Towards Advancement of Continuous Fiber Composite Additive Manufacturing

Abstract

Additive manufacturing (AM) of composite materials could play an unlimited role in the future of advanced engineering structures, particularly in aerospace. Specifically, fiber reinforced polymers (both thermoplastic and thermoset) offer incredible weight savings, with mechanical properties comparable to metal alloys. In turn, AM can provide design freedom and unlimited component complexity, qualities unavailable from traditional methods of manufacturing with composites. AM technologies, including fused deposition modelling in particular, have undergone rapid growth within industry and academia in the last several decades; new materials are being developed frequently. However, contributions from the printing process to the “printed” material properties are often overlooked, which are of critical importance to material reliability and aerospace applications. In this effort the printability, material property variability and potential applications of a novel filament with high volume fraction of continuous fiber reinforcement were evaluated. The material is a new prototype system manufactured by Toray Industries, which consists of a 6k tow of continuous carbon fibers (CCF) within a polyphenylene sulfide (PPS) matrix. Filaments of CCF/PPS with fiber volume fractions between 30 and 50% nominal fiber volume fraction were printed, and results were compared with those achieved with commercially available composite material systems. Multiple design of experiments were performed to understand the effect of process parameters on the printed material quality, including nozzle Z-height, nozzle temperature, printing speed, and material flow rate. Results showed that the printed quality in terms of dimensionality and roughness, matrix crystallinity, and fiber distribution within the printed filament were a function of the printing parameters. The prototype Toray filament achieved a tensile strength that exceeded 2 GPa, an elastic modulus of 155 GPa and a strain to failure of approximately 1.5%. Complimentary Weibull analyses were performed and combined with microstructural evaluation to assess the characteristics of filament failure in the unprinted and printed state. Although the strength of the CCF/PPS filament is the highest reported of any composite printed using the FDM process, there are several sources of defects that substantially reduce the strength of the printed material, by as much as 25%. Hence, further process optimization is needed for this CCF /PPS system and other continuous fiber composite materials to reach their full potential when used to manufacture components by FDM.