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

• We research low cycle fatigue and ratcheting behaviors of 40Cr under stress tests.
• We define the shape instability life to describe the cyclic softening materials life.
• We distinguish the shape instability life and the fatigue fracture life.
• We found that the shape instability failures of disposable mechanical elements.

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.