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The Effect Of Interfacial Conformity On The Contact Adhesion And Sliding Friction Of Surfaces With Small Roughness
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Book Synopsis The Effect of Interfacial Conformity on the Contact, Adhesion, and Sliding Friction of Surfaces with Small Roughness by : Herbert Mark Stanley
Download or read book The Effect of Interfacial Conformity on the Contact, Adhesion, and Sliding Friction of Surfaces with Small Roughness written by Herbert Mark Stanley and published by . This book was released on 1993 with total page 310 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Optimization of Hard Disk Drive Components by : Matthew Arnold O'Hara
Download or read book Optimization of Hard Disk Drive Components written by Matthew Arnold O'Hara and published by . This book was released on 1997 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Contact Mechanics Modeling of Homogeneous and Layered Elastic-Plastic Media by : Zhichao Song
Download or read book Contact Mechanics Modeling of Homogeneous and Layered Elastic-Plastic Media written by Zhichao Song and published by . This book was released on 2012 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: The main objective of this dissertation was to analyze surface contact interaction at different length scales and to elucidate the effects of material properties (e.g., adhesion and mechanical properties), normal and shear (friction) surface tractions, and topography parameters (e.g., roughness) on contact deformation. To accomplish this objective, a surface adhesion model based on an interatomic potential was incorporated into finite element contact models of rough surfaces exhibiting multi-scale roughness described by statistical and fractal geometry models. The problem of a rigid sphere in contact with an elastic-plastic half-space was first examined in the light of finite element simulations. Four post-yield deformation regimes were identified and the boundaries of neighboring regimes were obtained by curve-fitting of finite element results. Material hardness was shown to significantly deviate from the similarity solution with decreasing elastic modulus-to-yield strength ratio and the logarithmic dependence of the mean contact pressure on the indentation depth was found to hold only when the plastic zone was completely surrounded by elastic material. Constitutive equations were first derived for elastic-perfectly plastic half-spaces from curve-fitting finite element results and were then extended to isotropic, power-law hardening half-spaces, using the concept of the effective strain, which correlates the indentation depth with the indenter size. Finite element simulations of unloading process and repetitive normal contact were used to correlate the residual indentation depth and the dissipated plastic energy with the maximum indentation depth. Elastic shakedown, plastic shakedown, and ratcheting were identified by tracking the accumulation of plasticity for different values of maximum contact load and elastic modulus-to-yield strength ratio. The semi-infinite half-space was characterized by three different regions, named ratcheting region, shakedown region and elastic region, as the distance to contact surface increases. The obtained results have direct implication in material property measurements obtained with indentation method, particularly for materials exhibiting strain hardening behavior, and provide insight into the accumulation of plasticity due to repetitive contact loading, which is important in the understanding of the contact fatigue life of contact-mode devices. Sliding contact between a rigid fractal surface exhibiting multi-scale roughness and an elastic-plastic half-space was examined to elucidate rough-surface deformation due to small-amplitude reciprocating sliding (fretting). Stick-slip at the asperity scale was analyzed based on Mindlin's theory and a friction model that accounts for both adhesion and plowing effects. Numerical results yield insight into the effects of surface roughness, contact pressure, oscillation amplitude, elastic modulus-to-yield strength ratio, and interfacial adhesion on the friction force, slip index, and energy dissipation. The results of this study illustrate the important role of the contact load and surface topography on the energy dissipation and fretting wear of small-amplitude oscillatory contacts. Surface adhesion modeled as surface traction obeying the Lennard-Jones (LJ) potential was incorporated into the contact analysis of a rigid sphere indenting an elastic half-space to study contact instabilities associated with instantaneous surface contact (jump-in) and detachment (jump-out). This surface traction was introduced into a finite element contact model in the form of nonlinear spring elements and the jump-in/jump-out condition obtained analytically was confirmed by finite element results. Then, adhesive contact between a rigid sphere and an elastic-plastic half-space was analyzed and the effect of plasticity on the pull-off force and the commencement of contact instabilities was interpreted in terms of a modified Tabor parameter. The developed finite element model with nonlinear spring elements representing adhesive surface interaction provides a physics-based, computationally-efficient technique for studying adhesive contacts. The obtained results provide explanation for the contact instabilities encountered during surface probing with microprobe tips and stiction (permanent adhesion) in contact-mode microdevices. Adhesive contact between a rigid sphere and a layered medium analyzed with the finite element method shed light into adhesion-induced contact deformation. Two modes of surface detachment were observed for perfect bonding of the film to the substrate - brittle- and ductile-like surface detachment. Simulation results illustrate the effects of the maximum surface separation, film thickness, film-to-substrate elastic property mismatch, and substrate yield strength on the mode of surface detachment and residual deformation. Introducing a cohesive model that allows for crack formation and growth along the film/substrate interface in the previous finite element model, a residual cohesive zone was found at the crack tip after complete unloading. Contact instabilities and interface delamination were interpreted by the competing effects of surface adhesion and interfacial cohesion. Crack closure and crack-tip opening displacement (CTOD) were studied by performing a parametric study of the cohesive strength, interfacial energy, surface energy, surface adhesive strength, substrate yield strength, and initial defect size. The obtained results can be used to explain thin-film failure in contact systems due to the effect of adhesion and to improve the endurance of thin-film media subjected to surface tractions. Adhesive contact of two elastic rough surfaces was analyzed by integrating asperity-scale constitutive equations into the model of Greenwood and Williamson (1966) to account for the effect of contact instabilities at asperity level on the macroscopic contact response. The strength of adhesion was found to be mostly affected by the Tabor parameter and the surface roughness. The widely used adhesion parameter of Fuller and Tabor (1977) was shown to be appropriate only for contact systems characterized by a high Tabor parameter. Therefore, a new adhesion parameter that governs the strength of adhesion of contact systems with a low Tabor parameter was introduced. Finally, a generalized adhesion parameter was derived by using the concept of the effective interatomic separation, defined as the ratio of the elastic stretch due to adhesion and the equilibrium interatomic distance. The research carried out in this dissertation provides fundamental understanding of the evolution of the stress and strain fields in contacting surfaces, the evolution of plasticity in indentation, the development of friction and dissipation of energy in fretting contacts, the occurrence of adhesion-induced contact instabilities and interfacial delamination, and the factors affecting the strength of adhesion for rough surfaces in normal contact. The results of this thesis have direct implications in various technologies, including high-efficiency gas turbines, magnetic storage devices, and microelectromechanical systems.
Book Synopsis International Encyclopedia of Ergonomics and Human Factors by : Waldemar Karwowski
Download or read book International Encyclopedia of Ergonomics and Human Factors written by Waldemar Karwowski and published by CRC Press. This book was released on 2001 with total page 712 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis International Encyclopedia of Ergonomics and Human Factors - 3 Volume Set by : Informa Healthcare
Download or read book International Encyclopedia of Ergonomics and Human Factors - 3 Volume Set written by Informa Healthcare and published by CRC Press. This book was released on 2000-12-14 with total page 1980 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first encyclopedia in the field, the International Encyclopedia of Ergonomics and Human Factors provides a comprehensive and authoritative compendium of current knowledge on ergonomics and human factors. It gives specific information on concepts and tools unique to ergonomics. About 500 entries, published in three volumes and on CD-ROM, are pre
Book Synopsis Modification of Adhesion and Friction by Surface Structuring by : Ying Bai
Download or read book Modification of Adhesion and Friction by Surface Structuring written by Ying Bai and published by . This book was released on 2014 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: Enhanced and selective adhesion, and controlled friction between contact surfaces are highly desirable mechanical properties for high-level functional materials. There are many instances in nature where such properties have been obtained by design of near-surface architecture. Inspired by many highly functional biological systems, we have explored bio-mimetic materials with different surface patterning, with the goal of designing surfaces that have unique combinations of contact mechanical properties. In the studies presented here, we show how: (a) highly selective adhesion can be achieved by complementarity of patterned charge and shape, and (b) how friction can be modulated by spatial variation in stiffness, and how structured surfaces interact with surface roughness. We consider how adhesion selectivity can be accomplished by complementarity of shape and inter-surface forces. We have studied an example each of charge and shape complementarity for selective adhesion between extended surfaces. First, we studied theoretically how surfaces patterned with stripes of charge interact with each other, and exhibit strong selectivity on rigid surfaces. However, deformability of the surfaces plays a crucial role in modulating adhesion by accommodating mismatches. To achieve shape complementarity, we designed and fabricated patterned elastomeric surfaces with lines of channels and complementary ridges with dimensions at the micrometer scale. We show that such surfaces have highly enhanced effective adhesion for shape complementary pairs and low adhesion between surfaces with a shape mismatch. We find that the pillar/channel combinations form defects to accommodate interfacial misalignment. These defects are interfacial dislocations. Adhesion between complementary surfaces is enhanced by crack trapping and friction, and attenuated due to the energy released by dislocation structures. In addition to enhanced adhesion, we studied the deliberate control of friction through near-surface micro-structures. Friction measurements on elastomeric surfaces patterned with periodic variation in stiffness show that it undergoes an "auto-roughening" transition under shear and this process can strongly attenuate overall sliding friction. Friction reduction is due to reduction of real contact area, as the initially full contact breaks up into partial contact at the interface. Finite element analysis demonstrates how auto-roughening depends on the modulus mismatch, frictional stress and normal displacement. A surface with random roughness is used to study sliding friction against micro-channel structures under fixed normal force. In contrast to a smooth surface, against which structured surfaces all have highly reduced sliding friction, the roughened surface can exhibit significantly larger frictional force on a structured surface. The enhancement of sliding friction is governed by channel depth, spacing and applied normal force.
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1992 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis How Surface Roughness Affects Adhesion by : Antoine Sanner
Download or read book How Surface Roughness Affects Adhesion written by Antoine Sanner and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: At atomic scales, all molecules attract each other, but macroscopic objects usually do not stick.The explanation for this apparent paradox is that most surfaces are rough, so that elastically stiff objects only touch on the top of their asperities. Geckos and insects have compliant fibrillar structures or soft pads at the tip of their feet that conform to surface roughness, sustaining enough adhesion to climb vertical walls. Understanding the role of surface roughness in adhesion is a challenge because surfaces exhibit roughness down to the atomic scale. In this thesis, my collaborators and I investigate the effect of surface roughness on adhesion in both stiff and compliant contact systems. I model adhesion theoretically, and I help experimentalists analyze surface topography over multiple scales. The combination of my new models and of the comprehensive surface topography characterization by Abhijeet Gujrati (University of Pittsburgh), allows us to unravel the role of surface roughness in adhesion experiments. Stiff materials do not stick because roughness prevents most of the surfaces to come into the range of molecular attraction. A recent theory quantifies this effect based on an approximate expression for the distribution of interfacial gaps near the contact edge. Joe Monti (Johns Hopkins University) and I benchmark this expression against gap distributions extracted from finely resolved numerical simulations. The theory is valid provided that adhesive stresses are weak and act over a range shorter than a geometrical parameter determined by small-scale roughness. Elastically soft (jelly-like) objects stick because the elastic penalty to deform into intimate contact is small compared to the gain in surface energy. However, theories based on this simple thermodynamic argument cannot explain the fact that in experiments, the force measured during retraction is often much higher than during indentation. This adhesion hysteresis can be caused by material specific irreversibility or elastic instabilities triggered by surface roughness. The role of these instabilities in adhesion hysteresis remains poorly understood because existing numerical and theoretical models cannot account for realistic roughness in soft contacts. I introduce an efficient crack-perturbation model for the contact of rough spheres, enabling large scale simulations with realistic surface roughness. By clarifying the link between adhesion hysteresis and classic pinning problems (for example fracture of heterogeneous materials and wetting angle hysteresis), this model allows me to derive a simple theoretical model linking adhesion hysteresis to surface roughness. In combination with the characterization of surface roughness over multiple scales, my models shed light on the role of elastic instabilities in adhesion experiments. Surfaces are rough from the macroscopic scale down to the atomic scale, and the lack of comprehensive roughness characterization is the major obstacle towards bringing theory and experiments together. Abhijeet Gujrati and collaborators measured the roughness of four diamond coatings over eight decades of length scales, enabling the application of adhesion theories on experiments performed with these samples. Besides the experimental challenge of determining roughness down to the atomic scale, an additional obstacle to the documentation of roughness is the technical complexity of established multiscale roughness measures such as the power spectral density. My collaborators and I address this problem by introducing the scale-dependent roughness parameters (SDRPs), a new analysis framework that is easy to interpret and to implement. This new analysis, together with several established techniques, is available to use through our web-service contact.engineering. We thereby encourage the community to measure, analyze and publish roughness over multiple length scales. The SDRP analysis computes the fluctuations of slopes and curvatures as a function of the lateral length scale. Slopes and curvatures are important ingredients for rough contact theories, but it remains unclear at which scales they matter. Luke Thimons (University of Pittsburgh) and I show that in macro-scale contacts between ruby spheres and diamond coatings, the roughness that critically affects adhesion is between lateral length scales of 43~nm to 1.8~μm. The large-scale cutoff is related to the finite radius of the spherical indenter, while the unimportance of small scales is due to plastic deformations and the long range of the adhesive interaction (5~nm). To determine the critical range of length scales, as well as the parameters of the adhesive interaction, we analyzed the experimental pull-off forces by combining surface topography characterization and numerical simulations. Adhesion is critical in applications such as microelectromechanical systems (MEMS), soft robotics and skin adhesives. Our insights provide guidance for practitioners which scales of roughness to control in order to tune adhesion, and our framework for surface topography characterization will allow a better overall understanding of surface topography across the community
Book Synopsis Understanding Contact Mechanics and Friction on Rough Surfaces by : Siddhesh Narayan Dalvi
Download or read book Understanding Contact Mechanics and Friction on Rough Surfaces written by Siddhesh Narayan Dalvi and published by . This book was released on 2020 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the mechanism of adhesion and friction in soft materials is critical to the fields of transportation (tires, wiper blades, seals etc.), prosthetics and soft robotics. Most surfaces are inherently rough and the interfacial area between two contacting bodies depends largely on the material properties and surface topography of the contacting bodies. Johnson, Kendall and Roberts (JKR) derived an equilibrium energy balance for the behavior of smooth elastic spherical bodies in adhesive contact that predicts a thermodynamic work of adhesion for two surfaces in contact. The JKR equation gives a reversible work of adhesion value during approach and retraction. However, viscoelastic dissipation, surface roughness and chemical bonding result in different work of adhesion values for approach and retraction. This discrepancy is termed adhesion hysteresis. Roughness is undermined as a cause of hysteresis in adhesion studies. Recently, a continuum mechanics model has been developed that predicts the work of adhesion on rough surfaces with known roughness in the form of power spectral density (PSD) function. To test the above mentioned theoretical model, we have conducted JKR experiments between highly cross-linked smooth polydimethylsiloxane (PDMS) of four different elastic moduli and diamond surfaces of four different crystal sizes and roughness.The rough diamond surfaces are characterized for topography using stylus profilometry, atomic force microscopy and in-situ transmission electron microscopy combined to give a comprehensive PSD. Results suggest that the observed work of adhesion during approach is equivalent to energy required to stretch the PDMS network at the surface and in the bulk to form the real rough contact area. However, in retraction work of adhesion is found to be proportional to the ratio of excess energy spent in the loading-unloading cycle and the true contact area obtained from topography indicating conformal contact matching fracture mechanics behavior. Thus, the study resolves adhesion hysteresis discrepancy on rough surfaces.It is known that adhesion hysteresis increases interfacial friction on rough surfaces. However, an experimentally proven quantitative model is still missing. Previous studies on smooth surfaces have shown that shear stress increases with velocity initially, reaching a maximum and then either plateaus out or decreases depending upon the modulus of the sliding elastomer. We have performed shear measurements with velocities ranging from nm/sec to cm/sec between PDMS elastomers and diamond surfaces. Data suggests higher shear stresses at lower velocities for rough surfaces and thus a shift for the peak previously observed on smooth surfaces. Additionally, there are states such as steady-state sliding, stick-slip and detachment waves with increasing stress in the same order. These states are found to occur at a critical stress and their onset is linearly proportional to the elastic modulus of the sliding rubber. The stress predictions using existing theories do not decouple adhesion and deformation energy losses during friction observed ex- perimentally on rough surfaces and further investigation is required in order to obtain a better friction model.
Book Synopsis Effect of Interfacial Friction on Adhesion by : Bi-min Zhang Newby
Download or read book Effect of Interfacial Friction on Adhesion written by Bi-min Zhang Newby and published by . This book was released on 1998 with total page 526 pages. Available in PDF, EPUB and Kindle. Book excerpt: Conventionally, the energy required to fracture an interface is predicted to be directly proportional to the thermodynamic work of adhesion. It has been observed, however, that on some low energy surfaces, the fracture energy of an adhesive deviates significantly from this rule. In viscoelastic systems, it is well known that most of the energy is dissipated by the viscous bulk materials near the crack tip region. What is, perhaps, not so widely known is that for a crack propagating at an asymmetric interface, a substantial amount of energy can be dissipated through a frictional mechanism near the crack tip region. This energy dissipation due to friction at and near the crack tip is being proposed to account for the discrepancies observed with adhesion on low energy surfaces. The objective of this research is to investigate the contribution of interfacial friction and associated slip processes to the total fracture energy.
Book Synopsis Asperity-scale Surface Mechanics - Implications to Adhesive Contacts and Microscale Deformation Behavior of Rough Surfaces by : Huaming Xu
Download or read book Asperity-scale Surface Mechanics - Implications to Adhesive Contacts and Microscale Deformation Behavior of Rough Surfaces written by Huaming Xu and published by . This book was released on 2012 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt: The principal objective of this dissertation was to develop numerical and analytical mechanics models accounting for nano-/micro-scale solid surface interaction. This was accomplished by developing finite element models of an asperity in adhesive sliding contact with a homogenous half-space and asperity micro-fracture due to normal and sliding contact of homogenous or layered half-spaces, and analytical models of nanoscale surface polishing and nanoparticle embedment on rough surfaces using a probabilistic approach. Adhesive interaction of a rigid asperity moving over a homogeneous elastic-plastic half-space was modeled by nonlinear springs obeying a constitutive law derived from the Lennard-Jones potential. The evolution of the normal and friction forces, subsurface stresses, and plastic deformation at steady-state sliding was examined in terms of the work of adhesion, interaction distance (interfacial gap), Maugis parameter, and plasticity parameter, using the finite element method (FEM). The deformation behavior of homogeneous elastic-perfectly plastic (EPP) and elastic-linear kinematic hardening plastic (ELKP) half-spaces subjected to repeated adhesive sliding contacts was also the objective of this analysis. Numerical results provided insight into the effects of the aforementioned parameters on the friction and normal forces, stress-strain response, and evolution of subsurface plasticity with the accumulation of sliding cycles. The steady-state mode of deformation due to repeated adhesive sliding contacts was examined for both EPP and ELKP material behavior. Subsurface cracking in a layered medium consisting of an elastic hard layer and an elastic-plastic substrate due to adhesive sliding against a rigid asperity was analyzed using linear elastic fracture mechanics (LEFM) and FEM model. The dominance of shear and tensile mode of crack propagation was examined in terms of the interaction depth, layer thickness, crack location, crack length, work of adhesion, and mechanical properties of the thin layer and substrate materials. The effect of adhesion on asperity failure due to normal contact was also studied. The crack growth direction, dominant fracture mode, and crack growth rate were predicted as functions of the initial crack position, asperity interaction distance, interfacial properties, and mechanical properties. FEM results showed the occurrence of different crack mechanisms, such as of crack-face opening, slip, and stick. The evolution of the surface topography during nanoscale surface polishing was studied with a three-dimensional stochastic model that accounts for a multi-scale (fractal) surface roughness and elastic, elastic-plastic, and fully-plastic deformation of the asperities on the polished surface caused by hard abrasive nanoparticles embedded in the soft surface layer of a rigid polishing countersurface. Numerical results of the steady-state roughness of the polished surface, material removal rate, and wear coefficient were determined in terms of the apparent contact pressure, polishing speed, original topography and mechanical properties of the polished surface, average size and density of the nanoparticles, and surface roughness of the polishing plate. The density of hard abrasive nanoparticles embedded in the soft countersurface was predicted by a probabilistic-hydrodynamic model in terms of the surface topographies, particle size distribution, applied forces, macroscopic geometry of the moving surfaces, surface kinematics, and fluid properties. The findings of this dissertation yield new insight into the deformation behavior of adhesive contacts involving homogeneous and layered half-spaces, from the single asperity level to surfaces with multi-asperity topographies. The significance of the interfacial properties and material properties on adhesive asperity sliding contact, the effects of interfacial adhesion and crack properties on asperity cracking and subsurface cracking, and the dependence of the surface topography evolution during nanoscale polishing on the surface topographies, material properties, and abrasive nanoparticle size were examined in the context of numerical and analytical results. The results of this thesis elucidate the mechanical aspects of surface contact interaction in nano/microscale engineering components and surfacing processes, such as hard-disk drives, micro-electro-mechanical systems, and nanoscale surface polishing, and provide insight into the underlying reasons leading to mechanical failure of homogeneous and layered half-spaces subjected to surface tractions. Solutions and FEM results for single-asperity contacts obtained in this work can be integrated into probabilistic analyses of contacting rough surfaces to advance the current state of contact mechanics of surfaces exhibiting multi-asperity topographies.
Book Synopsis Friction and Wear: From Elementary Mechanisms to Macroscopic Behavior by : Valentin L. Popov
Download or read book Friction and Wear: From Elementary Mechanisms to Macroscopic Behavior written by Valentin L. Popov and published by Frontiers Media SA. This book was released on 2019-08-21 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt: Friction and the interaction of surfaces can usually be felt at the scale of the contacting bodies. Indeed, phenomena such as the frictional resistance or the occurrence of wear can be observable with plain eye, but to characterize them and in order to make a prediction, a more detailed understanding at smaller scales is often required. These can include individual roughness peaks or single molecule interactions. In this Research Topic, we have gathered a collection of articles representing the state of the art in tribology’s endeavor to bridge the gap between nano scale elementary research and the macroscopic behavior of contacting bodies. These articles showcase the breadth of questions related to the interaction of micro and macro scale and give examples of successful transfer of insights from one to the other. We are delighted to present this Research Topic to the reader with the hope that it will further inspire and stimulate research in the field.
Book Synopsis Fundamentals of Machine Elements by : Steven R. Schmid
Download or read book Fundamentals of Machine Elements written by Steven R. Schmid and published by CRC Press. This book was released on 2014-07-18 with total page 627 pages. Available in PDF, EPUB and Kindle. Book excerpt: New and Improved SI Edition-Uses SI Units Exclusively in the TextAdapting to the changing nature of the engineering profession, this third edition of Fundamentals of Machine Elements aggressively delves into the fundamentals and design of machine elements with an SI version. This latest edition includes a plethora of pedagogy, providing a greater u
Book Synopsis Combustion Engines--reduction of Friction and Wear by :
Download or read book Combustion Engines--reduction of Friction and Wear written by and published by . This book was released on 1989 with total page 162 pages. Available in PDF, EPUB and Kindle. Book excerpt: The operation of combustion engines, both reciprocating and rotary, can be improved in many areas by the reduction of friction and wear. This collection of papers reviews improvements in traditional engines and also in Stirling and Wankel engines, together with future trends in anti-friction coatings. Specific topics covered include: ball and roller bearings, cylinder line materials and finishes, pistons and piston rings, filters and filtration, impact of friction and wear on fuel economy, and engine management regimes to reduce wear. These proceedings would be of interest to engineers and all involved in the pursuit of economy, reliability and longer working life in relation to the whole field of combustion engines.
Book Synopsis Contact Angle, Wettability and Adhesion, Volume 5 by : Kash L. Mittal
Download or read book Contact Angle, Wettability and Adhesion, Volume 5 written by Kash L. Mittal and published by CRC Press. This book was released on 2008-08-31 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume chronicles the proceedings of the 5th International Symposium on Contact Angle, Wettability and Adhesion, Toronto, Canada, June 2006. Wettability is of pivotal importance in many and varied arenas, ranging from mundane to micro-and nanofluidics to lithography to biomedical. It should be underscored that in the last years there has been
Download or read book Journal of Tribology written by and published by . This book was released on 2006 with total page 460 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Collective Behavior of Asperities as a Model for Friction and Adhesion by : Srivatsan Hulikal Sampath Kumaran
Download or read book Collective Behavior of Asperities as a Model for Friction and Adhesion written by Srivatsan Hulikal Sampath Kumaran and published by . This book was released on 2015 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding friction and adhesion in static and sliding contact of surfaces is important in numerous physical phenomena and technological applications. Most surfaces are rough at the microscale, and thus the real area of contact is only a fraction of the nominal area. The macroscopic frictional and adhesive response is determined by the collective behavior of the population of evolving and interacting microscopic contacts. This collective behavior can be very different from the behavior of individual contacts. It is thus important to understand how the macroscopic response emerges from the microscopic one. In this thesis, we develop a theoretical and computational framework to study the collective behavior. Our philosophy is to assume a simple behavior of a single asperity and study the collective response of an ensemble. Our work bridges the existing well-developed studies of single asperities with phenomenological laws that describe macroscopic rate-and-state behavior of frictional interfaces. We find that many aspects of the macroscopic behavior are robust with respect to the microscopic response. This explains why qualitatively similar frictional features are seen for a diverse range of materials. We first show that the collective response of an ensemble of one-dimensional independent viscoelastic elements interacting through a mean field reproduces many qualitative features of static and sliding friction evolution. The resulting macroscopic behavior is different from the microscopic one: for example, even if each contact is velocity-strengthening, the macroscopic behavior can be velocity-weakening. The framework is then extended to incorporate three-dimensional rough surfaces, long- range elastic interactions between contacts, and time-dependent material behaviors such as viscoelasticity and viscoplasticity. Interestingly, the mean field behavior dominates and the elastic interactions, though important from a quantitative perspective, do not change the qualitative macroscopic response. Finally, we examine the effect of adhesion on the frictional response as well as develop a force threshold model for adhesion and mode I interfacial cracks.
