Effects of hydrogen-altered yielding and work hardening on plastic-zone evolution: A finite-element analysis

• We conducted FEM analysis with hydrogen-affected yielding and work hardening.
• Hydrogen-affected work-hardening significantly increased the local plastic strain.
• Plastic-zone size at a crack tip was decreased by hydrogen-affected work-hardening.
• Hydrogen localization was simulated to enhance the localized plasticity even in FEM.

In the present paper, finite-element analysis of a cracked specimen was conducted using a unified model for the elastic–plastic deformation and hydrogen diffusion. We considered the effects of the hydrogen-reduced yielding strength and work-hardening coefficient and used a comparison parameter in the simulation of the hydrogen-localized plastic zone near a crack tip. We realized two important facts: (1) the normal component of the plastic strain in the direction of remote stress near the crack tip is significantly increased by the reduced work-hardening coefficient at the same stress-intensity factor; (2) the reduced work-hardening coefficient enhances the localization of the plastic zone when compared to the case using the normal component of the crack-tip plastic strain in the direction of remote stress, which probably determines the ductile–brittle transition of the fatigue-crack propagation mode under a hydrogen atmosphere. These results indicate that the reduction in work-hardening coefficient and the utilization of the crack-tip plastic strain as a parameter to organize the data play important roles in the prediction of the transition condition of hydrogen-accelerated fatigue-crack propagation.