Determination of rough surface contact stiffness coefficient

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Makina Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2017

Öğrenci: EMİNE GÜLŞAH YILDIRIM

Danışman: METİN AKKÖK

Özet:

In this thesis, the resistance against deformation under the effect of loading, which is simply called as stiffness, is investigated for the contacting bodies. The contact stiffness at mixed lubrication regime is tried to be found for line contact. Because of the mixed lubrication regime, the overall contact stiffness is investigated in two major parts as asperity stiffness and oil film stiffness which are considered to be connected in parallel in a spring model. Also, overall stiffness is calculated by regarding the contribution ratios of the asperity and oil stiffness. In this study, Greenwood and Williamson (GW) approach is taken as baseline to determine the contacting pressure. Despite GW model is based on symmetric surface roughness distribution using Gaussian function, the approach of the GW is converted to Weibull distribution to take into consideration asymmetric surface roughness where the skewness range is more convenient -1 < Sk < 1. Hence the loading and deformation can be defined for both symmetric and asymmetric height distributions. Thus, the contact stiffness is calculated for mixed lubrication regime. After analysis, it is found that contact stiffness is inversely proportional to speed and proportional to loading. Moreover, it is found that the non – dimensional total contact stiffness is almost independent of non – dimensional speed for small values of skewness. However, in the transition region as the skewness increases, a decrease in contact stiffness is observed. Besides, the film thickness between the contacting bodies is constant for different skewness values in the boundary lubrication regime and increases with speed in the mixed and hydrodynamic lubrication regime. The film thickness decreases as the skewness increases from negative values to positive values.