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The running-in and incipient micropitting of ground gear surfaces under mixed lubrication condition

Britton, William 2021. The running-in and incipient micropitting of ground gear surfaces under mixed lubrication condition. PhD Thesis, Cardiff University.
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Abstract

This thesis investigates the running-in and early-stage micropitting of ground surfaces operating in mixed elastohydrodynamic lubrication regimes representative of gear contacts. Micropitting is a common mode of fatigue failure for gears, for example those used in wind power or in the drivetrains of ships, however the mechanisms of micropitting are poorly understood. This work aims to better understand the role of contact conditions on micropitting. The effects of contact pressure, slide-roll ratio, and entrainment velocity were evaluated via a full factorial experimental programme with the aim of meeting three objectives: 1. To investigate their influence on surface modification during running-in 2. To investigate their influence on micropitting 3. To compare fatigue simulation results across a range of conditions to real tests The experimental investigation showed pressure to be the strongest influencing factor on both running-in and micropitting, inducing greater surface modification during running-in and increasing the extent of micropitting. Increased entrainment velocity was shown to reduce surface modification during running-in and to oppose the initiation of micropitting, however its effect weakened later in the test -particularly for the slower surface. The slide-roll ratio was shown to have the strongest influence on micropitting initiation and retained a strong effect on the fast surface throughout the test. Both during running-in and micropitting, complex two- and three-factor interaction effects were observed. Simulations of fatigue using rough surface profiles were performed for each experiment. Results indicate that accurate predictions of material failed may be obtained if an appropriate depth is selected for analysis. A model was devised to predict this depth, however further testing is required to confirm its applicability. Test disks which exhibited non-uniform micropitting behaviour were investigated using Scanning Electron Microscopy. Plastic deformation regions and areas of microstructural change were observed in the near-surface of the test disks. This work made several novel contributions to the field, which will add to the understanding and prevention of fatigue in gears. These include: • Assessment of the influence of pressure, slide-roll ratio and entrainment velocity on running-in and micropitting, without interference from confounded higher-order effects • The application of a structured experimental approach for comprehensive analysis of running-in, fatigue, and simulation • Development of an algorithm to detect micropits in surface scans • SEM investigation of microstructure in a sample which underwent both wear and fatigue

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Tribology , Mixed Lubrication , Rolling Contact Fatigue , Gear Fatigue , Running-in , Micropitting
Date of First Compliant Deposit: 12 July 2022
Last Modified: 12 Jul 2022 10:29
URI: https://orca.cardiff.ac.uk/id/eprint/151241

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