Metallurgical Investigation of a fractured low-pressure turbine rotor (LPTR) cover plate of an aeroengine

Abstract

A twin-engine fighter aircraft met with an accident immediately after take-off and had fallen into sea. Investigation showed that the primary cause of the accident was the fracture in the low-pressure turbine rotor (LPTR) cover plate of right hand (RH) engine. Fractography study confirmed that fractures in the cover plate have originated from incipient fatigue cracks that were developed at the pin-holes meant for assembly with the turbine disc. Investigation revealed that there was deficiency in joint preparation during refitment of the cover plate onto the disc after a fault repair servicing. As a result, there was fatigue crack initiation in multiple pin-holes and the fracture in the cover plate had occurred at these pre-existing fatigue crack locations. The situation was further aggravated because of use of pins possessing hardness substantially higher than that of the cover plate. Further, study of pin-holes on the cover plate of left hand (LH) engine showed that in general, the LPTR cover plate was susceptible to fatigue failure within the prescribed service life itself. In this article, a detailed analysis of the failure that led to the aircraft accident is presented.