Mean strain effect on multiaxial fatigue behavior of Ti-6Al-4V under non-proportional loading

Multiaxial low cycle fatigue behavior of Ti-6Al-4V under non-proportional loading is studied. Strain controlled multiaxial fatigue tests at room temperature were carried out under uniaxial and non-proportional loadings using tubular specimen. The strain paths employed were three types of proportional and two types of non-proportional loadings. The former are a push-pull straining, a reversed torsion straining and a push-pull strain with mean axial strain. The latter are a circular straining where axial and shear strains have 90 degree phase difference and a reversed torsion straining with constant axial strain. In data correlation by Mises’ equivalent strain range, failure lives in the circler straining test were about 1/10 of that in the push-pull test. The failure lives in the reversed torsion with constant axial strain were affected by not only non-proportionality but also mean/constant strain. This study discusses the fatigue property and evaluation of failure life under non-proportional loading with mean strain. INTRODUCTION Ti-6Al-4V alloy is frequently used as a material in rotating aero engine because this material has properties of high strength, light weight and corrosion resistance. The rotating aero engine receives cyclic loading under thermal and mechanical stresses which cause multiaxial low cycle fatigue (LCF). Under non-proportional loading in which principal directions of stress and strain are changed in a cycle, previous studies have reported a drastic reduction in failure life accompanies an additional cyclic hardening, which depends on material [1-8]. In addition, some studies in view of mean