Analysis of the Reliability of a Jet Engine Compressor Rotor Blade Containing a Fatigue Crack

Abstract

The reliability of a jet engine compressor rotor blade containing a fatigue crack has been assessed based on the eddy current inspection (ECI) response of both the actual rotor blade and bolt hole specimens containing cracks of known lengths. The detection threshold and the probability of detection (POD) curve have been determined. A dynamic Bayesian network (DBN) model was used to quantify uncertainties. The model encompasses a realistic ECI response model, so that it is possible to consider all relevant inspection data types. Factors which contribute the most to the variation of crack length have been determined by sensitivity analysis and have been calibrated using the field inspection data. Part of the inspection data was used to validate the calibrated model, and a Bayes factor of 9.93 which corresponds to a confidence level of 91% has been obtained. Based on the control level for the reliability index βctrl = 3, and the reliability indices calculated from the calibrated model, the recommended interval for the first inspection has been determined as 1600 hrs. This interval is smaller than the current interval which is 3200 hrs.