Velocity Jump of Crack Propagation in Viscoelastic Solids

A crack in a viscoelastic solid exhibits velocity jump, i.e.. the propagation velocity changes abruptly in a narrow range of the applied load. However, the mechanism had been unsolved until recently. This review introduces past findings on velocity jumps in viscoelastic solids, focusing on our studies. We have developed an exactly solvable model that exhibits the velocity jump. From the mathematical solution, we have elucidated that the velocity jump is caused by a dynamic glass transition in the vicinity of the crack tip. Also, we have provided a guiding principle for toughening viscoelastic solids. Recently, the predictions of the model have been confirmed by experiments and numerical simulations.