Characterization of Low-cycle Fatigue Parameters

Aims: To characterize the fatigue parameters of some stainless steels at a wide range of temperatures, and also to evaluate the influence of temperature on their mechanical properties.

Methodology: Two ferritic stainless steels and one austenitic stainless steel were tested. Tensile tests under Isothermal condition are performed at room temperature and at elevated temperatures with the interval of 100ºC. Isothermal total strain-controlled fully-reversed low-cycle fatigue tests are performed at different total strain amplitudes ranging from 0.3% to 0.7% at different temperatures with a constant strain rate of 2×10-3 /s. The effect of temperature on elastic modulus, 0.2% yield strength, and ultimate tensile strength is demonstrated graphically. And, variation of reversals to failure with total strain amplitudes and temperatures are analyzed. Materials' constants concerning tensile and low-cycle fatigue behavior are calculated. A fatigue parameter under anisothermal condition is also assessed.

Results: The austenitic steel shows higher strength under monotonic tensile loading and lower fatigue strength under total strain-controlled fully-reversed low-cycle fatigue tests compare to others. Material strength decreases with increasing temperature. For a given total strain amplitude at low-cycle fatigue condition, when the temperature increases from room temperature to moderate elevated temperatures, fatigue lives are higher compared to that of room temperature, and then fatigue life decreases with the further increased temperature. And, fatigue life is reduced significantly with the increasing strain amplitude for all materials considered. The fatigue parameter under anisothermal condition is found realistic from the viewpoint of safety in design.

Conclusion: Fatigue properties of materials are essential in the design and practice of mechanical structures and components subjected to cyclic loading at wide range of operating temperatures. This research contains useful monotonic and fatigue parameters which would be advantageous for the application in design and practice.