Anisotropic cyclic deformation of additively manufactured 316L stainless steel at 400 °C: Experiment and constitutive model

Abstract

Anisotropic microstructures and defect distributions impart a strong build-orientation dependence to the cyclic deformation behaviour of additively manufactured metallic materials. Accurately capturing this anisotropy through tailored cyclic elasto-plastic constitutive models is critical for ensuring structural integrity. This study investigates the high-temperature anisotropic cyclic plasticity of 316L stainless steel fabricated by laser powder bed fusion (L-PBF) through a combination of experimental investigation and constitutive modelling. Experimental results reveal that horizontally built specimens exhibit higher yield stress, leading to increased stress amplitude and reduced ratchetting strain compared to their vertically built counterparts. The L-PBF 316L stainless steel exhibits cyclic hardening, followed by a cyclic softening stage, with the pronounced cyclic hardening observed in the horizontally built specimens. Both the cyclic softening/hardening behavior and ratchetting exhibit strong dependence on applied strain and stress amplitudes. To model the anisotropic cyclic plasticity of L-PBF 316L stainless steel, a novel cyclic elasto-plastic constitutive model is developed. The model integrates Hill's anisotropic yield criterion, superimposed isotropic hardening, a modified Ohno-Karim kinematic hardening law, and a novel memory surface to capture the amplitude- and orientation-dependent cyclic plasticity. Moreover, the evolution of anisotropy under cyclic loading is modelled by introducing the accumulated plastic strain-dependent coefficient matrix into the Hill’s parameters. Simulations agree well with experimental results, offering a theoretical basis for evaluating the service performance of additively manufactured metallic components.