FE Modelling of the Fatigue Behaviour of L-PBF Inconel 718 with As-Built Surfaces

Abstract

The evaluation of fatigue properties of additively manufactured metal parts with surfaces at the as-built state is matter of great interest since it has been demonstrated that surface roughness has a key influence on high-cycle fatigue properties of components. As-built surfaces contain notch-like features that work as stress concentration sites where fatigue crack nucleation may occur. These typical morphologies due to Laser-Powder Bed Fusion (L-PBF) processing need to be considered in evaluating the fatigue performance; therefore, parameters related to as-built surface quality should be investigated and considered in part design. An innovative fatigue test method using miniature specimens is adopted to evaluate fatigue strength of the material; different specimen orientations are produced and tested. The fatigue results show the directional nature of the as-built surface and the surface differences introduced by the specimen orientation. In this work, as-built surfaces are investigated with two methodologies: microscopical observation of specimen cross section and optical interferometer observation of specimen surface. The irregular profiles are digitally reconstructed and evaluated via finite element analysis and the stress distributions interpreted. A correlation between stress-based parameters of surface models and fatigue strength is attempted.