An important role of elastic vortices in unsteady propagation of longitudinal shear cracks in brittle materials

The paper is devoted to the numerical study of some fundamental aspects of longitudinal shear crack propagation in sub-Rayleigh and supershear regimes. The simulation was carried out with use of particle-based movable cellular automaton method. It is shown that a well-known phenomenon of shear crack acceleration towards longitudinal wave speed is explained by the formation and development of elastic vortex traveling ahead of the crack tip at a shear wave velocity. The stress concentration area ahead of the crack tip revealed by different authors is connected with the elastic vortex. Shear crack accelerates towards the longitudinal wave speed through the formation of a daughter crack by the mechanism of shearing (the daughter crack is formed in the center of elastic vortex). Analysis of sub-Raleigh-to-intersonic transition showed that the condition of this transition can be expressed in terms of dimensionless geometrical crack parameter.