Effects of Build Orientation on Mode III Fracture Load of Additively Manufactured Polylactic Acid Material

This study investigates the mode III fracture behavior of polylactic acid (PLA) fabricated by additive manufacturing (AM) through both experimental testing and numerical simulation. While AM is widely used in structural applications, research on mode III fracture behavior remains limited, particularly regarding the influence of build orientation on shear-driven failure. In this study, transverse shear cracked plate specimens were fabricated using fused filament fabrication (FFF) in three build orientations: horizontal, lateral, and vertical. These specimens were tested under mode III loading using a newly designed tensile testing fixture to determine the fracture toughness of PLA for each orientation. Young’s modulus values, obtained from tensile tests on dog-bone specimens, were used to compute the mode III fracture energy. Numerical simulations were performed using the extended finite element method (XFEM) to predict fracture load and crack propagation. The results showed close agreement with experiments, with deviations of 1.1%, 8.5%, and 0.4% for horizontal, lateral, and vertical orientations, respectively. The closest agreement was observed for vertically printed specimens, attributed to the intrinsic nature of mode III loading. These findings highlight the potential of XFEM as a reliable tool for predicting shear-driven fracture behavior in FFF-printed PLA across different build orientations, supporting improved structural evaluation and design decisions.