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In experiments that involve contact with adhesion between two surfaces, as found in atomic force microscopy or nanoindentation, two distinct contact force (P ) vs. indentation-depth (h) curves are often measured depending on whether the indenter moves towards or away from the sample. The origin of this hysteresis is not well understood and is often attributed to moisture, plasticity or viscoelasticity. We present experiments, atomistic simulations and continuum mechanics models that will show that hysteresis can exist without these effects, and that its magnitude depends on surface roughness. We explain the observed hysteresis as the result of a series of surface instabilities, where the contact area grows or recedes by a finite amount. We also demonstrate that when this is the case material properties can be estimated uniquely from contact experiments even when the measured P -h curves are not unique. The hysteresis energy loss during contact is also a measure of the adhesive toughness of the contact interface. We show experimentally that roughness can both increase and decrease the adhesive toughness of the contact interface. We show through numerical simulation of continuum adhesive contact models that the contact interface is optimally tough at conditions at which the contact region is at the cusp of the transition through which it turns form being mostly simply connected to being predominantly multiply connected.
Book Synopsis Mechanics of Hysteretic Adhesive Elastic Mechanical Contact Between Rough Surfaces by : Haneesh Kesari
Download or read book Mechanics of Hysteretic Adhesive Elastic Mechanical Contact Between Rough Surfaces written by Haneesh Kesari and published by Stanford University. This book was released on 2011 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: In experiments that involve contact with adhesion between two surfaces, as found in atomic force microscopy or nanoindentation, two distinct contact force (P ) vs. indentation-depth (h) curves are often measured depending on whether the indenter moves towards or away from the sample. The origin of this hysteresis is not well understood and is often attributed to moisture, plasticity or viscoelasticity. We present experiments, atomistic simulations and continuum mechanics models that will show that hysteresis can exist without these effects, and that its magnitude depends on surface roughness. We explain the observed hysteresis as the result of a series of surface instabilities, where the contact area grows or recedes by a finite amount. We also demonstrate that when this is the case material properties can be estimated uniquely from contact experiments even when the measured P -h curves are not unique. The hysteresis energy loss during contact is also a measure of the adhesive toughness of the contact interface. We show experimentally that roughness can both increase and decrease the adhesive toughness of the contact interface. We show through numerical simulation of continuum adhesive contact models that the contact interface is optimally tough at conditions at which the contact region is at the cusp of the transition through which it turns form being mostly simply connected to being predominantly multiply connected.
In experiments that involve contact with adhesion between two surfaces, as found in atomic force microscopy or nanoindentation, two distinct contact force (P) vs. indentation-depth (h) curves are often measured depending on whether the indenter moves towards or away from the sample. The origin of this hysteresis is not well understood and is often attributed to moisture, plasticity or viscoelasticity. We present experiments, atomistic simulations and continuum mechanics models that will show that hysteresis can exist without these effects, and that its magnitude depends on surface roughness. We explain the observed hysteresis as the result of a series of surface instabilities, where the contact area grows or recedes by a finite amount. We also demonstrate that when this is the case material properties can be estimated uniquely from contact experiments even when the measured P -h curves are not unique. The hysteresis energy loss during contact is also a measure of the adhesive toughness of the contact interface. We show experimentally that roughness can both increase and decrease the adhesive toughness of the contact interface. We show through numerical simulation of continuum adhesive contact models that the contact interface is optimally tough at conditions at which the contact region is at the cusp of the transition through which it turns form being mostly simply connected to being predominantly multiply connected.
Book Synopsis Mechanics of Hysteretic Adhesive Elastic Mechanical Contact Between Rough Surfaces by : Haneesh Kesari
Download or read book Mechanics of Hysteretic Adhesive Elastic Mechanical Contact Between Rough Surfaces written by Haneesh Kesari and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In experiments that involve contact with adhesion between two surfaces, as found in atomic force microscopy or nanoindentation, two distinct contact force (P) vs. indentation-depth (h) curves are often measured depending on whether the indenter moves towards or away from the sample. The origin of this hysteresis is not well understood and is often attributed to moisture, plasticity or viscoelasticity. We present experiments, atomistic simulations and continuum mechanics models that will show that hysteresis can exist without these effects, and that its magnitude depends on surface roughness. We explain the observed hysteresis as the result of a series of surface instabilities, where the contact area grows or recedes by a finite amount. We also demonstrate that when this is the case material properties can be estimated uniquely from contact experiments even when the measured P -h curves are not unique. The hysteresis energy loss during contact is also a measure of the adhesive toughness of the contact interface. We show experimentally that roughness can both increase and decrease the adhesive toughness of the contact interface. We show through numerical simulation of continuum adhesive contact models that the contact interface is optimally tough at conditions at which the contact region is at the cusp of the transition through which it turns form being mostly simply connected to being predominantly multiply connected.
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 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.
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 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.
This open access book contains a structured collection of the complete solutions of all essential axisymmetric contact problems. Based on a systematic distinction regarding the type of contact, the regime of friction and the contact geometry, a multitude of technically relevant contact problems from mechanical engineering, the automotive industry and medical engineering are discussed. In addition to contact problems between isotropic elastic and viscoelastic media, contact problems between transversal-isotropic elastic materials and functionally graded materials are addressed, too. The optimization of the latter is a focus of current research especially in the fields of actuator technology and biomechanics. The book takes into account adhesive effects which allow access to contact-mechanical questions about micro- and nano-electromechanical systems. Solutions of the contact problems include both the relationships between the macroscopic force, displacement and contact length, as well as the stress and displacement fields at the surface and, if appropriate, within the half-space medium. Solutions are always obtained with the simplest available method - usually with the method of dimensionality reduction (MDR) or approaches which use the solution of the non-adhesive normal contact problem to solve the respective contact problem.
Book Synopsis Handbook of Contact Mechanics by : Valentin L. Popov
Download or read book Handbook of Contact Mechanics written by Valentin L. Popov and published by Springer. This book was released on 2019-04-26 with total page 357 pages. Available in PDF, EPUB and Kindle. Book excerpt: This open access book contains a structured collection of the complete solutions of all essential axisymmetric contact problems. Based on a systematic distinction regarding the type of contact, the regime of friction and the contact geometry, a multitude of technically relevant contact problems from mechanical engineering, the automotive industry and medical engineering are discussed. In addition to contact problems between isotropic elastic and viscoelastic media, contact problems between transversal-isotropic elastic materials and functionally graded materials are addressed, too. The optimization of the latter is a focus of current research especially in the fields of actuator technology and biomechanics. The book takes into account adhesive effects which allow access to contact-mechanical questions about micro- and nano-electromechanical systems. Solutions of the contact problems include both the relationships between the macroscopic force, displacement and contact length, as well as the stress and displacement fields at the surface and, if appropriate, within the half-space medium. Solutions are always obtained with the simplest available method - usually with the method of dimensionality reduction (MDR) or approaches which use the solution of the non-adhesive normal contact problem to solve the respective contact problem.
Book Synopsis Contact mechanics perspective of tribology by : Irina Goryacheva
Download or read book Contact mechanics perspective of tribology written by Irina Goryacheva and published by Frontiers Media SA. This book was released on 2021-06-04 with total page 391 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Friction, lubrication, adhesion, and wear are prevalent physical phenomena in everyday life and in many key technologies. This book explains how these tribological phenomena originate from atomistic and microscale physical phenomena and shows how this understanding can be used to solve macroscale tribology problems.
Book Synopsis Tribology on the Small Scale by : C. Mathew Mate
Download or read book Tribology on the Small Scale written by C. Mathew Mate and published by Oxford Graduate Texts. This book was released on 2019 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt: Friction, lubrication, adhesion, and wear are prevalent physical phenomena in everyday life and in many key technologies. This book explains how these tribological phenomena originate from atomistic and microscale physical phenomena and shows how this understanding can be used to solve macroscale tribology problems.
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 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.
This is targeted at professionals and graduate students working in disciplines where flow of adhesive particles plays a significant role.
Book Synopsis Adhesive Particle Flow by : Jeffery S. Marshall
Download or read book Adhesive Particle Flow written by Jeffery S. Marshall and published by Cambridge University Press. This book was released on 2014-03-31 with total page 361 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is targeted at professionals and graduate students working in disciplines where flow of adhesive particles plays a significant role.
The comprehensive reference and textbook serves as a timely, practical introduction to the principles of nanotribology and nanomechanics. Assuming some familiarity with macroscopic tribology, the book comprises chapters by internationally recognized experts, who integrate knowledge of the field from the mechanics and materials-science perspectives. They cover key measurement techniques, their applications, and theoretical modelling of interfaces, each beginning their contributions with macro- and progressing to microconcepts.
Book Synopsis Nanotribology and Nanomechanics II by : Bharat Bhushan
Download or read book Nanotribology and Nanomechanics II written by Bharat Bhushan and published by Springer Science & Business Media. This book was released on 2011-05-30 with total page 1025 pages. Available in PDF, EPUB and Kindle. Book excerpt: The comprehensive reference and textbook serves as a timely, practical introduction to the principles of nanotribology and nanomechanics. Assuming some familiarity with macroscopic tribology, the book comprises chapters by internationally recognized experts, who integrate knowledge of the field from the mechanics and materials-science perspectives. They cover key measurement techniques, their applications, and theoretical modelling of interfaces, each beginning their contributions with macro- and progressing to microconcepts.
