Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781723053351 Category : Languages : en Pages : 112
Book Description
Helicopter loading histories applied to notch metal samples are used as examples, and their fatigue lives are calculated by using a simplified version of the local strain approach. This simplified method has the advantage that it requires knowing the loading history in only the reduced form of ranges and means and number of cycles from the rain-flow cycle counting method. The calculated lives compare favorably with test data. Khosrovaneh, A. K. and Dowling, N. E. and Berens, A. P. and Gallagher, J. P. Unspecified Center CUMULATIVE DAMAGE; FATIGUE LIFE; HELICOPTER PERFORMANCE; LOAD DISTRIBUTION (FORCES); STRAIN RATE; DISTRIBUTION FUNCTIONS; ESTIMATES; PALMGREN-MINER RULE; PREDICTION ANALYSIS TECHNIQUES; RANDOM LOADS...
Author: Publisher: ISBN: Category : Languages : en Pages : 74
Book Description
Fatigue life estimation of helicopter dynamic components is a complex process that is currently achieved through many different methods. The objective of this study was to review existing methods and to develop a standardized method that could be used by the Army for reliably predicting operational life. This report presents results of a detailed review of fatigue life methods used by five helicopter manufacturers as determined by site visits and literature reviews. Recommendations for a standardized method are presented in areas of mission spectra definition, flight strain survey techniques, laboratory fatigue strength characterization, and safe-life calculation procedures.
Author: NE. Dowling Publisher: ISBN: Category : Cracking (fracturing) Languages : en Pages : 22
Book Description
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.
Author: PE. Irving Publisher: ISBN: Category : Crack closure Languages : en Pages : 16
Book Description
Variable amplitude loading spectra have been developed from service data gathered on a helicopter rotor head. Over 90% of the cycles have r values between 0.7 and 0.9. Variable amplitude fatigue crack growth tests have been performed using the modified rotorcraft spectra on CT specimens of 10-2-3 ?-titanium alloy and a 7010 aluminium alloy. Samples were subjected to variations on the original loading spectrum where smaller load cycles had been progressively removed. Crack closure was monitored at intervals throughout selected load sequences. The results showed that the small range, high mean cycles originating in rotor vibrations contributed over 80% of the crack growth damage. In the titanium samples the contribution of the different parts of the spectrum could be predicted using a simple summation of constant amplitude crack growth increments, without load interaction effects. In the aluminium alloy, the situation was more complicated, with a reduced contribution of the small cycles. The implications for damage tolerance in helicopter components are discussed.
Author: National Aeronautics and Space Administration (NASA)
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Author: John M. Potter
Author: NE. Dowling
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Author: Abolhassan Khosrow Khosrovaneh
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Author: PE. Irving
Author: Gary R. Halford