The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Itzhak Green - One of the best experts on this subject based on the ideXlab platform.
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the thermoelastic behavior of thrust washer bearings considering mixed lubrication Asperity Contact and thermoviscous effects
Tribology Transactions, 2008Co-Authors: Robert L. Jackson, Itzhak GreenAbstract:A comprehensive numerical model is developed to investigate the behavior of a tilted thrust washer bearing. The goal of this work is to investigate the physical phenomena that distress the bearing system. This work includes thermoelastic deformations, which have been neglected in previous studies. The thrust washer bearing is subjected to non-axisymmetric loads within the planetary gear sets of automatic transmissions and consists of flat-faced washers placed between an idle helical gear and an adjacent carrier face. Various coupled numerical schemes model sliding friction, boundary lubrication, Asperity Contact, thermo-mechanical deformation, thermoviscous effects, and full-film lubrication. The model provides predictions of frictional torque, bearing temperature, hydrodynamic lift, and other indicators of bearing performance. The numerical model and theoretical predictions confirm the experimental results, showing that the bearing under consideration is very susceptible to the mechanisms of thermoelasti...
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a statistical model of elasto plastic Asperity Contact between rough surfaces
Tribology International, 2006Co-Authors: Robert L. Jackson, Itzhak GreenAbstract:This work models statistically elasto-plastic Contact between two rough surfaces using the results of a previous finite element analysis of an elasto-plastic sphere in Contact with a rigid flat. The individual Asperity Contact model used accounts for a varying geometrical hardness effect that has recently been documented in previous works (where geometrical hardness is defined as the uniform pressure found during fully plastic Contact). The Contact between real surfaces with known material and surface properties, such as the elastic modulus, yield strength, and roughness are modeled. The Asperity is modeled as an elastic-perfectly plastic material. The model produces predictions for Contact area, Contact force, and surface separation. The results of this model are compared to other existing models of Asperity Contact. Agreement exists in some cases and in other cases it corrects flaws, especially at large deformations. The model developed by Chang, Etsion and Bogy is also shown to have serious flaws when compared to the others. This work also identifies significant limitations of the statistical models (including that of Greenwood and Williamson).
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The Behavior of Thrust Washer Bearings Considering Mixed Lubrication and Asperity Contact
Tribology Transactions, 2006Co-Authors: Robert L. Jackson, Itzhak GreenAbstract:The behavior and life of a tilted flat thrust washer bearing is modeled by a comprehensive numerical code. The goal is to investigate the conditions that distress thrust washer bearings through numerical techniques. The thrust washer bearing supports non-axisymmetric loads within the planetary gear sets of automatic transmissions and consists of flat-faced washers placed between an idle helical gear and its Contacting face. Because of non-axisymmetric loading, the gears and washers tilt in relation to the carrier, forming a converging gap that may produce hydrodynamic lift. Various coupled numerical schemes model sliding friction, boundary lubrication, Asperity Contact, thermo-viscous effects, and full film lubrication. The model provides predictions of frictional torque, bearing temperature, hydrodynamic lift, and other indicators of bearing performance. The results show that the bearing operates in the regimes of boundary lubrication, mixed lubrication, and full-film lubrication, and that the bearing ca...
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The Thermoelastic Behavior of Thrust Washer Bearings Considering Boundary Lubrication and Asperity Contact
World Tribology Congress III Volume 2, 2005Co-Authors: Robert L. Jackson, Itzhak GreenAbstract:The behavior and life of a tilted flat thrust washer bearing is modeled by a comprehensive numerical code. The goal is to investigate the conditions that distress thrust washer bearings through numerical techniques. This work includes thermo-mechanical deformations (which have been neglected in previous studies). The thrust washer bearing supports non-axisymmetric loads within the planetary gear sets of automatic transmissions and consists of flat-faced washers placed between an idle helical gear and its Contacting face. Various coupled numerical schemes model sliding friction, boundary lubrication, Asperity Contact, thermo-mechanical deformation, thermo-viscous effects, and full film lubrication. The model provides predictions of frictional torque, bearing temperature, hydrodynamic lift and other indicators of bearing performance. The experimental and numerical results show that the bearing is very susceptible to the mechanism of thermoelastic instability (TEI). Theoretical predictions indeed predict that the washer may operate in the range of TEI.Copyright © 2005 by ASME
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a transient dynamic analysis of mechanical seals including Asperity Contact and face deformation
Tribology Transactions, 2002Co-Authors: Itzhak GreenAbstract:Face seals are typically designed to be in Contact at standstill. However, as speed and pressure build up, the seal faces deform from their factory flat conditions because of viscous and dry friction heating, as well as mechanical and centrifugal effects. It is imperative that such deformations form a converging gap for radial flow to ensure stable operation and to promote favorable dynamic tracking between stator and rotor. A numerical simulation is presented for the transient response of a face seal that is subjected to forcing misalignments while speeds and pressures are ramped up and down. Asperity Contact forces and transient face deformation caused by viscous heating are included. A new closed-form solution is obtained for the elastoplastic Contact model, which allows seamless transition between Contacting and nonContacting modes of operation. The model is then used to calculate face Contact forces that occur predominantly during startup and shutdown. The viscous heating model shows that the time-de...
Robert L. Jackson - One of the best experts on this subject based on the ideXlab platform.
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Elastic-plastic axisymmetric sinusoidal surface Asperity Contact
2016 IEEE 62nd Holm Conference on Electrical Contacts (Holm), 2016Co-Authors: Swarna Saha, Robert L. JacksonAbstract:Closed-form finite-element empirical solutions are available for elastic-plastic spherical and sinusoidal Contact. However, some of these models do not consider the effect of interaction with adjacent asperities or require extensive numerical resources because they employ a full 3-D model. The present work has considered these factors during modeling. The current finite element model (FEM) represents an axisymmetric elastic-plastic sinusoidal surface in Contact with a rigid flat for a wide range of material properties and different values of the amplitude to wavelength ratio. The numerical results are compared with the existing elastic-plastic spherical Contact model. Empirical equations are derived for the critical pressure at which two surface will reach complete Contact. Complete Contact occurs when there is no gap remaining between two Contacting surfaces. An equation for the critical value of the amplitude of the sinusoidal Asperity below which it will deform completely elastically from initial to complete Contact is also established. The current study finds that for the cases which have amplitudes that fall below the critical value, and are elastic in nature, that the previously published perfectly elastic model can be used. The results are applicable for almost all kinds of metallic materials.
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The Influence of Thermal Expansion and Plastic Deformation on a Thermo-Electro Mechanical Spherical Asperity Contact
2012 IEEE 58th Holm Conference on Electrical Contacts (Holm), 2012Co-Authors: Hamed Ghaednia, Amir Rostami, Robert L. JacksonAbstract:Electrical Contacts are expected to be influenced by coupled thermo-electro mechanical mechanisms. In this paper a single spherical Asperity Contact has been investigated with a coupled finite element thermo-electro mechanical approach. Thermo-electro mechanical behavior of a sphere in Contact with a block has been analyzed while focusing on the effect of plastic deformation and thermal expansion. A finite element model is developed to analyze different cases and various parameters. Stress distribution, voltage drop and temperature profile have been presented. Results suggest that the thermal expansion influences the Contact resistance significantly only for cases where the interferences are small. The thermal expansion decreases the Contact resistance at a given interference, probably by effectively increasing the Contact force. A non-dimensional parameter is derived to predict whether or not the influence of thermal expansion is important on an electrical Contact.
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Effects of Lattice Orientation and Size on Molecular Asperity Contact Models
ASME STLE 2009 International Joint Tribology Conference, 2009Co-Authors: J. Robert Polchow, Wei Huang, Robert L. JacksonAbstract:Surface asperities can range widely in size. Therefore it is important to characterize the effect of size and scale on the Contact mechanics. This work presents a molecular model of Asperity Contact in order to characterize small scale Asperity Contact. The effects of lattice orientation and radius (number of particles) are examined. It appears that lattice orientation has a noticeable effect, but nominally may not be important in the Contact of asperities and rough surfaces. The size appears to be important until a certain minimum size is achieved.© 2009 ASME
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the thermoelastic behavior of thrust washer bearings considering mixed lubrication Asperity Contact and thermoviscous effects
Tribology Transactions, 2008Co-Authors: Robert L. Jackson, Itzhak GreenAbstract:A comprehensive numerical model is developed to investigate the behavior of a tilted thrust washer bearing. The goal of this work is to investigate the physical phenomena that distress the bearing system. This work includes thermoelastic deformations, which have been neglected in previous studies. The thrust washer bearing is subjected to non-axisymmetric loads within the planetary gear sets of automatic transmissions and consists of flat-faced washers placed between an idle helical gear and an adjacent carrier face. Various coupled numerical schemes model sliding friction, boundary lubrication, Asperity Contact, thermo-mechanical deformation, thermoviscous effects, and full-film lubrication. The model provides predictions of frictional torque, bearing temperature, hydrodynamic lift, and other indicators of bearing performance. The numerical model and theoretical predictions confirm the experimental results, showing that the bearing under consideration is very susceptible to the mechanisms of thermoelasti...
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Experimental and Analytical Investigation of a Dynamic Gas Squeeze Film Bearing Including Asperity Contact Effects
Tribology Transactions, 2008Co-Authors: Manoj Mahajan, Robert L. Jackson, George T. FlowersAbstract:This work presents a theoretical and experimental investigation of a flat circular gas squeeze film bearing. The thickness and the pressure profile of the gas squeeze film are obtained by simultaneously solving the Reynolds equation and the equation of motion for the squeeze film bearing. This work also accounts for the force due to Asperity Contact in the equation of motion. When the surfaces are in Contact, the model predicts the Contact force as a function of film thickness. Computational simulations were performed to study the development of the squeeze film from its initial state to a pseudo-steady state and also to evaluate its load- carrying capacity. For certain cases, the simulation results correlate well with the preestablished analytical results. However, corrections must be made to the preestablished analytical equations when they are used out of their effective range. In the experimental study, the squeeze film was developed by an applied relative normal motion between two parallel plates, of...
Tian Tian - One of the best experts on this subject based on the ideXlab platform.
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flash temperature and anti wear tribofilm growth mechanisms by Asperity Contact in top ring liner conjunction of ic engines
Tribology International, 2020Co-Authors: Qin Zhang, Wang Zhang, Si Ren, Zhe Chen, Tian TianAbstract:Abstract Understanding the growth mechanism of tribofilms at the top of the liner in IC engines is of great importance to protecting the sealing function of the top ring. In present study, the transient heat transfer is investigated between the ring and the liner in the top dead center (TDC) area with considerations of Asperity Contact pressure, boundary friction coefficient and reciprocating piston motion. A 3D transient model is developed to predict the evolutions of effective heat partition and conduction between the Contact surfaces. It is revealed that the flash temperature in the Asperity Contact pairs of the top-ring/liner conjunction is remarkably higher than the steady-state liner temperature, therefore significantly enhancing the growth rate of anti-wear film formation based on a stress-activated Arrhenius model. The results show that the Asperity Contact model and the flash temperature model can be employed as an engineering tool for anti-wear tribofilm prediction in top-ring/liner conjunction of IC engines.
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Flash temperature and anti-wear tribofilm growth mechanisms by Asperity Contact in top-ring/liner conjunction of IC engines
Tribology International, 2020Co-Authors: Qin Zhang, Wang Zhang, Si Ren, Zhe Chen, Tian TianAbstract:Abstract Understanding the growth mechanism of tribofilms at the top of the liner in IC engines is of great importance to protecting the sealing function of the top ring. In present study, the transient heat transfer is investigated between the ring and the liner in the top dead center (TDC) area with considerations of Asperity Contact pressure, boundary friction coefficient and reciprocating piston motion. A 3D transient model is developed to predict the evolutions of effective heat partition and conduction between the Contact surfaces. It is revealed that the flash temperature in the Asperity Contact pairs of the top-ring/liner conjunction is remarkably higher than the steady-state liner temperature, therefore significantly enhancing the growth rate of anti-wear film formation based on a stress-activated Arrhenius model. The results show that the Asperity Contact model and the flash temperature model can be employed as an engineering tool for anti-wear tribofilm prediction in top-ring/liner conjunction of IC engines.
Qin Zhang - One of the best experts on this subject based on the ideXlab platform.
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flash temperature and anti wear tribofilm growth mechanisms by Asperity Contact in top ring liner conjunction of ic engines
Tribology International, 2020Co-Authors: Qin Zhang, Wang Zhang, Si Ren, Zhe Chen, Tian TianAbstract:Abstract Understanding the growth mechanism of tribofilms at the top of the liner in IC engines is of great importance to protecting the sealing function of the top ring. In present study, the transient heat transfer is investigated between the ring and the liner in the top dead center (TDC) area with considerations of Asperity Contact pressure, boundary friction coefficient and reciprocating piston motion. A 3D transient model is developed to predict the evolutions of effective heat partition and conduction between the Contact surfaces. It is revealed that the flash temperature in the Asperity Contact pairs of the top-ring/liner conjunction is remarkably higher than the steady-state liner temperature, therefore significantly enhancing the growth rate of anti-wear film formation based on a stress-activated Arrhenius model. The results show that the Asperity Contact model and the flash temperature model can be employed as an engineering tool for anti-wear tribofilm prediction in top-ring/liner conjunction of IC engines.
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Flash temperature and anti-wear tribofilm growth mechanisms by Asperity Contact in top-ring/liner conjunction of IC engines
Tribology International, 2020Co-Authors: Qin Zhang, Wang Zhang, Si Ren, Zhe Chen, Tian TianAbstract:Abstract Understanding the growth mechanism of tribofilms at the top of the liner in IC engines is of great importance to protecting the sealing function of the top ring. In present study, the transient heat transfer is investigated between the ring and the liner in the top dead center (TDC) area with considerations of Asperity Contact pressure, boundary friction coefficient and reciprocating piston motion. A 3D transient model is developed to predict the evolutions of effective heat partition and conduction between the Contact surfaces. It is revealed that the flash temperature in the Asperity Contact pairs of the top-ring/liner conjunction is remarkably higher than the steady-state liner temperature, therefore significantly enhancing the growth rate of anti-wear film formation based on a stress-activated Arrhenius model. The results show that the Asperity Contact model and the flash temperature model can be employed as an engineering tool for anti-wear tribofilm prediction in top-ring/liner conjunction of IC engines.
Shiping Huang - One of the best experts on this subject based on the ideXlab platform.
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Micromechanical stress–displacement model for rough interfaces: Effect of Asperity Contact orientation on closure and shear behavior
International Journal of Solids and Structures, 2012Co-Authors: Anil Misra, Shiping HuangAbstract:Abstract The coupled normal-shear Contact behavior of rough surfaces remains a problem of interest with applications in many practical engineering problems. In this paper, we have further developed a micromechanical approach for obtaining the stress–displacement behavior of rough interfaces. The micromechanical approach considers the mechanics of Asperity Contacts and utilizes statistical description of interface roughness. Here we have focused upon the role of Asperity Contact orientations. To that end, we have incorporated Asperity Contact relative curvature distribution in our model and derived a relationship for the extent of Asperity Contact orientations in terms of the Asperity Contact relative curvature and interface closure. This relationship allows us to define the range of Asperity Contact orientation as the interface is subjected to combined normal and shear loading. We have consequently refined our stress–displacement relationship and its numerical evaluation procedure to include the Asperity Contact relative curvature distributions. We find that the Asperity Contact relative curvature has a significant effect on the extent of Asperity Contact orientation, and consequently on the shear behavior of the interface. We also find that the coupling between the normal and the shear responses, the interface frictional strength and the shear displacement hardening behavior are closely related to the extent of Asperity Contact orientations.
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micromechanical stress displacement model for rough interfaces effect of Asperity Contact orientation on closure and shear behavior
International Journal of Solids and Structures, 2012Co-Authors: Anil Misra, Shiping HuangAbstract:Abstract The coupled normal-shear Contact behavior of rough surfaces remains a problem of interest with applications in many practical engineering problems. In this paper, we have further developed a micromechanical approach for obtaining the stress–displacement behavior of rough interfaces. The micromechanical approach considers the mechanics of Asperity Contacts and utilizes statistical description of interface roughness. Here we have focused upon the role of Asperity Contact orientations. To that end, we have incorporated Asperity Contact relative curvature distribution in our model and derived a relationship for the extent of Asperity Contact orientations in terms of the Asperity Contact relative curvature and interface closure. This relationship allows us to define the range of Asperity Contact orientation as the interface is subjected to combined normal and shear loading. We have consequently refined our stress–displacement relationship and its numerical evaluation procedure to include the Asperity Contact relative curvature distributions. We find that the Asperity Contact relative curvature has a significant effect on the extent of Asperity Contact orientation, and consequently on the shear behavior of the interface. We also find that the coupling between the normal and the shear responses, the interface frictional strength and the shear displacement hardening behavior are closely related to the extent of Asperity Contact orientations.
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Effect of Loading Induced Anisotropy on the Shear Behavior of Rough Interfaces
2011Co-Authors: Anil Misra, Shiping HuangAbstract:We have utilized a statistical method to model the shear behavior of rough Contacts. In contrast to the traditional statistical methods, which only describe the Asperity height and curvature distributions, we have introduced a Contact orientation distribution in our analysis. We have also incorporated Asperity Contact sliding and developed an incremental scheme for computing the stress-displacement relationship. Using this enhanced model, we can demarcate the boundary between elastically deforming and sliding Asperity Contact orientations under given loading. Consequently, we can describe the shear-normal coupling as well as the effects of inherent anisotropy and the induced anisotropy of the sheared interfaces.
