Microscale Initiation And Propagation Of Yielding In Duplex Stainless Steel Under Multiaxial Loading

Abstract

A major challenge for modeling the mechanics of engineering alloys is linking phenomena across multiple length scales. In this work, the link between crystal plasticity, occurring at the microscale, and macroscopic yielding is explored for biaxial loading of dual phase alloys. In particular, dual phase austenitic-ferritic stainless steel LDX-2101 is studied. However, the analysis is generally applicable to a range of single and dual phase alloys. Combined neutron diffraction experiments and polycrystalline finite element simulations are used to investigate the elasto-plastic deformation of LDX-2101 under biaxial loading. A new formulation of strength-to-stiffness parameter is developed for generalized multiaxial loading. The strength-to-stiffness parameter exhibits strong correlation with the macroscopic stress at which subgrain regions of a polycrystal yield. In contrast, traditional Schmid and Taylor factors do not correlate to the macroscopic stress at which yielding occurs, for materials with high single-crystal elastic anisotropy. The strength-to-stiffness analysis is extended into a methodology for predicting the macroscopic stress at which subgrain regions yield. A new, physically-based yield criterion is also developed. The yield criterion is based on detecting the existence of a yield band, an interconnected region of yielded material that separates opposing domain surfaces. The new yield criterion is used in conjunction with simulated and predicted spatial distributions of yielding to evaluate the yield surface for LDX-2101 in biaxial stress space. The combination of the spatial yield distribution prediction algorithm and new yield criterion provides a fast, accurate methodology for yield surface evaluation.