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Plastic deformation and residual stress of surface roughness asperities in elastohydrodynamic contact with consideration of surface fatigue

Al-Mayali, Maasi 2017. Plastic deformation and residual stress of surface roughness asperities in elastohydrodynamic contact with consideration of surface fatigue. PhD Thesis, Cardiff University.
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Micropitting is a contact initiated fatigue failure on the scale of surface roughness features that occurs in lubricated concentrated contacts which are subject to combined sliding and rolling motion. It is a significant problem in hardened and ground gears which, due to the surface roughness, operate in a micro-elastohydrodynamic lubrication (micro-EHL) regime, causing cyclic loads as the roughness features interact. To gain a much clearer understanding of the failure mechanism that is associated with rough surface elastohydrodynamic lubrication (EHL), a full theoretical model of the lubrication of gear contacts under rough surface and micro-EHL conditions is presented in this thesis. In addition, the study offers some important insights in to the influence of residual stresses on the fatigue life of rough surfaces. This significant residual stress, resulting from plastic deformation of rough surface asperities during the initial running-in process, has been instrumental in our understanding of the micropitting phenomenon. The Abaqus FEA package has been used to perform a full elastic-plastic contact analysis of real rough surfaces using profiles taken from the surfaces of unrun test disks, which are used in micropitting tests. The analysis provides a detailed view of the plastic deformation, and the magnitude and distribution of the residual stress fields at the asperity level. The residual geometry and stress field obtained over a range of applied loads are then used to introduce the residual stress in elastic fatigue calculations based on Micro-EHL simulations. Fatigue damage and fatigue life is then obtained at the scale of the surface roughness asperities by using multiaxial and variable amplitude fatigue models based on a critical plane approach. The results obtained allow the effects of the residual stress due to running-in to be quantified. The analysis method is also applied to test disk experiments to compare the predicted fatigue life with the observed onset of micropitting.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Micropitting; Contact Fatigue; Micro-EHL; Mixed lubrication; Surface roughness; Running-in.
Date of First Compliant Deposit: 14 August 2017
Last Modified: 20 Apr 2021 13:59

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