SEDL / STP / STP1006-EB / STP10354S

Simplified Analysis of Helicopter Fatigue Loading Spectra

Dowling, NE
Professor and graduate research assistant, Virginia Polytechnic Institute and State University, Blacksburg, VA

Khosrovaneh, AK
Professor and graduate research assistant, Virginia Polytechnic Institute and State University, Blacksburg, VA

Pages: 22    Published: Jan 1989

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Abstract

In employing the Palmgren-Miner rule for irregular loading spectra applied to notched mbers, it is necessary to employ rain-flow or an equivalent cycle counting method, and also to consider the accelerated damage at low stress levels due to the presence of high-level cycles. Additional interactions between high and low stress levels, which are associated with local notch mean stress effects, also occur and can be specifically analyzed using the local strain approach. A simplified application of the local strain approach is described that results in upper and lower bounds on life being calculated. This is applied with reasonable success to the standard helicopter loading spectra Helix and Felix, and a much simplified version of Helix is proposed that consists of repetitions of a single typical flight.