Browsing by Subject "Friction"
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Item Open Access Atomic force microscopy: Methods and applications(Elsevier, 2017) Baykara, Mehmet Z.; Schwarz, U. D.; Lindon, J.; Tranter, G. E.; Koppenaal, D.This chapter provides an overview of atomic force microscopy, covering the fundamental aspects of the associated instrumentation and methodology as well as representative results from the literature highlighting a variety of application areas. In particular, atomic-resolution imaging and spectroscopy capabilities are emphasized, in addition to applications in biology, nanotribology and catalysis research. Finally, an outlook on emerging aspects and future prospects of atomic force microscopy is provided.Item Open Access Atomic scale study of friction and energy dissipation(Elsevier, 2003-05) Çıracı, Salim; Buldum, A.This paper presents an analysis of the interaction energy and various forces between two surfaces, and the microscopic study of friction. Atomic-scale simulations of dry sliding friction and boundary lubrication are based on the classical molecular dynamics (CMD) calculations using realistic empirical potentials. The dry sliding of a single metal asperity on an incommensurate substrate surface exhibits a quasi-periodic variation of the lateral force with two different stick-slip stage involving two structural transformation followed by a wear. The contact area of the asperity increases discontinuously with increasing normal force. Xe atoms placed between two atomically flat Ni surfaces screen the Ni-Ni interaction, decrease the corrugation of the potential energy as well as the friction force at submonolayer coverage. We present a phononic model of energy dissipation from an asperity to the substrates. (C) 2003 Elsevier Science B.V. All rights reserved.Item Open Access Atomic scale study of superlow friction between hydrogenated diamond surfaces(American Physical Society, 2004) Dag, S.; Çıracı, SalimStrong attractive interaction between two clean diamond (001) slabs turns repulsive upon the hydrogenation of surfaces. This repulsive interaction serves as if a boundary lubricant and prevents the sliding surfaces from being closer to each other even under high normal forces. As a result, calculated lateral force variation generated during sliding has small magnitude under high constant loading forces. Superlow friction observed earlier between diamondlike carbon-coated surfaces can be understood by the steady repulsive interaction between sliding surfaces, as well as strong and stiff carbon-carbon and carbon-hydrogen bonds which do not favor energy dissipation. In ambient conditions, the steady repulsive interaction is, however, destroyed by oxygen atoms which chemically modify those stiff surface bonds.Item Open Access Computational homogenization of soft matter friction: Isogeometric framework and elastic boundary layers(John Wiley and Sons Ltd, 2014) Temizer, I.SUMMARY: A computational contact homogenization framework is established for the modeling and simulation of soft matter friction. The main challenges toward the realization of the framework are (1) the establishment of a frictional contact algorithm that displays an optimal combination of accuracy, efficiency, and robustness and plays a central role in (2) the construction of a micromechanical contact test within which samples of arbitrary size may be embedded and which is not restricted to a single deformable body. The former challenge is addressed through the extension of mixed variational formulations of contact mechanics to a mortar-based isogeometric setting where the augmented Lagrangian approach serves as the constraint enforcement method. The latter challenge is addressed through the concept of periodic embedding, with which a periodically replicated C1-continuous interface topography is realized across which not only pending but also ensuing contact among simulation cells will be automatically captured. Two-dimensional and three-dimensional investigations with unilateral/bilateral periodic/random roughness on two elastic micromechanical samples demonstrate the overall framework and the nature of the macroscopic frictional response. © 2014 John Wiley & Sons, Ltd.Item Open Access First-principles study of superlow friction between hydrogenated diamond surfaces(ASME, 2005) Çıracı, Salim; Dağ, SefaAttractive interaction between two clean diamond(001) slabs turns repulsive upon the hydrogenation of surfaces. Even under high loading forces, this repulsive interaction prevents the sliding surfaces from being closer to each other. As a result, calculated lateral force variation generated during sliding has small magnitude under high constant loading forces. Superlow friction observed earlier between diamond like carbon coated surfaces can be understood by the steady repulsive interaction between sliding surfaces, as well as strong and stiff carbon-carbon and carbon-hydrogen bonds which do not favor energy dissipation. In ambient conditions, the steady repulsive interaction is, however, destroyed by oxygenation of hydrogenated surface.Item Open Access Frictional properties of quasi-two-dimensional materials from the Prandtl-Tomlinson model(2016-09) Adeel, ShaharyarTribology, the study of friction, is both an old theoretical problem in physics and an area of great practical importance. The invention of experimental instruments such as Atomic Force Microscope (AFM) has lead to the emergence of the eld of nanotribology, the exploration of friction phenomenon at the nanoscale. While more complete descriptions of friction make use of density functional theory (DFT) and molecular dynamics (MD) simulations, many essential features of frictional phenomena are accurately modeled by so called "reduced order models" such as the Prandtl-Tomlinson (PT) Model. We illustrate the PT model in both one-dimensional and two-dimensional forms via application to various crystal lattice surfaces (cubic, planar hexagonal) and reproduce important results from the literature by solving the resulting Langevin equation within the PT model. We also discuss the parameter dependence in this model via relevant simulations. We then generalize the PT model to a three-dimensional case and analyse quasi-two-dimensional systems. These systems thus exhibit a small amount of "buckling" - i.e. with out-of-plane basis atoms. The equations of motion of the Prandtl-Tomlinson model are solved numerically and the resulting friction force curves, tip path and lattice are analysed comparatively. The results agree with underlying theory and make testable predictions. We conclude that our generalized, three-dimensional PT model is a good approximation to the frictional dynamics at this scale for these systems and has the advantage of being computationally less intensive than full scale MD or DFT calculations.Item Open Access A gPC-based approach to uncertain transonic aerodynamics(2010) Simon F.; Guillen P.; Sagaut P.; Lucor, D.The present paper focus on the stochastic response of a two-dimensional transonic airfoil to parametric uncertainties. Both the freestream Mach number and the angle of attack are considered as random parameters and the generalized Polynomial Chaos (gPC) theory is coupled with standard deterministic numerical simulations through a spectral collocation projection methodology. The results allow for a better understanding of the flow sensitivity to such uncertainties and underline the coupling process between the stochastic parameters. Two kinds of non-linearities are critical with respect to the skin-friction uncertainties: on one hand, the leeward shock movement characteristic of the supercritical profile and on the other hand, the boundary-layer separation on the aft part of the airfoil downstream the shock. The sensitivity analysis, thanks to the Sobol' decomposition, shows that a strong non-linear coupling exists between the uncertain parameters. Comparisons with the one-dimensional cases demonstrate that the multi-dimensional parametric study is required to get the correct shape and magnitude of the standard deviation distributions of the flow quantities such as pressure and skin-friction. © 2009 Elsevier B.V.Item Embargo Investigating elastic recovery of monocrystalline silicon during plunging experiments with chamfered diamond tools(Elsevier Inc., 2023-08-03) Karpat, YiğitThis study investigates the relationship between elastic recovery and friction during ductile mode machining of monocrystalline silicon. Plunging experiments were performed on an ultra-precision CNC machining center as the silicon work material was rotated. This approach allowed for investigating the combined effect of varying crystal directions and increasing depth on elastic recovery, pressures, and friction. A diamond cutting tool with a chamfered edge that maintains a constant negative rake along the cutting edge was used in plunging tests. Considering the importance of flank face contact area on friction and pressure distributions at the cutting zone, a non-linear expression is proposed to model the elastic recovery ratio as a function of groove depth. It is then employed in an analytical machining model to calculate the variation of pressure and coefficient of friction. The influences of pressure variation and changes in pressure direction as the machining mode transitions from ductile to brittle are investigated based on resolved stresses on the identified active slip plane. The methodology proposed in this study can be extended to study other monocrystalline materials, and the findings can be utilized in the process planning of advanced optics manufacturing.Item Open Access Investigating flank face friction during precision micro cutting of commercially pure titanium via plunging tests with diamond grooving tools(Elsevier, 2022-01) Karpat, YiğitThis study investigates flank face friction while micro machining commercially pure titanium (cp-Ti grade 2) work material considering size effects. It is important to understand friction phenomena at the tool flank and work material surface since they affect the surface integrity of the machined parts. A single crystal diamond grooving tool is used in machining experiments to reduce the influence of cutting edge radius. In addition, plunging type of cutting experiments were performed to investigate the influence of flank face contact on the machined surface. A friction model which is based on work and tool material properties is proposed to model the contribution of adhesion and deformation of the flank face coefficient of friction. The results show that for the cp-Ti and diamond tool pair, adhesion seems to be the dominant model of friction and also contributes to the size effect. The deformation friction becomes more dominant during the chip formation stage. When cutting edge effect is eliminated, the influences of flank and rake face friction on the size effect are shown.Item Open Access A mixed formulation of mortar-based contact with friction(Elsevier, 2013) Temizer, I.A classical three-field mixed variational formulation of frictionless contact is extended to the frictional regime. The construction of the variational framework with respect to a curvilinear coordinate system naturally induces projected mortar counterparts of tangential kinetic and kinematic quantities while automatically satisfying incremental objectivity of the associated discrete penalty-regularized mortar constraints. Mixed contact variables that contribute to the boundary value problem are then obtained through unconstrained, lumped or constrained recovery approaches, complemented by Uzawa augmentations. Patch tests and surface locking studies are presented together with local and global quality monitors of the contact interactions in two- and three-dimensional settings at the infinitesimal and finite deformation regimes. © 2012 Elsevier B.V.Item Open Access Model description of friction on planar and buckled two dimensional materials(2018-01) Uzlu, Hasan BurkayThe law of friction has been known since the 18th century but yet, the development on the tribology field was established in the last decades mainly by the invention of frictional force microscope (FFM), which enabled scientist to study friction on atomic levels. To describe the friction phenomena at nanoscale, molecular dynamics (MD) and density functional theory (DFT) models are commonly used, popular models and detailed information about friction can be obtained via those models. On the other hand, reduced-order simplified models such as Prandtl-Tomlinson (PT) model can also provide essential information about friction phenomena and understanding a phenomenon via a simplified model is always motivate. In this thesis, Prandtl-Tomlinson model is generalized into three dimensions and the model is illustrated in both two and three dimensions on various quasi two dimensional crystal structures such as graphene, silicene, germanene and hexagonal boron nitride. By solving the equation of motion of the PT model numerically, friction curves and some parametric dependences of the friction such as anisotropy and friction dependence on external loading force is analyzed. We concluded that the PT model in three dimensions provides good results and can be used to analyze friction phenomena to save from computational cost in MD and DFT models.Item Open Access A model-based investigation of tool-chip friction during precision micro cutting of commercially pure titanium alloy(Inderscience Publishers, 2022) Aksin, Alp; Karpat, YiğitUnderstanding interaction between the cutting tool edge radius and the work material is essential to identify the conditions leading to superior surface finish during the micromachining process. The interaction between friction angle and effective rake angle has been investigated based on a slip-line field-based machining model from the literature. Machining forces and cut chip thickness values were obtained from orthogonal cutting tests and employed in the process model. The proposed model also allows for calculating material properties such as shear flow stress and fracture toughness. The proposed model can successfully simulate machining forces during shearing-dominated machining conditions. The results showed the importance of flank and rake face friction in micro-scale machining.Item Open Access Nanocomposite glass coatings containing hexagonal boron nitride nanoparticles(Pergamon Press, 2016) Çamurlu, H. E.; Akarsu, E.; Arslan, O.; Mathur, S.Glass coatings composed of SiO2-K2O-Li2O, containing non-modified and fluorosilane modified hexagonal boron nitride (hBN) nanoparticles, were prepared on stainless steel plates through sol-gel spin-coating method. Coatings were examined by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), atomic force microscopy (AFM) and thermo-gravimetric analysis (TGA). 1.3-2.5 μm thick uniform coatings were obtained after curing at 500 °C for 1 h. The coatings adhered well to the steel substrates. It was determined by salt spray tests that the coatings enhance corrosion resistance. The aim of hydrophobic fluorosilane modification of hBN nanoparticles was to enrich hBN quantity on the top surface of the coatings. Coatings containing fluorosilane modified hBN nanoparticles presented slightly lower friction coefficient values than the other coatings.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.Item Open Access Nanotribological properties of the h-BN/Au(111) interface: a DFT study(American Chemical Society, 2019) Baksi, M.; Toffoli, D.; Gülseren, Oğuz; Üstünel, H.Understanding the quantum-mechanical origins of friction forces has become increasingly important in the past decades with the advent of nanotechnology. At the nanometer scale, the universal Amontons–Coulomb laws cease to be valid, and each interface requires individual scrutiny. Because of the well-known lubricating properties of two-dimensional materials, a significant amount of research has been performed in an effort to understand interfaces they form with one another. However, the interfaces between these two-dimensional materials and metals red from a tribological point of view, important for such applications as friction force microscopy, have yet to be thoroughly investigated. In the current work, we present a detailed density functional theory investigation of the hexagonal BN/Au(111) interface. Because of a good agreement between their characteristic lengths, a high level of commensurability is achieved in a suitably constructed model between the bulk surfaces of the two materials. As a result of our calculations, we find that the corrugation in the potential energy surface and the lateral forces in this interface are low compared to other similar interfaces. The friction coefficient falls rapidly with increasing load down to 0.005 for the largest loads considered. In contrast, Aun clusters (n = 1, 4, 13, and 19) sliding on the h-BN surface exhibit much larger lateral forces, indicating strong size and edge effects. The reduction of energy corrugation in going from the Au4 to the Au19 cluster may already indicate a decreasing trend with increasing size even at this very small scale.Item Open Access Nonlinear laser lithography for enhanced tribological properties(IEEE, 2015-05) Gnilitskyi, I.; Pavlov, Ihor; Rotundo, F.; Orazi, L.; Martini, C.; İlday, Fatih ÖmerThis paper investigates a new field for application of femtosecond laser-induced periodic surface structures (LIPSS). We designed an innovative solution to reduce coefficient of friction of mechanical parts by using the nonlinear laser lithography technique (NLL). © 2015 OSA.Item Open Access Observer based friction cancellation in mechanical systems(IEEE, 2014-10) Odabaş, Caner; Morgül, ÖmerAn adaptive nonlinear observer based friction compensation for a special time delayed system is presented in this paper. Considering existing delay, an available Coulomb observer is modified and closed loop system is formed by using a Smith predictor based controller as if the process is delay free. Implemented hierarchical feedback system structure provides two-degree of freedom and controls both velocity and position separately. For this purpose, controller parametrization method is used to extend Smith predictor structure to the position control loop for different types of inputs and disturbance attenuation. Simulation results demonstrate that without requiring much information about friction force, the method can significantly improve the performance of a control system in which it is applied. © 2014 Institute of Control, Robotics and Systems (ICROS).Item Open Access Physically-based simulation of hair strips in real-time(UNION Agency - Science Press, 2005) Taşkıran, Hasan Dogu; Güdükbay, UğurIn this paper, we present our implementation of physically-based simulation of hair strips. We used a mass-spring model followed by a hybrid approach where particle systems and the method of clustering of hair strands are employed. All the forces related to springs are implemented: gravity, repulsions from collisions (head and ground), absorption (ground only), frictions (ground and air), internal spring frictions. Real-time performance is achieved for physically-based simulation of hair strips and promising results in terms of the realistic hair behavior and hair rendering are obtained. Copyright UNION Agency - Science Press.Item Open Access Reduced density matrix approach to phononic dissipation in friction(2000) Özpineci, A.; Leitner, D. M.; Çıracı, SalimUnderstanding mechanisms for energy dissipation from nanoparticles in contact with large samples is a central problem in describing friction microscopically. Calculation of the reduced density matrix appears to be the most suitable method to study such systems that are coupled to a large environment. In this paper, the time evolution of the reduced density matrix has been evaluated for an arbitrary system coupled to a heat reservoir. The formalism is then applied to study the vibrational relaxation following the stick-slip motion of an asperity on a surface. The frequency and temperature dependence of the relaxation time is also determined. Predictions of the reduced density matrix are compared with those obtained by using the Golden Rule approach.Item Open Access Structural superlubricity of platinum on graphite under ambient conditions: the effects of chemistry and geometry(American Institute of Physics Inc., 2017) Özoǧul, A.; Ipek, S.; Durgun, Engin; Baykara, M. Z.An investigation of the frictional behavior of platinum nanoparticles laterally manipulated on graphite has been conducted to answer the question of whether the recent observation of structural superlubricity under ambient conditions [E. Cihan, S. Ipek, E. Durgun, and M. Z. Baykara, Nat. Commun. 7, 12055 (2016)] is exclusively limited to the gold-graphite interface. Platinum nanoparticles have been prepared by e-beam evaporation of a thin film of platinum on graphite, followed by post-deposition annealing. Morphological and structural characterization of the nanoparticles has been performed via scanning electron microscopy and transmission electron microscopy, revealing a crystalline structure with no evidence of oxidation under ambient conditions. Lateral manipulation experiments have been performed via atomic force microscopy under ambient conditions, whereby results indicate the occurrence of structural superlubricity at mesoscopic interfaces of 4000-75 000 nm2, with a noticeably higher magnitude of friction forces when compared with gold nanoparticles of similar contact areas situated on graphite. Ab initio simulations of sliding involving platinum and gold slabs on graphite confirm the experimental observations, whereby the higher magnitude of friction forces is attributed to stronger energy barriers encountered by platinum atoms sliding on graphite, when compared with gold. On the other hand, as predicted by theory, the scaling power between friction force and contact size is found to be independent of the chemical identity of the sliding atoms, but to be determined by the geometric qualities of the interface, as characterized by an average "sharpness score" assigned to the nanoparticles.