Notch fatigue life prediction considering nonproportionality of local loading path under multiaxial cyclic loading

摘要

An innovative numerical methodology is presented for fatigue lifetime estimation of notched bodies experiencing multiaxial cyclic loadings. In the presented methodology, an evaluation approach of the local nonproportionality factor F for notched specimens, which defines F as the ratio of the pseudoshear strain range at 45 degrees to the maximum shear plane and the maximum shear strain range, is proposed and discussed deeply. The proposed evaluation method is incorporated into the material cyclic stress-strain equation for purpose of describing the nonproportional hardening behavior for some material. The comparison between multiaxial elastic-plastic finite element analysis (FEA) and experimentally measured strains for S460N steel notched specimens shows that the proposed nonproportionality factor estimation method is effective. Subsequently, the notch stresses and strains calculated utilizing multiaxial elastic-plastic FEA are used as input data to the critical plane-based fatigue life prediction methodology. The prediction results are satisfactory for the 7050-T7451 aluminum alloy and GH4169 superalloy notched specimens under multiaxial cyclic loading.