Instability in dynamic fracture

Jay Fineberg, Steven P. Gross, M. Marder, and Harry L. Swinney

Department of Physics and Center for Nonlinear Dynamics, The University of Texas, Austin, Texas 78712

Received 4 December 1990

Cracks in brittle materials have terminal velocities far below theoretical predictions. To address this problem we have investigated the propagation of cracks in a brittle plastic (polymethylmethacrylate). Velocity measurements with resolution an order of magnitude better than past experiments reveal the existence of a critical velocity at which the velocity begins to oscillate, the mean acceleration drops sharply, and a pattern is formed on the fracture surface. Thus the dynamics of cracks may be governed by a dynamical instability.