New nanomaterials and nanoparticles are currently under investigation as lubricants or lubricant additives due to their unusual properties compared to traditional materials. One of the objectives of this work is to investigate the tribological properties of these materials in relation to surface topography. Chemical etching and metal evaporation methods were employed to prepare surfaces with various topographies. Surfaces were sheared with the use of a nanotribometer and characterized with an atomic force and scanning electron microscopes. For a system consisting of ZnS nanowires dispersed in dodecane sheared across ductile surfaces, it was found that the geometry of the nanowire relative to the surface topography plays a significant role. Moreover, for brittle surfaces, it was found that beyond a certain roughness the frictional properties remain unchanged. In addition, this work is also intended to explore novel lubricants with nanoparticle additives in efforts to control friction and wear. A system consisting of silica nanoparticles dispersed in ionic liquids was examined at various concentrations. It was found that an optimum concentration of nanoparticles exists and yields the best tribological properties. Such work represents an important step in understanding the tribological properties of nanoparticle lubricant additives in general; one that may ultimately provide the guidelines necessary for designing novel, low-friction, and wear-controlling nanoparticle-based lubrication systems that minimize energy and material losses due to friction.

From previous research, it has been proven that rock roughness and closure are two important factors for stability of backfilled stope and exposed backfill. In order to estimate the important parameters of roughness, several investigations have been conducted in other scientific fields to study roughness. The results showed that the important roughness parameters are application-dependent. In geology and rock mechanics the Joint Roughness Coefficient (JRC) is a critical factor that incorporates the roughness in stability problems. Although JRC is widely used, it is very subjective and highly depends on the experience of the individual conducting the analysis. During the last several decades there were attempts to use different methods such as fractal geometry, Fourier analysis, analytical methods, etc. to convert a random surface profile into a JRC. The goal of the current research is to estimate with greater accuracy the contribution of roughness to the shear strength of the interface at the paste-rock contact when backfilling. Four hundred and fifty backfill samples were constructed and tested in a shear box. The variables of the tests are three: binder percentage, roughness and cure time. From the test results the importance of each of those parameters to the final shear strength of the paste-rock interface was estimated. The normal stress that acts on the samples is also a critical factor. From the tests that were tried, it was concluded that there are limits in normal stress for which roughness is important. / Thesis (Master, Mining Engineering) -- Queen's University, 2009-08-27 16:07:21.916

The present thesis investigates the friction properties of total knee replacement components using lubricating fluids of different composition and rheology. The first stage of the thesis involves characterization of the rheological properties of hyaluronic acid (HA)/bovine calf serum (BCS) solutions. With increased concentration and molecular weight of HA, higher viscosities and more pronounced shear thinning in steady shear flow was observed. In dynamic oscillatory flow, the elastic character of the solutions became more pronounced and the cross-over frequency decreased upon increasing concentration and molecular weight of HA. The second part of the thesis involves the determination of a method by which the coefficient of friction is estimated using a linear reciprocating wear testing machine with spherical metal indenters articulating on flat UHMWPE samples and deionised (D.I.) water lubrication. A characteristic periodic pattern in the friction behaviour was observed and the coefficient of friction was computed by calculating the average of 30 points about the midpoint between reversals and using the average of three cycles. The third part of the thesis involves the investigation of the effect of fluid composition on the coefficient of friction in knee replacement components. With increased concentration of HA in solution (0-1mg/mL), the coefficient of friction of HA/BCS solutions decreased. However, with HA/BCS solutions of higher HA concentrations (above 1mg/mL), no significant difference in the coefficient of friction was observed. Similar behavior was observed with HA/Albumin solutions. With HA/ D.I. water solutions, the coefficient of friction was almost identical irrespective of the concentration of HA in solution. Significant difference in the rheological properties of HA/D.I. water solutions did not affect the coefficient of friction. The Stribeck analysis revealed that the coefficient of friction with HA/BCS and HA/D.I. water lubrication was not governed by hydrodynamic conditions. The fourth part of this thesis involved characterization of lubricating fluids before and after friction testing. Absorbance and dynamic light scattering measurements of HA/BCS solutions and of HA/Albumin solutions indicate a rise in turbidity and the presence of larger size particles in these solutions after friction testing. The ninhydrin test confirmed the presence of protein in the precipitates obtained following testing. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-09-24 14:06:41.437

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Friction stir processing (FSP) has recently become an effective microstructural modifications technique. Reported results showed that for different alloys, FSP produces very fine equiaxed and homogeneous grain structure. FSP is considered to be a new processing technique and more experimental and analytical investigations are needed to advance the industrial utilization of FSP. Most of the work that has been done in the friction stir processing field is experimental and limited modeling activities have been conducted. Attempts to develop a predictive model to correlate the resulting microstructure with process parameters are scarce. In this work, commercial 5052 Aluminum alloy sheets are friction stir processed at different rotational and translational speeds. The effects of process parameters on the resulting microstructure and mechanical properties are investigated. The results show that FSP produces very fine and homogenous grain structure, and it is observed that smaller grain size structure is obtained at lower rotational speeds. It is also observed that the hardness of the processed sheet depends strongly on the rotational and translational speeds and varies widely within the processed region. The results suggest that the temperature achieved during processing plays an important role in determining the microstructure and properties of the processed sheet. In addition, a new modeling approach based on experiments and theory is proposed to predict the grain size of the friction stir processed material as a function of process parameters. The proposed approach involves determination of the strain rate distribution in the processed (deformation) zone based on the velocity fields of the material and correlating the strain rate distribution with the average grain size of the resulting microstructure using Zener-Holloman parameter.

This thesis addresses the open questions of providing a cosmological model describing an accelerated expanding Universe without violating the energy conditions or a model that contributes to the physical interpretation of the dark energy. The former case is analyzed considering a closed model based on a regular lattice of black holes using the Einstein equation in vacuum. In the latter case I will connect the dark energy to the Shan-Chen equation of state. A comparison between these two proposals is then discussed. As a complementary topic I will discuss the motion of test particles in a general relativistic spacetime undergoing friction effects. This is modeled following the formalism of Poynting-Robertson whose link with the Stokes’ formula is presented. The cases of geodesic and non-geodesic motion are compared and contrasted for Schwarzschild, Tolman, Pant-Sah and Friedman metrics respectively.