Failure analysis of a horizontal hinge pin from an army cargo helicopter

A horizontal hinge pin (HHP) assembly from an army cargo helicopter was examined to determine the root cause of ring and roller spalling and fracture. Chemical analyses, metallography and hardness testing indicated that the rings and rollers conformed to the material requirements of the governing drawing. Metallography and visual and scanning electron microscopy indicated the failure likely initiated in the lag ring due to rolling contact fatigue (RCF) because of high service loads. Evidence of subsurface crack initiation was observed.