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Influence of kinetic friction on the critical velocity of stick-slip motion
ABSTRACTS Copies of original a?-licles a?‘e best obtained direct lo the jourual iu which tkey appeared. of joto-uals can be found in a reference book
by writing The addresses suck as
ALLUM, K. G. and FORBES, E. S. The load-carrying mechanism of organic sulphur compounds-application of electron probe microanalysis Transactions of the American Society of Lubrication Engineers, Vol 11, No 2 (April 1968) pp 162-175 There is considerable controversy in the literature on the mode of action of organic sulphur compounds as loadcarrying additives. Previous four-ball extreme pressure and wear tests have suggested that under mixed lubrication (antiwear) conditions, organic disulphides are adsorbed onto the metal surface with clearage of the sulphur-sulphur bond to form an iron mercaptide layer. However, in the extremepressure region, clearage of the carbon-sulphur bond results in an inorganic sulphur-containing layer. The different relative performances in the mixed lubrication and extremepressure regions are thus readily explained. A detailed examination of the wear scars obtained with certain disulphldes, using an electron-probe microanalyzer, is reported. This new technique of studying the nature of worn surfaces lends strong support to the suggested mechanism of the action of organic disulphides. The results of this study also offer an explanation for the apparently conflicting rigtest results often reported in the literature. (7 figures, 3 tables, 25 references) (Tribology 1968, abstract 137)
ANDREASON, S. Passage of electric current through rolling bearings Ballbearing Journal, No 153 (June 1968) pp 6-12 Damage may be caused by passing electric current through a rolling bearing in motion. Electrical damage is characterised by craters and/or fluting on the bearing surfaces. Brief theoretical discussion and equations relating temperature, current, position and other parameters are derived for the contact zone. The mode of current passage across contact zone is discussed. The damage and wear encountered is described and suggestions given for avoiding this, including keeping the voltage across the contact zone as low as possible, shunt and series resistances, and optimisation of the lubricant-film thickness. (Tribology 1968, abstract 138)
AN-NO, J. N., WALOWIT, J. A. and ALLEN, C. E. Micro-asperity lubrication Transactions of the American Society of Mechanical Engineers, Journal of Lubrication Technologv, Vol 90. Series F. No 2 (Aoril 1968) DD 351-355 Large load-supporting capability has been observed between parallel surfaces of a rotary-shaft face-seal when one of the surfaces contains micro-asperities in the form of circular cylinders with 0.012in diameter and 100pm height, covering about one third of the surface. A theory is presented in which the load-support is attributed to small tilts on the tops of the asperities. Experimental data on lubricant-film thickness versus applied load are correlated well by this theory assuming an average tilt of 0.86pm, for the 0.012in diameter asperities investigated. Torque data obtained by a thermal technique are also correlated by this theory in the form of a plot of the coefficient friction versus Hersey number. Although direct evidence for the presence of small tilts of the asperity tops is lacking, it has been demonstrated that the load-support is even further increased when the tops are purposely rounded. It is concluded that the theory developed correlates well with the experimental data, and that the use of planned micro-asperities is an effective method,for lubricating the parallel surfaces of face-seals and thrust-bearings. (Tribology 1968, abstract 139) 250
TFUBOLOGY
November
1968
‘Ulorld
Lisl of Scieutific ’ Witlirrgs Press Guide’, for Amcr-icau journals
aud Teclwicat Publicaliorrs’, Newspaper Press Direclor-y’ ouly, ‘Ayers’.
aud,
APPLEDOORN, J. K. The present state of lubrication and its rehtion to rheology Transactions of the American Society of Mechanical Engineers, Journal of Lubrication Technology, Vol 90, No 3, Series F (July 1968) pp 526-530 In thick-film lubrication, Reynolds’ equation is generally satisfactory. However, the assumptions made in deriving this equation cannot be justified for non-Newtonian, viscoelastic liquids. It is concluded that no satisfactory mathematical treatment is yet available for calculating the loadcarrying capacity of such liquids. In thin-film lubrication, elastohydrodynamic calculations indicate that the lubricant film may be quite thick even under heavily loaded conditions, but discrepancies exist between calculation and experiment. These can be explained by assuming non-Newtonian behav-iour, or unusual viscoelastic effects, but the assumptions are largely unfounded. There is virtually complete absence of data on the behaviour of liquids under impact loading. Such data are needed to establish whether thin-film lubrication is mainly chemical or physical. (19 references) (Tribology 1968, abstract 140)
APPLEDOGRN, J. K. and TAO, F. F. The lubricity characteristics of heavy aromatics Wear, Vol 12, No 2 (August 1968) pp 117-130 Heavy aromatic hydrocarbons are the most probable cause of the good lubricating characteristics of petroleum oils. As little as 2% can greatly reduce wear and friction and increase the load-carrying capacity of paraffins. These mixtures of heavy aromatics and paraffins are much better than either component alone. Condensed-ring heavy aromatics show another unusual behaviour: in the absence of water and oxygen, they will scuff at very low loads. The unusual behaviour of these heavy aromatics is attributed to a little-understood decomposition reaction at the rubbing surface and not to oxidation or reaction with the metal. (5 figures, 13 tables, 5 references) (Tribology 1968, abstract 141)
BANERJEE, A. K. Influence of kinetic friction on the critical velocity of stick-slip motion Wear, Vol 12, No 2 (August 1968) pp 10’7-116 Recent experiments have raised doubts about the validity of the concept of static friction. A kinetic-friction-dependent analysis of critical velocity for stock-slip motion is therefore given. The difficulties of predicting the precise nature of friction are pointed out. A steady-state nonlinear friction-velocity relationship is assumed for the problem under critical velocity conditions. The equation of motion is solved, assuming weak nonlinearity, by the method of Krylov and Bogolyubov. The critical velocity condition is shown to be attained when the overall system damping changes from negative, for auto-oscillation, to positive, for smooth sliding. Numerical results show how such an analysis can explain the decrease in critical velocity with a decrease in the slope of the friction-velocity curve, and also the elimination of stick-slip for a rising type of kinetic friction. (7 figures, 13 references) (Tribology 1968, abstract 142)
by writing The addresses suck as
ALLUM, K. G. and FORBES, E. S. The load-carrying mechanism of organic sulphur compounds-application of electron probe microanalysis Transactions of the American Society of Lubrication Engineers, Vol 11, No 2 (April 1968) pp 162-175 There is considerable controversy in the literature on the mode of action of organic sulphur compounds as loadcarrying additives. Previous four-ball extreme pressure and wear tests have suggested that under mixed lubrication (antiwear) conditions, organic disulphides are adsorbed onto the metal surface with clearage of the sulphur-sulphur bond to form an iron mercaptide layer. However, in the extremepressure region, clearage of the carbon-sulphur bond results in an inorganic sulphur-containing layer. The different relative performances in the mixed lubrication and extremepressure regions are thus readily explained. A detailed examination of the wear scars obtained with certain disulphldes, using an electron-probe microanalyzer, is reported. This new technique of studying the nature of worn surfaces lends strong support to the suggested mechanism of the action of organic disulphides. The results of this study also offer an explanation for the apparently conflicting rigtest results often reported in the literature. (7 figures, 3 tables, 25 references) (Tribology 1968, abstract 137)
ANDREASON, S. Passage of electric current through rolling bearings Ballbearing Journal, No 153 (June 1968) pp 6-12 Damage may be caused by passing electric current through a rolling bearing in motion. Electrical damage is characterised by craters and/or fluting on the bearing surfaces. Brief theoretical discussion and equations relating temperature, current, position and other parameters are derived for the contact zone. The mode of current passage across contact zone is discussed. The damage and wear encountered is described and suggestions given for avoiding this, including keeping the voltage across the contact zone as low as possible, shunt and series resistances, and optimisation of the lubricant-film thickness. (Tribology 1968, abstract 138)
AN-NO, J. N., WALOWIT, J. A. and ALLEN, C. E. Micro-asperity lubrication Transactions of the American Society of Mechanical Engineers, Journal of Lubrication Technologv, Vol 90. Series F. No 2 (Aoril 1968) DD 351-355 Large load-supporting capability has been observed between parallel surfaces of a rotary-shaft face-seal when one of the surfaces contains micro-asperities in the form of circular cylinders with 0.012in diameter and 100pm height, covering about one third of the surface. A theory is presented in which the load-support is attributed to small tilts on the tops of the asperities. Experimental data on lubricant-film thickness versus applied load are correlated well by this theory assuming an average tilt of 0.86pm, for the 0.012in diameter asperities investigated. Torque data obtained by a thermal technique are also correlated by this theory in the form of a plot of the coefficient friction versus Hersey number. Although direct evidence for the presence of small tilts of the asperity tops is lacking, it has been demonstrated that the load-support is even further increased when the tops are purposely rounded. It is concluded that the theory developed correlates well with the experimental data, and that the use of planned micro-asperities is an effective method,for lubricating the parallel surfaces of face-seals and thrust-bearings. (Tribology 1968, abstract 139) 250
TFUBOLOGY
November
1968
‘Ulorld
Lisl of Scieutific ’ Witlirrgs Press Guide’, for Amcr-icau journals
aud Teclwicat Publicaliorrs’, Newspaper Press Direclor-y’ ouly, ‘Ayers’.
aud,
APPLEDOORN, J. K. The present state of lubrication and its rehtion to rheology Transactions of the American Society of Mechanical Engineers, Journal of Lubrication Technology, Vol 90, No 3, Series F (July 1968) pp 526-530 In thick-film lubrication, Reynolds’ equation is generally satisfactory. However, the assumptions made in deriving this equation cannot be justified for non-Newtonian, viscoelastic liquids. It is concluded that no satisfactory mathematical treatment is yet available for calculating the loadcarrying capacity of such liquids. In thin-film lubrication, elastohydrodynamic calculations indicate that the lubricant film may be quite thick even under heavily loaded conditions, but discrepancies exist between calculation and experiment. These can be explained by assuming non-Newtonian behav-iour, or unusual viscoelastic effects, but the assumptions are largely unfounded. There is virtually complete absence of data on the behaviour of liquids under impact loading. Such data are needed to establish whether thin-film lubrication is mainly chemical or physical. (19 references) (Tribology 1968, abstract 140)
APPLEDOGRN, J. K. and TAO, F. F. The lubricity characteristics of heavy aromatics Wear, Vol 12, No 2 (August 1968) pp 117-130 Heavy aromatic hydrocarbons are the most probable cause of the good lubricating characteristics of petroleum oils. As little as 2% can greatly reduce wear and friction and increase the load-carrying capacity of paraffins. These mixtures of heavy aromatics and paraffins are much better than either component alone. Condensed-ring heavy aromatics show another unusual behaviour: in the absence of water and oxygen, they will scuff at very low loads. The unusual behaviour of these heavy aromatics is attributed to a little-understood decomposition reaction at the rubbing surface and not to oxidation or reaction with the metal. (5 figures, 13 tables, 5 references) (Tribology 1968, abstract 141)
BANERJEE, A. K. Influence of kinetic friction on the critical velocity of stick-slip motion Wear, Vol 12, No 2 (August 1968) pp 10’7-116 Recent experiments have raised doubts about the validity of the concept of static friction. A kinetic-friction-dependent analysis of critical velocity for stock-slip motion is therefore given. The difficulties of predicting the precise nature of friction are pointed out. A steady-state nonlinear friction-velocity relationship is assumed for the problem under critical velocity conditions. The equation of motion is solved, assuming weak nonlinearity, by the method of Krylov and Bogolyubov. The critical velocity condition is shown to be attained when the overall system damping changes from negative, for auto-oscillation, to positive, for smooth sliding. Numerical results show how such an analysis can explain the decrease in critical velocity with a decrease in the slope of the friction-velocity curve, and also the elimination of stick-slip for a rising type of kinetic friction. (7 figures, 13 references) (Tribology 1968, abstract 142)