Low cycle fatigue and ratcheting properties of steel 40Cr under stress controlled tests

In order to extend the allowable stress range in the design of disposable mechanical elements, the stress controlled low cycle fatigue and ratcheting behaviors of steel 40Cr are investigated. The shape instability life is defined to describe the life of cyclic softening materials under high stress conditions. The test results show that the relation between the maximum stress and the shape instability life is linear-logarithmic. The similar relation also exists between the stress ratio and the shape instability life. Taking the shape instability life into account, the allowable stress is highly improved in the design of disposable mechanical elements.