Early-time dynamics of fluid-driven cracks

Pressure-driven flow at a point source, facilitated by a needle inserted in a brittle elastic matrix, creates a radial fracture of penny shape. Although this phenomenon has been studied on a large time scale, the early time dynamics of these fluid-driven cracks are still not well understood. Here, we present our findings on the shape transition of fluid-driven fractures. At the initial stage, a crack forms and propagates in the axial direction, with respect to the orientation of the needle. The crack then shifts to a penny shape, when the propagation shifts from axial to radial, characterized by a peak in the pressure profile during the liquid infusion. We also used scaling laws to validate the radial and width profiles of these cracks for viscous and toughness-dominated regimes.