Analysis of the fracture of a turbine blade on a turbojet engine

The fracture on a turbine blade of a turbojet engine has been investigated to see the cause of crack initiation. The fractured turbine blade did not seem to have suffered any damages by foreign objects. The turbine blade had initially cracked by a fatigue mechanism over a period of time and then fractured by the overload at the last moment.The crack initiated at the subsurface or close to the surface and showed the cleavage-like features. The segregated area of Ti and Mo, caused usually by improper manufacturing process, is found by the microstructure and EDX analysis of the blade. The crack initiated at this area and was due to the stress concentration at the segregation of Ti and Mo near the blade surface.