Toward fail-safe and optimized lightweight gears: Experimental analysis of fatigue performance and crack propagation

The structural integrity of gears is crucial for their performance and longevity, particularly in applications where safety is crucial, as in aeronautical applications. In particular, thin-rim gears may face catastrophic or safe failure according to the crack propagation direction. Experimental data about this topic are very rare in the literature. This study investigates the effects of gear geometry, specifically the backup ratio, on crack propagation behavior and fatigue limit by means of experimental fatigue tests performed using an original setup of single-tooth bending test. Results confirmed that gears with lower backup ratios exhibit higher stress concentrations and an increased likelihood of catastrophic failure. Comparisons with existing literature suggest that for intermediate backup ratios, crack propagation direction is influenced by both geometry and operational factors such as centrifugal loads. The findings provide essential insights into gear design optimization, emphasizing the importance of backup ratio selection in ensuring safe and predictable failure modes.