A method for enhancing interlayer strength of continuous fiber 3D printed parts

Abstract

This invention discloses a method for enhancing the interlayer strength of continuous fiber 3D printed parts, belonging to the field of composite material manufacturing technology. The method includes the following steps: Step 1, carbon fiber pretreatment; Step 2, prepreg filament preparation; Step 3, additive manufacturing of interlocking structures: using the prepreg filament obtained in Step 2 for 3D printing, during the printing process, laser preheating and regular tapping are used to form protruding structures in each layer. In subsequent layers, laser preheating and tapping are used to form hook-like protruding structures, achieving interlayer interlocking; Step 4, carbon nanotube pretreatment; Step 5, placing the printed part obtained in Step 3 in a solvent, adding an activating agent, and then adding the aminated carbon nanotubes obtained in Step 4, allowing the carbon nanotubes to be grafted onto the carbon fiber surface through an amidation reaction, forming a root structure. This invention can effectively enhance the interlayer peel strength in the layer height direction, meeting the high strength requirements of aircraft structural components.

Description

Technical Field

[0001] This invention relates to the field of composite material manufacturing technology, and in particular to a method for enhancing the interlayer strength of continuous fiber 3D printed parts. Background Technology

[0002] Continuous fiber additive manufacturing is an advanced 3D printing technology that creates composite material parts with high strength and stiffness by combining continuous reinforcing fibers, such as carbon fiber and glass fiber, with thermoplastics or other matrix materials.

[0003] While continuous fiber additive manufacturing offers many advantages, it also presents challenges and limitations, with interlayer weakness being a prominent issue. This weakness occurs during the printing process when insufficient bonding between different layers leads to a decline in the mechanical properties of the finished product, particularly in the direction perpendicular to the fiber. Furthermore, interlayer weakness makes the finished product prone to delamination under stress, significantly reducing tensile and flexural strength, especially in the direction perpendicular to the fiber. This also reduces the overall reliability and lifespan of the finished product, especially under dynamic loads or harsh environmental conditions.

[0004] Carbon fiber reinforced composites have been widely used in high-end equipment applications due to their advantages such as high specific strength and specific stiffness, strong designability, good fatigue performance, corrosion resistance and integral molding.

[0005] Thermoplastic composite additive manufacturing technology has significant advantages in realizing the integrated molding of complex composite components. At the same time, the manufacturing process is simple and does not require mold forming, which can significantly reduce the processing cycle and manufacturing cost of composite materials, and realize the rapid iterative upgrade of composite component. Furthermore, continuous carbon fiber reinforced thermoplastic composite additive manufacturing technology, with its high degree of freedom forming process, can replace components that are difficult to process with traditional composite manufacturing processes and are forced to use materials such as metals with thermoplastic composites, thereby achieving component lightweighting.

[0006] However, due to the "layer-by-layer" forming method of additive manufacturing, 3D printed parts are subject to significant application limitations due to their relatively weak interlayer strength. In particular, the fiber content ratio of continuous fiber parts, which is much higher than that of chopped fiber 3D printed parts, leads to further weakening of interlayer strength. Therefore, the failure modes of continuous fiber 3D printed parts are usually interlayer delamination, cracking, or debonding under lateral loads.

[0007] To address the above issues, researchers have employed various strategies to improve the interlaminar properties of continuous fiber components, primarily through improving prepreg properties and post-processing assembly. However, in practical applications, existing technologies suffer from limitations due to the complexity of post-processing, the need for new equipment, and the fact that they only enhance transverse interlaminar shear strength without significantly improving interlaminar peel strength.

[0008] Chinese patent application CN109291461A, published on February 1, 2019, discloses an additive manufacturing method for interlayer micro-rod reinforced continuous fiber reinforced composite materials. The method involves first completing an integrated process of composite material preparation and molding to obtain the target part; then, fibers are impregnated with resin and pultruded using a micro-diameter rod process, followed by cutting to obtain micro-rods; finally, the micro-rods are loaded into a nail gun and injected into the target part, which has been pre-softened by environmental heating. If the target part is a plate-like component with a thickness of less than 3 cm, only one micro-rod insertion is required; otherwise, multiple insertions are required until the target part reaches the required thickness. The target part with the implanted microrods is then placed in a constant temperature chamber for post-heating treatment to facilitate the formation of a better bonding interface between the target part and the microrods.

[0009] The additive manufacturing method for interlayer micro-rod reinforced continuous fiber reinforced composite materials disclosed in this patent application enables the rapid manufacturing of high-performance continuous fiber reinforced composite extruded components with balanced or controllable properties in all directions. However, since it mainly involves preparing conventional continuous fiber 3D printed parts, and then embedding resin-impregnated fibers into the parts using a nail gun to achieve interlayer reinforcement, it only enhances the transverse shear strength of the interlayer and does not affect the interlayer peel strength in the layer height direction, thus still failing to meet the high strength requirements of aircraft structural components. Summary of the Invention

[0010] In order to overcome the shortcomings of the prior art, the present invention provides a method for enhancing the interlayer strength of continuous fiber 3D printed parts. The present invention can effectively enhance the interlayer peel strength in the layer height direction, and meet the high strength requirements of aircraft structural parts.

[0011] This invention is achieved through the following technical solution: A method for enhancing the interlayer strength of continuous fiber 3D printed parts includes the following steps: Step 1: Carbon fiber pretreatment: The continuous fibers are cleaned, dried and oxidized to obtain surface-activated carbon fibers; Step 2, Prepreg Preparation: The carbon fibers obtained in Step 1 are combined with a thermoplastic resin matrix containing active functional groups to prepare prepreg. Step 3, Interlocking Structure Additive Manufacturing: 3D printing is performed using the prepreg filament obtained in Step 2. During the printing process, protruding structures are formed in each layer by laser preheating and regular tapping. In subsequent layers, the protruding structures are formed into hook shapes by laser preheating and tapping, thus achieving interlocking between layers. Step 4: Carbon nanotube pretreatment: Carbon nanotubes are acidified, activated, and amination treated to obtain amination-treated carbon nanotubes. Step 5: Post-processing preparation of root system structure: Place the printed part obtained in step 3 in a solvent, add an activating reagent, and then add the aminated carbon nanotubes obtained in step 4. The carbon nanotubes are grafted onto the carbon fiber surface through an amidation reaction to form a root system structure.

[0012] In step one, the cleaning process involves ultrasonic cleaning with deionized water for 10-30 minutes.

[0013] In step one, the drying process involves drying at 100-120°C for 1-2 hours.

[0014] In step one, the oxidation treatment involves immersing the carbon fiber in a mixture of concentrated nitric acid and concentrated sulfuric acid for 1-4 hours.

[0015] The volume ratio of concentrated nitric acid to concentrated sulfuric acid is 3:1.

[0016] In step one, after oxidation treatment, rinse with deionized water until pH is neutral, and then dry at 100-120°C for 1-2 hours.

[0017] In step two, the thermoplastic resin is one or more of polyamide, polycarbonate, polyetherimide, and polyphenylene sulfide.

[0018] In step two, the carbon fibers are spread into monofilaments or sheets using a mechanical fiber spreader, and then impregnated in a resin bath heated to a molten state.

[0019] In step three, during the 3D printing process, a laser preheating device is set in front of the printing nozzle, and a regular tapping device is set around the printing nozzle. The tapping device is equipped with a heating thermocouple and uses polytetrafluoroethylene for edge protection.

[0020] The tapping device moves with the printing nozzle and contacts the uncured viscous resin in a regular pattern. The high-temperature metal at the bottom binds the resin to the fiber and pulls it up to form a uniformly arranged protruding structure.

[0021] In step three, when printing the next layer, the laser preheating device raises the surface temperature of the protruding structure to a semi-molten state. After being tapped, it forms a hook-shaped protrusion on the edge of the elytra. Then, the printing nozzle covers the next layer of resin on top to form an interlocking structure.

[0022] In step four, the carbon nanotubes are multi-walled carbon nanotubes. The acid washing pretreatment is performed by acid treatment, followed by activation of the carboxyl groups with an activating reagent, and finally grafting of amino groups with ethylenediamine.

[0023] The activating agent is N,N'-dicyclohexylcarbodiimide or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide.

[0024] In step five, the printed part is placed in N,N-dimethylformamide solvent, an activating agent is added, and the mixture is stirred at room temperature for 2-24 hours. Then, the aminated carbon nanotubes are dispersed in dimethyl sulfoxide and added to the N,N-dimethylformamide solution. The mixture is stirred at room temperature for another 2-24 hours to allow the carbon nanotubes to be grafted onto the carbon fibers through an amidation reaction.

[0025] The beneficial effects of this invention are mainly reflected in the following aspects: 1. Compared with the prior art, the present invention can effectively enhance the interlayer peel strength in the layer height direction, and meet the high strength requirements of aircraft structural components.

[0026] 2. This invention constructs an interlocking elytra structure through a "preheating-tapping" process during printing, which significantly improves the interlayer shear strength and interlayer peel strength of continuous fiber 3D printed parts; at the same time, the post-processing grafting of carbon nanotubes forms a root system structure, which further fills the pores and enhances the interlayer bonding, thereby effectively solving the defect of poor interlayer performance of 3D printed parts.

[0027] 3. Based on additive manufacturing technology, this invention can effectively solve the defects of poor interlayer shear performance and interlayer peel strength of 3D printed parts by simply adjusting the printing process and post-processing process, thereby broadening the application scenarios of continuous fiber 3D printed parts.

[0028] 4. This invention, by introducing biomimetic design concepts and optimizing both the printing process and post-processing process, achieves improved interlayer performance of continuous fiber 3D printed parts.

[0029] 5. This invention introduces a "sheath interlocking" structural design between the layers of a continuous fiber 3D printed part through a "preheating-tapping-deposition-tapping" process, which can effectively increase the interlayer shear and interlayer peel strength.

[0030] 6. This invention introduces a "root system" structure design between the layers of continuous fiber 3D printed parts through a post-processing technique of grafting carbon nanotubes onto the surface of continuous carbon fibers. This fills the pores of the printed parts and reduces the delamination starting point, thereby further improving the interlayer shear and interlayer peel strength. Attached Figure Description

[0031] The present invention will now be further described in detail with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0032] Example 1 See Figure 1 A method for enhancing the interlayer strength of continuous fiber 3D printed parts includes the following steps: Step 1: Carbon fiber pretreatment: The continuous fibers are cleaned, dried and oxidized to obtain surface-activated carbon fibers; Step 2, Prepreg Preparation: The carbon fibers obtained in Step 1 are combined with a thermoplastic resin matrix containing active functional groups to prepare prepreg. Step 3, Interlocking Structure Additive Manufacturing: 3D printing is performed using the prepreg filament obtained in Step 2. During the printing process, protruding structures are formed in each layer by laser preheating and regular tapping. In subsequent layers, the protruding structures are formed into hook shapes by laser preheating and tapping, thus achieving interlocking between layers. Step 4: Carbon nanotube pretreatment: Carbon nanotubes are acidified, activated, and amination treated to obtain amination-treated carbon nanotubes. Step 5: Post-processing preparation of root system structure: Place the printed part obtained in step 3 in a solvent, add an activating reagent, and then add the aminated carbon nanotubes obtained in step 4. The carbon nanotubes are grafted onto the carbon fiber surface through an amidation reaction to form a root system structure.

[0033] This embodiment is the most basic implementation method. Compared with the prior art, it can effectively enhance the interlayer peel strength in the layer height direction and meet the high strength requirements of aircraft structural components.

[0034] Example 2 See Figure 1 A method for enhancing the interlayer strength of continuous fiber 3D printed parts includes the following steps: Step 1: Carbon fiber pretreatment: The continuous fibers are cleaned, dried and oxidized to obtain surface-activated carbon fibers; Step 2, Prepreg Preparation: The carbon fibers obtained in Step 1 are combined with a thermoplastic resin matrix containing active functional groups to prepare prepreg. Step 3, Interlocking Structure Additive Manufacturing: 3D printing is performed using the prepreg filament obtained in Step 2. During the printing process, protruding structures are formed in each layer by laser preheating and regular tapping. In subsequent layers, the protruding structures are formed into hook shapes by laser preheating and tapping, thus achieving interlocking between layers. Step 4: Carbon nanotube pretreatment: Carbon nanotubes are acidified, activated, and amination treated to obtain amination-treated carbon nanotubes. Step 5: Post-processing preparation of root system structure: Place the printed part obtained in step 3 in a solvent, add an activating reagent, and then add the aminated carbon nanotubes obtained in step 4. The carbon nanotubes are grafted onto the carbon fiber surface through an amidation reaction to form a root system structure.

[0035] Preferably, in step one, the cleaning is performed by ultrasonic cleaning with deionized water for 10 minutes.

[0036] In step one, the drying process involves drying at 100°C for 1 hour.

[0037] In step one, the oxidation treatment involves immersing the carbon fiber in a mixture of concentrated nitric acid and concentrated sulfuric acid for 1 hour.

[0038] This embodiment is a preferred implementation method. By constructing the elytra interlocking structure through the "preheating-tapping" process during printing, the interlayer shear strength and interlayer peel strength of the continuous fiber 3D printed parts are significantly improved. At the same time, the post-processing grafting of carbon nanotubes forms a root system structure, which further fills the pores and enhances the interlayer bonding, thereby effectively solving the defect of poor interlayer performance of 3D printed parts.

[0039] Example 3 See Figure 1 A method for enhancing the interlayer strength of continuous fiber 3D printed parts includes the following steps: Step 1: Carbon fiber pretreatment: The continuous fibers are cleaned, dried and oxidized to obtain surface-activated carbon fibers; Step 2, Prepreg Preparation: The carbon fibers obtained in Step 1 are combined with a thermoplastic resin matrix containing active functional groups to prepare prepreg. Step 3, Interlocking Structure Additive Manufacturing: 3D printing is performed using the prepreg filament obtained in Step 2. During the printing process, protruding structures are formed in each layer by laser preheating and regular tapping. In subsequent layers, the protruding structures are formed into hook shapes by laser preheating and tapping, thus achieving interlocking between layers. Step 4: Carbon nanotube pretreatment: Carbon nanotubes are acidified, activated, and amination treated to obtain amination-treated carbon nanotubes. Step 5: Post-processing preparation of root system structure: Place the printed part obtained in step 3 in a solvent, add an activating reagent, and then add the aminated carbon nanotubes obtained in step 4. The carbon nanotubes are grafted onto the carbon fiber surface through an amidation reaction to form a root system structure.

[0040] In step one, the cleaning process involves ultrasonic cleaning with deionized water for 15 minutes.

[0041] In step one, the drying process involves drying at 105°C for 1.5 hours.

[0042] In step one, the oxidation treatment involves immersing the carbon fiber in a mixture of concentrated nitric acid and concentrated sulfuric acid for 2 hours.

[0043] The volume ratio of concentrated nitric acid to concentrated sulfuric acid is 3:1.

[0044] In step one, after oxidation treatment, the sample is rinsed with deionized water until the pH is neutral, and then dried at 100°C for 1 hour.

[0045] In step two, the thermoplastic resin is polyamide.

[0046] This embodiment is a preferred implementation method. Based on additive manufacturing technology, by making simple adjustments to the printing process and post-processing process, the defects of poor interlayer shear performance and interlayer peel strength of 3D printed parts can be effectively solved, thereby broadening the application scenarios of continuous fiber 3D printed parts.

[0047] Example 4 See Figure 1 A method for enhancing the interlayer strength of continuous fiber 3D printed parts includes the following steps: Step 1: Carbon fiber pretreatment: The continuous fibers are cleaned, dried and oxidized to obtain surface-activated carbon fibers; Step 2, Prepreg Preparation: The carbon fibers obtained in Step 1 are combined with a thermoplastic resin matrix containing active functional groups to prepare prepreg. Step 3, Interlocking Structure Additive Manufacturing: 3D printing is performed using the prepreg filament obtained in Step 2. During the printing process, protruding structures are formed in each layer by laser preheating and regular tapping. In subsequent layers, the protruding structures are formed into hook shapes by laser preheating and tapping, thus achieving interlocking between layers. Step 4: Carbon nanotube pretreatment: Carbon nanotubes are acidified, activated, and amination treated to obtain amination-treated carbon nanotubes. Step 5: Post-processing preparation of root system structure: Place the printed part obtained in step 3 in a solvent, add an activating reagent, and then add the aminated carbon nanotubes obtained in step 4. The carbon nanotubes are grafted onto the carbon fiber surface through an amidation reaction to form a root system structure.

[0048] In step one, the cleaning process involves ultrasonic cleaning with deionized water for 25 minutes.

[0049] In step one, the drying process involves drying at 110°C for 2 hours.

[0050] In step one, the oxidation treatment involves immersing the carbon fiber in a mixture of concentrated nitric acid and concentrated sulfuric acid for 3 hours.

[0051] The volume ratio of concentrated nitric acid to concentrated sulfuric acid is 3:1.

[0052] In a further preferred embodiment, in step one, after oxidation treatment, the sample is rinsed with deionized water until the pH is neutral, and then dried at 110°C for 2 hours.

[0053] In step two, the thermoplastic resin is polycarbonate.

[0054] In step two, the carbon fibers are spread into monofilaments or sheets using a mechanical fiber spreader, and then impregnated in a resin bath heated to a molten state.

[0055] In step three, during the 3D printing process, a laser preheating device is set in front of the printing nozzle, and a regular tapping device is set around the printing nozzle. The tapping device is equipped with a heating thermocouple and uses polytetrafluoroethylene for edge protection.

[0056] The tapping device moves with the printing nozzle and contacts the uncured viscous resin in a regular pattern. The high-temperature metal at the bottom binds the resin to the fiber and pulls it up to form a uniformly arranged protruding structure.

[0057] This embodiment is a preferred implementation method. By introducing biomimetic design concepts and optimizing both the printing process and post-processing process, the interlayer performance of continuous fiber 3D printed parts is improved.

[0058] Example 5 See Figure 1 A method for enhancing the interlayer strength of continuous fiber 3D printed parts includes the following steps: Step 1: Carbon fiber pretreatment: The continuous fibers are cleaned, dried and oxidized to obtain surface-activated carbon fibers; Step 2, Prepreg Preparation: The carbon fibers obtained in Step 1 are combined with a thermoplastic resin matrix containing active functional groups to prepare prepreg. Step 3, Interlocking Structure Additive Manufacturing: 3D printing is performed using the prepreg filament obtained in Step 2. During the printing process, protruding structures are formed in each layer by laser preheating and regular tapping. In subsequent layers, the protruding structures are formed into hook shapes by laser preheating and tapping, thus achieving interlocking between layers. Step 4: Carbon nanotube pretreatment: Carbon nanotubes are acidified, activated, and amination treated to obtain amination-treated carbon nanotubes. Step 5: Post-processing preparation of root system structure: Place the printed part obtained in step 3 in a solvent, add an activating reagent, and then add the aminated carbon nanotubes obtained in step 4. The carbon nanotubes are grafted onto the carbon fiber surface through an amidation reaction to form a root system structure.

[0059] In step one, the cleaning process involves ultrasonic cleaning with deionized water for 25 minutes.

[0060] In step one, the drying process involves drying at 120°C for 2 hours.

[0061] In step one, the oxidation treatment involves immersing the carbon fiber in a mixture of concentrated nitric acid and concentrated sulfuric acid for 3 hours.

[0062] The volume ratio of concentrated nitric acid to concentrated sulfuric acid is 3:1.

[0063] In step one, after oxidation treatment, the sample is rinsed with deionized water until the pH is neutral, and then dried at 110°C for 1 hour.

[0064] In step two, the thermoplastic resin is polyetherimide.

[0065] In step two, the carbon fibers are spread into monofilaments or sheets using a mechanical fiber spreader, and then impregnated in a resin bath heated to a molten state.

[0066] In step three, during the 3D printing process, a laser preheating device is set in front of the printing nozzle, and a regular tapping device is set around the printing nozzle. The tapping device is equipped with a heating thermocouple and uses polytetrafluoroethylene for edge protection.

[0067] The tapping device moves with the printing nozzle and contacts the uncured viscous resin in a regular pattern. The high-temperature metal at the bottom binds the resin to the fiber and pulls it up to form a uniformly arranged protruding structure.

[0068] In step three, when printing the next layer, the laser preheating device raises the surface temperature of the protruding structure to a semi-molten state. After being tapped, it forms a hook-shaped protrusion on the edge of the elytra. Then, the printing nozzle covers the next layer of resin on top to form an interlocking structure.

[0069] In step four, the carbon nanotubes are multi-walled carbon nanotubes. The acid washing pretreatment is performed by acid treatment, followed by activation of the carboxyl groups with an activating reagent, and finally grafting of amino groups with ethylenediamine.

[0070] The activating agent is N,N'-dicyclohexylcarbodiimide.

[0071] This embodiment is a preferred implementation method. By introducing a "sheath interlocking" structure design between the layers of the continuous fiber 3D printed part through the process of "preheating-tapping-deposition-tapping", the interlayer shear and interlayer peel strength can be effectively increased.

[0072] Example 6 See Figure 1 A method for enhancing the interlayer strength of continuous fiber 3D printed parts includes the following steps: Step 1: Carbon fiber pretreatment: The continuous fibers are cleaned, dried and oxidized to obtain surface-activated carbon fibers; Step 2, Prepreg Preparation: The carbon fibers obtained in Step 1 are combined with a thermoplastic resin matrix containing active functional groups to prepare prepreg. Step 3, Interlocking Structure Additive Manufacturing: 3D printing is performed using the prepreg filament obtained in Step 2. During the printing process, protruding structures are formed in each layer by laser preheating and regular tapping. In subsequent layers, the protruding structures are formed into hook shapes by laser preheating and tapping, thus achieving interlocking between layers. Step 4: Carbon nanotube pretreatment: Carbon nanotubes are acidified, activated, and amination treated to obtain amination-treated carbon nanotubes. Step 5: Post-processing preparation of root system structure: Place the printed part obtained in step 3 in a solvent, add an activating reagent, and then add the aminated carbon nanotubes obtained in step 4. The carbon nanotubes are grafted onto the carbon fiber surface through an amidation reaction to form a root system structure.

[0073] In step one, the cleaning process involves ultrasonic cleaning with deionized water for 30 minutes.

[0074] In step one, the drying process involves drying at 120°C for 2 hours.

[0075] In step one, the oxidation treatment involves immersing the carbon fiber in a mixture of concentrated nitric acid and concentrated sulfuric acid for 4 hours.

[0076] The volume ratio of concentrated nitric acid to concentrated sulfuric acid is 3:1.

[0077] In step one, after oxidation treatment, the sample is rinsed with deionized water until the pH is neutral, and then dried at 120°C for 2 hours.

[0078] In step two, the thermoplastic resin is polyphenylene sulfide.

[0079] In step two, the carbon fibers are spread into monofilaments or sheets using a mechanical fiber spreader, and then impregnated in a resin bath heated to a molten state.

[0080] More preferably, in step three, during the 3D printing process, a laser preheating device is set in front of the printing nozzle, and a regular tapping device is set around the printing nozzle. The tapping device is equipped with a heating thermocouple and uses polytetrafluoroethylene for edge protection.

[0081] The tapping device moves with the printing nozzle and contacts the uncured viscous resin in a regular pattern. The high-temperature metal at the bottom binds the resin to the fiber and pulls it up to form a uniformly arranged protruding structure.

[0082] In step three, when printing the next layer, the laser preheating device raises the surface temperature of the protruding structure to a semi-molten state. After being tapped, it forms a hook-shaped protrusion on the edge of the elytra. Then, the printing nozzle covers the next layer of resin on top to form an interlocking structure.

[0083] In step four, the carbon nanotubes are multi-walled carbon nanotubes. The acid washing pretreatment is performed by acid treatment, followed by activation of the carboxyl groups with an activating reagent, and finally grafting of amino groups with ethylenediamine.

[0084] The activating agent is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide.

[0085] In step five, the printed part is placed in N,N-dimethylformamide solvent, an activating agent is added, and the mixture is stirred at room temperature for 2-24 hours. Then, the aminated carbon nanotubes are dispersed in dimethyl sulfoxide and added to the N,N-dimethylformamide solution. The mixture is stirred at room temperature for another 2-24 hours to allow the carbon nanotubes to be grafted onto the carbon fibers through an amidation reaction.

[0086] This embodiment is the best implementation method. By grafting carbon nanotubes onto the surface of continuous carbon fibers in the post-processing, a "root system" structure design is introduced between the layers of the continuous fiber 3D printed part. At the same time, it fills the pores of the printed part and reduces the delamination starting point, which can further improve the interlayer shear and interlayer peel strength.

[0087] The invention will now be illustrated using a continuous carbon fiber reinforced nylon composite material as an example: Carbon fiber surface carboxylation pretreatment: Place the carbon fiber in a container containing deionized water and ultrasonically clean for 30 minutes to remove surface grease and impurities; rinse thoroughly with deionized water to ensure no residue; place the cleaned carbon fiber in an oven and dry at 120°C for 2 hours to remove moisture; mix concentrated nitric acid and concentrated sulfuric acid in a 3:1 ratio, place the dried carbon fiber in the oxidant solution, ensuring the fiber is completely submerged, and stir for 2 hours at room temperature; remove the oxidized carbon fiber from the solution and rinse with plenty of deionized water until the pH value is close to neutral; place the cleaned carbon fiber in an oven and dry at 100°C for 2 hours to remove moisture.

[0088] Preparation of prepreg yarn of continuous carbon fiber reinforced nylon composite material: The nylon resin is heated to 220°C to a molten state to ensure that the resin is completely melted and has good fluidity; the molten nylon resin is poured into the impregnation tank, and the pretreated carbon fiber is passed through the impregnation tank to ensure that the fiber is completely immersed. At the same time, a pressure roller or traction device is used to ensure that the fiber is uniformly impregnated.

[0089] Additive manufacturing of continuous fiber reinforced parts: The obtained continuous carbon fiber reinforced nylon composite material is loaded into a 3D printer, the printing temperature is set to 190℃, the printing speed is set to 30mm / s, the slicing code is imported, the laser preheating device is started, the tapping frequency is set to 5 times / s, and the printing program is started.

[0090] Pretreatment for amination of carbon nanotube surface: Weigh 5g of multi-walled carbon nanotubes and disperse them in 500mL of ethanol. Sonicate for 30 minutes to ensure uniform dispersion. Dissolve 5g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 5g of N-hydroxysuccinimide in 200mL of ethanol to prepare activator solutions. Pour the dispersed carbon nanotube solution into the activator solutions and stir at room temperature for 1 hour. Dissolve 5g of 3-aminopropyltriethoxysilane in 200mL of ethanol to prepare an amination reagent solution. Pour the activated carbon nanotube solution into the amination reagent solution and stir at room temperature for 2 hours. Remove the carbon nanotubes and rinse them repeatedly with deionized water until the pH of the rinsing solution is close to neutral. Place the cleaned carbon nanotubes in an oven and dry them at 100°C for 2 hours to remove moisture.

[0091] Post-grafting treatment: The obtained continuous fiber reinforced part was placed in N,N-dimethylformamide solvent and N,N'-dicyclohexylcarbodiimide activating agent was added. The mixture was stirred at room temperature for 8 hours. Aminated carbon nanotubes were dispersed in dimethyl sulfoxide organic solvent and ultrasonically treated for 30 minutes. The dispersed carbon nanotube solution was added to the continuous fiber part solution and mixed. The mixture was heated in a 60°C water bath for 12 hours. The continuous fiber reinforced part was removed, washed with deionized water, and dried in a vacuum drying oven to obtain the final molded part.

[0092] Test methods: The interlayer shear properties of continuous fiber 3D printed parts were tested using a universal testing machine according to the method specified in ASTM D2344; the interlayer peeling properties of continuous fiber 3D printed parts were tested using the method specified in ASTM D1876.

[0093] The test results are shown in Table 1: Table 1

[0094] As shown in Table 1, the reinforced continuous fiber 3D printed parts prepared by the present invention have significantly improved interlaminar shear strength and interlaminar peel strength compared with conventional continuous fiber reinforced composite material 3D printed parts.

Claims

1. A method for enhancing the interlayer strength of continuous fiber 3D printed parts, characterized in that, Includes the following steps: Step 1: Carbon fiber pretreatment: The continuous fibers are cleaned, dried and oxidized to obtain surface-activated carbon fibers; Step 2, Prepreg Preparation: The carbon fibers obtained in Step 1 are combined with a thermoplastic resin matrix containing active functional groups to prepare prepreg. Step 3, Interlocking Structure Additive Manufacturing: 3D printing is performed using the prepreg filament obtained in Step 2. During the printing process, protruding structures are formed in each layer by laser preheating and regular tapping. In subsequent layers, the protruding structures are formed into hook shapes by laser preheating and tapping, thus achieving interlocking between layers. Step 4: Carbon nanotube pretreatment: Carbon nanotubes are acidified, activated, and amination treated to obtain amination-treated carbon nanotubes. Step 5: Post-processing preparation of root system structure: Place the printed part obtained in step 3 in a solvent, add an activating reagent, and then add the aminated carbon nanotubes obtained in step 4. The carbon nanotubes are grafted onto the carbon fiber surface through an amidation reaction to form a root system structure.

2. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 1, characterized in that: In step one, the cleaning process involves ultrasonic cleaning with deionized water for 10-30 minutes.

3. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 1, characterized in that: In step one, the drying process involves drying at 100-120°C for 1-2 hours.

4. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 1, characterized in that: In step one, the oxidation treatment involves immersing the carbon fiber in a mixture of concentrated nitric acid and concentrated sulfuric acid for 1-4 hours.

5. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 4, characterized in that: The volume ratio of concentrated nitric acid to concentrated sulfuric acid is 3:

1.

6. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 1, characterized in that: In step one, after oxidation treatment, rinse with deionized water until pH is neutral, and then dry at 100-120°C for 1-2 hours.

7. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 1, characterized in that: In step two, the thermoplastic resin is one or more of polyamide, polycarbonate, polyetherimide, and polyphenylene sulfide.

8. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 1, characterized in that: In step two, the carbon fibers are spread into monofilaments or sheets using a mechanical fiber spreader, and then impregnated in a resin bath heated to a molten state.

9. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 1, characterized in that: In step three, during the 3D printing process, a laser preheating device is set in front of the printing nozzle, and a regular tapping device is set around the printing nozzle. The tapping device is equipped with a heating thermocouple and uses polytetrafluoroethylene for edge protection.

10. A method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 9, characterized in that: The tapping device moves with the printing nozzle and contacts the uncured viscous resin in a regular pattern. The high-temperature metal at the bottom binds the resin to the fiber and pulls it up to form a uniformly arranged protruding structure.

11. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 1, characterized in that: In step three, when printing the next layer, the laser preheating device raises the surface temperature of the protruding structure to a semi-molten state. After being tapped, it forms a hook-shaped protrusion on the edge of the elytra. Then, the printing nozzle covers the next layer of resin on top to form an interlocking structure.

12. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 1, characterized in that: In step four, the carbon nanotubes are multi-walled carbon nanotubes. The acid washing pretreatment is performed by acid treatment, followed by activation of the carboxyl groups with an activating reagent, and finally grafting of amino groups with ethylenediamine.

13. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 12, characterized in that: The activating agent is N,N'-dicyclohexylcarbodiimide or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide.

14. The method for enhancing the interlayer strength of continuous fiber 3D printed parts according to claim 12, characterized in that: In step five, the printed part is placed in N,N-dimethylformamide solvent, an activating agent is added, and the mixture is stirred at room temperature for 2-24 hours. Then, the aminated carbon nanotubes are dispersed in dimethyl sulfoxide and added to the N,N-dimethylformamide solution. The mixture is stirred at room temperature for another 2-24 hours to allow the carbon nanotubes to be grafted onto the carbon fibers through an amidation reaction.

Images