Fatigue-life prediction of additively manufactured material: Effects of heat treatment and build orientation

In this study, the crack-growth approach is used to predict the fatigue life of 17-4 precipitation hardening (PH) stainless steel (SS) fabricated via an additive manufacturing (AM) system in different orientations (ie, vertical and horizontal) before and after heat treatment. To perform fatigue-life calculations, the effective stress intensity factor as a function of crack-growth rate was obtained from testing modified compact specimens with different crack orientations in as-built and heat-treated conditions. The plasticity-induced crack closure model, FASTRAN, was used to calculate fatigue lives based on the size of process-induced defects. Results indicated that in the presence of large voids (ie, lack-of-fusion defects), the total fatigue life of AM 17-4 PH SS in as-built and heat-treated conditions is dominated by crack growth. Effect of build orientation on fatigue life of AM 17-4 PH SS was also captured based on the size of defects projected on a plane perpendicular to the loading direction.