Fatigue performance of additive manufactured metals under variable amplitude service loading conditions including multiaxial stresses and notch effects: Experiments and modelling

Additive manufacturing technology has gained significant attention in recent years. However, due to lack of sufficient understanding of their fatigue behavior under service loading conditions, design of critical load carrying parts using this technique is still at early stages. These conditions include multiaxial stress states, notches and stress concentrations, and variable amplitude load cycles. Some of the distinguishing features of AM metals as compared to the conventionally fabricated metals include defects, surface roughness, anisotropy and build orientation effects, and residual stresses due to the fast solidification during the fabrication process. These factors resulting from AM processes may significantly affect the fatigue performance of AM parts under multiaxial variable amplitude loading. In this work, unnotched and notched fatigue behavior of two commonly used AM metals with different surface roughness conditions were studied under variable amplitude multiaxial loads. Both crack initiation approach using critical plane-based model and fracture mechanics approach using crack growth from the rough surface or surface defects at the notch were used to estimate the fatigue lives. Fatigue estimations are then compared to the experimental results