Determination of Safe Life Retirement Time of Helicopter Dynamic Components based on a Fretting Deterioration Model

摘要

Fatigue retirement times of helicopter dynamic components arecalculated based on Safe Life methodology. In this approach, the aircraft’susage spectrum, the component loading spectrum, and the component’s SNcurve, are combined in order to determine the critical retirement time ofthe component. An IAF S-65C-3 main rotor upper hub, with spline teethwear findings was analyzed and the retirement time calculated was foundto be inapplicable using standard S-N reduction method. Alternatively,considering the fact that fatigue and fretting are similarly time dependent,a fretting deterioration model was developed in order to calculate thecomponent’s retirement time which incorporates actual wear conditions.Several in-service wear measurements were taken in order to calibrate themodel. Then, this data was used to progressively accumulate the fatiguedamage under the temporary wear conditions and the final fatigue life wasdetermined. This approach ultimately allowed for the expansion of thecalculated retirement time.