Influence of continuous fiber reinforcement on tensile properties in fused filament fabricated specimens

Current state-of-the-art additive manufacturing (AM) devices enable the reinforcement of components by embedding continuous fibers into the polymer matrix. In this study we investigate the effect of different continuous fiber reinforcement materials and number of continuous fiber reinforced layers on tensile strength as well as AM build quality. Tensile test specimens were built from short carbon fiber reinforced nylon embedded with continuous carbon fibers (OCF) or glass fibers (OGF) respectively. For the investigation of AM quality and failure behavior, X-ray computed tomography (XCT) scans were performed before and after tensile load. XCT investigations revealed systematic print errors such as asymmetric fiber placement and insufficiently pre-impregnated raw fiber material. Furthermore, desirably good interlaminar but low intralaminar bonding quality of continuous fibers could be observed. Tensile experiments revealed positive correlation between ultimate strength and number of continuous fiber reinforced layers. However, variance in ultimate strength increases with number of fiber reinforced layers suggesting reduced reliability. Generally, high part to part variations in print quality severely influence tensile strength.