A strain energy-based approach to the low-cycle fatigue damage mechanism in a high-strength spring steel

Abstract

Low-cycle fatigue tests were conducted using smooth, cylindrical specimens under a strain-controlled, fully reversed condition for a high-strength spring steel heat treated to different strength levels. The variation of the cyclic deformation substructure was observed with a transmission electron microscope (TEM). The results indicate that the average plastic strain energy dissipated per cycle (Delta W-ps) is an important parameter upon which a consistent evaluation of the cyclic stress-strain, the strain-life, and the plastic strain energy-life relationships is made feasible. Furthermore, the total plastic strain energy dissipated prior to failure (W-f), determined on the basis of Delta W-ps, is proven to be another important parameter, from the variation of which the extent of local damage accumulation can be evaluated. Confirmed by the results of TEM observations, a strain localization-induced damage mechanism is proposed and discussed.