Observation and a simple model of plumose pattern on fracture surfaces of drying pastes

Plumose pattern often appears on the fracture surface of drying pastes. We show a few experimental results of the crack propagation in the drying pastes. We find that the crack propagation sometimes exhibits jump motions. We have also performed an experiment of the crack propagation in a tilted container where the crack propagates from the deeper to shallower sides. This experimental result suggests the importance of the movement of water content. We propose a simple coupled map lattice model. In the numerical simulation, a plumose-like pattern appears owing to the instability of the flat surface of the fracture. The numerical simulation reproduces the jump motions in the crack propagation. We have performed another experiment where a vertical streak pattern appears when the crack propagates downward by cutting into the top surface of the drying paste.