Failure Analysis of a Bend Pulley Shaft of a Triple Conveyor: A Case of Premature Rotating Bending Fatigue

This article illustrates the failure analysis of the bend pulley shaft, which prematurely failed after a service life of 4 months compared to an expected service life of 10 years. Failure analysis comprised the collection of background information, on-site observations, visual observations, fractography using scanning electron microscopy, chemical analysis, macro-etching, microstructural investigation using optical microscopy and SEM coupled with hardness, tensile tests, and Charpy impact toughness measurement. The clearly visible beach marks on the fracture surface confirmed the nature of the failure to be fatigue. Fractography revealed the presence of striations, which are microscopic signatures of fatigue failure. Despite acceptable strength and elongation, the failed shaft showed lower impact toughness than the desired value. Microstructural analysis revealed an as-cast structure, indicating an improper forging ratio to break the as-cast structure. Further, severe non-metallic inclusions were observed, which are known to reduce the fatigue life of rotating components. Recommendations are provided to improve the metallurgical aspects of the shaft to prevent the recurrence of similar failures in the future.