Grady’s model of the dynamic fragmentation process, in which the average fragment size is determined by balancing the local kinetic energy and the surface energy, is modified to include the stored elastic (strain) energy. The revised model predicts that the strain energy should dominate for brittle materials, with low fracture toughness and high fracture‐initiation stress. This conclusion is not borne out, however, by limited experimental data on brittle steels, even when the kinetic‐energy density is small compared with the strain‐energy density.