Analytical Techniques for Helicopter Component Reliability

An effective analytical approach without Monte Carlo simulation was previously presented by the U.S. Army (Ref. [1]) to evaluate fatigue reliability of helicopter dynamic components. This analytical approach required selection of a reference S/N curve for damage evaluation. Overall reliability of a given life was based on the assumption of weighted sums of the equivalent damage rates of all steps in the load spectrum. A sensitivity study indicated that the reference S/N curve chosen might influence the accuracy of the solution. This paper is a follow-on development of the analytical reliability approach. Reliability is evaluated using the S/N curve that produces the same damage sum at its retirement time when load and usage are applied in distributions. The method does not require selection of a reference S/N curve or the weighted reliability assumption. It is easier to understand and implement from a computation point of view. Reliability results of the AHS Round Robin problems (Refs. [2] and [3]) will be presented using both analytical approaches and compared to Monte Carlo simulation solutions. The solution times are also compared to illustrate effectiveness of the proposed analytical approaches.