Browsing by Subject "Lubrication"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Open Access Formulation of the Reynolds equation on a time-dependent lubrication surface(Royal Society of London, 2016) Temizer, I.; Stupkiewicz, S.The Reynolds equation, which describes the lubrication effect arising through the interaction of two physical surfaces that are separated by a thin fluid film, is formulated with respect to a continuously evolving third surface that is described by a time-dependent curvilinear coordinate system. The proposed formulation essentially addresses lubrication mechanics at interfaces undergoing large deformations and a priori satisfies all objectivity requirements, neither of which are features of the classical Reynolds equation. As such, this formulation may be particularly suitable for non-stationary elastohydrodynamic lubrication problems associated with soft interfaces. The ability of the formulation to capture finite-deformation effects and the influence of the choice of the third surface are illustrated through analytical examples. © 2016 The Author(s).Item Open Access Homogenization-based design of surface textures in hydrodynamic lubrication(John Wiley and Sons Ltd, 2016) Waseem, A.; Temizer, İ.; Kato, J.; Terada, K.An optimization framework is developed for surface texture design in hydrodynamic lubrication. The microscopic model of the lubrication interface is based on the Reynolds equation, and the macroscopic response is characterized through homogenization. The microscale setting assumes a unilateral periodic texture but implicitly accounts for the bilateral motion of the surfaces. The surface texture in a unit cell is described indirectly through the film thickness, which is allowed to vary between prescribed minimum and maximum values according to a morphology variable distribution that is obtained through the filtering of a design variable. The design and morphology variables are discretized using either element-wise constant values or through first-order elements. In addition to sharp textures, which are characterized by pillars and holes that induce sudden transitions between extreme film thickness values, the framework can also attain a variety of non-standard smoothly varying surface textures with a macroscopically isotropic or anisotropic response. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.Item Open Access Micro-texture design and optimization in hydrodynamic lubrication via two-scale analysis(Springer Verlag, 2017) Waseem, A.; Temizer, İ.; Kato, J.; Terada, K.A novel computational surface engineering framework is developed to design micro-textures which can optimize the macroscopic response of hydrodynamically lubricated interfaces. All macroscopic objectives are formulated and analyzed within a homogenization-based two-scale setting and the micro-texture design is achieved through topology optimization schemes. Two non-standard aspects of this multiscale optimization problem, namely the temporal and spatial variations in the homogenized response of the micro-texture, are individually addressed. Extensive numerical investigations demonstrate the ability of the framework to deliver optimal micro-texture designs as well as the influence of major problem parameters. © 2017, Springer-Verlag Berlin Heidelberg.Item Open Access Microscopic design and optimization of hydrodynamically lubricated dissipative interfaces(John Wiley & Sons, Ltd., 2019) Çakal, Berkay Alp; Temizer, İlker; Terada, K.; Kato, J.A homogenization‐based topology optimization framework is developed, which can endow hydrodynamically lubricated interfaces with a micro‐texture, to achieve optimal macroscopic responses by addressing both dissipative and nondissipative physics at the interface. With respect to the homogenization aspects of the problem, the thermodynamic consistency of the two‐scale formulation is explicitly analyzed and verified. With respect to the topology optimization aspects, a variational approach to sensitivity analysis is pursued. Subsequently, these are employed in micro‐texture design studies, which address microscopic and macroscopic objectives. The influence of dissipation on the optimization results is demonstrated through extensive numerical investigations, which also highlight the importance of working in a sufficiently flexible design space that can deliver nearly optimal micro‐texture geometries.Item Open Access Nanoscale tribology of graphene grown by chemical vapor deposition and transferred onto silicon oxide substrates(Cambridge University Press, 2016) Demirbaş, T.; Baykara, M. Z.We present a comprehensive nanoscale tribological characterization of single-layer graphene grown by chemical vapor deposition (CVD) and transferred onto silicon oxide (SiO2) substrates. Specifically, the nanotribological properties of graphene samples are studied via atomic force microscopy (AFM) under ambient conditions using calibrated probes, by measuring the evolution of friction force with increasing normal load. The effect of using different probes and post-transfer cleaning procedures on frictional behavior is evaluated. A new method of quantifying lubrication performance based on measured friction coefficient ratios of graphene and SiO2 is introduced. A comparison of lubrication properties with mechanically-exfoliated graphene is performed. Results indicate that CVD-grown graphene constitutes a very good solid lubricant on SiO2, reducing friction coefficients by ∼ 90% for all investigated samples. Finally, the effect of wrinkles associated with CVD-grown graphene on measured friction values is quantitatively analyzed, with results revealing a substantial increase in friction on these structural defects.