Dislocation dynamics simulation of fatigue crack initiation

Abstract

This study was conducted to get basic information concerning fatigue crack initiation through dislocation dynamics simulation. This simulation was based upon the movement of discrete edge dislocations on slip planes vertical to the surface under a cyclic applied shear stress. The equation which rigorously describes the shear stress acting on dislocations near the surface was obtained using the concept of image dislocations. The result of the simulation showed that no slip step was formed only by the movement of dislocations generated from a dislocation source because the same number of dislocations with the opposite sign alternately escaped from the surface. However, it was found that the formation of a slip step occurred under the existence of sessile dislocations randomly distributed in the material. That is because the stress field of the sessile dislocations disturbed the behavior of movable dislocations. Furthermore, the result of the simulation concerning plural slip planes showed that a fatigue crack can be produced by the growth of each slip step under the existence of the sessile dislocations.