Crack front waves are disturbances that propagate without attenuation
along the edge of a propagating crack. They have a role in the development
of crack front disorder during propagation through material containing
small heterogeneity. They were observed in computer
experiments by J R Rice and their existence was confirmed analytically
by Ramanathan and Fisher, from an analytic solution produced by
Movchan and Willis for the stress produced when a crack front is
dynamically perturbed. Their existence has also been confirmed
experimentally by E Sharon. The talk will outline the solution
of Movchan and Willis, and describe recent extensions to deal with
viscoelastic material response. When viscoelastic damping is small,
perturbation theory can be employed to estimate the rate of decay
of the wave. Such decay has been observed in experiments on PMMA
by Sharon but quantitative evaluation has not yet been performed.
The waves observed and analysed to date have been for crack
propagation under Mode I (opening mode) loading. An investigation is
under way of the corresponding problem for propagation under loading
in Modes II and III (shear modes). Preliminary results suggest that
crack front waves exist for some but not all crack speeds and
mode mixity. These results will be presented. They are surprising and
feedback from the audience will be welcomed.
