Documents disponibles écrits par cet auteur

An analytical model for the basic design calculations of journal bearings / R. K. Naffin in Transactions of the ASME . Journal of tribology, Vol. 132 N° 2 (Avril 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 132 N° 2 (Avril 2010) . - 07 p. Titre : An analytical model for the basic design calculations of journal bearings Type de document : texte imprimé Auteurs : R. K. Naffin, Auteur ; L. Chang, Auteur Année de publication : 2011 Article en page(s) : 07 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Calculation  Machine  bearings Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : This paper presents an analytical model for the basic design calculations of plain journal bearings. The model yields reasonable accuracy as compared with published numerical solutions under the same conditions. The principles and procedures of the formulations are presented along with accuracy analyses. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] An analytical model for the basic design calculations of journal bearings [texte imprimé] / R. K. Naffin, Auteur ; L. Chang, Auteur . - 2011 . - 07 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 132 N° 2 (Avril 2010) . - 07 p. Mots-clés : Calculation  Machine  bearings Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : This paper presents an analytical model for the basic design calculations of plain journal bearings. The model yields reasonable accuracy as compared with published numerical solutions under the same conditions. The principles and procedures of the formulations are presented along with accuracy analyses. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]

A baseline theory for the design of oil-lubricated centrally pivoted plane-pad thrust bearings / L. Chang in Transactions of the ASME . Journal of tribology, Vol. 132 N° 4 (Octobre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 132 N° 4 (Octobre 2010) . - 06 p. Titre : A baseline theory for the design of oil-lubricated centrally pivoted plane-pad thrust bearings Type de document : texte imprimé Auteurs : L. Chang, Auteur Année de publication : 2011 Article en page(s) : 06 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Friction  Lubrication  Machine  bearings Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A baseline theory is developed in this paper for the design of oil-lubricated centrally pivoted plane-pad thrust bearings. By focusing on the hydrodynamics generated by the viscosity-temperature effects of the lubricating oil, a mathematical model is derived with a single dimensionless parameter Wth. The nominal value of Wth is 0.1 for typical pad bearings in current industrial practice. The theory suggests two important design calculations for centrally pivoted plane-pad bearings: (1) The minimum oil film thickness in the bearing is about 0.65 of the film thickness determined using the classical isothermal lubrication theory with the pad pivoted at the maximum-load optimum location. Thus, by setting the film thickness to 1.54 times the design requirement, one may carry out design selections and calculations using the classical theory. (2) The friction in the bearing is about 1.7 times the value determined using the classical theory at the maximum-load optimum condition and with the film thickness equal to the design requirement. Thus, one may also use the classical theory to meaningfully calculate the friction and power loss in the centrally pivoted plane-pad bearing systems. The theory is developed based on fundamental lubrication science, order of magnitude analyses of the assumptions, and supporting evidence from numerical literature case studies. It would be a conservative baseline theory for the bearing design as other complicated and/or incidental mechanisms would help provide a design factor of safety. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] A baseline theory for the design of oil-lubricated centrally pivoted plane-pad thrust bearings [texte imprimé] / L. Chang, Auteur . - 2011 . - 06 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 132 N° 4 (Octobre 2010) . - 06 p. Mots-clés : Friction  Lubrication  Machine  bearings Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : A baseline theory is developed in this paper for the design of oil-lubricated centrally pivoted plane-pad thrust bearings. By focusing on the hydrodynamics generated by the viscosity-temperature effects of the lubricating oil, a mathematical model is derived with a single dimensionless parameter Wth. The nominal value of Wth is 0.1 for typical pad bearings in current industrial practice. The theory suggests two important design calculations for centrally pivoted plane-pad bearings: (1) The minimum oil film thickness in the bearing is about 0.65 of the film thickness determined using the classical isothermal lubrication theory with the pad pivoted at the maximum-load optimum location. Thus, by setting the film thickness to 1.54 times the design requirement, one may carry out design selections and calculations using the classical theory. (2) The friction in the bearing is about 1.7 times the value determined using the classical theory at the maximum-load optimum condition and with the film thickness equal to the design requirement. Thus, one may also use the classical theory to meaningfully calculate the friction and power loss in the centrally pivoted plane-pad bearing systems. The theory is developed based on fundamental lubrication science, order of magnitude analyses of the assumptions, and supporting evidence from numerical literature case studies. It would be a conservative baseline theory for the bearing design as other complicated and/or incidental mechanisms would help provide a design factor of safety. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]

Effect of a miscible polymeric diluent on complex formation between isotactic and syndiotactic poly(methyl methacrylate) / L. Chang in Industrial & engineering chemistry research, Vol. 48 N° 7 (Avril 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 7 (Avril 2009) . - pp. 3432–3440 Titre : Effect of a miscible polymeric diluent on complex formation between isotactic and syndiotactic poly(methyl methacrylate) Type de document : texte imprimé Auteurs : L. Chang, Auteur ; E. M. Woo, Auteur Année de publication : 2009 Article en page(s) : pp. 3432–3440 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Syndiotactic  poly(methyl  methacrylate)Thermal  treatment  Isotactic  Miscible  polymeric Résumé : Formation of a stereocomplex structure in a blend of isotactic and syndiotactic poly(methyl methacrylate)s (iPMMA/sPMMA) was found to be significantly enhanced by introducing a mutual miscible diluent of poly(ethylene oxide) (PEO) in the blend, even when prepared using a kinetically hindered noncomplexing CHCl3 solvent. Mechanisms and influencing factors, such as thermal treatment, annealing temperature, annealing time, or PEO content in blends, on structures of stereocomplexes in the ternary iPMMA/sPMMA/PEO blends are discussed. WAXD result showed that addition of PEO in the iPMMA/sPMMA blend did not alter the crystal cells in the complexes. Melting peaks associated with the complexes were analyzed for discerning possible structural mechanisms. When annealed at specific temperatures, multiple endothermic peaks of the complexes increased in intensity as PEO contents increased in the ternary blends. Analysis shows that the lower melting peak (P1) represents shorter stereocomplex sequences or stereocomplex detached from PEO or connected with partial PEO, but the higher melting peak (P3) is related to the stereocomplex physically interconnected in the presence of PEO. The PEO molecules are thought to more easily interact with the stereocomplexes in blends by acting as a plasticizer, which decreases Tg of the more rigid PMMA chain segments. Physical interaction or miscibility-enhanced chain entanglement probably exists between PEO and the stereocomplex of tactic PMMAs, leading to stereocomplex formation in the iPMMA/sPMMA/PEO ternary blend. FT-IR characterization provided evidence of weak interactions between PEO and the stereocomplex of PMMA. IR peaks sensitive to complex structures with respect to temperature were analyzed for discerning effects by adding PEO. The stereocomplex formation of ternary blends with PEO is due to the weak interaction of ester groups and methoxy groups between PMMA and PEO. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801488u [article] Effect of a miscible polymeric diluent on complex formation between isotactic and syndiotactic poly(methyl methacrylate) [texte imprimé] / L. Chang, Auteur ; E. M. Woo, Auteur . - 2009 . - pp. 3432–3440. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 7 (Avril 2009) . - pp. 3432–3440 Mots-clés : Syndiotactic  poly(methyl  methacrylate)Thermal  treatment  Isotactic  Miscible  polymeric Résumé : Formation of a stereocomplex structure in a blend of isotactic and syndiotactic poly(methyl methacrylate)s (iPMMA/sPMMA) was found to be significantly enhanced by introducing a mutual miscible diluent of poly(ethylene oxide) (PEO) in the blend, even when prepared using a kinetically hindered noncomplexing CHCl3 solvent. Mechanisms and influencing factors, such as thermal treatment, annealing temperature, annealing time, or PEO content in blends, on structures of stereocomplexes in the ternary iPMMA/sPMMA/PEO blends are discussed. WAXD result showed that addition of PEO in the iPMMA/sPMMA blend did not alter the crystal cells in the complexes. Melting peaks associated with the complexes were analyzed for discerning possible structural mechanisms. When annealed at specific temperatures, multiple endothermic peaks of the complexes increased in intensity as PEO contents increased in the ternary blends. Analysis shows that the lower melting peak (P1) represents shorter stereocomplex sequences or stereocomplex detached from PEO or connected with partial PEO, but the higher melting peak (P3) is related to the stereocomplex physically interconnected in the presence of PEO. The PEO molecules are thought to more easily interact with the stereocomplexes in blends by acting as a plasticizer, which decreases Tg of the more rigid PMMA chain segments. Physical interaction or miscibility-enhanced chain entanglement probably exists between PEO and the stereocomplex of tactic PMMAs, leading to stereocomplex formation in the iPMMA/sPMMA/PEO ternary blend. FT-IR characterization provided evidence of weak interactions between PEO and the stereocomplex of PMMA. IR peaks sensitive to complex structures with respect to temperature were analyzed for discerning effects by adding PEO. The stereocomplex formation of ternary blends with PEO is due to the weak interaction of ester groups and methoxy groups between PMMA and PEO. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie801488u

Modeling of asperity collisions and their effects in a frictionless sliding contact of nominally flat metallic surfaces / L. Chang in Transactions of the ASME . Journal of tribology, Vol. 130 n°3 (Juillet 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 7 p. Titre : Modeling of asperity collisions and their effects in a frictionless sliding contact of nominally flat metallic surfaces Type de document : texte imprimé Auteurs : L. Chang, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Collisions  (Physics)  Metal  surfaces  Modeling  Stress  Force  Electrical  resistance  Equations  Motion Résumé : The collision process of a pair of asperities on two opposing surfaces is modeled in frictionless sliding motion with an analytically traceable approach. Equations of a sufficiently general representation are derived for the contact force, the load-carrying capacity, and the motion resistance of the asperity collision. A system model of the contact of two nominally flat metallic surfaces is subsequently developed incorporating the effects of asperity microcontact collisions. Results of a general nature are presented of the load capacity and motion resistance of the contact system in sliding motion. The model and the results may provide a first-order approximation of the effects of the asperity collisions in a sliding contact system. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468061 [article] Modeling of asperity collisions and their effects in a frictionless sliding contact of nominally flat metallic surfaces [texte imprimé] / L. Chang, Auteur . - 2008 . - 7 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 7 p. Mots-clés : Collisions  (Physics)  Metal  surfaces  Modeling  Stress  Force  Electrical  resistance  Equations  Motion Résumé : The collision process of a pair of asperities on two opposing surfaces is modeled in frictionless sliding motion with an analytically traceable approach. Equations of a sufficiently general representation are derived for the contact force, the load-carrying capacity, and the motion resistance of the asperity collision. A system model of the contact of two nominally flat metallic surfaces is subsequently developed incorporating the effects of asperity microcontact collisions. Results of a general nature are presented of the load capacity and motion resistance of the contact system in sliding motion. The model and the results may provide a first-order approximation of the effects of the asperity collisions in a sliding contact system. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468061