Low-Cycle Fatigue Behavior Under Biaxial Strain Distribution

This paper presents a linear cumulative damage theory considering macroscopically both elastic and plastic straining to define behavior in the low-cycle fatigue region of the classic S-N curve. A combined strain mode was considered throughout the study with biaxiality effects accounted for through the von Mises theory. An experimental evaluation was conducted to determine the validity of the theory. The biaxial strain mode was provided by centrifugally loading 6-in-dia rotors. Experimentation on SAE 4340 steel alloy supported the damage theory and confirmed the existence of exponential relationships between equivalent elastic strains with cyclic life and equivalent plastic strains with life similar to those contained in the literature for uniaxially loaded specimens. A limited evaluation of an aluminum casting material, C 355-T61, also supported this exponential dependency.