Crack propagation in viscoelastic solids

We study crack propagation in a viscoelastic solid. Using simple arguments, we derive equations for the velocity dependence of the crack-tip radius, a(v), and for the energy per unit area to propagate the crack, G(v). For a viscoelastic modulus E(omega) which increases as omega(1-s) (0 < s < 1) in the transition region between the rubbery region and the glassy region, we find that a(v)similar to G(v)similar to v(alpha) with alpha=(1-s)/(2-s). The theory is in good agreement with experiment.