Abstract
This paper presents a failure analysis of a helical gear used in gearbox of a bus, which is made from AISI 8620 steel. The helical gear had been in service about three years when several teeth failed. The failed helical gear had a number of adjacent teeth and random teeth breakage at one end of teeth. An evaluation of the failed helical gear was undertaken to assess its integrity that included a visual examination, photo documentation, chemical analysis, micro-hardness measurement, and metallographic examination. The failure zones were examined with the help of a scanning electron microscope equipped with EDX facility. Results indicate that teeth of the helical gear failed by fatigue with a fatigue crack initiation from destructive pitting and spalling region at one end of tooth in the vicinity of the pitch line because of misalignment.
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