In aeronautical industry, flight safety is the first and foremost concern. Structural failure in aero engine aids to high risk in flight safety and human lives. High Cycle Fatigue (HCF) failure accounts for forty percent of blade structural failure. All critical components in the aero engine are life limited components and are replaced when its prescribed life is reached. Earlier components are designed as per safe-life design philosophy. Ninety percent of the critical components are retired utilizing less than fifty percent of its safe-life capability. Extending the life of component reduces the operating cost and lowers downtime for the fleet operator.
This paper describes the life extension methodology used for a first stage axial compressor blade of turbo-shaft engine. The blade which has completed its safe life in the aircraft in service is identified. The studies are carried out to determine the residual life of the blade to extend the life. First stage axial compressor blade is made from titanium alloy and is fixed with the disc by pins. The force on the blade due to aerodynamic excitation which is required for life estimation is predicted using CFD tools followed by the estimation of alternate stress on the blade using FEM tools. Stress based life estimation methodology is used to estimate HCF life of the blade under engine operating condition. The estimated life of the blade is to be confirmed in rig testing. Life completed blades are identified from different engines for testing of the residual life. Metallurgical studies are carried out on the specimens from the blade to check the residual properties. The blades which qualify after the dimension inspection and crack detection are used for testing residual life. The blades are tested in vibration test rig facility in which incremental fatigue testing method is employed. The blades are excited by the electro-dynamic shaker at its first natural frequency (1F mode) and the amplitude is increased in steps in a steady interval of time. The HCF life of the blade is calculated by Miner’s hypothesis. The residual life of the blade is estimated by vibration rig testing and is compared with the numerical estimation. It is found that the residual life of the life completed component has got potential life of one more overhaul.