1,721,020 research outputs found
Partial surface texturing: A mechanism for local flow reconditioning in lubricated contacts
No full textThe texture hydrodynamics occurring in optimized steady-state lubricated contacts is theoretically investigated recurring to the recent Bruggeman texture hydrodynamics model. In particular, an attempt is made to unravel the intimate relationship between the texture-induced local flow properties and the macroscopic characteristics of the contact such as friction and supported load. The existence of different mechanisms of fluid flow harvesting and channeling is discussed, highlighting their strict relationship to the particular texture physical and topological properties. Whilst their single-species optimization does not produce particularly interesting performances in comparison to classical geometries, their optimized synergistic interaction, instead, provides a remarkable load generation and friction reduction almost independently from the macroscopic geometrical characteristics of the contact. The provided discussion can be easily extended to other contact geometries, such as for journal bearings, wet clutches and dynamic sealings, as well as to bio-tribology and soft contact applications
Maximize Tribological Properties in (Elasto-)Hydrodynamic Contacts Through the Mechanism of Local Flow Reconditioning: the Role of Partial Surface Texturing
No full textComputational Rough Contact Mechanics Based on Fourier Finite Element Formulation and Residuals Molecular Dynamics: An Application to Rubber Friction
No full textThe friction of sliding wet textured surfaces: The Bruggeman effective medium approach revisited
No full textThe mean field fluid dynamics and the friction occurring in the wet sliding contact between inhomogeneous surfaces, characterized by a deterministically repeated pattern of microdefects, are modelled within the Bruggeman effective medium theory. By comparing with the results of an accurate numerical homogenization of the flow equations, and with asymptotic solutions, we discuss the validity of the mean field model and its limitations in relation to the occurrence of clustering and interference effects. Finally, an analytical upgrade to the Bruggeman approach, allowing for inclusion of the clustering effect, is presented and discussed
Textured surface hydrodynamic lubrication: Discussion
No full textWe discuss on a recently presented theory of textured surface hydrodynamic lubrication (Scaraggi, Phys Rev E, 2012). The model, based on the Bruggeman effective medium approach, allows to analytically evaluate the effects of a generic texture shape, distribution, and area density on the macroscopic hydrodynamic characteristics of the contact, such as friction and supported load. In this study, we apply the cited theory to practical cases, and in particular we derive the flow and shear stress tensors for two limiting conditions, i.e., for isotropic (circular inclusion in isotropic medium) and perfectly anisotropic (infinite slit inclusion) flow conductivities. These results are then used to perform near-optimum design calculations for the simplest case of one- and two-dimensional thrustbearing geometries. Finally, a comparison with published results is presented and discussed. The developed theory may be a very useful tool in the process of evaluating the lubrication performances of sliding microtextured surfaces and for the near-optimum design of a textured pair, where texturing could be achieved by both physical (e.g., microstructuring) and chemical surface manipulation
Lubrication of textured surfaces: A general theory for flow and shear stress factors
No full textWe report on a mean field theory of textured surface lubrication. We study the fluid flow dynamics occurring at the interface as a function of the texture characteristics, e.g. texture area density, shape and distribution of microstructures, and local slip lengths. The present results may be very important for the investigation of tailored microtextured surfaces for low-friction hydrodynamic applications
Optimal textures for increasing the load support in a thrust bearing pad geometry
No full textWe present the calculation results of optimal texture geometries which maximize the supported load for a three-dimensional thrust bearing pad. By making use of the recently developed mean field theory of texture hydrodynamics, we develop an efficient multigrid optimization procedure based on the sequential genetic and conjugate gradient optimization. We show that our model allows to determine optimal solutions based on a two-scale hierarchy of structures, and the existence of particularly effective optimal geometries is presented and discussed
Nematic liquid crystals in a spatially step-wise magnetic field
No full textWe study the molecular reorientation induced by a textured external field in a nematic liquid crystal (nLC). In particular, we consider an infinitely wide cell with strong planar anchoring boundary conditions, subjected to a spatially periodic piecewise magnetic field. In the framework of the Frank’s continuum theory, we use the perturbation analysis to study in detail the field-induced splay-bend Freedericksz transition. A numerical approach, based on the finite differences method, is instead employed to solve the fully nonlinear equations. At high field strengths, an analytic approach allows us to draw the bulk profile of the director in terms of elliptic integrals. Finally, through the application of the Bruggeman texture hydrodynamics theory, we qualitatively discuss on the LCs piecewise director configuration under sliding interfaces, which can be adopted to actively regulate friction. Our study opens the pathway for the application of highly controlled nLC texturing for tribotronics
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