PRINCIPAL STRESS MODEL FOR MULTI-AXIAL FATIGUE OF PRELOADED THREADED FASTENERS

A principal stress-based high cycle fatigue (HCF) model is proposed for cyclic multiaxial stresses in threaded fasteners under tensile-shear loading. The proposed model uses the fastener principle stress amplitude in order to construct mean stress adjusted S-N curves for multi-axial stresses. Experimental validation is provided using an MTS fatigue testing system, with a special fixture that would allow combined cyclic tensile-shear loading of the fastener at various angles relative to the axis of the MTS grip axis. Experimentally validated multiaxial fatigue model is compared to classical uniaxial S-N curves. Detailed discussion of the model results is provided.