[...]We show that the dynamically preferred unstable wavelength is governed by the balance of the destabilizing effect of far-field stresses and the stabilizing effect of cohesive forces on the process
zone scale, and we derive a theoretical estimate for this scale using a new propagation law for curved cracks in three dimensions. The rotation angles of coarsened facets are also compared to theoretical
predictions and available experimental data.
Pons, A. J.; Karma, A. Helical crack-front instability in mixed-mode fracture. "Nature", 04 Març 2010, vol. 464, p. 85-89.