Strength and fracture behaviour of polymer matrix composite layered structures made by additive manufacturing

Abstract

In this paper, studies on the tensile strength, fracture initiation and propagation behaviour of composite material layered shell structures manufactured by extrusion based additive manufacturing (AM) is reported. To understand the basic mechanical behaviour, simple tension tests have been conducted on ASTM-D638 specimens of carbon fiber and natural fiber reinforced polymer matrix composites made by AM in different modes as well as directly in filament form using a filament extruder. The tensile strengths reveal that the internal defects unique to additive manufacturing, such as lack of fusion (LOF) sites and voids, play crucial role in the macroscopic fracture. Based on the tensile test results, finite element analysis of shell structures typical of below-knee prosthetic sockets has been conducted to predict the fracture initiation sites and propagation paths. The analysis results have shown close correlation with the experimental observation of the fracture phenomenon in the prosthetic sockets given to pilot test amputees.