From the observation of persistent slip band(PSB) initiation and of its morphology and dislocation structure, a possible mechanism for PSB formation was proposed. It was suggested that once the spacing between matrix walls and the width of the matrix walls reached the critical values, the collapse of a matrix wall that was caused by the unbalance of the forces exerted by crew segments could induce collapse of an adjacent matrix wall. Therefore a persistent slip line(PSL) was formed consequently. Along the PSL, the neighbor screw segments would strongly activate and finally induce the formation of the ladder structure of a PSB. The features of the deformation bands (DBs) in copper single crystals under cyclic straining were surveyed. A model was proposed to account for the formation of DBs. In this model, both crystal rotation and dislocation density variation induced by cyclic straining was considered. The gradual lattice rotation caused by tension and compression irreversibility is the main driving force for the DBs formation. The drastic release of mobile dislocations resisted by the primary slip bands is the direct trigger for the DBs formation.
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