Multiaxial fatigue behaviour of Sintered Steels under combined in and out of phase bending and torsion

Abstract

AbstractThis paper discusses the fatigue behaviour of sintered steels under multiaxial loading. These steels are the Fe‐1.5% Cu and the Fe‐2.0% Cu‐2.5% Ni, sintered at low and high temperatures, in the densities 7.1 and 7.4 g/cm3, which are used in the production of several ready to assemble automotive parts.Fully reversed or pulsating combined loading with constant frequency and amplitudes acting in and out of phase, was applied to round notched specimens (Ktb = 1.49, Ktt = 1.24) in the finite fatigue life region (104 ≤ Nf ≤ 2 · 106).The mechanics of crack initiation and propagation as well as rupture were studied using fractography and microfractography. These analyses led to a mechanical model based on local normal stresses for the fatigue life evaluation.The fatigue life evaluation on the base of the local bending stress obtained under uniaxial loading describes the test results for in phase combined bending and torsion satisfactorily. But the increase of fatigue strength and life by out of phase loading is overestimated in the case of fully reversed loading. However for design purposes the out of phase loading can be neglected because of its beneficial effect in increasing fatigue life for this type of material. If the dependence of the different stress concentrations under combined in and out of phase loading on the supportable local bending stress obtained under uniaxial loadings is considered, then the calculation procedure covers all test results.