Finite element simulation of plastic deformation of FCC polycrystals
A finite element formulation based on crystal plasticity constitutive models has been developed for metal forming modelling. This formulation can be applied to nonhomogeneous boundary-value problems of polycrystal metals under large deformation which are characterized by deformation-induced anisotropy. An important feature of this model is its capability simulate the evolution of crystallographic texture and estimate its influences on the material behaviour during the deformation processes of FCC metals deforming by crystallographic slip. Using the developed finite element code, uniaxial behaviours of aluminum polycrystals under uniform deformation have been studied. The influence of the slip-rate sensitivity, latent hardening and the imposed strain rate on the constitutive responses have been investigated. The results have revealed that microstructure and microscopic properties play important roles on the stress-strain responses, as well as on texture evolution. Tensile instability in a round bar, as a typical strain localization mode, has been analysed with the concern on the influences of various microscopic and macroscopic parameters on development of instability. The main features of the overall responses and the texture evolution have been nicely captured by our analyses. The formability of FCC polycrystalline metals has been simulated numerically by the finite element analysis. In particular, the influences of microstructure and texture on the forming limit diagram are assessed. Critical strains for localized necking failures in thin sheets are determined for a variety of deformation paths. Various microstructural effects considered, which include slip-system hardening, material strain-rate sensitivity, initial texture, as well as the evolution of texture and microstructural hardening. Finally, the macro and microscopic aspects of large strain torsion of both fixed-end and free-end solid bars have been analysed using the polycrystal deformation model and a specific finite element mesh. Again, the effects of microscopic parameters are assessed. The predicted overall responses and textures are in reasonably qualitative agreement with experiments. Overall, the good predictive capabilities of the developed finite element formulation for simulating the stress-strain responses and the evolution of texture under both homogeneous and nonhomogeneous deformation conditions are demonstrated by comparing numerical simulations against experimental measurements and the predictions using other models in various deformation modes. The crystal constitutive model has been implemented as a user subroutine in the commerical finite element code ABAQUS (1995). A description of the implementation is given in this thesis.
- Génie – Thèses