Fused filament fabrication (FFF) is one of the fastest growing types of additive manufacturing technologies, mainly because it enables printing of lightweight and complex structures, usually with the minimum cost, time and waste of material, which can be hardly achievable by conventional manufacturing methods. On the other hand, the mechanical performance of the 3D-printed parts is limited compared to those by other manufacturing methods due to their inherent imperfections like poor interlayer bonding, the presence of voids in the part structure, and warpage/interlayer debonding, the latter resulting from shrinkage following crystallization and/or CTE mismatch in the repeated heating/cooling during printing. In order to overcome these drawbacks, different strategies have been developed, including using fiber-reinforcements in 3D-printed parts. Parts printed with composite materials, such as carbon fiber, offer significant strength and stiffness advantages compared to standard thermoplastics. The main purpose of adding short or continuous fibers (carbon fiber, fiberglass, Kevlar, etc.) as the reinforcement of the polymer is to 1) act as a mechanical reinforcement and 2) mitigate residual stress resulting from the printing process. When compared to the pure polymer prints, the stiffness, strength, fatigue and impact resistance of fiber reinforced composites are considerably higher than pure polymers. These mechanical properties can be further enhanced by employing the optimum layer thickness, infill pattern, raster angle, number of reinforced layers and deposition temperature of the filament.
In this study, a Mark-Two 3D-printer from âMarkforgedâ was used to generate specimens with two types of materials; pure PA6 (Polyamide 6) and a composite consisting of chopped carbon fibers in PA6. The Mark-Two printer allows the variation of several printing parameters which could potentially modify the mechanical response of the final produced part, including fiber orientation (raster angle), infill density, fill pattern, type of reinforced material and layer height. In this work, we evaluate the impact of these variables on the modulus of elasticity, the ultimate tensile strength and Poissonâs ratio of different configurations. We also analyze specimen cross sections using Scanning Electron Microscopy (SEM) to provide insight into the failure mechanisms as a function of AM process variables.
