Prediction of crystallographic texture evolution and anisotropic stress-strain response during large plastic deformation in alpha-titanium alloys /

by Wu, Xianping.; Kalidindi, Surya.; Doherty, R. D.; College of, Drexel University.

Prediction of Crystallographic Texture Evolution and Anisotropic Stress-strain Response during Large Plastic Deformation in ?-Titanium Alloys Xianping Wu Prof. Surya R. Kalidindi Prof. Roger D. Doherty A new Taylor-type polycrystalline model has been developed to simulate the evolution of crystallographic texture and the anisotropic stress-strain response during large plastic deformation in ?-titanium alloys at room temperature. Crystallographic slip, deformation twinning, and slip inside twinned regions were all considered as contributing mechanisms for the plastic strain in the model. This was accomplished by treating the dominant twin systems in a given crystal as independent grains once the total twin volume fraction in that crystal reached a predetermined saturation value. The newly formed grains were allowed to independently undergo further slip and the concomitant lattice rotation, but further twinning was prohibited. New descriptions have been established for slip and twin hardening and the complex coupling between them. Good predictions were obtained for the overall anisotropic stress-strain response and texture evolution in several different monotonic deformation paths on annealed, initially textured samples of two different chemical compositions of ?-titanium alloys. The polycrystalline plasticity model presented here is built on the Taylor assumption of uniform deformation gradient in all of the constituent grains. The effects of this gross simplification have been evaluated by comparing the predicted stress and strain distributions between Taylor model and the more sophisticated finite element models that relax the assumption of the uniform strain. The anisotropy of the plastic behavior was xii observed to strongly influence the deviation of the Taylor model predictions from the finite element model predictions when comparing the stress and strain distributions in deformed polycrystalline ?-titanium with initially random texture. The slip parameters established using the crystal plasticity model developed here were utilized in a novel spectral framework, called Microstructure Sensitive Design (MSD), for constructing elastic-plastic property closures in hexagonal polycrystals. The main focus was on the influence of the crystallographic texture (in the hcp polycrystals) on the components of the macroscale anisotropic elastic stiffness, macroscale anisotropic tensile yield, and the macroscale R-ratios (ratio of the transverse strains in tensile deformation mode) exhibited by the material. 1