea and α-methacrylic acid passivated 2-ethyl-4-methylimidazole or a mixture of any two, the filler is asbestos powder or quartz powder, and the toughness of the carbon fiber epoxy resin prepreg is improved by the epoxy resin toughening method.

2. The high-toughness carbon fiber epoxy resin prepreg according to claim 1, characterized in that: The carbon fiber is prepared by dry-jet wet spinning, with a specification of T700 grade 12K and a linear density of 800±15g / km.

3. The high-toughness carbon fiber epoxy resin prepreg according to claim 1, characterized in that: The surface density of the high-toughness carbon fiber epoxy resin prepreg is 125±5g / m 2 , the epoxy resin mass content is 33±2%.

4. The high-toughness carbon fiber epoxy resin prepreg according to claim 1, characterized in that: The epoxy resin toughening method comprises the following steps: Step 1.1, prepare epoxy resin mixture: place epoxy resin and accelerator in a dry container and preheat until completely melted, the preheating temperature is 55-60°C, and the time is 65-75 minutes; Step 1.2, primary toughening: add the epoxy resin mixture of step 1.1 to the primary toughening agent and stir thoroughly for 15-30 minutes; Step 1.3: Then, place the preheated resin in a grinder and add the secondary toughening agent, then knead for 15-30 minutes, and cool it down to 40-50°C at room temperature; finally, place the ground resin mixture in a cold storage at ≤-18°C for use; Step 1.4: Place the kneaded resin mixture in a reactor at a temperature of 75-95°C, evacuate, add filler, turn on the high-speed shaft and dispersion disk to stir and disperse, and mix for 30-60 minutes before discharging; Step 1.5: Finally, cool the mixture to room temperature and store it in a cold storage at ≤-18°C until use.

5. The high-toughness carbon fiber epoxy resin prepreg according to claim 4, characterized in that: The preparation method comprises the following steps: Step 2.1, the epoxy resin mixture obtained in step 1.4 is subjected to a casting process to form a smooth and uniform epoxy resin film on a release paper; Step 2.2: Pull the carbon fiber tow onto the epoxy film in step 2.1, and impregnate the epoxy resin film into the carbon fiber tow to obtain a prepreg semi-finished product; Step 2.3, drying the prepreg semi-finished product; Step 2.4: Place the isolation film on the product dried in step 2.3; Step 2.5: Use a winding device to wind up the product in step 2.4 to obtain a carbon fiber prepreg.

6. A rocket engine casing, characterized in that: The carbon fiber epoxy resin prepreg having high toughness is prepared from the high toughness carbon fiber epoxy resin prepreg according to any one of claims 1 to 5.

7. The rocket engine casing according to claim 6, characterized in that: The preparation method comprises the following steps: Step 3.1, mold preparation: clean all surfaces except the bottom of the mold and the surfaces of fasteners and pins to remove oil and impurities; Step 3.2, cutting: cutting the prepreg into sheets, sealing the cut sheets in vacuum bags and storing them for future use; Step 3.3, laying: Lay the cut pieces on the mold according to the design requirements; Step 3.4: Make a vacuum bag: Lay a peelable cloth, a non-porous isolation film, and a layer of N4 breathable felt on the surface of the product in sequence. All auxiliary materials should be overlapped and laid. The height of the peelable cloth should be consistent with the height of the mold, and the bottom edge should be 40mm. Wrap the sealing strip with a non-porous isolation film and adhere it to the four sides of the mold. Place the bases of the two vacuum quick connectors on the forming mold. Pad the bottom surface of the vacuum quick connector with two layers of breathable felt. After vacuuming, perform an airtightness test. Step 3.5, curing: transfer the mold to the autoclave and conduct a vacuum leak test before curing. The autoclave door can be closed only after the airtightness meets the standard. The mold base selects the slowest mold temperature, the pressure increase rate is 0.30 bar / min, and the pressure reduction rate is 0.50 bar / min. The target temperature of the first section is set to 181°C, the heating rate is 2°C / min, and the holding time is 120 minutes. The air temperature of the second section is set to 50°C, the cooling rate does not exceed 3°C / min, and the target temperature is set to 59°C. Start pressurizing and start pressurizing to 6 bar. When the mold temperature drops below 60°C, release the pressure and open the autoclave.

8. The rocket engine casing according to claim 7, characterized in that: The airtightness test requirements in step 3.4 are: the vacuum degree reaches above 950mbar, and the pressure drop does not exceed 20mbar within 5 minutes.

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