Probabilistic analysis of aircraft gas turbine disk life and reliability

Two series of low-cycle-fatigue (LCF) test data for two different groups of aircraft gas turbine engine compressor-disk geometries were reanalyzed and compared by using Weibull statistics. Both groups of disks were manufactur ed from titanium (Ti-6Al-4V) alloy, A probabilistic computer code called Pr obable Cause was used to predict disk life and reliability. A material-life factor A was determined for the titanium (Ti-6Al-4V) alloy by using fatigu e disk data and was applied to predict disk life as a function of speed. A comparison was made with results from the currently used life prediction me thod, which is based on crack growth rate. Applying an endurance limit to t he computer code did not significantly affect the predicted lives under eng ine operating conditions. Failure location predictions correlated with expe rimentally observed failure locations in the LCF tests. A reasonable correl ation was obtained between the disk lives predicted by using the Probable C ause code and those predicted by using a modified crack growth method. Both methods slightly overpredicted life for one disk group and significantly u nderpredicted it for the other.