Fully-coupled continuum damage model for simulation of plasticity dominated hydrogen embrittlement mechanisms

Abstract

The mechanical properties of steel are degraded due to the presence of hydrogen, also known as hydrogen embrittlement (HE). Simulations of hydrogen embrittlement at a continuum level can assist in characterizing the detrimental effect that is associated with the introduction of hydrogen regarding the structural integrity of steel structures. Such simulations require the implementation of both hydrogen diffusion and hydrogen assisted material degradation. The present study presents a framework for finite element simulations combining these aspects in a fully coupled way, with diffusion driven by hydrogen concentration, stress triaxiality gradient and plastic strain rate, and damage based on the ductile damage model known as the Complete Gurson Model (CGM). Hydrogen assisted degradation is modeled through acceleration of void growth, nucleation or coalescence, based on the HELP or HESIV mechanisms as underlying physical basis. The proposed model is the first fully-coupled continuum micromechanics-based damage model that accounts for the plasticity dominated HE mechanisms. The effect of element size and time increments is evaluated, establishing guidelines to use the model. Moreover, results of simulations of a tensile test on a hydrogen charged notched specimen are given, to provide an illustrative example of the capabilities of the framework. The well-known ductility loss due to hydrogen is observed in the simulation results.