Fatigue crack growth simulation in a generator fan blade

Abstract

The blades of Iran Montazer-Ghaem-Unit4 power plant failed just 10 h after resuming operation following the last overhaul. The initial investigation showed that the design shortcoming was the main cause of the failure. A series of analytical, finite element and experimental analysis were utilized to determine the steady-state stresses and dynamic characteristic of the blade. It is concluded that the blade fracture was due to high cycle fatigue resulting from a bending mode of resonant vibration which probably caused by aero dynamical disturbances. Moreover the simulation of the blade with final crack conformed that the ductile fracture could be occurred under these stresses. Nevertheless, the vendor did not approve the fracture analysis report especially about the fatigue stresses. So the question rose whether the estimated stresses could impose fatigue crack propagation during 10 h or not. This manuscript attempted to simulate the crack propagation and fatigue life of the blades. The simulation has been done by numerical solution of exact model. Also, for initial rough estimation of fatigue life, a simplified analytic model has been used to calculate the stress intensity factors. In both model the displacements and stress intensity factors were computed on the crack near the leading edge to calculate crack propagation trajectories and crack growth rate. The modified Paris model and FNK model have been used to estimate the fatigue crack growth rate.