Failure Analysis of Off-Highway Hypoid Gear Due to Non-metallic Inclusion

The present work investigates the failure of a rear axle hypoid gear that failed during fatigue life testing before meeting the criteria. The failure being in contrary to the historical field failure where the mating pinion gear fails as the primary member became critical and hence detailed failure analysis was carried out. Failure analysis involving fractography, magnetic particle inspection, microstructural analysis, hardness tests, scanning electron microscopy, electron discharge spectroscopy was carried out. Meticulous failure analysis revealed that the hypoid gear failed due to the presence of non-metallic inclusion. SEM and EDX analysis further supported the analysis showing aluminum, calcium, magnesium along with oxygen as major constituents. The work also provided recommendations in the form of process modifications at the steel plant to avoid such kind of failures.