Here you find a preprint version of a paper published in PRL 95, 114301 (2005) [also see Eur. Phys. J. E. 17, 261-281 (2005)] where the authors present a theory to explain why instabilities, e.g. stick-slip motion, is observed when cracks propagate in rubber materials. Although the theory is also compared with some experiments, I would be interested to find additional experimental data for a better comparison. In particular, the theory predicts an increase of temperature at the crack tip of about 800K (when thermal degradation is taken into account - see Eur. Phys. J. E. 17, 261-281 (2005)) so I'm wondering whether anyone has recently carried out experiments aimed to measure the increase of temperature at the tip of propagating crack in viscoelastic materials.