Failure analysis and reliability improvement of small turbine engine blades

Abstract

A series of analysis and testing procedures for small turbine engines blades are presented. These procedures can be used to (i) verify the critical failure modes, and (ii) propose approaches for improving the performance, reliability and safety of engine blades in service. The procedures include metallographic examination, chemical ingredient analysis, vibration and modal analysis, stress analysis, fatigue life prediction and modal testings with and without coating. For the particular small turbine engine considered, it is demonstrated that the most probable failure mode for blades is fatigue fracture rather than creep fracture. Possible approaches to enhance the fatigue performance and reliability of engine blades have been proposed and investigated. These include the surface coating, the use of high strength material, and a reduction of the number of stators. Among these approaches, a reduction of the number of stators from 17 to 14 is most beneficial, because it removes vibrational frequencies of the turbine engine from the operating frequencies, thus significantly reducing the vibrational level of engine blades. The vibrational stress in blades can thus be reduced to a level below the fatigue limit.