Two-dimensional lattice models of crack branching give rise to fragmen
tation if disorder is introduced in the model. The resulting fragment-
size distribution is analyzed within a simple analytical model and by
numerical simulations. The analytical model gives, under rather genera
l conditions, a power-law distribution over the entire size range. In
the specific case studied, the exponent ranges from -infinity to -0.5,
depending on the stopping probability of cracks. The analytical resul
ts are consistent with the numerical simulations.