A holistic analysis of the size effect on the bending fatigue limit of gears with module below 5 mm

This study presents a comprehensive analysis of the size effect on the bending fatigue strength of gears with a normal module below 5 mm, focusing on both case-carburized and nitrided variants. While the size effect in case-carburized gears has been extensively investigated and quantified through empirical studies, the corresponding data for nitrided gears remain limited. By aggregating and evaluating experimental results from various sources, this work identifies trends in size-dependent fatigue performance and compares them to general mechanical size effect models. The findings reveal that current standards, such as ISO 6336, underestimate the fatigue strength of small-sized gears. The study highlights the need for a distinct and reliable size factor also for nitrided gears to fully exploit their load-carrying potential in modern engineering applications.