Tensile cracks can shatter classical speed limits

Brittle materials fail by means of rapid cracks. Classical fracture mechanics describes the motion of tensile cracks that dissipate released elastic energy within a point-like zone at their tips. Within this framework, a "classical"tensile crack cannot exceed the Rayleigh wave speed, cR. Using brittle neohookean materials, we experimentally demonstrate the existence of "supershear"tensile cracks that exceed shear wave speeds, cR. Supershear cracks smoothly accelerate beyond cR, to speeds that could approach dilatation wave speeds. Supershear dynamics are governed by different principles than those guiding "classical"cracks; this fracture mode is excited at critical (material dependent) applied strains. This nonclassical mode of tensile fracture represents a fundamental shift in our understanding of the fracture process.