A new constitutive model for hexagonal close-packed sheet metals under uniaxial cyclic loading

This study develops a new phenomenological constitutive model to capture the unique, evolving cyclic elastoplastic behaviours of hexagonal close-packed (HCP) sheet metals under uniaxial loading condition. This new constitutive model is developed by adopting the concepts of multiple-yield surface approaches and a combined isotropic-kinematic hardening rule. Three phenomenological modes, including tension (T), compression (C), and untwining (UT), are considered to represent the hardening evolution of the materials, including twining/untwining behaviours. Three different hardening laws are applied, and a Cazacu-Barlat 2004 (CB2004) type yield surface is assigned to each deformation mode. The UT hardening parameters are defined as functions of plastic pre-strains to mitigate interpolation errors caused by parameter determination processes of existing models. The new constitutive model is numerically implemented for finite element analysis via the UMAT subroutine available in a commonly-used commercial finite element analysis (FEA) package "” Abaqus and validated by experimental data available from literature. The obtained results show that the new constitutive model can precisely capture mechanical behaviours of HCP sheet metals, e.g., stress-strain curves, compared to those experimental results.