Continuum mechanics and thermodynamics in the theory of cracking

In a series of at least four theoretical papers, Stevens and Guiu have claimed to have invalidated the accepted continuum mechanics derivation of the Orowan—Irwin equation for elastic fracture; and to have discovered paradoxes in thermo-dynamic formulations. The purpose of this paper is to reassure readers of the continued validity of accepted theories. A first principles thermodynamic derivation of the Orowan—Irwin equation is given; and the validity of the continuum mechanics treatment is substantiated. A postscript includes a little thermodynamic philosophy.