Incorporation of solid lubricant into micro-reservoirs produced by laser surface texturing (LST) ... more Incorporation of solid lubricant into micro-reservoirs produced by laser surface texturing (LST) and its effect on the adhesion and wear life of burnished films is studied. In order to improve the adhesion between the ground steel and the MoS2 burnished film, a sub-layer of nanoparticles was burnished on a virgin steel surface. Ultrasonic radiation (sonochemical synthesis) was used for synthesis of nanostructured materials. Some types of nanoparticles of sulfides and selenides as MoSe, MoSe2/C core–shells, PbSe, ZnSe, WSe, CdZnSe, MoS2, WS2 and Ni core–carbon shells were chosen for the analysis of their friction and adhesion properties. The adhesion and wear life of solid lubricant films were evaluated. Some types of the friction and wear rigs were used for the evaluation of the adhesion and the wear life of burnished layers. The burnished CdZnSe film showing maximum value of the friction coefficients was chosen as the materials providing the best adhesion. MoS2 particles were burnished on the surface of CdZnSe sub-layer. The adhesion between MoS2 and CdZnSe films was analyzed. The strong transfer of the MoS2 layers on the surface of the CdZnSe film was observed. The wear life of a MoS2 film on a steel substrate was compared with similar films on the CdZnSe sub-layer. The wear life of the MoS2 film on a sub-layer was more than twice as long as that for a MoS2 film on a steel substrate. The study of the friction and wear behaviour of CdZnSe + MoS2 films on LST surfaces confirm the results of the experiments on ground steel surfaces. The increase in the wear life is explained by the high adhesion and density of MoS2 film burnished on a CdZnSe sub-layer.
The present study focuses on modeling the effect of elastomer surface texturing in soft elasto-hy... more The present study focuses on modeling the effect of elastomer surface texturing in soft elasto-hydrodynamic lubrication. The model consists of an elastomer with spherical microdimples sliding at a constant velocity relative to a rigid and smooth counterpart in the presence of viscous lubricant. The hydrodynamic lubrication and the elasticity problems are solved simultaneously for the cases of full and partial texturing of the elastomer surface. Load carrying capacity and friction force are evaluated by integration of the pressure and shear stress fields in the viscous lubricant, respectively. A parametric analysis is performed to obtain the optimum surface texturing parameters for maximum load and minimum friction.
The effect of material properties and surface roughness on the contribution of asperities and sph... more The effect of material properties and surface roughness on the contribution of asperities and sphere bulk displacements to the total displacement of a rough spherical contact is investigated. A dimensionless transition load, above which the contribution of the bulk displacement exceeds the contribution of the asperities displacement, is found as a function of the plasticity index and dimensionless critical interference of the sphere bulk. A criterion is proposed for evaluating the importance of surface roughness in calculating the displacement of a rough spherical contact. Some experimental results with a spherical micro-contact are presented to verify the model.
A theoretical model is developed to study the effect of dwell time on the junction growth and sta... more 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.
International Journal of Solids and Structures, 2010
The unloading process of an elastic–plastic spherical contact under stick contact condition is an... more The unloading process of an elastic–plastic spherical contact under stick contact condition is analyzed for various material properties. The evolution of normal and shear stress distribution at the contact area as well as the residual profile of the sphere and residual von Mises stresses inside the sphere are presented. Empirical expressions for the residual interference and for the evolution of the interference and contact area during the unloading are provided. Good agreement with experimental results is shown.
In the present work, we report on the wear behavior and adhesion of diamond films deposited on st... more In the present work, we report on the wear behavior and adhesion of diamond films deposited on steel coated by a Cr–N interlayer. The wear behavior of the diamond films was studied under fretting conditions. Fretting was used as a typical wear process occurring during vibration and friction. Wear grooves obtained after the fretting test under different loads and for different numbers of cycles were studied by profilometry, high-resolution scanning electron microscopy and electron probe microbeam analysis. The adhesion of the deposited diamond films was measured by using scratch and indentation tests. The fracture behavior of the diamond film/nitrided chromium interlayer complex under different conditions was studied and correlated to the interlayer nitridation conditions.
Journal of Tribology-transactions of The Asme, 2010
... below 8, to higher plasticity index values by accounting for fully plastically deformed asper... more ... below 8, to higher plasticity index values by accounting for fully plastically deformed asperities based on finite element results by Jackson and Green [2005, A Finite Element Study of Elasto-Plastic Hemispherical Contact Against a ... Tribology and mechanical contacts. ...
The creep of a polymer sphere in contact with a rigid flat under a constant normal load is invest... more The creep of a polymer sphere in contact with a rigid flat under a constant normal load is investigated numerically by a finite element method. A simplified form of the modified time hardening is used for the constitutive material model. A new dimensionless form of the creep displacement is suggested, which enables a universal solution of the problem for any contact time based on a conveniently selected reference time. The model may be applicable to other materials which can be described by the modified time hardening model including biological materials.
Cu substrates were laser-clad with a Ni-based powder using a CW–CO2 laser. In order to obtain suf... more Cu substrates were laser-clad with a Ni-based powder using a CW–CO2 laser. In order to obtain sufficient absorption of the laser irradiation by the substrate a Ni–B–Si plasma-sprayed layer was deposited on the Cu substrate and remelted prior to the cladding process. High hardness values in the range of 5 to 5.4 GPa were achieved for the laser-clad Cu surfaces, compared with a Cu substrate hardness of ∼1.3 GPa. The high hardness of the Ni-based cladding is due to a microstructure consisting mainly of Ni dendrites and Ni and Ni3B lamellae. However, the large number of brittle boride phases at the interfaces between the cladding, the plasma-sprayed layer, and the substrate causes cracks during cooling owing to high thermal stresses. Tribological tests of the claddings reveal poor adhesive friction and wear properties with a tendency to seizure when sliding against steel under dry conditions. Abrasive wear coefficients of ∼0.1 were obtained for the claddings when abraded by #320 emery paper. Some correlation was found between the cladding thickness and the tribological properties due to thickness induced defects in the cladding.
Application of CVD diamond films as hard coating on tools may offer, in addition to their mechani... more Application of CVD diamond films as hard coating on tools may offer, in addition to their mechanical properties, also low friction coefficient. In this sense [100]-textured films are potentially advantageous over non-textured films due to their lower roughness. In the present work we demonstrate the capability to deposit [100]-textured diamond films on steel substrates coated with a nitrided chromium thin interlayer, and assess their tribological properties. The [100]-textured diamond films were deposited by MW-PACVD using a methane-hydrogen gas mixture with the addition of minute amounts of nitrogen in the ppm level. Continuous, textured films of good adhesion, and improved tribological properties were obtained. Scanning electron microscopy (SEM), Raman spectroscopy and friction coefficient measurements were used for characterization of the deposited films.
A theoretical basis is presented for a previous fully empirical development of the unified approa... more A theoretical basis is presented for a previous fully empirical development of the unified approach to fretting that was based on a new similarity criterion termed slip index. It is shown that the slip index can be analytically derived from any friction loop geometry and hence, can be used for the characterization of any fretting system.
Incorporation of solid lubricant into micro-reservoirs produced by laser surface texturing (LST) ... more Incorporation of solid lubricant into micro-reservoirs produced by laser surface texturing (LST) and its effect on the adhesion and wear life of burnished films is studied. In order to improve the adhesion between the ground steel and the MoS2 burnished film, a sub-layer of nanoparticles was burnished on a virgin steel surface. Ultrasonic radiation (sonochemical synthesis) was used for synthesis of nanostructured materials. Some types of nanoparticles of sulfides and selenides as MoSe, MoSe2/C core–shells, PbSe, ZnSe, WSe, CdZnSe, MoS2, WS2 and Ni core–carbon shells were chosen for the analysis of their friction and adhesion properties. The adhesion and wear life of solid lubricant films were evaluated. Some types of the friction and wear rigs were used for the evaluation of the adhesion and the wear life of burnished layers. The burnished CdZnSe film showing maximum value of the friction coefficients was chosen as the materials providing the best adhesion. MoS2 particles were burnished on the surface of CdZnSe sub-layer. The adhesion between MoS2 and CdZnSe films was analyzed. The strong transfer of the MoS2 layers on the surface of the CdZnSe film was observed. The wear life of a MoS2 film on a steel substrate was compared with similar films on the CdZnSe sub-layer. The wear life of the MoS2 film on a sub-layer was more than twice as long as that for a MoS2 film on a steel substrate. The study of the friction and wear behaviour of CdZnSe + MoS2 films on LST surfaces confirm the results of the experiments on ground steel surfaces. The increase in the wear life is explained by the high adhesion and density of MoS2 film burnished on a CdZnSe sub-layer.
The present study focuses on modeling the effect of elastomer surface texturing in soft elasto-hy... more The present study focuses on modeling the effect of elastomer surface texturing in soft elasto-hydrodynamic lubrication. The model consists of an elastomer with spherical microdimples sliding at a constant velocity relative to a rigid and smooth counterpart in the presence of viscous lubricant. The hydrodynamic lubrication and the elasticity problems are solved simultaneously for the cases of full and partial texturing of the elastomer surface. Load carrying capacity and friction force are evaluated by integration of the pressure and shear stress fields in the viscous lubricant, respectively. A parametric analysis is performed to obtain the optimum surface texturing parameters for maximum load and minimum friction.
The effect of material properties and surface roughness on the contribution of asperities and sph... more The effect of material properties and surface roughness on the contribution of asperities and sphere bulk displacements to the total displacement of a rough spherical contact is investigated. A dimensionless transition load, above which the contribution of the bulk displacement exceeds the contribution of the asperities displacement, is found as a function of the plasticity index and dimensionless critical interference of the sphere bulk. A criterion is proposed for evaluating the importance of surface roughness in calculating the displacement of a rough spherical contact. Some experimental results with a spherical micro-contact are presented to verify the model.
A theoretical model is developed to study the effect of dwell time on the junction growth and sta... more 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.
International Journal of Solids and Structures, 2010
The unloading process of an elastic–plastic spherical contact under stick contact condition is an... more The unloading process of an elastic–plastic spherical contact under stick contact condition is analyzed for various material properties. The evolution of normal and shear stress distribution at the contact area as well as the residual profile of the sphere and residual von Mises stresses inside the sphere are presented. Empirical expressions for the residual interference and for the evolution of the interference and contact area during the unloading are provided. Good agreement with experimental results is shown.
In the present work, we report on the wear behavior and adhesion of diamond films deposited on st... more In the present work, we report on the wear behavior and adhesion of diamond films deposited on steel coated by a Cr–N interlayer. The wear behavior of the diamond films was studied under fretting conditions. Fretting was used as a typical wear process occurring during vibration and friction. Wear grooves obtained after the fretting test under different loads and for different numbers of cycles were studied by profilometry, high-resolution scanning electron microscopy and electron probe microbeam analysis. The adhesion of the deposited diamond films was measured by using scratch and indentation tests. The fracture behavior of the diamond film/nitrided chromium interlayer complex under different conditions was studied and correlated to the interlayer nitridation conditions.
Journal of Tribology-transactions of The Asme, 2010
... below 8, to higher plasticity index values by accounting for fully plastically deformed asper... more ... below 8, to higher plasticity index values by accounting for fully plastically deformed asperities based on finite element results by Jackson and Green [2005, A Finite Element Study of Elasto-Plastic Hemispherical Contact Against a ... Tribology and mechanical contacts. ...
The creep of a polymer sphere in contact with a rigid flat under a constant normal load is invest... more The creep of a polymer sphere in contact with a rigid flat under a constant normal load is investigated numerically by a finite element method. A simplified form of the modified time hardening is used for the constitutive material model. A new dimensionless form of the creep displacement is suggested, which enables a universal solution of the problem for any contact time based on a conveniently selected reference time. The model may be applicable to other materials which can be described by the modified time hardening model including biological materials.
Cu substrates were laser-clad with a Ni-based powder using a CW–CO2 laser. In order to obtain suf... more Cu substrates were laser-clad with a Ni-based powder using a CW–CO2 laser. In order to obtain sufficient absorption of the laser irradiation by the substrate a Ni–B–Si plasma-sprayed layer was deposited on the Cu substrate and remelted prior to the cladding process. High hardness values in the range of 5 to 5.4 GPa were achieved for the laser-clad Cu surfaces, compared with a Cu substrate hardness of ∼1.3 GPa. The high hardness of the Ni-based cladding is due to a microstructure consisting mainly of Ni dendrites and Ni and Ni3B lamellae. However, the large number of brittle boride phases at the interfaces between the cladding, the plasma-sprayed layer, and the substrate causes cracks during cooling owing to high thermal stresses. Tribological tests of the claddings reveal poor adhesive friction and wear properties with a tendency to seizure when sliding against steel under dry conditions. Abrasive wear coefficients of ∼0.1 were obtained for the claddings when abraded by #320 emery paper. Some correlation was found between the cladding thickness and the tribological properties due to thickness induced defects in the cladding.
Application of CVD diamond films as hard coating on tools may offer, in addition to their mechani... more Application of CVD diamond films as hard coating on tools may offer, in addition to their mechanical properties, also low friction coefficient. In this sense [100]-textured films are potentially advantageous over non-textured films due to their lower roughness. In the present work we demonstrate the capability to deposit [100]-textured diamond films on steel substrates coated with a nitrided chromium thin interlayer, and assess their tribological properties. The [100]-textured diamond films were deposited by MW-PACVD using a methane-hydrogen gas mixture with the addition of minute amounts of nitrogen in the ppm level. Continuous, textured films of good adhesion, and improved tribological properties were obtained. Scanning electron microscopy (SEM), Raman spectroscopy and friction coefficient measurements were used for characterization of the deposited films.
A theoretical basis is presented for a previous fully empirical development of the unified approa... more A theoretical basis is presented for a previous fully empirical development of the unified approach to fretting that was based on a new similarity criterion termed slip index. It is shown that the slip index can be analytically derived from any friction loop geometry and hence, can be used for the characterization of any fretting system.
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