Modelling the effect of hydrogen on ductile tearing resistance of steels

The effect of hydrogen on the mechanical behaviour of steels is twofold: it affects the local yield strength and it accelerates material damage. On the other hand, the diffusion behaviour is influenced by the hydrostatic stress, the plastic deformation and the strain rate. This requires a coupled model of deformation, damage, hydrogen sorption and diffusion. The deformation behaviour is described by von Mises plasticity with isotropic hardening, and crack extension is simulated by a cohesive zone model. The local hydrogen concentration, which is obtained from the sorption and diffusion analysis, causes a reduction in the yield strength and the cohesive strength. Crack extension in a C(T) specimen of a ferritic steel under hydrogen charging is simulated by fully coupled finite element analyses of hydrogen kinetics and mechanical behaviour. The simulation results are compared with test results.