Effects of cyclic loading on fatigue properties of austenite stainless steel

Fatigue properties of stainless steels have been investigated by various researchers. The present work examined fatigue properties under various cyclic loading conditions to determine the significant factors of loading condition to fatigue strength (σ_e). From this approach, no clear frequency effects on the S-N_f relation were detected, but clear R-ratio effects were identified on fatigue strength. A higher R-ratio yielded higher σ_e, and a clear correlation was observed between R-ratio and endurance limit. A different trend was observed for the S-N_f curve when the stress value on the ordinate of the S-Nf relation was plotted using the maximum tensile stress (σ_max). However, the S-N_f curves obtained overlaid each other when using stress amplitude (σ_a) instead of σ_max. Fatigue properties were analyzed further using several relations proposed previously, such as modified Goodman relation. In this case, the fatigue data obtained were clearly approximated by an elliptical relation. Severe microstructural damage arising from plastic deformation was observed in the sample fractured under the R = −1 condition, where striation was a main failure mode. In contrast, no clear microstructural damages were observed in the samples fractured at R = 0.1 even when a higher maximum tensile stress was applied (e.g., σ_max = 60% σ_UTS), where ripple-like failure was the dominant feature.