DYNAMIC STRESSES AT A MOVING CRACK-TIP IN A MODEL OF FRACTURE PROPAGATION

The steady-state propagation of a mode I crack in a laterally strained strip is examined. The displacement field satisfies the usual equatio n of motion for an isotropic two-dimensional elastic medium while the tractions on the fracture surface include a viscous dissipative term r ecently introduced by J. S. Langer and H. Nakanishi [Phys. Rev. E 48, 439 (1993)]. The stress field at the crack tip is calculated and found to change qualitatively as the crack speed increases beyond a certain critical value. Such a dynamical modification of the crack tip stress field has an interesting indication that steady-state crack propagati on above the critical speed may be unstable.