Influence of Cycle Counting methods on Fatigue Life Estimation of Critical Rotorcraft Components

We present an analysis of the influence of various cycle counting approaches on the estimated fatigue life for critical rotorcraft components. The entire study is demonstrated using the pitch link of a utility helicopter similar to the UH-60 Black Hawk helicopter as a representative component. Different counting methods predict fatigue life differently due to the varied fundamental parameters or approaches they take to characterize the stress profile. Hence, it becomes vital to choose an appropriate method for a particular application so that it does not over or under predict fatigue life during the design process. Based on this, we investigated four methods namely, Rainflow, Peak, Level and Range counting