The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Izhak Etsion - One of the best experts on this subject based on the ideXlab platform.
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the effect of surface roughness on static friction and Junction Growth of an elastic plastic spherical contact
Journal of Tribology-transactions of The Asme, 2009Co-Authors: Denis Cohen, Y Kligerman, Izhak EtsionAbstract:A model for elastic-plastic spherical contact of rough surfaces under combined normal and tangential loadings, with full stick contact condition, is presented. The model allows evaluation of the effect of surface roughness on the real contact area, static friction and Junction Growth under small normal loads. It is shown that as the normal load approaches a certain threshold value, which depends on the plasticity index, the results of the present rough surface model approach these of previous corresponding models for smooth sphere and a rigid flat. At normal load values below the threshold load, the correlation of the present results and published experimental results is much better in comparison with the results of the smooth surface models.
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A Model for Contact and Static Friction of Nominally Flat Rough Surfaces Under Full Stick Contact Condition model for elastic-plastic nominally flat contacting rough surfaces under combined
2009Co-Authors: Denis Cohen, Y Kligerman, Izhak EtsionAbstract:normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of Junction Growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results. DOI: 10.1115/1.2908925
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Very Early Stage of Elastic-Plastic Spherical Contact Fretting
ASME STLE 2009 International Joint Tribology Conference, 2009Co-Authors: Andrey Ovcharenko, Izhak EtsionAbstract:The contact area, friction force and relative displacement evolution at the very early stage of fretting are investigated experimentally. Copper and steel spheres of various diameters are loaded against a hard sapphire flat by a range of normal loads deep into the elastic-plastic regime of deformation. A reciprocating tangential loading is then applied with a maximum loading below the static friction to avoid gross slip. Real-time and in situ direct measurements of the contact area, along with accurate measurements of the friction force and relative displacement, reveal substantial Junction Growth and energy dissipation mainly in the first loading cycle. The so called “slip amplitude” is found to be attributed to residual tangential plastic deformation rather than to interfacial slip. Elastic shake-down is observed for the 2.5% hardening steel spheres while plastic shake-down is observed in the case of the elastic perfectly plastic copper spheres.Copyright © 2009 by ASME
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a model for contact and static friction of nominally flat rough surfaces under full stick contact condition
Journal of Tribology-transactions of The Asme, 2008Co-Authors: Denis Cohen, Y Kligerman, Izhak EtsionAbstract:A model for elastic-plastic nominally flat contacting rough surfaces under combined normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of Junction Growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results.
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in situ and real time optical investigation of Junction Growth in spherical elastic plastic contact
Wear, 2008Co-Authors: Andrey Ovcharenko, Gregory Halperin, Izhak EtsionAbstract:Abstract The contact area evolution during pre-sliding (Junction Growth) of copper spheres loaded against a hard sapphire flat is investigated experimentally. Tests are performed with a novel test rig for real-time and in situ direct measurements that provide, for the first time, a new insight of the Junction Growth mechanism. It is found that Junction Growth at sliding inception can cause up to 45% increase in the initial contact area that is formed under normal preload alone. Good correlation is found between the present experimental results and a theoretical model for medium and high normal preloads.
Alain Debec - One of the best experts on this subject based on the ideXlab platform.
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Shaggy, the Homolog of Glycogen Synthase Kinase 3, Controls Neuromuscular Junction Growth in Drosophila
Journal of Neuroscience, 2004Co-Authors: Marie-laure Parmentier, Bénédicte Franco, Laurent Bogdanik, Joël Bockaert, Yves Grau, Y. Bobinnec, Alain DebecAbstract:A protein-trap screen using the Drosophila neuromuscular Junction (NMJ) as a model synapse was performed to identify genes that control synaptic structure or plasticity. We found that Shaggy (Sgg), the Drosophila homolog of the mammalian glycogen synthase kinases 3 alpha and beta, two serine-threonine kinases, was concentrated at this synapse. Using various combinations of mutant alleles of shaggy, we found that Shaggy negatively controlled the NMJ Growth. Moreover, tissue-specific expression of a dominant-negative Sgg indicated that this kinase is required in the motoneuron, but not in the muscle, to control NMJ Growth. Finally, we show that Sgg controlled the microtubule cytoskeleton dynamics in the motoneuron and that Futsch, a microtubule-associated protein, was required for Shaggy function on synaptic Growth.glycogen synthase kinase, synaptic plasticity
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shaggy the homolog of glycogen synthase kinase 3 controls neuromuscular Junction Growth in drosophila
The Journal of Neuroscience, 2004Co-Authors: Bénédicte Franco, Marie-laure Parmentier, Laurent Bogdanik, Joël Bockaert, Y. Bobinnec, Alain Debec, Yves GrauAbstract:A protein-trap screen using the Drosophila neuromuscular Junction (NMJ) as a model synapse was performed to identify genes that control synaptic structure or plasticity. We found that Shaggy (Sgg), the Drosophila homolog of the mammalian glycogen synthase kinases 3 α and β, two serine-threonine kinases, was concentrated at this synapse. Using various combinations of mutant alleles of shaggy, we found that Shaggy negatively controlled the NMJ Growth. Moreover, tissue-specific expression of a dominant-negative Sgg indicated that this kinase is required in the motoneuron, but not in the muscle, to control NMJ Growth. Finally, we show that Sgg controlled the microtubule cytoskeleton dynamics in the motoneuron and that Futsch, a microtubule-associated protein, was required for Shaggy function on synaptic Growth.
Y Kligerman - One of the best experts on this subject based on the ideXlab platform.
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The Effect of Dwell Time on the Static Friction in Creeping Elastic–Plastic Polymer Spherical Contact
Tribology Letters, 2009Co-Authors: S. Malamut, Y Kligerman, I EtsionAbstract:A theoretical model is developed to study the effect of dwell time on the Junction Growth and static friction of a creeping polymer sphere in contact with a rigid flat under full stick contact condition. A rapid normal loading into the elastic–plastic contact regime is followed by a rest period during which creep takes place causing contact area Growth, and stress relaxation that can completely eliminate the plastic zone in the sphere. At the end of this rest time, an increasing tangential loading is applied to the flat till sliding inception occurs. During this loading step, further increase of the contact area and reappearing of a plastic zone in the sphere take place. An increase in static friction resulting from the dwell time during the creep stage is clearly demonstrated and explained.
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the effect of surface roughness on static friction and Junction Growth of an elastic plastic spherical contact
Journal of Tribology-transactions of The Asme, 2009Co-Authors: Denis Cohen, Y Kligerman, Izhak EtsionAbstract:A model for elastic-plastic spherical contact of rough surfaces under combined normal and tangential loadings, with full stick contact condition, is presented. The model allows evaluation of the effect of surface roughness on the real contact area, static friction and Junction Growth under small normal loads. It is shown that as the normal load approaches a certain threshold value, which depends on the plasticity index, the results of the present rough surface model approach these of previous corresponding models for smooth sphere and a rigid flat. At normal load values below the threshold load, the correlation of the present results and published experimental results is much better in comparison with the results of the smooth surface models.
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A Model for Contact and Static Friction of Nominally Flat Rough Surfaces Under Full Stick Contact Condition model for elastic-plastic nominally flat contacting rough surfaces under combined
2009Co-Authors: Denis Cohen, Y Kligerman, Izhak EtsionAbstract:normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of Junction Growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results. DOI: 10.1115/1.2908925
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a model for contact and static friction of nominally flat rough surfaces under full stick contact condition
Journal of Tribology-transactions of The Asme, 2008Co-Authors: Denis Cohen, Y Kligerman, Izhak EtsionAbstract:A model for elastic-plastic nominally flat contacting rough surfaces under combined normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of Junction Growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results.
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A Model for Junction Growth of a Spherical Contact Under Full Stick Condition
Journal of Tribology, 2007Co-Authors: Victor Brizmer, Y Kligerman, Izhak EtsionAbstract:The evolution of the contact area (Junction Growth) of an elastic-plastic preloaded spherical contact subjected to an additional tangential loading is investigated theoretically. The normal preloading, under full stick condition, leads to the formation of a Junction that can support additional tangential load. A gradual increase of this tangential load, while the normal preload remains constant, can incept plasticity of the contact zone in case the initial normal preload was elastic or enhance an existing one, thus lowering the tangential stiffness of the Junction. Finally, the tangential stiffness approaches zero, which corresponds to sliding inception (i.e., loss of stability). The evolution of the contact area during the tangential loading prior to sliding inception reveals an essential Junction Growth which depends on the magnitude of the normal preload. The mechanism causing this Junction Growth seems to be new points of the sphere surface, which originally lay outside of the initial contact area that are coming into contact with the rigid flat during the tangential loading. The theoretical results for the Junction Growth obtained in the present work correlate well with some limited experiments.
Thomas Lecuit - One of the best experts on this subject based on the ideXlab platform.
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Local and tissue-scale forces drive oriented Junction Growth during tissue extension
Nature Cell Biology, 2015Co-Authors: Claudio Collinet, Matteo Rauzi, Pierre-françois Lenne, Thomas LecuitAbstract:Convergence–extension is a widespread morphogenetic process driven by polarized cell intercalation. In the Drosophila germ band, epithelial intercalation comprises loss of Junctions between anterior–posterior neighbours followed by Growth of new Junctions between dorsal–ventral neighbours. Much is known about how active stresses drive polarized Junction shrinkage. However, it is unclear how tissue convergence–extension emerges from local Junction remodelling and what the specific role, if any, of Junction Growth is. Here we report that tissue convergence and extension correlate mostly with new Junction Growth. Simulations and in vivo mechanical perturbations reveal that Junction Growth is due to local polarized stresses driven by medial actomyosin contractions. Moreover, we find that tissue-scale pulling forces at the boundary with the invaginating posterior midgut actively participate in tissue extension by orienting Junction Growth. Thus, tissue extension is akin to a polarized fluid flow that requires parallel and concerted local and tissue-scale forces to drive Junction Growth and cell–cell displacement. Lecuit and colleagues use live imaging and laser ablation approaches to show that germ-band extension of the Drosophila embryo is associated with new Junction Growth, which is dependent on both tissue-level and local forces.
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local and tissue scale forces drive oriented Junction Growth during tissue extension
Nature Cell Biology, 2015Co-Authors: Claudio Collinet, Matteo Rauzi, Pierre-françois Lenne, Thomas LecuitAbstract:Convergence-extension is a widespread morphogenetic process driven by polarized cell intercalation. In the Drosophila germ band, epithelial intercalation comprises loss of Junctions between anterior-posterior neighbours followed by Growth of new Junctions between dorsal-ventral neighbours. Much is known about how active stresses drive polarized Junction shrinkage. However, it is unclear how tissue convergence-extension emerges from local Junction remodelling and what the specific role, if any, of Junction Growth is. Here we report that tissue convergence and extension correlate mostly with new Junction Growth. Simulations and in vivo mechanical perturbations reveal that Junction Growth is due to local polarized stresses driven by medial actomyosin contractions. Moreover, we find that tissue-scale pulling forces at the boundary with the invaginating posterior midgut actively participate in tissue extension by orienting Junction Growth. Thus, tissue extension is akin to a polarized fluid flow that requires parallel and concerted local and tissue-scale forces to drive Junction Growth and cell-cell displacement.
Tungsheng Yang - One of the best experts on this subject based on the ideXlab platform.
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a new mechanism of asperity flattening in sliding contact the role of tool elastic microwedge
Journal of Tribology-transactions of The Asme, 2003Co-Authors: Tungsheng YangAbstract:Based on real-time observation of the workpiece surface in a series of Lo and Tsai's (2002) compression-sliding experiment, it is found that the asperity contact area is much greater than that evaluated by the existing theorems such as the Junction-Growth theorem. With the aid of finite element analysis, it is verified that the tool sliding motion along with the minute elastic deformation (microwedge) of the tool surface around the asperity peaks increase the asperity contact area significantly even in a frictionless sliding. The microwedge induces a component of force along the sliding direction on the asperity. A combination of flattening and smearing effects can therefore aid in expanding the contact area. The greater the wedge angle, the stronger the propellent effect. An incremental model has also been developed to predict the evolution of contact area daring sliding. The numerical simulation compares well with the experimental results. The new mechanism not only introduces an important tribological variable to forming processes, but also brings in a new concept of surface quality control for processes having a considerable sliding distance between workpiece and tool such as ironing, forging, and extrusion. New processes performing high relative sliding velocity can therefore be developed to ameliorate the brightness of products.
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A New Mechanism of Asperity Flattening in Sliding Contact—The Role of Tool Elastic Microwedge
Journal of Tribology, 2003Co-Authors: Tungsheng YangAbstract:Based on real-time observation of the workpiece surface in a series of Lo and Tsai's (2002) compression-sliding experiment, it is found that the asperity contact area is much greater than that evaluated by the existing theorems such as the Junction-Growth theorem. With the aid of finite element analysis, it is verified that the tool sliding motion along with the minute elastic deformation (microwedge) of the tool surface around the asperity peaks increase the asperity contact area significantly even in a frictionless sliding. The microwedge induces a component of force along the sliding direction on the asperity. A combination of flattening and smearing effects can therefore aid in expanding the contact area. The greater the wedge angle, the stronger the propellent effect. An incremental model has also been developed to predict the evolution of contact area daring sliding. The numerical simulation compares well with the experimental results. The new mechanism not only introduces an important tribological variable to forming processes, but also brings in a new concept of surface quality control for processes having a considerable sliding distance between workpiece and tool such as ironing, forging, and extrusion. New processes performing high relative sliding velocity can therefore be developed to ameliorate the brightness of products.
