Accumulation and mechanism of the fatigue damage for a nickel based superalloy

The fatigue damage accumulation investigations were performed for high and low cycle fatigue loading regime for the nickel based superalloy frequently used in the aviation industry. Definition of the damage parameter proposed by Johnson in [2], modified to be applicable for cyclic loading, was used to quantify damage. In the modified definition, the accumulated equivalent plastic strain was used as the damage indicator instead of axial strain. Analysis of the variations of hysteresis loop allowed to plot damage indicator as the function of load cycle number and finally to plot damage parameter as the function of the life ratio. This kind of plot, known as the Damage Curve, enables identification of the fatigue damage accumulation model appropriate for the investigated material and applied loading regime. Fractography and structural observations performed on damaged specimens allowed to identify damage mechanism for the alloy in question.