Knowledge Bank

Gear teeth in mesh undergo cyclic forces as the teeth rotate in and out of contact. The resultant contact and bending stresses produce fatigue damage, which can lead to failure through contact surface degradation and tooth breakage through the root fillet. The fatigue process occurs in two distinct phases, crack initiation and propagation. Many proposed diagnostic techniques to detect onset of gear failure rely on changes in mechanical properties due to crack growth. Moreover, theoretical studies to predict fatigue crack growth rate rely on only a few experimental measurements for their validation with little extension to gears. The focus of this study is to develop an optically based system for measuring the crack growth rate in the tooth root of a spur gear at the onset of crack propagation. A gear single-tooth bending machine coupled with a high-speed camera is utilized to demonstrate this new methodology. A digital image correlation technique is developed to compute crack length during each load cycle, in order to obtain a cyclic crack growth rate.