On the growth of cracks under mixed-mode I plus III loading

We examine the growth of cracks under mixed-mode I + III loading conditions. Specially designed specimen configurations are used to identify that crack front fragmentation occurs through nucleation of nearly regularly spaced daughter cracks, and that coarsening of this spacing during growth increases through an elastic shielding mechanism. It is shown further that linkage of the daughter cracks does not occur concurrently with the formation of the primary system of daughter cracks, but at a later stage of the growth of the daughter cracks. A mechanism of the combined growth of the parent and daughter cracks under mixed-mode I + III loading is suggested for capturing the pattern formation of the echelon crack patterns observed in laboratory experiments and field observations.