Determination of rough surface contact stiffness coefficient

Yıldırım, Emine Gülşah
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. 


Prediction of damage in R/C shear panels subjected to reversed cyclic loading
Hindi, R; Mansour, M; Dicleli, Murat (Informa UK Limited, 2005-01-01)
In this paper, the damage prediction of shear-dominated reinforced concrete (RC) elements subjected to reversed cyclic shear is presented using an existing damage model. The damage model is primarily based on the monotonic energy dissipating capacity of structural elements before and after the application of reversed cyclic loading. Therefore, it could be universally applicable to different types of structural members, including shear-dominated RC members. The applicability of the damage model to shear-domi...
Comparison of damage mechanisms in curved composite laminates under static and fatigue loading
Tasdemir, B.; Çöker, Demirkan (Elsevier BV, 2019-04-01)
In this paper, damage progression in curved CFRP composite laminates are experimentally investigated for static and fatigue loadings. Two different cross-ply laminate thicknesses are examined with grouped plies to elucidate the failure mechanisms. A test fixture is designed to apply moment/axial combined loading to curved specimens and DIC method is used to obtain the strain distribution in the curved region until failure. Our major finding is that under fatigue loading, the failure location and mechanism a...
Modeling and simulation of coefficient of friction on gear teeth contacts
Okşayan, Yeliz; Akkök, Metin; Department of Mechanical Engineering (2014)
Friction is defined as the resistance to motion between two dry or lubricated contacted surfaces. The contact load, contact geometry, surface speeds, surface roughness parameters and oil properties affect the lubrication condition or regime. The purpose of this thesis is to develop a mixed EHL (Elastohydrodynamic Lubrication) model that is capable of calculating the variation of friction coefficient between gear teeth contacts. Gear systems operate commonly in mixed EHL regime where the elastic deformations...
Determination of critical submergence depth at horizontal intakes under asymmetric flow conditions
Göğüş, Mustafa; Köken, Mete; Haspolat, Emre (2015-07-03)
The purpose of the present study is to investigate the hydraulic conditions of air-entraining vortices under asymmetrical flow conditions and derive a general expression to determine the critical submergence depth required for the formation of these vortices at horizontal intake pipes. A series of experiments were conducted in a model composed of a concrete reservoir and intake pipe which was mounted horizontally to the reservoir. Three pipes of different diameters were tested with adjustable plexiglass sid...
Characterization of Ag/TlInSe2/Ag structure
QASRAWI, ATEF FAYEZ HASAN; Hasanlı, Nızamı (Wiley, 2011-07-01)
In this work, the current voltage characteristics of Ag/TlInSe2/Ag and In/TlInSe2/In structures, the incident light intensity and time dependencies of photocurrent as well as the response time-illumination intensity dependence of Ag/TlInSe2/Ag structures have been studied. For bias voltages larger than 1200. and 4.0 V, the current injection was found to be space charge limited and was assigned to the existing of deep and shallow hole traps being located at 210 and 16 meV for Ag and In-contacted samples, res...
Citation Formats
E. G. Yıldırım, “Determination of rough surface contact stiffness coefficient,” M.S. - Master of Science, Middle East Technical University, 2017.