Abstract: Using the mode I weight function of Willis et al. (1995)for a moving crack in combination with the model method of Rice et al. the instabilityphenomena of the crack front, how does it begin to surround andpenetratevarious arrays of asperities are investigated. The numerical results showthat the oscillatory crack tip motion through brittle, locallyheterogeneous materials results from constructive destructiveinterference of stress waves that can lead to continuing fluctuation of the crack front and propagat...