Micro-pitting failure of gear tooth surfaces – the influence of running-in and residual stress
This project concerns micropitting, a serious form of erosive wear affecting high duty hardened gears.
This project is advertised as part of the EPSRC Doctoral Training Partnership. It is currently not available to self-funded applicants. Find out more information about the DTP including how to apply.
It is associated with roughness effects and surface fatigue and is a particular problem in wind turbine gearboxes. Damage begins in the form of small surface pits 10–30 m in diameter and rapidly progresses ultimately leading to tooth failure. Heavily loaded gears operate under “mixed lubrication”, where surfaces are separated by a hydrodynamic film of lubricant, but the most aggressive surface roughness features (asperities) penetrate the lubricant film to make direct metallic contact. This leads to high cyclic contact stresses, resulting in contact fatigue failure of the surface asperities.
Recent work at Cardiff has identified that there is a link between initial running-in of the surfaces and subsequent micropitting failure. It is our hypothesis that this is due to residual stresses caused when prominent asperities undergo plastic deformation during initial running in. These asperities are therefore more susceptible to fatigue failure (micropitting).
This project will thoroughly investigate the link between running-in and micropitting. A thorough experimental programme will be conducted where representative surfaces will be run-in using a power-recirculating disc machine, under typical loads and sliding speeds. These surfaces will then be used in contact fatigue tests until they micropit. In-situ profilometry will be used to track surface roughness features to assess their level of initial plastic deformation and subsequent pitting failure. Using the surface roughness profiles, finite element models will be constructed to evaluate the residual stress fields developed during the running-in process. These results, plus mixed-elastohydrodynamic lubrication simulations to predict cyclic contact stresses, will enable prediction of fatigue life of the surface roughness features.
Using the combination of careful experimental work with the state-of-the-art lubrication simulation software, this project aims to develop detailed insight into the observed links between running-in and micropitting.