Mean stress effect on fatigue strength of stainless steel

• The mean stress effect was investigated for Type 316 stainless steel.
• Maximum stress, stress amplitude and mean strain had little effect on fatigue life.
• Mean stress shortened fatigue life in the studied strain range.
• Fatigue life was the same under true effective strain range even for mean stress.
• The reduction in fatigue life due to mean stress was estimated conservatively.

Influence of mean stress on fatigue life and fatigue limit was investigated for Type 316 stainless steel. The results for prestrained specimens revealed that fatigue life was almost the same in the same strain range regardless of stress amplitude, maximum peak stress and mean strain. The fatigue life was shortened when applying the mean stress for the same strain range, whereas it was increased for the same stress amplitude. It was shown that the reduction in fatigue life was brought about by the change in the effective strain range, which was caused by the increase in minimum peak stress and the ratcheting strain. The fatigue life could be predicted conservatively even if the mean strain was applied by assuming the effective strain range to be equal to the total strain range (by assuming the crack mouth to be never closed). It was concluded that the mean stress correction was not necessary for the load-controlled cyclic loading and for the region where the ratcheting strain was constrained.