On the crack mechanics of hard ferromagnets

This work presents the formal evaluation of the driving force that acts on a straight-through crack in an elastic hard ferromagnet in which both ferromagnetic exchange forces and gyroscopic magnetic-spin inertia are taken into account phenomenologically. This is achieved following two avenues, one relating the driving force to a global material force (so-called configurational force) on the material manifold by exploiting the equation of balance of pseudomomentum, and the other relying upon the construction of the energy-release rate on a pure energy basis. The latter is shown to be none other than the power dissipated by the former global force. The path-independence of the associated J-integral holds only when both material and spin inertia are neglected. The proofs use estimates of the singularity order of various fields and are first given within the fully dynamical framework of finite strains. (C) 1997 Elsevier Science Ltd.