Coupling aspects in the simulation of hydrogen-induced stress-corrosion cracking


Modelling of hydrogen-induced stress-corrosion cracking (HISCC) has to consider coupling effects between the mechanical and the diffusion field quantities. Four main topics are addressed: i) surface kinetics, ii) diffusion, iii) deformation and iv) crack growth. Surface kinetics is realised by a chemisorptions model, hydrogen diffusion is formulated by an enhanced diffusion equation including effects of plastic deformation, deformation rate and hydrostatic pressure, deformation is described by von Mises plasticity, and crack growth is simulated by a cohesive model, where both yield and cohesive strength depend on the hydrogen concentration. The effect of atomic hydrogen on the local yield strength is modelled by the so-called HELP (Hydrogen-Enhanced Localised Plasticity) approach, and the influence on the cohesive strength is taken into account by the so-called HEDE (Hydrogen-Enhanced DEcohesion) model. As the two models predict contrary effects of atomic hydrogen on the material behaviour, namely a decrease of the local yield strength resulting in larger plastic deformations and a reduction of the cohesive strength and energy inducing lower ductility, respectively, the coupling phenomena are studied in detail. The model is verified by comparing experimentally measured and numerically simulated CTOD R-curves of C(T) specimens.
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