Application of Continuous Carbon Fiber Reinforcement
The principle of using fiber reinforcement in composite materials is that the reinforcing fibers are generally more wear resistant, stronger, and have better mechanical properties than the matrix material. When composites are subjected to bending or shear damage, the reinforcing fibers are pulled out of the matrix and absorb energy from the applied loads. Within a certain length range, longer fibers absorb more energy during pull-out, increasing the strength of the composite. For composites with the same volume content, longer individual fibers mean fewer fibers, reducing stress concentration and improving overall performance. In addition, continuous, longer carbon fibers provide better lubrication, reducing friction and wear, and decreasing the formation of abrasive debris.
Due to tooling limitations, complex carbon fiber reinforced thermoplastic (CFRTP) components are typically joined in multiple pieces, making the joints the weakest points. The quality of the joints directly affects the fatigue strength and service life of CFRTP components. Common joining methods include mechanical joining, cementing, and welding. Welding, which utilizes the secondary melting properties of the thermoplastic resin, provides better joint strength and environmental adaptability than adhesive bonding, and avoids stress concentration from mechanical joints. Welding is also faster and easier to automate.
Laser welding, a non-contact method, offers high speed, high strength, low vibration stress, and suitability for complex structures, showing good prospects for CFRTP welding. Recent research has explored laser penetration welding and laser direct joining technology. Laser penetration welding can join transparent resins, CFRTP, opaque resins and metal materials. The Ningbo Institute of Materials, Chinese Academy of Sciences, used laser direct joining technology to join CFRTP with stainless steel and aluminum alloy, and found that the joint strength exceeded that of the resin matrix, although the joint quality needs improvement.
Current 3D printing research on carbon fiber reinforced thermoplastic composites mainly focuses on short carbon fibers, with limited research on continuous carbon fibers and weak interlayer adhesion, which affects bending performance.
Unlike traditional FDM technology, a new printhead design uses polylactic acid (PLA) as the thermoplastic matrix and continuous carbon fibers as reinforcement. The printhead includes an extrusion motor, heater block, carbon fiber tubing and nozzle. During printing, the thermoplastic material melts and the carbon fibers fuse with the molten material, which is propelled by the extrusion motor and extruded from the nozzle. This process enables 3D printing of continuous carbon fiber reinforced thermoplastic composites.
