Anisotropic fatigue crack growth in selective laser melted SS316L: integrated experimental and molecular dynamics investigation

This study investigates fatigue crack growth in selective laser melted (SLM) SS316L using an integrated experimental and molecular dynamics (MD) framework to elucidate anisotropic crack propagation mechanisms across macroscopic and atomistic scales. Fatigue crack growth rate (FCGR) tests were conducted in the build and transverse directions to quantify orientation-dependent behaviour. Complementary MD simulations were performed on polycrystalline models with systematically varied grain size to resolve atomistic crack evolution and crack-tip plasticity. Experimentally, the build direction exhibited higher FCGR over the tested loading conditions, with Paris law parameters = 8.63 10 ^–10 and = 3.53, compared with = 1.74 10 ^–10 and = 4.23 in the transverse direction. Fractography indicated predominantly intergranular fracture in the build direction, whereas secondary crack formation in the transverse orientation contributed to crack growth retardation. MD simulations reproduced the observed anisotropy and revealed stress-ratio-dependent crack growth kinetics, with pronounced dislocation activity governing crack-tip plasticity. Higher stress ratios increased crack opening displacement in the simulations, contributing to directional differences in crack growth resistance. Overall, the combined experimental–atomistic approach provides physical insight into fatigue crack growth anisotropy in SLM SS316L, supporting structural integrity assessment and design optimisation of load-bearing additively manufactured components.