A simple model for viscoelastic crack propagation

When a crack propagate in a viscoelastic solid energy dissipation can occur very far from the crack tip where the stress field may be very different from the $r^{-1/2}$ singular form expected close to the crack tip. Most theories of crack propagation focus on the near crack-tip region. Remarkable, here I show that a simple theory which does not account for the nature of the stress field in the near crack-tip region result in a crack propagation energy in semi-quantitative agreement with a theory based on the stress field in the near crack-tip region. I consider both opening and closing crack propagation, and show that for closing crack propagation in viscoelastic solids, some energy dissipation processes must occur in thecrack tip process zone.