A PROPOSED CRITERION FOR FATIGUE THRESHOLD: DISLOCATION SUBSTRUCTURE APPROACH

Abstract— A model for fatigue threshold has been proposed based on the dislocation subgrain cell structure that evolves at the crack tip in steels during the fatigue deformation process. The stabilized subgrain cells that develop in the material act as impenetrable barriers to dislocations in slip band pile‐ups that emanate from the fatigue crack tip. The blocking of these dislocations tends to limit crack growth that occurs by crack tip emission of dislocations, thereby leading ultimately to the fatigue threshold condition. The grain size effect on threshold is deduced to be an indirect effect as it is proposed that the subgrain cell size is the controlling substructural parameter at the threshold stress intensity level. The subgrain cell size is shown to be proportional to the one‐third power of the initial grain size.