The cost of aero engine and its maintenance is going higher day by day, the life of the critical parts and its availability play a major role to keep the fleet in operation. Engine components works under extremely high stress levels so the life of the components is limited. Most of the critical components are retired by the operator before they reach their theoretical life. The uncertainty in accurate life prediction induces the risk which is the cause for premature retirement. Metallurgical study of the life expired components and fatigue/fracture methodologies are used to estimate the residual useful life of the components.
This paper describes the life extension methodology used for an axial compressor disc of turbo-shaft engine. The disc has completed its safe life in the aircraft. The studies are carried out to determine the residual life of the disc to extend the life. Two life completed disc are identified. Specimens are cut from the disc for tensile test and LCF tests. Probable mission cycles for the aircraft are collected and fatigue cycle data are prepared. Finite element based stress analysis is carried out using Ansys software with multi axial loads. Based on the stress analysis, disc bore and pin hole are identified as critical area. The computed stress–strain response is used to predict the fatigue crack initiation life using effective strain range parameters on the critical areas. Fatigue damage for different mission cycles are also calculated using critical plane approach. The plane where crack initiate is called critical plane and it is calculated iteratively based on the nodal stress result. Life for different mission cycle is calculated and minimum life of all the cycle is determined. This calculated life gives the amount of residual life available and the scope for life extension. The disc is tested in cyclic spin test rig to confirm the remaining potential life. The test results are 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.