Microstructure informed constitutive models and SPH crystal plasticity modelling approaches

Anxin Ma

Interdisciplinary Centre for Advanced Materials Simulation, Ruhr-University Bochum

Wednesday, 22.03.2017, 17:00
WW8, Room 2.018-2, Dr.-Mack-Str. 77, Fürth

During the deformation of polycrystals, pronounced strain gradients may occur due to mis- orientations and eigen strains of phase transformation. Hence, even under globally uni-axial and homogeneous strains, internal stresses will arise that must be characterized by nonlocal plasticity models.

Constitutive model for Transformation Induced Plasticity (TRIP) assisted steels is proposed that considers the elastic-plastic deformation of ferrite and austenite, the austenite-martensite phase transformation and the elastic deformation of martensite. Within this model, an explicit relation between martensite nucleation and plastic deformation within an austenite grain has been established. In particular, strain-induced martensite nucleation and stress-assisted martensite growth have been included in one model with the help of a thermodynamic principle. With this model, we found consistently with experiment that the TRIP effect enhances the effective work hardening rate and hence is beneficial for improving strength and ductility of steels. The mechanical anisotropy produced by stress-assisted and strain-induced phase transformations are significantly different.

Crystal plasticity (CP) modelling approach based on smooth-particle hydrodynamics (SPH) has been developed to study multi-physical processes with severe deformation of crystalline materials. The approach has been employed to simulate FCC polycrystals under the equal-channel angular pressing (ECAP) condition. It was found that the polycrystal contains four distinct regions with different deformation mechanisms. The CP-SPH developed here thus is demonstrated to be a powerful tool to study grain refinement under severe plastic deformation.