Lubrificatia ex-poro-hidrodinamica (XPHD), mecanism care genereaza film fluid autoportant prin ex... more Lubrificatia ex-poro-hidrodinamica (XPHD), mecanism care genereaza film fluid autoportant prin expulzarea lubrifiantului imbibat intr-un strat poros foarte compresibil (HCPL), este puternic dependenta de variatia permeabilitatii structurii poroase. Aceasta lucrare studiaza variatia permeabilitatii cu deformatia HCPL. Experimentele au fost realizate pe doua materiale poroase imbibate cu glicerina, comprimate cu viteza constanta cu un indentor sferic. S-a analizat atat faza de comprimare, cat si cea de decomprimare. Rezultatele din faza de comprimare au fost utilizate pentru evaluarea permeabilitatii pe baza unui model teoretic publicat anterior. Se arata ca permeabilitatea variaza cu viteza de deformare a HCPL si deci ca notiunea de permeabilitate dinamica trebuie luata in considerare. Ex-poro-hydrodynamic (XPHD) lubrication, a mechanism that generates self-sustained films when highly compressible porous layers (HCPL) imbibed with liquids are squeezed, is strongly dependent on permea...
The use of temperature and pressure induced deformations to generate hydrodynamic lift-off for fl... more The use of temperature and pressure induced deformations to generate hydrodynamic lift-off for flat and parallel surfaces is relatively new and scarcely present in literature. The present paper analyses theoretically the load carrying capacity of a typical thrust bearing with elastic pad in order to define optimal pad parameters. The study is made using the original Thrust Bearing Analysis (TBA) Software based on finite differences solution of flow and thermal equations and finite elements solution for solid structure equations. The results, presented for the equivalent slider, have primary revealed that the load carrying capacity of such a bearing is comparable with a similar tilting-pad bearing. The parametric analysis shows the existence of optimal dimensions for maximum load capacity.
Fluid flow through highly compressible porous layers (HCPL) subjected to external loads is known ... more Fluid flow through highly compressible porous layers (HCPL) subjected to external loads is known as ex-poro-hydrodynamic (XPHD) lubrication. Several models have been proposed for squeeze in XPHD conditions and analytical solutions were obtained based on a significant number of simplifications. Consequently, an analysis of these simplifications effects is necessary to define the limits of applicability of the analytical solutions and the corresponding degree of approximation. The present study investigates the accuracy of these approximations by comparison with numerical solution of modified Reynolds equation based on finite difference method. The analysis is developed for sphere/plane configuration in two loading cases: constant force loading and impact loading, respectively. It is found that for almost all loading conditions and a large range of dimensionless parameters the two term approximation produces acceptable errors with respect to the exact solution.
Ex-poro-hydrodynamic (XPHD) lubrication describes the lifting effect produced by the flow of flui... more Ex-poro-hydrodynamic (XPHD) lubrication describes the lifting effect produced by the flow of fluid through an extremely compressible porous material subjected to compression. Studies published recently on the behaviour of such materials, for various configurations, reveal good potential in shock absorption. The present study addresses the case of an infinitely long cylinder that impacts a highly compressible porous layer interposed between the cylinder and a rigid plane. Based on a 1D flow model, the lift effects for squeeze at constant speed, constant force and impact loading, respectively are analyzed.
Abstract During last two decades it was theoretically and experimentally proved that the fluid sq... more Abstract During last two decades it was theoretically and experimentally proved that the fluid squeeze out from a soft and porous layer under the action of an external impact load produces high lifting forces. For high porosity, the elastic forces generated by the solid phase are negligible. The mechanism, strongly dependent on permeability variation with layer compression, can be used for shock absorbing devices. One of the key parameters for maximum impact damping is the initial porosity of the soft layer. This analysis provides a simple, analytical solution for optimum initial porosity that minimizes the peak impact force, for impact squeeze between two perfectly rigid and impermeable flat disks of a highly compressible porous layer imbibed with Newtonian liquid. The solution is based on a quasi-static Darcy flow approach. The comparison of predicted values with the experimental data from impact tests made on a gas gun test-rig, show good agreement for medium impact speed.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2011
The objective of this article is the study of the load-carrying capacity of a Rayleigh step slide... more The objective of this article is the study of the load-carrying capacity of a Rayleigh step slider (RSS) for both direct motion (+RSS – which generates lifting effects) and reverse motion (−RSS – which generates suction or cavitational effects). Normal force was measured on a pin-on-disc test rig, with two lubricants (SAE-20 W-50 oil and glycerin) at four speeds and three values of film thickness. During reverse motion (−RSS), cavitational effects have been observed for some test cases. It is supposed that surface tension influences the appearance of cavitational effects, and a modified capillary number, Ca+, is proposed as indicator of cavitation inception. Close-up views taken near the trailing edge of the pin show the occurrence of several streamers, typical for cavitational effects, only when Ca+ > 2. Numerical simulation as well as approximate analytical models are presented for both directions of motion. The comparison of predicted theoretical results with the experimental ...
ASME/STLE 2007 International Joint Tribology Conference, Parts A and B, 2007
Surface texturing has been shown to have friction reducing / load capacity increasing effects in ... more Surface texturing has been shown to have friction reducing / load capacity increasing effects in parallel sliders, as well as in cylinder-liner contacts and in hydrodynamic seals. However, if texture is to be regarded as the sole mean of hydrodynamic lift in parallel sliders, or as a way of improving hydrodynamic performance in slider, thrust and journal bearings, several issues have to be addressed, such as optimal texturing parameters and corresponding performance gains. This paper deals with these issues in the case of a plane inclined textured slider. Parametric studies are conducted to determine optimal texturing extents, dimple depth and texturing density, as well as the influence of the operating conditions on these optimal texturing parameters.
This chapter deals with explanation of friction in lubricated contacts. Friction is the resistanc... more This chapter deals with explanation of friction in lubricated contacts. Friction is the resistance to motion that occurs when one body slides over another. The resistive force acting in the opposite direction of the relative motion is known as the friction force. The friction force has two forms: the force required to initiate sliding, known as the static friction force, and the force necessary to maintain the sliding, called the kinetic friction force. This chapter discusses four regimes of Stribeck's curve that shows different regimes of lubrication can occur in a lubricated sliding contact, depending on the relative speed. These regimes also depend on the pressures occurring in the lubricating film. Regime I: it is called boundary lubrication for conformal contacts, whereas for nonconformal contacts, this regime is known as extreme pressure (EP) lubrication. The main feature of boundary lubrication in comparison with solid-to-solid contact is that although the reduction in the friction coefficient is less important, the reduction in wear is impressive. Regime II: corresponds to mixed lubrication in which several mechanisms act simultaneously. This regime is a transition regime between boundary lubrication and hydrodynamic lubrication for low-pressure films or between extreme pressure lubrication and elastohydrodynamic lubrication for highpressure films. Regime III: corresponds to hydrodynamic (HD) lubrication for low-pressure films, or to elastohydrodynamic (EHD) lubrication for high-pressure films. And lastly, regime IV: it is characterized by superlaminar flow in hydrodynamic lubrication. This regime occurs for high-relative-speeds, low-viscosity lubricants or very large dimensions.
Lubrificatia ex-poro-hidrodinamica (XPHD), mecanism care genereaza film fluid autoportant prin ex... more Lubrificatia ex-poro-hidrodinamica (XPHD), mecanism care genereaza film fluid autoportant prin expulzarea lubrifiantului imbibat intr-un strat poros foarte compresibil (HCPL), este puternic dependenta de variatia permeabilitatii structurii poroase. Aceasta lucrare studiaza variatia permeabilitatii cu deformatia HCPL. Experimentele au fost realizate pe doua materiale poroase imbibate cu glicerina, comprimate cu viteza constanta cu un indentor sferic. S-a analizat atat faza de comprimare, cat si cea de decomprimare. Rezultatele din faza de comprimare au fost utilizate pentru evaluarea permeabilitatii pe baza unui model teoretic publicat anterior. Se arata ca permeabilitatea variaza cu viteza de deformare a HCPL si deci ca notiunea de permeabilitate dinamica trebuie luata in considerare. Ex-poro-hydrodynamic (XPHD) lubrication, a mechanism that generates self-sustained films when highly compressible porous layers (HCPL) imbibed with liquids are squeezed, is strongly dependent on permea...
The use of temperature and pressure induced deformations to generate hydrodynamic lift-off for fl... more The use of temperature and pressure induced deformations to generate hydrodynamic lift-off for flat and parallel surfaces is relatively new and scarcely present in literature. The present paper analyses theoretically the load carrying capacity of a typical thrust bearing with elastic pad in order to define optimal pad parameters. The study is made using the original Thrust Bearing Analysis (TBA) Software based on finite differences solution of flow and thermal equations and finite elements solution for solid structure equations. The results, presented for the equivalent slider, have primary revealed that the load carrying capacity of such a bearing is comparable with a similar tilting-pad bearing. The parametric analysis shows the existence of optimal dimensions for maximum load capacity.
Fluid flow through highly compressible porous layers (HCPL) subjected to external loads is known ... more Fluid flow through highly compressible porous layers (HCPL) subjected to external loads is known as ex-poro-hydrodynamic (XPHD) lubrication. Several models have been proposed for squeeze in XPHD conditions and analytical solutions were obtained based on a significant number of simplifications. Consequently, an analysis of these simplifications effects is necessary to define the limits of applicability of the analytical solutions and the corresponding degree of approximation. The present study investigates the accuracy of these approximations by comparison with numerical solution of modified Reynolds equation based on finite difference method. The analysis is developed for sphere/plane configuration in two loading cases: constant force loading and impact loading, respectively. It is found that for almost all loading conditions and a large range of dimensionless parameters the two term approximation produces acceptable errors with respect to the exact solution.
Ex-poro-hydrodynamic (XPHD) lubrication describes the lifting effect produced by the flow of flui... more Ex-poro-hydrodynamic (XPHD) lubrication describes the lifting effect produced by the flow of fluid through an extremely compressible porous material subjected to compression. Studies published recently on the behaviour of such materials, for various configurations, reveal good potential in shock absorption. The present study addresses the case of an infinitely long cylinder that impacts a highly compressible porous layer interposed between the cylinder and a rigid plane. Based on a 1D flow model, the lift effects for squeeze at constant speed, constant force and impact loading, respectively are analyzed.
Abstract During last two decades it was theoretically and experimentally proved that the fluid sq... more Abstract During last two decades it was theoretically and experimentally proved that the fluid squeeze out from a soft and porous layer under the action of an external impact load produces high lifting forces. For high porosity, the elastic forces generated by the solid phase are negligible. The mechanism, strongly dependent on permeability variation with layer compression, can be used for shock absorbing devices. One of the key parameters for maximum impact damping is the initial porosity of the soft layer. This analysis provides a simple, analytical solution for optimum initial porosity that minimizes the peak impact force, for impact squeeze between two perfectly rigid and impermeable flat disks of a highly compressible porous layer imbibed with Newtonian liquid. The solution is based on a quasi-static Darcy flow approach. The comparison of predicted values with the experimental data from impact tests made on a gas gun test-rig, show good agreement for medium impact speed.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2011
The objective of this article is the study of the load-carrying capacity of a Rayleigh step slide... more The objective of this article is the study of the load-carrying capacity of a Rayleigh step slider (RSS) for both direct motion (+RSS – which generates lifting effects) and reverse motion (−RSS – which generates suction or cavitational effects). Normal force was measured on a pin-on-disc test rig, with two lubricants (SAE-20 W-50 oil and glycerin) at four speeds and three values of film thickness. During reverse motion (−RSS), cavitational effects have been observed for some test cases. It is supposed that surface tension influences the appearance of cavitational effects, and a modified capillary number, Ca+, is proposed as indicator of cavitation inception. Close-up views taken near the trailing edge of the pin show the occurrence of several streamers, typical for cavitational effects, only when Ca+ > 2. Numerical simulation as well as approximate analytical models are presented for both directions of motion. The comparison of predicted theoretical results with the experimental ...
ASME/STLE 2007 International Joint Tribology Conference, Parts A and B, 2007
Surface texturing has been shown to have friction reducing / load capacity increasing effects in ... more Surface texturing has been shown to have friction reducing / load capacity increasing effects in parallel sliders, as well as in cylinder-liner contacts and in hydrodynamic seals. However, if texture is to be regarded as the sole mean of hydrodynamic lift in parallel sliders, or as a way of improving hydrodynamic performance in slider, thrust and journal bearings, several issues have to be addressed, such as optimal texturing parameters and corresponding performance gains. This paper deals with these issues in the case of a plane inclined textured slider. Parametric studies are conducted to determine optimal texturing extents, dimple depth and texturing density, as well as the influence of the operating conditions on these optimal texturing parameters.
This chapter deals with explanation of friction in lubricated contacts. Friction is the resistanc... more This chapter deals with explanation of friction in lubricated contacts. Friction is the resistance to motion that occurs when one body slides over another. The resistive force acting in the opposite direction of the relative motion is known as the friction force. The friction force has two forms: the force required to initiate sliding, known as the static friction force, and the force necessary to maintain the sliding, called the kinetic friction force. This chapter discusses four regimes of Stribeck's curve that shows different regimes of lubrication can occur in a lubricated sliding contact, depending on the relative speed. These regimes also depend on the pressures occurring in the lubricating film. Regime I: it is called boundary lubrication for conformal contacts, whereas for nonconformal contacts, this regime is known as extreme pressure (EP) lubrication. The main feature of boundary lubrication in comparison with solid-to-solid contact is that although the reduction in the friction coefficient is less important, the reduction in wear is impressive. Regime II: corresponds to mixed lubrication in which several mechanisms act simultaneously. This regime is a transition regime between boundary lubrication and hydrodynamic lubrication for low-pressure films or between extreme pressure lubrication and elastohydrodynamic lubrication for highpressure films. Regime III: corresponds to hydrodynamic (HD) lubrication for low-pressure films, or to elastohydrodynamic (EHD) lubrication for high-pressure films. And lastly, regime IV: it is characterized by superlaminar flow in hydrodynamic lubrication. This regime occurs for high-relative-speeds, low-viscosity lubricants or very large dimensions.
Uploads