Non-linear dynamical analysis of crack surface perturbations and their dependence on velocity and direction

The fracture surfaces of single crystal [1 0 0] silicon specimens, fractured under three-point bending (3PB) and subjected to a high strain energy upon cracking, revealed exceptional surface perturbations, generated during the unstable propagation. While macroscopically the crack is propagating on the (1 1 1) low energy cleavage plane, microscopic examination revealed small angled deviations from and fluctuations along that plane. Furthermore, while the crack is propagating at a velocity of nearly 3000 m/s in the [1 1̄ 0] direction, its velocity in the [1 1 2̄] direction is two orders of magnitude lower, with distinctive surface perturbations. The amplitude and complexity of the perturbations increase as the normal velocity vector changes its direction and magnitude. These perturbations were recorded with a profilometer and analyzed using non-linear dynamical analysis tools. This study provides an opportunity to interpret surface phenomena of one of the most general cases of fracture and to study the effect of major variables on the nature of the perturbations involved, such as the local crack tip velocity and the crystallographic orientations. It is shown that the surface perturbations are chaotic deterministic in nature and can be described by high order non-linear differential equations; the order of the equation varying with the variations of the local velocity and direction.