The remainder of this talk will focus on the propagation of an extended crack front through a stiff material. High-speed imaging is used to establish that fluid-driven, penny-shaped, planar mode-I cracks propagate through a series of stick-break instabilities. The forward propagation of an existing fracture front always occurs through an initial rupture, nucleated at some localized position, followed by very rapid transverse expansion of the crack front at velocities that can be controlled ex...
