A methodology is described for probabilistic assessment of the fatigue life of a high pressure turbine in a turboprop engine subjected to a complex load history. A logarithmic performance function was derived by fitting a closed form equation to the results of the engine model perturbations. The methodology incorporated the same basic engine models, including heat transfer, structural and crack growth models, used in a deterministic fatigue life analysis. The performance function yielded a good approximation of fatigue life over a wide range of the random vriables. First order reliability methods (FORM) were used to compute the probability of failure and sensitivity of the fatigue life to the engine parameters for the first stage turbine disk rim for three performance levels. The sensitivity analysis showed the burner outlet temperature (BOT) to be the random varable to which the fatigue life was most sensitve, indicating that concentrating engineering resources on reducing the mean value and/or reducing the scatter of BOT may be the most efficient way to increase fatigue life. A discrete time-dependent random variable capability was developed using a hybrid Monte Carlo method. The computationally intensive engine models were not used directly in the Monte Carlo simulation. Instead, the Monte Carlo simulation used a computationally efficient, approximate crack growth function derived by fitting a family of curves to the results of the engine model perturbations. A computational method was used to determine the probability of failure of the system of the overall high pressure turbine. The probabilities for four individual failure modes were computed using FORM. System failure was defined as the union of the individual failure modes. The probability of this union was computed through first and second order bounds. The method also provided sensitivity information about the effect of each random variable on the individual fwilure probabilites, as well as the system failure probability. The BOT was found to be the random vriable to which the fatigue life of the overall turbine was most sensitve.
Development of a reliability-based fatigue life model for gas turbine engine structures
Entwicklung eines auf Zuverlässigkeitsabschätzungen basierenden Modells für die Ermüdungslebensdauer von Konstruktionsteilen von Gasturbinenmaschinen
Engineering Fracture Mechanics ; 53 , 5 ; 807-828
1996
22 Seiten, 11 Bilder, 6 Tabellen, 23 Quellen
Aufsatz (Zeitschrift)
Englisch
Fatigue Life and Reliability of Randomly Excited Structures
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