Phase field study of the instabilities of crack front under mixed mode loading and plane stress.

The instabilities of an initially tilted crack front under mode I loading in a finite size sample under plane stress condition is studied using a phase field model. Simulations show, that below a critical initial tilt angle the crack front relaxes smoothly toward a mid-sample crack front as was observed in recent experiments in gels and the agreement between experiments and simulations on the relaxation is quantitative. Nevertheless, there is a strong discrepancy between the experimental value of the critical angle above which the crack front is no longer stable and the one computed nmerically. The possible reasons for this are discussed using numerical experiments.