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’.