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Mixed elastohydrodynamic lubrication and fatigue calculation for rough surface contacts using a synthesised running-in model

Al-Asadi, Hassneen 2020. Mixed elastohydrodynamic lubrication and fatigue calculation for rough surface contacts using a synthesised running-in model. PhD Thesis, Cardiff University.
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This thesis presents a method to investigate the contact and deformation of rough surfaces such as those found on the teeth of gears. As-manufactured rough surfaces undergo a process known as “running-in”, in which the geometry of the surface is changed by interaction with the counterface when they are first loaded together. The process of surface roughness modification in machine elements when loads are applied was studied. This is a plastic deformation that modifies the roughness asperities to form the surface finish that characterises the components during their useful life. Protection of heavily loaded machine element surfaces is provided by mixed elastohydrodynamic lubrication (EHL) which depends critically on the component surface roughness. A procedure was developed to synthesise the running-in process based on real as- manufactured profiles. Surface roughness profiles obtained from transverse ground test disks were used to simulate asperity modification during running-in under load. This simulation is based on a detailed analysis of the way in which the surface roughness asperity tips change shape during running-in. Information on these changes was extracted by measuring surface roughness profiles before and after running-in and quantifying the statistical changes seen in the asperity tip radii of curvature. The surfaces were run against each other in mixed EHL analyses and the radius of curvature of asperity peaks subjected to extreme loading was increased in a controlled fashion to synthesise plastic deformation. The process was developed by comparison with the corresponding run-in profiles and with observed changes in asperity peak radii of curvature. Simulations were conducted for a range of different surface roughness pairs with various operating conditions. The synthesised and measured run-in surfaces were compared in various ways. Their geometry was examined in terms of form and asperity peak radii of curvature. Rolling / sliding EHL contact analyses were performed and their behaviour in terms of peak asperity pressure and direct asperity contact was assessed. The transient mixed EHL analysis results were used to apply surface loading to the rough profiles to obtain stress histories, which were the basis of the fatigue modelling then carried out. Finally, experimental work was implemented to detect the micropits developing on the rough iv surfaces using surface measurements taken during endurance tests, and a good agreement was found when compared with numerical fatigue model.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: synthesised running-in; mixed EHL; Plastic deformation; asperity radii of curvature; detect the micropits; numerical fatigue model.
Date of First Compliant Deposit: 17 March 2020
Last Modified: 13 Mar 2021 02:25

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