Influence of material extrusion parameters on fracture mechanisms of polylactic acid under three-point bending

Abstract

In this work, a thorough fracture assessment of additive manufactured specimens made by 3D printed polylactic acid (PLA) under three-point bending is presented. This polymer is widely used in additive manufacturing for numerous applications, gaining prominence in fields such as biomechanics. Prismatic fully dense specimens and lattice structure specimens with different raster orientations and densities were fabricated using the material extrusion-based additive manufacturing technique. The objective is to analyse the effect of relevant process parameters on the fracture mechanism of short beam specimens tested under three-point bending. Digital image correlation and computed tomography have been used to measure the full field displacement and internal defects, respectively. Furthermore, the theory of critical distances was applied to assess the mechanical strength of lattice structure specimens. The results have shown the strong influence of raster orientation on the mechanical strength and fracture patterns even for negative air gap values. The transition from brittle to ductile failure was observed when changing density and raster orientation. Lastly, neck-shaped defects were detected in knots of specimens manufactured with a grid pattern. Defects in grid pattern specimens appear due to the prescribed path followed by the extruder during the building process. They were the main source causing a decrease in the mechanical strength and fracture trajectories. The objective of this research is to enhance the knowledge on the mechanical response of 3D printed components and to give an in-depth failure assessment.