Initial Behavior of Hysteresis Loop of Low Carbon Steels under Repeated Load : Theoretical Treatment on the multiplying model of dislocations

Abstract

This is a second report of authors aiming to clarify the mechanism of the initial increase of the plastic strain amplitude Δep of low carbon steels under fatigue load. Close observations showed that a sharp increase of Δep took place after a gradual growth, and this gradual growing process had been analyzed in the first report by developing the interaction models between dislocations and solute carbon atoms under repeated load. Therefore, in this report, a sharp increase of Δep is theoretically dealt with by establishing a multiplying model of dislocation loops from the Frank-Read sources whose activation took place following the cease of the increase in the length of the movable dislocation lines upon reaching the strong pinning points. It is shown that the derived theory satisfactorily explains the experimental trend.