EFFECT OF AXIAL-TORSIONAL STRAINING PHASE ON ELEVATED-TEMPERATURE BIAXIAL LOW-CYCLE FATIGUE LIFE IN SUS 304 STAINLESS STEEL.

The fatigue life under out-of-phase straining was found to be shorter than that under in-phase straining when compared at the same Mises equivalent strain range or maximum shear strain range. From the observation of slip-bands and micro-cracks on the specimen surface by means of a replica method, this appeared to be due to the change in fracture mode arising from the difference in macroscopic strain condition between in-phase and out-of-phase straining. Accordingly, a unified correlation for both the in-phase and out-of-phase biaxial fatigue lives could be obtained by expanding the Brown-Miller's theory of equivalent shear strain which contains the maximum shear strain and the normal strain across the maximum shear plane as the factors controlling the fatigue crack initiation and propagation under biaxial loading.