Environmentally assisted cracking (EAC) is the result of an interaction between a material under stress and its environment. Crack propagation under EAC conditions requires a mechanical and an electrochemical loading. The crack growth rate (CGR) is dependent on the principal variables describing this two-fold loading. The mechanico-electrochemical (MEC) diagram pictures this dependency. The diagram is independent of the mechanism of EAC. However, the principal loading variables are not. The variables are not arbitrary system variables but principal variables, evaluated at the crack tip, which determine the crack's propagation. A MEC diagram for stress corrosion cracking (SCC) will generally be based on the principal variables of stress intensity and crack-tip electrode potential and the one for hydrogen-induced cracking (HIC) on the principal variables of stress intensity and crack-tip pH. Literature data support the diagram and some EAC models predict the shape of the CGR contours. Each MEC diagram is only valid for a particular material-environment combination. However, based on models, the influence of sensitization or yield strength on SCC can be pictured. Even the shape of crack fronts can be reasoned in terms of the MEC diagram. Constructing and using the MEC diagram has become feasible because of the recent development of computational electrochemistry (CEC) software.

Subject
Environmental cracking, Materials, Stress intensity, Crack propagation, Corrosion cracking, Stress cracking, Pure water, Springs, Constants, Current densities, Contours, Stress corrosion cracking, Electrode potential
Keywords:
environmentally assisted cracking, crack propagation rate
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2004
Association for Materials Protection and Performance (AMPP)
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