Continuous fiber-reinforced composite materials are the main materials of the spacecraft structure at home and abroad, with the advantages of low density and high strength. However, the traditional manufacturing process is complicated and costly. Using 3D printing to produce continuous carbon fiber-reinforced composite materials can achieve a more flexible design, while helping to save resources and time, thus attracting widespread attention. On May 5, China has achieved the first 3D printing of continuous fiber-reinforced composite materials in space internationally, which is expected to achieve space station orbit construction.
Most of the existing 3D printed continuous fiber reinforced composite materials are thermoplastic materials. Compared with thermoplastic materials, thermoset materials have better mechanical properties, heat resistance, and solvent resistance. Therefore, 3D printed continuous fiber reinforced thermoset materials It is expected to achieve more excellent mechanical properties and thermal properties.
Recently, Kun (Kelvin) Fu of the University of Delaware in the United States has developed a dynamic capillary-driven 3D printing technology, called partial in-plane assisted heating 3D printing (LITA), which realizes the continuous carbon fiber reinforced thermosetting composite printing The volume fraction of the fiber in the printed material is 58.6%, and the mechanical strength and modulus can reach 810MPa and 108GPa, respectively. The related work is titled "Dynamic Capillary-Driven Additive Manufacturing of Continuous Carbon Fiber Composite" and was recently published in "Matter".
The LITA technology is based on the continuous capillary action of the liquid resin between the carbon fibers. The specific process is: the heater locally heats the dried carbon fiber, and a temperature gradient is formed along the fiber direction, so that the liquid thermosetting resin on the fiber from low temperature to high temperature area It has a reduced viscosity, which will cause it to flow into the adjacent carbon fibers due to capillary force. At the same time, the higher temperature will cause the liquid resin to solidify, achieve rapid and simultaneous infusion and curing, and can cure the composite material into Any 3D shape. Compared with traditional atmospheric heating, this local heating method can achieve faster curing speed and higher curing degree of printed materials.
The researchers chose a resistive carbon nanotube Joule heater with fast heating speed, good temperature control, and small contact area to provide a controlled and stable heating source for carbon fiber. On this basis, the researchers conducted a detailed study on the perfusion and solidification of the liquid polymer between the fibers, and found that the liquid resin cured quickly in situ when the carbon fiber was injected. The liquid resin can even overcome the gravity under the action of capillary and move vertically upward between the carbon fibers. The composite material is densified due to the capillary action of the liquid resin between the fibers, thereby achieving a higher fiber volume fraction and helping to improve the performance of the material.
The researchers realized the LITA-based 3D printing by processing the print head with integrated liquid transportation and heating functions. The printing path is controlled by an automated mechanical arm and can be printed on two-dimensional, three-dimensional substrates or free space. The SEM photo confirmed the dense structure of the printed material, no voids and defects appeared, and the three-dimensional reconstruction results of the tomography also verified that there was no fiber damage or voids during the printing process, indicating that this printing method can produce well-structured continuous fiber reinforcement Thermosetting composite material. The highly ordered and tightly arranged carbon fibers also give the composite material excellent mechanical properties. The tensile strength and modulus of the material can reach 810MPa and 108GPa, respectively. Compared with the existing literature, it shows the highest tensile strength and the best use temperature.
This printing technology can print complex geometric shapes on flat surfaces, conformal structures on curved surfaces, and even print in free space. Compared with the existing composite printing method, this printing technology shows obvious advantages in many aspects such as fiber length, polymer temperature, print formability, geometric complexity and versatility.
Summary
The researchers chose continuous industrial-grade carbon fiber and high-performance epoxy resin to achieve 3D printing of continuous fiber-reinforced thermosetting materials. The developed 3D printing technology is easy to process high-performance composite materials and is expected to provide a fast, energy-saving and large-scale 3D The printing method provides new opportunities for designing and manufacturing three-dimensional complex structures with engineering structures and multi-functions.
Related links: https://www.sciencedirect.com/science/article/pii/S2590238520301818#!