Computational modeling of coupled oxygen transport and mechanical deformation in titanium structures subjected to extreme environments

Abstract

This dissertation presents a multiphysics model to simulate and predict the deformation and failure of metallic materials and structures subjected to extreme loading and environmental conditions. The particular focus has been on the titanium alloy Ti-6-2-4-2-S. In order to formulate an accurate computational model to characterize and to predict behavior, all three physical processes that significantly affect the response (i.e., the thermal state, the transport of oxygen into the material and the mechanical deformation) are simulated in a coupled manner. The key contribution of the proposed model is to identify all the physical processes and their coupling mechanisms. More specifically, transport model is constructed, and implemented using the mixed finite element approach to idealize the coupling between oxygen transport and mechanical deformation processes. Viscoelastic-viscoplastic deformation model is formulated to realize the loss of ductility, viscoplastic stress hardening, stress relaxation and change of cyclic response in extreme temperature. The models were calibrated with experimental observations. The proposed model displayed an excellent capability to describe the embrittlement induced by oxygen transport, mechanical response and dissipation mechanisms in titanium structures subjected to high temperatures and mechanical loads.