The RED criterion for fatigue life assessment of metals under non-proportional loading

In the present paper, a novel criterion for fatigue life assessment of engineering components under multiaxial low-cycle fatigue regime is proposed. The criterion, named Refined Equivalent Deformation (RED) criterion, allows to take into account, when the load is non-proportional, the fatigue strength decrease experimentally observed for those metals sensitive to non-proportionality. The criterion is applied to two different metals (304 stainless steel and 6061 aluminum alloy) characterised by different non-proportional sensitivities. The accuracy of such a criterion is compared with those of other criteria available in the literature.