Abstract
Surface markings left by an unsteadily propagating cleavage crack in NaCl single crystals have been studied by electron microscopy as a function of accelerations and decelerations of the crack. As a result, a comprehensive description of the sequence of markings present between two successive stopped crack fronts has been obtained. Models arc proposed illustrating the manner in which the activation of the longitudinal and transverse slip systems and their interaction can account for the cleavage markings observed.