Multiaxial fatigue strength of severely notched cast iron specimens

The present work deals with multiaxial fatigue strength of severely notched cast iron (EN-GJS400). Circumferentially V-notched specimens are tested under combined tension and torsion loading, both in-phase and out-of-phase, with two nominal load ratios, R = −1 and R = 0. All axis-symmetric specimens are characterized by a constant notch tip radius (less than 0.1 mm), a notch depth of 4 mm and a V-notch angle of 90°. The results from multiaxial tests are discussed together with those obtained under pure tension and pure torsion loading from notched specimens with the same geometry. Altogether more than eighty new fatigue data (10 Wöhler curves) are summarised in terms of normal and shear stresses. Afterwards, all fatigue strength data are given also in terms of the local strain energy density averaged over a material-dependent control volume surrounding the V-notch tip. The dependency of the control volume size as a function of the loading mode is investigated showing the necessity to introduce for the cast iron EN-GJS400 a different value of the control volume radius under tension and under torsion.