Fatigue Failure of the Input Shaft Used in Gearbox

This research focuses on performing a root cause analysis of the untimely shaft failure in a gearbox utilized at a steel mill industry. The shaft failure occurred unexpectedly after approximately one year of service, which is significantly shorter than the anticipated working life of 4–5 years. To understand the reasons behind the early failure, the investigation encompassed a range of activities, including field examinations, interviews with production engineers and operators, as well as metallurgical examinations. From the results, it was determined that the shaft failure resulted from a fatigue fracture, which was evident from the presence of beach marks and striations on the fracture surface. In conclusion, the investigation confirms that the shaft failure resulted from a fatigue fracture, and the early failure was cause of significant stress concentration at the keyway corner and the step diameter. These conditions ultimately led to the initiation of fatigue cracks around the heat-affected zone of the weld, their propagation from the welded area, and ultimately the final fracture. When modifying existing machines by replacing critical components, a thorough analysis of possible consequences must be performed. This process should be approached with great care to ensure careful consideration of the potential outcomes.