Abstract:
Many technical papers describe turbocharger turbine/compressor failures caused by foreign object damage, contaminated lube oil, lack of lubrication, high exhaust temperatures, low cycle fatigue, or overspeed. However, High Cycle Fatigue (HCF) is a potential failure mode that has not been widely assessed. This paper describes steps to investigate an HCF fatigue failure of a turbine blade. Metallurgical analysis determined that the failure surfaces are indicative of fatigue and that the initiation location coincided with the location of maximum stress as identified by finite element modal analysis. High Cycle Fatigue was identified as the root cause of the failures. Finite element based modal analysis indicates that the turbine blade could quickly fail if the turbocharger is operated at one of several resonant speeds since turbine blade resonances occur at very frequencies. HCF analysis with combined modal and stress analyses coupled with a high altitude engine test using the candidate turbocharger is recommended for the new turbocharger to ensure high reliability of the compressor and turbine from an HCF perspective.