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Papers by Spiridon S . Cretu
The separation between the contacting surfaces in wheel-rail contact depends on many variables su... more The separation between the contacting surfaces in wheel-rail contact depends on many variables such as wheel and rail profiles, rail inclination, gauge, and lateral displacement. Although the S1002 wheel profile and UIC60 rail seems to be the most common combination in the European rail sector currently, interoperability is still affected by the different values of the rail inclination, which can vary between 1/40, 1/30 and 1/20. This study analyses some particular cases in Romania, where the S78 wheel profile is commonly used, in conjunction with rail types UIC49 and UIC60, with rail inclination 1/20. The paper presents the wheel-rail contact model, developed mainly to analyse and estimate the impact of wheel and rail profile modifications caused by wear, and of lateral displacements, as well. A fast and robust algorithm has been developed and applied to solve the stress state in the general case of non-Hertzian contacts, to enable the analysis of the pressure distributions and det...
La connaissance du mecanisme du frottement entre les rouleaux et la cage permet une appreciation ... more La connaissance du mecanisme du frottement entre les rouleaux et la cage permet une appreciation plus realiste des performance des rouleaux. Le travail decrit un tribometre qui peut reproduire les conditions de fonctionnement (les materiaux, la geometrie, les charges, la cinematique, le lubrifiant) presentes dans les contacts entre le rouleau et la cage du roulement avec des rouleaux coniques 30206. La modelisation analytique est realisee par l'application de la theorie hydrodynamique des contacts lineaires, y compris les effets de la rugosite des surfaces. Les resultats experimentaux et analytiques montrent que les conditions hydrodynamiques (particulierement pour les charges faibles), les coefficients du frottement peuvent depasser les valeurs habituelles du coefficient du frottement. L'etude experimentale et analytique presentee dans ce travail peut etre appliquee egalement aux roulements avec des rouleaux cylindriques.
ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 1, 2010
Wheel and rail in service undergo continual wear and plastic deformation at the surface, so that ... more Wheel and rail in service undergo continual wear and plastic deformation at the surface, so that in time all wheel profiles will be different. The optimization by grinding a worn rail profile to minimize contact stresses requires the development of a software to reconstruct a rail ...
Applied Mechanics and Materials, 2014
This paper presents a numerical model to calculate wear during rolling contact due to micro-slip.... more This paper presents a numerical model to calculate wear during rolling contact due to micro-slip. Having as initial condition a corrugated rail it is shown the influence of the corrugation wavelength and the dynamic effects of the normal force on the wear creation. Experimental results are presented in order to reveal the influence of roughness when studying the stick-slip phenomenon.
S u m m a r y Field experience supports the idea that the available analysis and design tools of ... more S u m m a r y Field experience supports the idea that the available analysis and design tools of rolling bearings require increased sophistication. To obtain the load distribution in the general case of angular-contact ball bearing a quasi-static equilibrium model was developed, as a first step of the analysis. The effects induced by the centrifugal forces, gyroscopic moments and misalignments between bearing’s rings were included. The lubricant parameters, traction forces and fluid drag acting on both balls and races have been further included in a advanced quasi-dynamic model. The distinctive idea of the model is the ability to quantify the presence of the misalignment and its influence on internal load distribution, as well as on power losses. The quasi-dynamic model has been validated by comparisons achieved with results mentioned in the open literature, as well, as with experimental results obtained by authors. A new formula for the evaluation of frictional torque is finally pr...
La connaissance du mecanisme du frottement entre les rouleaux et la cage permet une appreciation ... more La connaissance du mecanisme du frottement entre les rouleaux et la cage permet une appreciation plus realiste des performance des rouleaux. Le travail decrit un tribometre qui peut reproduire les conditions de fonctionnement (les materiaux, la geometrie, les charges, la cinematique, le lubrifiant) presentes dans les contacts entre le rouleau et la cage du roulement avec des rouleaux coniques 30206. La modelisation analytique est realisee par l'application de la theorie hydrodynamique des contacts lineaires, y compris les effets de la rugosite des surfaces. Les resultats experimentaux et analytiques montrent que les conditions hydrodynamiques (particulierement pour les charges faibles), les coefficients du frottement peuvent depasser les valeurs habituelles du coefficient du frottement. L'etude experimentale et analytique presentee dans ce travail peut etre appliquee egalement aux roulements avec des rouleaux cylindriques.
Many studies regarding the ball motion for bearings running in a normal range of operating condit... more Many studies regarding the ball motion for bearings running in a normal range of operating conditions have been reported, but in incorrect running the references are insufficiently. The brake effect on the ball bearing’s cage can lead to abnormal operation characterised by gross sliding speed between ball and inner race and occasionally to premature bearing failure, that is usually micro-scuffing or scuffing. For these conditions the known kinematics hypothesis cannot be used. Based on the power loss equilibrium regarding the ball-races and ball-cage interactions, a simplified analytical kinematics model has been developed by authors. Under sliding conditions, the Kinematics model developed is correlated to the scuffing model that relies on the dissipation function of energy dissipated within the EHD oil film. Both models leads to perform a computational algorithm to estimate the scuffing risk for an angular contact ball bearing, useful for the bearings designers and users.
Studii si cercetari de inframicrobiologie, 1955
Wheel and rail in service undergo continual wear and plastic deformation at the surface, so that ... more Wheel and rail in service undergo continual wear and plastic deformation at the surface, so that in time all wheel profiles will be different. The optimization by grinding a worn rail profile to minimize contact stresses requires the development of a software to reconstruct a rail ...
Wear
Study of Rolling Bearing Fatigue Life With Mineral Oil Lubrication. NG Popinceanu, MD Gafitanu, H... more Study of Rolling Bearing Fatigue Life With Mineral Oil Lubrication. NG Popinceanu, MD Gafitanu, H Nastase, EN Diaconescu, SS Cretu Wear 22:11, 21-37, 10/1972. 31 Mechanical Properties(MD).
European journal of mechanical and environmental engineering, 1995
Cet article traite du roulement a rouleaux cylindriques, type NUP, avec collets coniques et extre... more Cet article traite du roulement a rouleaux cylindriques, type NUP, avec collets coniques et extremites spheriques des rouleaux. Le modele mathematique presente est base sur le calcul vectoriel applique a une situation d'equilibre quasi-dynamique. Le roulement est charge suivant trois degres de liberte et les rouleaux se deplacent selon un mouvement plan-parallele. On prend en consideration l'effet de la vitesse elevee sur les rouleaux charges. Le frottement interieur est neglige, et les deformations du contact sont considerees dans le domaine elastique. Les interactions elastiques entre les rouleaux cylindriques et les chemins de roulement sont mises en evidence au niveau des contacts. Par l'introduction du modele sur l'ordinateur,la distribution des charges interieures est calculee pour differentes charges exterieures, vitesses de travail et jeux internes.
There is little agreement in the literature on what scuffing is, what causes it, or what appearan... more There is little agreement in the literature on what scuffing is, what causes it, or what appearance is. From a strictly mechanical point of view, the estimation of bearing's scuffing risk supposes to settle the interdependence between the Kinematics, dynamic, lubrication and friction phenomena realised in bearing's rolling contacts subjected to an important sliding. Our research focused on a specified angular contact ball-bearing realised an experimental and theoretical modelisation both on discs test specimen and ball bearings. Some scuffing tests have been carried out on the high-speed twin-disk machine available at LMC facilities. Another series of scuffing tests were applied on the 7206 angular contact ball bearing included in an original test rig. An energetically criterion to estimate scuffing limits has been proposed. The proposed scuffing criterion is sufficiently effective and reliable for designers and producers in order to offer a covering tool related to scuffing...
Journal of The Balkan Tribological Association, 2014
Many engineering surfaces can not be represented by a Gaussian distribution. A computer program p... more Many engineering surfaces can not be represented by a Gaussian distribution. A computer program paper has been developed to generate non-Gaussian surfaces with specified standard deviation, autocorrelation length, skewness and kurtosis were studied at different values of Sic and K. The Johnson translator system, based on 3 transformations of the Gaussian distribution, has been involved to classify the surface texture.
Influence de contraintes de compression residuelles sur la resistance a la fatigue d'un roule... more Influence de contraintes de compression residuelles sur la resistance a la fatigue d'un roulement a billes
The separation between the contacting surfaces in wheel-rail contact depends on many variables su... more The separation between the contacting surfaces in wheel-rail contact depends on many variables such as wheel and rail profiles, rail inclination, gauge, and lateral displacement. Although the S1002 wheel profile and UIC60 rail seems to be the most common combination in the European rail sector currently, interoperability is still affected by the different values of the rail inclination, which can vary between 1/40, 1/30 and 1/20. This study analyses some particular cases in Romania, where the S78 wheel profile is commonly used, in conjunction with rail types UIC49 and UIC60, with rail inclination 1/20. The paper presents the wheel-rail contact model, developed mainly to analyse and estimate the impact of wheel and rail profile modifications caused by wear, and of lateral displacements, as well. A fast and robust algorithm has been developed and applied to solve the stress state in the general case of non-Hertzian contacts, to enable the analysis of the pressure distributions and det...
La connaissance du mecanisme du frottement entre les rouleaux et la cage permet une appreciation ... more La connaissance du mecanisme du frottement entre les rouleaux et la cage permet une appreciation plus realiste des performance des rouleaux. Le travail decrit un tribometre qui peut reproduire les conditions de fonctionnement (les materiaux, la geometrie, les charges, la cinematique, le lubrifiant) presentes dans les contacts entre le rouleau et la cage du roulement avec des rouleaux coniques 30206. La modelisation analytique est realisee par l'application de la theorie hydrodynamique des contacts lineaires, y compris les effets de la rugosite des surfaces. Les resultats experimentaux et analytiques montrent que les conditions hydrodynamiques (particulierement pour les charges faibles), les coefficients du frottement peuvent depasser les valeurs habituelles du coefficient du frottement. L'etude experimentale et analytique presentee dans ce travail peut etre appliquee egalement aux roulements avec des rouleaux cylindriques.
ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 1, 2010
Wheel and rail in service undergo continual wear and plastic deformation at the surface, so that ... more Wheel and rail in service undergo continual wear and plastic deformation at the surface, so that in time all wheel profiles will be different. The optimization by grinding a worn rail profile to minimize contact stresses requires the development of a software to reconstruct a rail ...
Applied Mechanics and Materials, 2014
This paper presents a numerical model to calculate wear during rolling contact due to micro-slip.... more This paper presents a numerical model to calculate wear during rolling contact due to micro-slip. Having as initial condition a corrugated rail it is shown the influence of the corrugation wavelength and the dynamic effects of the normal force on the wear creation. Experimental results are presented in order to reveal the influence of roughness when studying the stick-slip phenomenon.
S u m m a r y Field experience supports the idea that the available analysis and design tools of ... more S u m m a r y Field experience supports the idea that the available analysis and design tools of rolling bearings require increased sophistication. To obtain the load distribution in the general case of angular-contact ball bearing a quasi-static equilibrium model was developed, as a first step of the analysis. The effects induced by the centrifugal forces, gyroscopic moments and misalignments between bearing’s rings were included. The lubricant parameters, traction forces and fluid drag acting on both balls and races have been further included in a advanced quasi-dynamic model. The distinctive idea of the model is the ability to quantify the presence of the misalignment and its influence on internal load distribution, as well as on power losses. The quasi-dynamic model has been validated by comparisons achieved with results mentioned in the open literature, as well, as with experimental results obtained by authors. A new formula for the evaluation of frictional torque is finally pr...
La connaissance du mecanisme du frottement entre les rouleaux et la cage permet une appreciation ... more La connaissance du mecanisme du frottement entre les rouleaux et la cage permet une appreciation plus realiste des performance des rouleaux. Le travail decrit un tribometre qui peut reproduire les conditions de fonctionnement (les materiaux, la geometrie, les charges, la cinematique, le lubrifiant) presentes dans les contacts entre le rouleau et la cage du roulement avec des rouleaux coniques 30206. La modelisation analytique est realisee par l'application de la theorie hydrodynamique des contacts lineaires, y compris les effets de la rugosite des surfaces. Les resultats experimentaux et analytiques montrent que les conditions hydrodynamiques (particulierement pour les charges faibles), les coefficients du frottement peuvent depasser les valeurs habituelles du coefficient du frottement. L'etude experimentale et analytique presentee dans ce travail peut etre appliquee egalement aux roulements avec des rouleaux cylindriques.
Many studies regarding the ball motion for bearings running in a normal range of operating condit... more Many studies regarding the ball motion for bearings running in a normal range of operating conditions have been reported, but in incorrect running the references are insufficiently. The brake effect on the ball bearing’s cage can lead to abnormal operation characterised by gross sliding speed between ball and inner race and occasionally to premature bearing failure, that is usually micro-scuffing or scuffing. For these conditions the known kinematics hypothesis cannot be used. Based on the power loss equilibrium regarding the ball-races and ball-cage interactions, a simplified analytical kinematics model has been developed by authors. Under sliding conditions, the Kinematics model developed is correlated to the scuffing model that relies on the dissipation function of energy dissipated within the EHD oil film. Both models leads to perform a computational algorithm to estimate the scuffing risk for an angular contact ball bearing, useful for the bearings designers and users.
Studii si cercetari de inframicrobiologie, 1955
Wheel and rail in service undergo continual wear and plastic deformation at the surface, so that ... more Wheel and rail in service undergo continual wear and plastic deformation at the surface, so that in time all wheel profiles will be different. The optimization by grinding a worn rail profile to minimize contact stresses requires the development of a software to reconstruct a rail ...
Wear
Study of Rolling Bearing Fatigue Life With Mineral Oil Lubrication. NG Popinceanu, MD Gafitanu, H... more Study of Rolling Bearing Fatigue Life With Mineral Oil Lubrication. NG Popinceanu, MD Gafitanu, H Nastase, EN Diaconescu, SS Cretu Wear 22:11, 21-37, 10/1972. 31 Mechanical Properties(MD).
European journal of mechanical and environmental engineering, 1995
Cet article traite du roulement a rouleaux cylindriques, type NUP, avec collets coniques et extre... more Cet article traite du roulement a rouleaux cylindriques, type NUP, avec collets coniques et extremites spheriques des rouleaux. Le modele mathematique presente est base sur le calcul vectoriel applique a une situation d'equilibre quasi-dynamique. Le roulement est charge suivant trois degres de liberte et les rouleaux se deplacent selon un mouvement plan-parallele. On prend en consideration l'effet de la vitesse elevee sur les rouleaux charges. Le frottement interieur est neglige, et les deformations du contact sont considerees dans le domaine elastique. Les interactions elastiques entre les rouleaux cylindriques et les chemins de roulement sont mises en evidence au niveau des contacts. Par l'introduction du modele sur l'ordinateur,la distribution des charges interieures est calculee pour differentes charges exterieures, vitesses de travail et jeux internes.
There is little agreement in the literature on what scuffing is, what causes it, or what appearan... more There is little agreement in the literature on what scuffing is, what causes it, or what appearance is. From a strictly mechanical point of view, the estimation of bearing's scuffing risk supposes to settle the interdependence between the Kinematics, dynamic, lubrication and friction phenomena realised in bearing's rolling contacts subjected to an important sliding. Our research focused on a specified angular contact ball-bearing realised an experimental and theoretical modelisation both on discs test specimen and ball bearings. Some scuffing tests have been carried out on the high-speed twin-disk machine available at LMC facilities. Another series of scuffing tests were applied on the 7206 angular contact ball bearing included in an original test rig. An energetically criterion to estimate scuffing limits has been proposed. The proposed scuffing criterion is sufficiently effective and reliable for designers and producers in order to offer a covering tool related to scuffing...
Journal of The Balkan Tribological Association, 2014
Many engineering surfaces can not be represented by a Gaussian distribution. A computer program p... more Many engineering surfaces can not be represented by a Gaussian distribution. A computer program paper has been developed to generate non-Gaussian surfaces with specified standard deviation, autocorrelation length, skewness and kurtosis were studied at different values of Sic and K. The Johnson translator system, based on 3 transformations of the Gaussian distribution, has been involved to classify the surface texture.
Influence de contraintes de compression residuelles sur la resistance a la fatigue d'un roule... more Influence de contraintes de compression residuelles sur la resistance a la fatigue d'un roulement a billes