A coupled theory for diffusion of hydrogen and large elastic-plastic deformations of metals

Abstract

A thermodynamically-consistent coupled-theory which accounts for diffusion of hydrogen, trapping of hydrogen, diffusion of heat, and large elastic-plastic deformations of metals is developed. Our theoretical framework places the widely-used notion of an "equilibrium" between hydrogen residing in normal interstitial lattice sites and hydrogen trapped at microstructural defects, within a thermodynamically-consistent framework. The theory has been numerically implemented in a finite element program. Using the numerical capability we study two important problems. First, we show the importance of using a prescribed chemical potential boundary condition in modeling the boundary between a metal system and a hydrogen atmosphere at a given partial pressure and temperature; specifically, we perform simulations using this boundary condition and compare our simulations to those in the published literature. Secondly, the effects of hydrogen on the plastic deformation of metals is studied through simulations of plane-strain tensile deformation and three-point bending of U-Notched specimens. Our simulations on the effects of hydrogen on three-point bending of U-notched specimens are shown to be in good qualitative agreement with published experiments.