Current Practices in Structural Analysis and Testing of Aero-Engine Main Shafts

Gas turbine engines are widely used in both Military and Civil Aircrafts. The power generated at the turbine is transmitted to compressor through Engine main shafts. These shafts are classified as Class-I critical components of the engine. During the flight operating conditions engine main shafts are subjected to complex loading conditions, such as Torsional, Centrifugal, Thermal, Gyroscopic etc… The combination of these loads lead to multimode failure mechanisms, such as Low cycle Fatigue (LCF), High cycle Fatigue (HCF) and Ductile overload failures in shafts. Designing of shafts for structural integrity is very critical in single engine aircrafts, as the failure of any one shaft may result in the failure of engine, which in turn may lead to the catastrophic failure of the entire aircraft. The complex geometry of the shafts calls for combination of design tools for stress and life estimation of these parts (both analytical and finite element method (FEM)) backed up by extensive material and component test programs. In the present paper structural analysis and life estimation is carried out on Low Pressure Spool and Spline Coupling under various engine operating conditions. The design analysis cycle consists of several phases, such as Heat Transfer Analysis, Structural Analysis, Optimization and Fatigue Lifing. Detailed modeling and stress analysis carried out to evaluate the strength of the splines is also presented. This paper highlights the methodology of design subjected to clearance of stipulated MIL 5007 D/E specifications to ensure the structural integrity. Based on the stress analysis, a Stress Test Schedule is prepared to carry-out the testing at shaft fatigue rig facility. In the testing facility, mechanical testing of the shaft assembly is carried out to establish strength and fatigue life of the shafts. Brief results on the material tests carried out and fatigue life testing of full scale component are also presented.