High temperature nonproportional low cycle fatigue using fifteen loading paths

Abstract This paper discusses effects of nonproportional loading on low cycle fatigue lives for Type 304 stainless steel hollow cylinder specimens at 923 K. Strain controlled axial–torsion low cycle fatigue tests were performed using fifteen proportional and nonproportional strain paths at a strain rate of 0.1%/s. Nonproportional straining significantly reduced fatigue lives of the steel at 923 K. Reduction in fatigue life due to nonproportional straining reached about 80% compared with the proportional straining in specific strain paths. The nonproportional strains, Δ ɛ NP and Δ e NP ∗ , and energy parameter, Δ σ I Δ ɛ I , successfully correlated proportional and nonproportional fatigue lives but ASME equivalent strain gave significantly unconservative estimates.