Data for: Tensile cracks can shatter classical speed limits

Brittle materials fail by means of rapid cracks. At their tips, tensile cracks dissipate elastic energy stored in the surrounding material to create newly fractured surfaces, precisely maintaining `energy balance’ by exactly equating the energy flux with dissipation. Using energy balance, fracture mechanics perfectly describes crack motions; accelerating from nucleation to their maximal speed of cR, the Rayleigh wave speed. Beyond cR, tensile fracture is generally considered to be impossible. By the use of brittle hydrogels, we experimentally demonstrate that a wholly new and different class of tensile cracks that move faster than the shear wave speed, cs, exists. The principle of energy balance no longer dictates their dynamics; this new branch of cracks smoothly surpasses cs to reach unprecedented speeds that approach the speed of dilatation waves. The transition from `classical’ cracks to these `supershear’ cracks takes place at critical values of applied strains. We, furthermore, show that the values of these, rather moderate (12–14%), critical strains are intimately related to the microscopic material structure. This new mode of tensile fracture represents a fundamental paradigm shift in our understanding of ‘how things break’.