Two-parameter characterization of low cycle, hysteretic fatigue data

The aim of this research is to characterize the development of fatigue damage by means of stress-strain hysteresis. Experiments were conducted on 14 specimens made of cold-finished unannealed AISI 1018 steel. Results demonstrate that the mechanical hysteresis loop areas, when plotted as a function of the number of loading cycles, show significant variations and demonstrate the three principal stages concerning the progress of the fatigue failure-initial accommodation, accretion of damage and terminal failure. These three stages of fatigue are marked by the transitions at cycles N (2) and N (3). Experimental results show that although fatigue life N (f) ranges from 2644 cycles to 108 992 cycles, the ratios of N (2)/N (f) and N (3)/N (f) tend to be stable: N (2)/N (f)=10.7%, N (3)/N (f)=91.3%.