A multiaxial fatigue life criterion for non-symmetrical and non-proportional elasto-plastic deformation

A new low-cycle multiaxial fatigue criterion based on the concept of effective strain is proposed. The effective shear strain y(eff) is derived by averaging shear strains acting on all planes at a material point during a loading cycle. The criterion, in the form of a generalised Smith-Watson-Topper expression, can take into account of the effect of non-symmetrical loading cycles. The advantage of the proposed criterion relies on the minimum number of material parameters to be identified. The uniaxial stress-strain curve, the basic strain-life curve (Manson-Coffin) and an additional experiment curve obtained from zero to tension strain controlled axial fatigue tests are sufficient to apply the proposed criterion in all loading conditions. Different sets of proportional and non-proportional multiaxial strain controlled low-cycle fatigue test results have been compared with the predicted life, showing in all cases a good agreeement with the criterion.