A unified model of environment-assisted cracking

Environment-assisted cracking is caused by enhanced crack-tip plastic deformation. Lattice resistance to shear slip is caused by the periodic fluctuation of the misfit energy across a slip plane. Lu et al. have shown that hydrogen reduces the misfit energy, slip resistance and resistance to dislocation motion. The 1s orbital of a hydrogen atom in a metal is not full, and the electron of the atom moves and reacts as a valence electron. The resistances to shear slip and dislocation generation at a crack tip are reduced by hydrogen electrons and hydrogen nuclei. Crack-tip plastic deformation is thus enhanced, and crack growth rate is increased. The model of reduced resistance to crack-tip dislocation generation and enhanced crack-tip plastic deformation can be extended to liquid metal-assisted cracking and stress corrosion cracking if the valence electron(s) of a liquid metal or chemical reduces the misfit energy and the slip resistance sufficiently.