A viscoelastic–viscoplastic model of titanium structures subjected to thermo-chemo-mechanical environment.

This manuscript provides a new viscoelastic–viscoplastic deformation model for oxygen-assisted embrittlement and degradation of titanium structures subjected to combined loading and environments. The viscoelastic–viscoplastic formulation accounts for the creep/relaxation behavior at elevated temperatures within the coupled processes of oxygen transport and deformation. The viscoelastic behavior is modeled based on the Boltzmann integral and Prony series approximation of the time-dependent moduli. The concentration-dependent viscoplastic deformation response is idealized using a generalized Johnson–Cook plasticity model. The proposed deformation model is fully coupled with a transport model to describe the ingress of oxygen into the structure. The coupled transport-deformation model is implemented using a three-field formulation, in which concentration, displacement and pressure are evaluated as independent unknowns. The computational model was validated against experiments conducted in combined environments on the high temperature alloy Ti-6242S. A detailed investigation of the coupling mechanisms between the oxygen ingress induced embrittlement, relaxation and the inelastic deformation is provided, including partial validation of the interaction mechanisms based on experimental data. [ABSTRACT FROM AUTHOR]