The present work made use of existing thermal stress (fast moving distributed Hertzian heat source) solutions available to extend the isothermal stress solution to take into account effects of the flash temperature rise and the corresponding thermo-elastic stress components. The highlight of this new analytical model was the development of a thermo-mechanical yield factor, γ-factor, whereby critical conditions for which inelastic behaviour occurs can be predicted and the likelihood of failure estimated. The results of this work showed that failure by formation of welds can occur. This presumes that the prerequisite conditions of the failure of the fluid film and boundary lubrication and sufficient asperity interactions occur so that the average friction is high enough to produce a bulk surface stress which is sufficient to exceed the yield limit. Thus, an engineering explanation of how macro sliding/rolling contacting components (as opposed to lubricating systems) fail is available for the first time. A mechanism of weld-formation was also proposed. Initial scuffing is seen to be caused by the inability of the surface patch to shrink back elastically when flash temperature effects disappear. Subsequently, on the next contact encounter, it will lead to stress concentration and cause local melting and shearing of the patch, resulting in metallic welds smearing onto the faster moving body and thereby became what is known as a 'scuffed mark'. Experimental work on roller-on-disc dry sliding wear tests confirmed that the level of metal-to-metal friction experienced by rubbing hardened steels, even for mild wear conditions was within the range of friction coefficients required by the present analytical model to cause bulk plastic flow of the concentrated sliding/rolling contacting surfaces.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:639050 |
| Date | January 1995 |
| Creators | Siu, S. W. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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