Low cycle fatigue under tensile mean stresses where cyclic life extension occurs

Low cycle fatigue lives under mean stress conditions are usually correlated using modifications to the strain-life approach. However, under many practical conditions, the input data is in the form of stress amplitude and mean stress rather than strain amplitude and mean stress or strain and, because it may be difficult to assess the strain amplitudes, a stress-life approach may be preferable. Under low cycle fatigue with mean stresses, softer materials can sometimes show an increase in cycles to failure with increasing tensile mean stress and all mean stress modifications to stress-life equations describe the commoner condition of life reduction. This paper suggests a method of relating the failure life to imposed mean stress and stress amplitude for materials in which a tensile mean stress causes a life increase. It is shown to give reasonably good results when applied to data on copper.