Fatigue limit of circumferentially notched metastable austenitic stainless steel under positive/negative stress ratios: Synergistic effects of notch-root mechanistic singularity and phase transformation

Fatigue tests of circumferentially notched Type 304 austenitic stainless steel (ASS) illuminated the unique dependences of fatigue limit on the stress concentration factor, Kt, and stress ratio, R. Fatigue limit under negative R was superior to that under positive R, a result was unexpected from the empirical behavior of smooth ASS. Moreover, switching R from negative to positive apparently diminished the effect of Kt escalation on the deterioration of the fatigue limit. Consolidation of microhardness tests, microstructural observation, finite element analysis revealed that these anomalies stem from the presence/absence of cyclic plasticity and martensitic transformation, which dynamically strengthen the notch-root.

Automated summary

This study investigates the unique relationship between fatigue limit and stress concentration factor and stress ratio in austenitic stainless steel. Unexpectedly, the fatigue limit under negative stress ratio is superior to that under positive stress ratio, contrary to the behavior of smooth stainless steel. Switching from negative to positive stress ratio diminishes the effect of stress concentration factor on the deterioration of fatigue limit. Microhardness tests, microstructural observation, and finite element analysis reveal that these anomalies stem from the presence/absence of cyclic plasticity and martensitic transformation, dynamically strengthening the notch-root.