Process region influence on energy release rate and crack tip velocity during rapid crack propagation

A finite element model of a plate with an edge crack is investigated. A cell model of the material, with the cell size representing some characteristic intrinsic material length, is adopted. The size of the process region depends on the number of cells that have reached a state which is unstable at load control. The results show that the growth of the process region is a main factor responsible for the lack of a unique relation between the small scale yielding energy release rate and the crack tip velocity and also for the observed constant crack velocities that are significantly below the Rayleigh wave velocity. A rapidly propagating crack appears to meet an increase of the energy flow to the crack edge per unit of time by increasing the size of the process region rather than increasing its edge velocity.