Study On Large Strain Behavior Of Polycrystalline Materials Based On Polycrystal Plasticity Model

The plastidc deformation mechanisms are paid more attentions from scholars with development of material process technology. Researches on large strain behavior of metal materials from the view of numerical calculations lay a foundation for further understand plastic deformation meschimes. By means of experiments and numerial calculation, this paper studied systemically the large strain behavior of polycrystals with FCC crystal structure and HCP crystal structure by elastic visco-plastic self-consistent model with various self-consistent schemes. The main achievements are as follows:(1) Based on the elastic visco-plastic self-consistent model, taking into account the stress relaxation associated with twin nucleation, a new constitutive model model to describle twin nucleation, propagation and growth is developed. Two additional parameters are introduced to describle the threshold resolived shear stress of twin.(2) Various polycrystal plasticity models have been used to study the flow behavior and microscopic texture evolution of an initially ’isotropic’ OFHC copper under different deformation processes, including uniaxial tension, uniaxial compression, plane strain compression and simple shear. Furthermore, the effect of latent hardening coefficent q on prediction of texture evolution was discussed. The polycrystal plasticity models have been evaluated by comparing the predictions against corresponding experiments. The EVPSC model with the self-consistent schemes with grain interaction stiffness halfway between those of the limiting Secant(stiff) and Tangent(compliant) approximations give a better agreement with experiments.(3) By using elastic-viscoplastic self-consistent model, implemented in a specialpurpose finite-element method, the large strain behavior of OFHC copper under reverse torsion has been numerically studied. The stress-strain responses, Swift effect and texture evolution are obtained to reveal the role of polycrystal plasticity model on large strain behavior of FCC materials under torsion. Furthermore, the effect of pre-shear strain during reverse torsion on texture evolution is analyzed. The Tangent model, which gives obvious different results than the other models and the experiments, is not recommended to model the FCC materials.(4) The recently developed large strain elastic visco-plastic self-consistent(EVPSC) model with various popular self-consistent schemes including the Affine, Meff, Secant and Tangent has been used to study the lattice strain evolutions in the standard 316 L austenitic stainless steel alloy under uniaxial tension. An assessment of the predictive capability of the self-consistent schemes has been made by comparing the predicted lattice strain evolutions and in-situ neutron diffraction measurements performed on the same material. It has been found that, among all the models examined, the EVPSC model with the limiting Secant(stiff) and Tangent(compliant) approximations diverges significantly from the experiments. The EVPSC model with the self-consistent schemes with grain interaction stiffness between the Secant and Tangent schemes give the best overall performance.(5) A rolled magnesium AZ31 B thick plate with a strong basal texture has been experimentally and numerically studied under uniaxial tension and compression and free-end torsion. The {1012}extension twinning during plastic deformation is closely related with the tension-compression yield asymmetry. By using EVPSC model, the relative activity, twin volume fraction and texture evolution were obtained to analyse the plastic deformation mechanisms and mechanical property. It has been demonstrated that the Swift effect in the material under free-end torsion is mainly due to extension twinning. Comparing the predicated results of lattice strain and texture evolution with two twinning models, TDT and PTR models, it is shown that the simulation results from TDT model is closer to experimental one.The research results enrich basic theory of crystal plasticity model and provide important basis for study on large strain behavior of metal materials.