Doctor of Philosophy (PhD)


Mechanical Engineering

Document Type



This dissertation is comprised of two major interrelated foci. The first focus is to investigate the effect of surface roughness on the behavior of dry contacting bodies through both deterministic and statistical approaches. In the current research, different statistical micro-contact models are employed together with the bulk deformation of the bounding solids to predict the characteristics of the dry rough line-contact and elliptical point-contact including the apparent pressure profile, contact dimensions and real area of contact. Further, based on the results of numerical simulations, useful relationships are provided for the contact characteristics. In addition, a robust approach for the deterministic prediction of pressure and tangential traction distributions in dry rough contact configuration subjected to stick-slip condition is presented with provision for elastic-fully plastic asperity effects. The second focus of this research involves the assessment of three of the most common types of degradation processes that are observed in contact mechanics. The first contact failure mechanism studied is the rolling/sliding contact fatigue wear. In this research, the principles of continuum damage mechanics (CDM) are applied to predict the rolling/sliding contact fatigue crack initiation, and the effect of variable loading on the fatigue behavior of rolling contact with provision for non-linear damage evolution is investigated. The estimated numbers of cycles to crack initiation are compared to the available experimental results revealing good agreement. The second contact degradation phenomenon involves the study of the adhesive wear for unlubricated and lubricated contacts. A method is presented that applies the principles of CDM to predict the Archard adhesive wear coefficient for unlubricated contacts. By carrying out pin-on-disk experiments, wear coefficients for a specific material are obtained and compared with the predicted values showing good agreement. Further, the load sharing concept is applied to develop an engineering model for lubricated wear with the consideration of the thermal effects. The third type of degradation studied is the so-called fretting fatigue which is a failure phenomenon observed in contacting bodies subjected to very small amplitude oscillatory motion. Using the deterministic model developed for stick-slip contact condition, the effect of surface roughness on the crack initiation risk in a fretting contact is investigated and compared with experimental observations. In order to investigate the last two degradation phenomena, the results obtained from the first objective are directly utilized.



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Committee Chair

Khonsari, Michael M.