Microstructural modeling by anisotropy Cosserat theory for nanotwinned copper

Abstract

An anisotropy Cosserat continuum model is established for nanotwinned copper by introducing the special orientation relationship between the twin and the matrix. The anisotropy effect induced by the difference in crystal orientation and the strain gradient effect induced by the inhomogeneous deformation between the twin and the matrix in grains are considered. The results obtained by the model with the same parameters of the anisotropy Cosserat elastoplastic constitutive have a good agreement with stress-strain curve of nanotwinned copper collected over different experimental studies with varying twin thickness from 15 nm to 100 nm and coarse grain copper (CG-Cu) with micron level grain size. The effect of twin spacing, twin thickness and preferred orientation on the mechanical performance of nanotwinned copper, such as yield strength, elastic modulus and hardening exponent is systematically studied based on the proposed model. Our results show that the anisotropy effect mainly affects elastic modulus and yield strength, the strain gradient effect affects yield strength and strain hardening rate. The results also demonstrated that appropriate preferred orientation and twin spacing of the nanotwinned copper could make the stress softening or uniform stress distribution by the coordinated deformation between different nanotwinned structures.