Universality in fragmentation

Fragmentation of a two-dimensional brittle solid by impact and "explosion," and a fluid by "explosion" are all shown to become critical. Thr critical points appear at a nonzero impact velocity, and at infinite explosion durat ion, respectively. Within the critical regimes, the fragment-size distribut ions satisfy a scaling form qualitatively similar to that of the cluster-si ze distribution of percolation, but they belong to another universality cla ss. Energy balance arguments give a correlation length exponent that is exa ctly one-half of its percolation value. A single crack dominates fragmentat ion in the slow-fracture limit, as expected.