Frozen impacted drop: From fragmentation to hierarchical crack patterns

We investigate experimentally the quenching of a liquid pancake, obtained through the impact of a water drop on a cold solid substrate ($0$ to $-60^\circ$C). We show that, below a certain substrate temperature, fractures appear on the frozen pancake and the crack patterns change from a 2D fragmentation regime to a hierarchical fracture regime as the thermal shock is stronger. The different regimes are discussed and the transition temperatures are estimated through classical fracture scaling arguments. Finally, a phase diagram presents how these regimes can be controlled by the drop impact parameters.