Failure Investigation of Components of Aero Engine No. HDR-80376U

The main bevel gear (pinion) is low alloy steel and has tempered martensitic microstcture. The case hardening was proper as was observed through microsturctural analysis and microhardness profile. The microhardness varied from 750 VHN at the case to 450 VHN at the core when measured along the thickness of the tooth. Therefore no material abnormality and flaws have been found in the bevel pinion to be a causative factor for the failure. However, fract-ographic examinations under SEM revealed dominant fatigue crack, which might have been initiated due to tooth bend-ing fatigue and this, might have caused the failure of the tooth. The main quill shaft has failed due to torsion overloading