Investigation on bending fatigue failure of a micro-gear through finite element analysis

A study on the root causes of bending fatigue failure of a micro straight bevel gear belonging to a lubricating pump was carried out. A series of examinations were performed to identify the possible causes of the failures including macroscopical inspection, geometrical examination, fractography investigation and other necessary metallurgical examinations. Further fault tree analysis was performed to find out all the potentially causes and to make our mind clear. Then some mechanics analyses through finite element method were carried out to give more comprehensive analysis. The influence rules of tooth back thickness and of tooth root fillet radius on stress concentration were obtained, and resonance possibility was denied. Besides some useful information were obtained through test signal analysis. Failure mechanism was concluded according to investigation results, the failure was attributed to the machining errors, which led to overlarge stress concentration at tooth root fillet and decrease the lifespan. Besides, serious fray occurred on the teeth remained as a secondary failure because of the bad engaging status. Finally some adjustments were recommended to improve the reliability.