The objective of this PhD thesis was the study of friction in carbon nanotubes by analytical methods and molecular dynamics simulations. The goal of this research was to characterize the properties of friction in nanotubes and from a more general point of view the understanding of the microscopic origin of friction. Indeed, the relative simplicity of the system allows us to interpret more easily the physical phenomenon observed than in larger systems. In order to achieve this goal, non-equilibrium statistical mechanics permitted first to develop models based on Langevin equations describing the dynamics of rotation and translation in double walled nanotubes. The molecular dynamics simulations then permitted to validate these analytical models, and thus to study general properties of friction such as the dependence on area of contact, temperature and the geometry of the nanotubes. The results obtained shows that the friction increases linearly with the sliding velocity or the angular velocity until very high values beyond that non-linearities appear enhancing dissipation. In the linear regime, it is shown that the proportionality factor between the dynamic friction force and the velocity is given by the time integral of the autocorrelation function of the restoring force for the sliding friction and of the torque for the rotational friction. Furthermore, a novel resonant friction phenomenon increasing significantly dissipation was observed for the sliding motion in certain types of nanotubes. The effect arises at sliding velocities corresponding to certain vibrational modes of the nanotubes. When the dynamics is described by the linear friction in velocity, the empirical law stating that friction is proportional to the area of contact is very well verified thanks to the molecular dynamics simulations. On the other hand, friction increases with temperature. The fact that friction increases as well with the area of contact as the temperature can be easily interpreted. Indeed, if the temperature is large enough so that the electronic effects can be negligible, dissipation is only due to the phonons. Indeed, it is the phonons who give the sliding or rotation energy to the other degrees of freedom until thermodynamic equilibrium is achieved. Thus, if the temperature increases, the coupling between the phonons and the rotational or translational motions increases, as well as friction. In the same manner, when the area of contact increases, the number of available phonons to transport energy increases, explaining thus the increase of the friction force.

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The lubrication of dry viscose fibres by a two component finish, and the lubrication of wet Iyocell fabric against metal, with various aqueous lubricant systems, has been studied. Secondary ion mass spectrometry (SIMS) was investigated as a means of providing direct chemical information from finished fibre surfaces. The composition and distribution of a two component finish applied to viscose fibres was determined successfully. When applying finish from a bath, the surface composition of the finished fibres was not controlled by the bath conditions. Increasing the concentration of finish in the bath did, however, increase the total amount of finish deposited, and increasing the concentration of antistat relative to lubricant in the bath increased the amount of antistat relative to lubricant deposited on the finished fibres. Fibre friction was determined using the capstan method. The friction forces, measured for finished viscose fibres, were correlated with the finish application conditions. Increasing the emulsion concentration in the finish bath reduced fibre/metal friction, but finish component ratio, emulsion concentration, dip time and bath temperature did not affect fibre/fibre friction. Spray applying the finish resulted in unfinished regions on the fibre surfaces and the electrical resistance of fibre bundles was not reduced. Bath application of finish did lower electrical resistance in comparison with unfinished fibre, but none of the bath deposition variables had a significant effect on electrical resistance.

Friction Stir Processing (FSP) is currently being considered for use in manufacture of the Navy's NiAl bronze propellers. Incorporating this technology may improve service performance and enable reduction of manufacturing time and cost. This program of research has employed miniature tensile sample designs to examine the distributions of longitudinal properties through the various regimes in a fusion weld. Also, the distributions of both longitudinal and transverse properties throughout the stir zones for selected FSP conditions were examined. Yield strengths were larger in various FSP conditions by at least a factor of two relative to fusion welds. Ultimate strengths were comparable in the weld pool and stir nugget. WidmanstaÌ tten microstructures and microvoid formation and coalescence in the fracture surface resulted in high ductilities in weld metal and the stir nugget. The thermomechanically affected zone of FSP and the heat affected zone of a fusion weld both exhibit low ductility. This may reflect formation of "a" upon heating to temperatures of 800-850 [degrees]C, followed by rapid cooling and transformation of the "a" to form martensitic transformation products in their respective microstructures. For a single-pass raster pattern, transverse ductility is lower than longitudinal ductility. For a multi-pass raster, transverse ductility is higher than longitudinal ductility. For multi-pass raster and spiral patterns in FSP, the data show that the mechanical properties are more nearly isotropic. / US Navy (USN) author.

This investigation is designed to find the net rate of decrease in the component of velocity parallel to the original direction of motion of a proton moving through an electron gas exhibiting a non-spherical velocity distribution.

Friction, binding and notching are the factors that contribute to resistance to sliding during orthodontic tooth movement. However, most attempts at reducing resistance aim only to reduce the archwire/ligature friction. In this study, a novel bracket with a unique design aimed to reduce all three components of resistance to sliding. Four types of brackets (passive and active self-ligating, traditionally ligated and the novel bracket, (n=5, each) were tested at 0, 2, 4, 6, and 8ᵒ of tip on a 0.019 x 0.025”archwire. The resistance to sliding values were recorded. At 0ᵒ, the passive self-ligating and novel bracket showed reduced resistance when compared to the traditionally ligated bracket (P< 0.05). At the other angles of tip, no differences were observed among the brackets. These data suggest that the novel bracket could potentially decrease the resistance to sliding during orthodontic treatment and further studies are indicated to test the improved bracket design.

Lubricants are used in numerous applications to control friction and protect moving parts from fatigue. These fluids consist of a variety of surface active chemistries competing for the surface to provide performance. In order to develop fluids that meet the ever-increasing requirements (from legislation and manufacturers), techniques that can provide insight into surface adsorption, in real time, and relate it back to performance are critical. The objective of this work is to determine if Quartz Crystal Microbalance with Dissipation (QCM-D) is an effective technique to investigate surfactant adsorption in regimes that are common to the transportation lubricant industry. QCM-D is employed to quantify the mass, characterize the morphology, and quantify the kinetics of adsorption of common friction modifiers. The adsorption information is then compared to macroscopic properties (friction and corrosion prevention) to determine if this technique can aid in formulating future lubricants.