Effects of voids and raster orientations on fatigue life of notched additively manufactured PLA components

Abstract

In this study, the fatigue life of notched polylactic acid (PLA) samples fabricated through the fused deposition modeling (FDM) technique was studied experimentally and numerically. The volumetric method based on the theory of critical distance was employed for fatigue life predictions. The effects of influential process parameters including raster orientation and FDM-induced defects such as voids or gaps inside the parts were examined on the fatigue strength reduction factors and fatigue lives. Circular and elliptical-shaped notch geometries were considered with various dimensions. Fatigue tests were conducted on notched and un-notched samples at the load ratio of 0.1. Predicted results were compared with experimental fatigue test data. Results revealed that the raster orientation parameter had a substantial impact on fatigue strength reduction factors and fatigue lives. The stress concentrations induced by the FDM process on the surfaces and inside the parts for the samples with 90° raster angles acted similar to the sharp notches, resulting in no substantial difference in fatigue life of notched and un-notched 3D-printed samples. In contrast, un-notched 3D-printed specimens with 0° raster orientations possessed higher fatigue lives as compared to the notched samples. While the volumetric approach efficiently predicted the fatigue lives of the samples with 90° raster orientations, it moderately underpredicted the fatigue lives of the samples with 0° raster angles.