Thermodynamics of the quasi-static growth of Griffith cracks

Restrictions on the quasi-static extension, or healing, of Griffith cracks are developed in the framework of irreversible thermodynamics. It is emphasized that thermodynamics requires that (G − 2γ)ι ⩾ 0, where ι is crack speed, G the Irwin energy release rate, and 2γ the work of reversible separation of the surfaces to be fractured. Implications for ‘lattice trapping’ models of cracks and for thermally-activated crack motion are discussed, as are the effects on crack growth and healing of a surface-reactive environment, in which case γ must be given a definition appropriate to adsorption-altered surface properties.