On the estimation of the cyclic plastic strain energy of dual-phase steels

Abstract

Low cycle fatigue tests were conducted on dual-phase steels containing a variety of ferrite-martensite microstructures. With the exception of the one which had a low volume per cent martensite (1.5%), these steels displayed deviation from the Masing behaviour: the extent of this deviation, interestingly, increased with the increase in cyclic strain hardening exponent. Consequently, a significant disparity was observed between the values of the average plastic strain energy per cycle (ΔW̅_P) calculated with the equations of Morrow, Quesnel and Kliman and Bily, based on the Masing material description, and those actually measured. It is shown that the equation developed by Lefebvre and Ellyin for non-Masing materials provides energy values comparable to the measured ones. Further, an empirical modification to Morrow's equation has been suggested, which yields a more reliable estimate of ΔW̅_P of the dual-phase steel regardless of the extent of deviation from the Masing behaviour.