Failure Analysis of a Ti-6Al-4V Rotating Main Rotor Component from an Army Helicopter

摘要

This paper discusses the failure analysis of a Ti-6Al-4V rotating main rotor component and contrasts the perspectives of the design/mechanical engineer and the manufacturing/materials engineer. Cracking initiated at mechanical marks located on the surface of the outer diameter of a planetary post at the transition radius and was propagated by high-cycle fatigue in service. These crack initiation defects were most likely produced by a machining or a surface finishing tool. Fractographic evidence suggests that high stresses were also encountered in service and played a significant role in the premature cracking of these components. The debate centers on whether the components would have failed in the absence of the surface defects. There were several manufacturers of this component, which are compared in this study. The workmanship on the outer diameter of the planetary post at the transition radius of a carrier that had not failed, manufactured by Company B, was superior to that of the two cracked carriers produced by Company A. However, analysis of the service conditions indicates that the components may have been loaded near the yield strength of the material.