Crack front waves: A 3D dynamic response to a local perturbation of tensile and shear cracks

Crack front waves are long-lived perturbations propagating along the crack front. They are triggered by heterogeneities on the crack plane, as for instance tough asperities, which disturb the crack front shape. Crack front waves are thought to leave a trace on fracture surfaces, and are important elements for post mortem analysis. This paper presents a numerical analysis of crack front waves for tensile and shear cracks in the subsonic regime. The elastodynamics calculations are conducted with a boundary integral method. They reveal that the propagation velocity of these waves is independent of the fracture mode. Moreover, using a Lorentz transformation, we demonstrate that their speed is constant within the crack front moving frame, with a value slightly lower than the Rayleigh wave speed. Finally, we shed a new light on how, in response to the interaction with an asperity of prescribed size and toughness contrast, these waves select a localized perturbation in the velocity profile of characteristic shape, width and amplitude.