Data for: Tensile cracks can shatter classical speed limits

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