Ph.D. Thesis Defense

Department of Materials Science and Engineering

Prediction of Crystallographic Texture Evolution and Anisotropic Stress-strain Response during Large Plastic Deformation in -Titanium Alloys

Given by: Xianping Wu

Advisors: Dr. Surya R. Kalidindi and Dr. Roger D. Doherty

Time: 10:00 am, September 15^th, 2006

Location: Hill Seminar Room (Lebow 240)

Abstract

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 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.

[loc]Hill Seminar Room, LeBow 240[/loc]