Hydrogen Transport to Fracture Sites in Metals and Alloys Multiphysics Modelling

Generalised continuum model of hydrogen transport to fracture loci is developed for the purposes of analysis of the hydrogenous environment assisted fracture (HEAF). The model combines the notions of the theories of gas flow, surface science, and diffusion and trapping in stressed solids. Derived flux and balance equations describe the species migration across different states (gas, adsorbed specie at the gas-metal interface, interstitial solute in metal bulk) and a variety of corresponding sites of energy minimums along the potential relief for hydrogen in a system. The model accounts for the local kinetics of hydrogen interchange between the closest dissimilar neighbour sites and for the nonlocal interaction of hydrogen trapping in definite positions with the species wandering in their farer surroundings. In particular situations, certain balance equations of the model may degenerate into equilibrium constraints, as well as some terms in the generalised equations may be insignificant. A series of known theories of hydrogen transport in material-environment system can be recovered then as particular limit cases of the generalised model. Presented theory can help clarifying the advantages and limitations of particularised models so that appropriate one may be chosen for the analysis of a particular HEAF case.