A microstructure-informed constitutive model for hierarchical materials with subgrain features

Abstract

Additively manufactured metal alloys often have a hierarchical microstructure consisting of subgrain features. The subgrain features, being smaller in size than grains, significantly influence the mechanical properties and anisotropy of the material. Recognizing the critical role of subgrain features, this work proposes a novel generalized microstructure-informed constitutive modeling framework for hierarchical materials using a mechanism-based crystal plasticity formulation. Considering direct energy deposited (DED) stainless steel (SS) 316 L as the reference material we first categorize subgrain features as a network of solidification cells and a scattered distribution of secondary phases. Then we advanced the state-of-the-art mechanism-based crystal plasticity formulation by explicitly accounting for the geometric and mechanistic effects of both cellular network and scattered secondary phase subgrain features. Homogenization schemes are developed to implement the constitutive model on a finite element analysis (FEA) framework. The anisotropy is realized as a natural outcome of a preferred alignment of cells in the build direction. The model is then calibrated using experimental data. Limited validation of the model is also performed. Results show that explicitly accounting for the subgrain features in a constitutive model allows one to accurately capture the macroscopic and microscopic response of a hierarchical material.