image: Researchers assessed recent studies on gear contact fatigue — when the gears that keep engines, helicopters, wind turbines and more in operation fail — to better understand the mechanisms that lead to such failure.
Credit: Friction, Tsinghua University Press
The primary failure in mechanical elements is gear contact fatigue — but it’s not clear how exactly these failures occur, according to an international team of researchers. They recently reviewed the latest developments in the field to frame out what’s known and the remaining questions for further work. In addition, they conducted their own gear fatigue assessments with multiple materials and production methods, from which they have proposed formulas for others to use in their evaluations.
They published their findings on Jan. 13 in Friction.
“The rapid evolution of advanced equipment that utilizes gears, including aviation engines, helicopters and wind turbines, imposes escalating demands for enhanced reliability, prolonged lifespan, increased power density and sustained durability of gears,” said corresponding author Huaiju Liu, associate professor, State Key Laboratory of Mechanical Transmission for Advanced Equipment, Chongqing University. “Gear contact fatigue issues, associated with materials, geometries and operating conditions, are crucial to modern gear design.”
To date, Liu said, researchers have conducted an enormous amount of theoretical and experimental studies to understand gear contact fatigue mechanisms. The current study focuses on compiling and categorizing key investigations within the field. In this paper, Liu and the team reviewed 187 studies and technical reports, as well as assessed major datasets from the American Society of Mechanical Engineers, NASA and more. The team also conducted their own experimental assessments on multiple materials with various manufacturing processes to obtain additional empirical evidence.
In one case study, the team evaluated 18CrNiMo7-6 gears — which are made of an alloy steel designed to perform well in highly demanding environments, like in airplanes, wind turbines, transmissions and more — across 10 different manufacturing combinations. They found that a composite manufacturing process using various metalworking approaches, including pre-shot peening, double shot peening and fine particle peening, improved the contact fatigue limit by 23.63% compared to the benchmark grinding state. That means that the gears made via this composite process can withstand higher loads for longer durations, the team said.
According to the researchers, these manufacturing processes focus on strengthening the surface of the gears — the most direct way to improve the fatigue limit. However, they cautioned, there are several overlapping factors that influence gear contact fatigue, many of which still are not clear.
“The gear contact fatigue failure mechanism is complicated because it is affected by various factors, including structural factors such as gear geometry and surface morphology; working conditions such as torque and speed; and material factors such as yield strength and residual stress,” Liu said. “Although some important factors have been identified, further studies are still being conducted to understand more influential factors and their interactions.”
The team also detailed specific direction for additional work needed in the field.
“Most fatigue models have focused only on single or limited factors while neglecting the intricate interactions among surface integrity parameters,” Liu said. “As a result, there is a pressing need to establish multifactor and multiscale models for gear contact fatigue that can be extensively validated through experiments and engineering practices.”
The researchers also pointed to the need for studies focused on how operating behavior and failure mechanisms pose significant challenges to achieving high-reliability and long-life gear design, as well as developing physical-data hybrid models that combine computational modeling with real-world observational data.
Other authors include Xiuhua Zhang and Caichao Zhu, State Key Laboratory of Mechanical Transmission for Advanced Equipment, Chongqing University; and Michael Geitner, Thomas Tobie and Karsten Stahl, School of Engineering and Design, Gear Research Center, Technical University of Munich.
The National Natural Science Foundation of China supported this work.
DOI Link:
https://doi.org/10.26599/FRICT.2025.9441078
Journal
Friction
Article Title
Gear contact fatigue: Models and tests
Article Publication Date
13-Jan-2026