MICROPITTING FAILURE OF GEAR TOOTH SURFACES
Lead Research Organisation:
Cardiff University
Department Name: Sch of Engineering
Abstract
EPSRC Portfolio Area: Performance and inspection of mechanical systems and structures (Maintain)
Description:
Micropitting 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 10-30m 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.
Aim of Project:
The aim of the project will be to thoroughly investigate the link between running-in and micropitting. This will be achieved by developing a method of taking real, measured surface roughness geometry information from run-in surfaces, and comparing this with as-manufactured surface geometry to determine the level of plastic deformation occurring during run-in. Finite element techniques will be developed to assess the resulting level of residual stress. The student will learn to use the mixed-elastohydrodynamic lubrication solvers and will incorporate techniques for evaluation of cyclic stress as part of a fatigue assessment of the gear surfaces.
Furthermore, the student will develop strong experimental skills, via an experimental programme 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.
Novelty/Value of work:
The outcomes of this project could have significant impact on designers and users of power transmission gearing, particularly in the renewable energy and aerospace industries.
Description:
Micropitting 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 10-30m 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.
Aim of Project:
The aim of the project will be to thoroughly investigate the link between running-in and micropitting. This will be achieved by developing a method of taking real, measured surface roughness geometry information from run-in surfaces, and comparing this with as-manufactured surface geometry to determine the level of plastic deformation occurring during run-in. Finite element techniques will be developed to assess the resulting level of residual stress. The student will learn to use the mixed-elastohydrodynamic lubrication solvers and will incorporate techniques for evaluation of cyclic stress as part of a fatigue assessment of the gear surfaces.
Furthermore, the student will develop strong experimental skills, via an experimental programme 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.
Novelty/Value of work:
The outcomes of this project could have significant impact on designers and users of power transmission gearing, particularly in the renewable energy and aerospace industries.
Organisations
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509449/1 | 01/10/2016 | 30/09/2021 | |||
| 1942836 | Studentship | EP/N509449/1 | 01/10/2017 | 30/09/2021 | William Britton |
| Title | Micropit Detection Software |
| Description | A novel technique was developed for the detection of micropits in ground gear surfaces, and software was written using MATLAB to implement this. The method uses areal scan data from a surface (for example, collected by a profilometer with an automated stage), and uses cross-correlation to straighten the asperities on the surface. A high-pass filter is then applied along all asperities to retain only short wavelength features on the surface. The edges of micropits are then detected by their gradients, and the micropits are then filled in using pit filling processes based on height in the high-pass filtered and straightened surfaces. |
| Type Of Material | Improvements to research infrastructure |
| Year Produced | 2019 |
| Provided To Others? | No |
| Impact | Development of this methodology / software enabled semi-automated analysis of micropitted surfaces in my experimental work. By employing surface replicas to take casts of surfaces between test stages and then applying this method to scans of those replicas, I have been able to obtain data on micropitting across a whole area during testing while previous work was limited to less reliable two-dimensional profile measurements. Other automated methodologies in the literature are limited to restrictive assumptions regarding micropit depth or shape, which limits their usefulness. Other researchers are limited to manual evaluation of very small areas. This methodology enables more accurate detection of micropits in scans of larger areas of surface. |
| Title | Micropitting Full Factorial Data Set with Centrepoint |
| Description | In this work a full factorial experimental programme with centrepoint test has been completed for early stage micropitting with conditions of: Max Hertzian pressure: 1.2GPa - 1.6GPa; Entrainment velocity: 2m/s - 4m/s; Slide Roll Ratio: 0.25 - 0.5. A full library of two-dimensional profiles measured on the disk, and physical replicas made using Acrulite (PMMA - based replica material) was created for each loadstage of each test. These are at (in Fast surface cycles) 0, 3k, 6k, 20k, 50k, 100k, 200k, 300k, 400k, 600k, 1 million, 1.5 million, and 2 million cycles. areal profilometer scans were made for replicas at 6k, 50k, 100k, 200k, 400k, 1 million, and 2 million fast surface cycles, with additional scans of the disks made in the un-run condition and at the end of test. For each test a set of micropitted disks also results. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2021 |
| Provided To Others? | No |
| Impact | This full factorial data set enables analysis of both individual test data for running-in and early stage micropitting, but also a full appraisal of the influence of pressure, entrainment velocity, and slide roll ratio (and their interactions) on running in and micropitting. The inclusion of a centrepoint test also allows for a basic assessment of whether or not these influences are linear. The range of operating conditions were chosen to be representative of those encountered for highly-loaded ground gear surfaces. Additionally, the micropitted disk pairs resulting from the experiments provide opportunities for analysis of microstructures beneath pitted surfaces under a range of conditions. |
| Description | IMechE Mission of Tribology 2019 Poster Presentation |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Postgraduate students |
| Results and Impact | A poster was presented at the IMechE Mission of Tribology research conference - a conference aimed primarily at PhD researchers in the field of tribology.This presented an overview of my work, including experimental, data analysis, simulation and metallurgical investication. This led to lengthy discussions of my work with several postgraduate researchers and academics from other institutions. Some early stage postgraduate researchers informed me that this was helpful in informing their own research plans. |
| Year(s) Of Engagement Activity | 2019 |