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Friction between ski and snow
LITERATURE AND CURRENT EVENTS The beginning of the relative sliding of two cylinders pressed together by a normal given force was observed by a photoelastic measuring technique. When the tangential force increases, the maximum shear point is seen to draw nearer the surface and to move in the direction of the tangential force, towards the escape edge. The value of the maximum shear increases with the tangential force. On an “Essentially Plastic” Mechanism of Wear of Mono- and Polycrystals by Friction. (in French) R. Courtel and P. Rougier, Comnpl. Rend., 258 (1964) 805-808. The damage caused by an unlubricated ball rubbing on 8 brass and polished copper at low speeds and under light loads was interpreted by considering that the rider runs on a superficial structure which has just been modified by the constitution of the frontal bulge. When a monocrystal is rubbed certain arrangements of the crystallographic planes underlying the friction surface appear to promote tearing, which is usually considered to be a result of adhesion and local weld phenomena. These arrangements were determined for some particular cases and a general law was proposed. On the Sliding Friction of a Light Alloy on Pure or Charged PTFE at Rapidly Variable Speeds (0 to 100 km/b), (in French) P. Nadal et nl., Cow@. Rend., 258 (1964) 3’82-3184. The study deals with the determination of the friction coefficient of a light alloy (AC; 5) sliding under different pressures on PTFE loaded with graphite and used in thin, stickable sheets. A modern tribometer permitted a large field of linear speeds and the corresponding friction to be examined. Determination of the Coefficient of Kinetic Friction in the Case of Extremely Small Displacements. I). H. Wiid and W. F. Beezhold, J. A$#. Phys., 35 (4) jr96+) x169-1175; 4 figs., 2 tables, 13 refs. This paper describes a simple technique for determining the coefficient of kinetic friction for cxtremcly small displacements. An attempt was made to obtain more information about the transition stage between the coefficients of static and kinetic friction. If the force of static friction persists over small distances before falling to the lower values of the kinetic friction, such distances in the case of steel on steel are probably smaller than 5 . 10-6 cm. With the exception of very soft metals higher values of the coefficient of static friction were obtained for impulsive forces than for slowly increasing tangential forces.
2.1
467
Adhesion
Adhesion of Rare Earth Metals. M. E. Sikorski and J. S. Courtney-Pratt, ASLE
Trans.,
7 (1964)
73-81.
Results of adhesion tests performed on yttrium (Y). as well as four rare earth metals, samarium (Sm), gadolinium (Gd), dysprosium (Dy), and holmium (Ho), are reported. A modification of the twist-compression bonding method was used to obtain the coefficients of adhesion. Low adhesion values for the above metals were obtained as expected on the basis of the crystal structure considerations. A proposal is made to apply the atomic “size-factor” criterion to the prediction of adhesion properties of dissimilar metals. An illustration of the method is given in terms of adhesion of iron to the above mentioned metals. (See also wear, 7 (1964) 144.) 2.2 Friction Vibrations Caused by Dry Friction. A. Watari and T. Sugimoto, Bull. JSME, 7 (25) (1964) 40-52; 28 figs., 5 refs. Self-excited vibrations caused by dry friction, which are generally expressed as a function of relative sliding velocities between two solid bodies, were analysed theoretically and observed experimentally. The characteristics of these vibrations were divided into two groups by the type of friction. One is experienced in the case of pure dry friction, where the amplitudes of steady vibration increase with the increase of sliding velocities and the frequencies are nearly equal to the natural frequency of the system. Another occurs in the case of boundary lubrication, where the amplitudes vary slowly with sliding velocities and the frequencies increase with the increase of sliding velocities. In the case of boundary lubrication, self-excited vibrations occur by hard excitation, even if the frictional force increases with the increase of relative velocities. Experimental results obtained from the case of dry friction show good agreement with the theoretical results. Friction between Feet and Ground. D. M. Badoux, Nntwe, zoz (1964) 266-267; 2 figs., 7 refs. ‘4 brief survey of the literature on anim,l locomotion is given. Preliminary experiments investigated the static friction and onset of motion of animal pads and hooves on an inclined plane. Friction between Ski and Snow. F. P. Bowden, New Scientist, 21 (1964) 275278; 4 figs., I table. If the snow is not too cold, the surface melting caused by the friction provides a lubricating film of water, which in turn reduces the friction. Although snow is unique in its propWear> 7 (1964) 466-475
468
LITERATURE
AND
CURRENT
erties, skiing is, in theory, possible on other materials, provided the speeds are great enough.
cient of friction of a steel pin sliding on a steel ring lubricated with three commercial greases, various experimental greases or pastes, and other components of greases. After break-in at room temperature, heat was applied which reduced the friction of the greases to about half their r”om temperature value. The friction increased on cooling. The opposite effect was observed with base oil. The phenomenon was demonstrated in a ball thrust bearing operatmg under boundary conditions as a reduction in torque with heating and an increase in torque on cooling. The reduction in friction with heating was found to bc due to the soap thickener. Pastes of CaCOz, fumed silica, and clay in oil, the base oil, and octadecane did not cause a reduction in friction. It was concluded that grease thickeners influence the friction of steel sliding on steel because of the formation of films on the snrface of the metal.
Friction and Deformation at High Temperature of Titanium Carbide. C. A. Brookes, Special Ceramirs 1962: Pruccedings of a Symposizr?x, British Ceramic Research Xssn. and Academic Press, New York, 1963. pp. 221x35. Recent work on the frictional properties, at high temperatures, of refractory compounds is reviewed and briefly discussed with reference to the adhesion theory of friction. Experiments on single crystals have revealed the onset of plastic deformation, due to frictional traction, and slip traces along the (I I I) planes of titanium carbide haxe been observed. .%lthough the bulk material undergoes a brittle-ductile transition the results indicate that no corresponding change in the coefficient of friction occurs. The mechanism of deformation and friction for polycrystalline specimens is discussed. Finally, a few comments are made on the possible “decoration”, by residual carbon, of lattice defects in titanium carbide crystals after etching.
Relative Influence of Various Factors on the Stick-Slip of Metals. G. Niemann and I<. Ehrlcnspiel, Lubrircc/io?z &zg., 21 (3) (1904) 84-86; 4 figs. Several of the essential factors which in fluence the stick-slip of metals have been investigated with test apparatus using a cylinder sliding on a plane. The relation between stick-slip and static friction is discussed. Jlethods for reducing stick slip and static friction are indicated.
The Friction of Clean Metals Immersed in Liquid Sodium. N. C. Balchin, But. J, Appl. P’hys., 13 (190~) .jk-5bg; g figs., r7 refs. hn apparatus for the measurement of friction is described, in which specimens are heated in a high vacuum (- 10-6 torr) to remove surface contamination such as oxide films and then immersed in liquid sodium. The friction between the specimens was mcasured both when they were dry and after immersion at temperatures from roe-r9o”C‘. In general, for specimens in liquid sodium, the frictional force was no longer proportional to load. Above a certain critical load, on the specimen, the I”-‘#0 g, depending coefficient of friction increased and asymptotically approached a higher constant value, about two-thirds of the dry friction. These results are consistent with the formation of a thin layer of a double oxide on thu surface of the specimen by a chemical reaction between the specimen, the liquid sodium and sodium nxidc dissolved in the latter.
The Effect of Angle between Direction of Sliding and Line of Contact on Friction and Wear of a Roller. F. Hirano and S. ‘isanabe, LL~~Y~CU~ZO?Z E~zg., 20 (2) (1904) 57-64; 7 figs., 7 tables, 9 refs. -\ flat plate was rubbed with a roller in sariens directions to investigate the effect of the angle between the direction of sliding and the line of contact of the roller on friction and xvear. The coefficient of friction and the amount of xear decrease with increase in angle. This directional effect is considerably affected by waviness of the plate. Surface roughness of the plate has littleinfluence upon the friction, but wear of the roller is apprcciably affcctcd by it. Grinding marks on the plate show a secondary effect on the friction. Coefficient of Friction as a Function of the Contact Temperature. (in Russian) N. AI. lilcment’cv, l’~st?zik .Ifas/rinosfi., 42
Friction of Greases and Grease Components during Boundary Lubrication. 1). Godfrey, ASLE Trms., 7 (1964) :4--31. Sleasurcments have been made of the cocffi3. LUBRICATION 3.1 Lztbviculim Approximate Methods for Time-dependent Gas-film Lubrication Problems. \V. A. Michael, ilSillE Trans., Swirs E, ,/_ ‘4ppl. Mech., jYJ (1963) 5og-j17.
EVENTS
(i9fi2) 43-45. For abstract see /fppZ. 203 .wn
‘7
(“9(‘4)
LUBRICANTS The pressure in a thin film of gas undergoing laminar, isothermal flow is given by the Reynolds equation, a nonlinear, second-order, parabolic-type partial differential equation. The Reynolds equation plays a central role in CT’eUY,j (1904)
460-~7.j
2.1
467
Adhesion
Adhesion of Rare Earth Metals. M. E. Sikorski and J. S. Courtney-Pratt, ASLE
Trans.,
7 (1964)
73-81.
Results of adhesion tests performed on yttrium (Y). as well as four rare earth metals, samarium (Sm), gadolinium (Gd), dysprosium (Dy), and holmium (Ho), are reported. A modification of the twist-compression bonding method was used to obtain the coefficients of adhesion. Low adhesion values for the above metals were obtained as expected on the basis of the crystal structure considerations. A proposal is made to apply the atomic “size-factor” criterion to the prediction of adhesion properties of dissimilar metals. An illustration of the method is given in terms of adhesion of iron to the above mentioned metals. (See also wear, 7 (1964) 144.) 2.2 Friction Vibrations Caused by Dry Friction. A. Watari and T. Sugimoto, Bull. JSME, 7 (25) (1964) 40-52; 28 figs., 5 refs. Self-excited vibrations caused by dry friction, which are generally expressed as a function of relative sliding velocities between two solid bodies, were analysed theoretically and observed experimentally. The characteristics of these vibrations were divided into two groups by the type of friction. One is experienced in the case of pure dry friction, where the amplitudes of steady vibration increase with the increase of sliding velocities and the frequencies are nearly equal to the natural frequency of the system. Another occurs in the case of boundary lubrication, where the amplitudes vary slowly with sliding velocities and the frequencies increase with the increase of sliding velocities. In the case of boundary lubrication, self-excited vibrations occur by hard excitation, even if the frictional force increases with the increase of relative velocities. Experimental results obtained from the case of dry friction show good agreement with the theoretical results. Friction between Feet and Ground. D. M. Badoux, Nntwe, zoz (1964) 266-267; 2 figs., 7 refs. ‘4 brief survey of the literature on anim,l locomotion is given. Preliminary experiments investigated the static friction and onset of motion of animal pads and hooves on an inclined plane. Friction between Ski and Snow. F. P. Bowden, New Scientist, 21 (1964) 275278; 4 figs., I table. If the snow is not too cold, the surface melting caused by the friction provides a lubricating film of water, which in turn reduces the friction. Although snow is unique in its propWear> 7 (1964) 466-475
468
LITERATURE
AND
CURRENT
erties, skiing is, in theory, possible on other materials, provided the speeds are great enough.
cient of friction of a steel pin sliding on a steel ring lubricated with three commercial greases, various experimental greases or pastes, and other components of greases. After break-in at room temperature, heat was applied which reduced the friction of the greases to about half their r”om temperature value. The friction increased on cooling. The opposite effect was observed with base oil. The phenomenon was demonstrated in a ball thrust bearing operatmg under boundary conditions as a reduction in torque with heating and an increase in torque on cooling. The reduction in friction with heating was found to bc due to the soap thickener. Pastes of CaCOz, fumed silica, and clay in oil, the base oil, and octadecane did not cause a reduction in friction. It was concluded that grease thickeners influence the friction of steel sliding on steel because of the formation of films on the snrface of the metal.
Friction and Deformation at High Temperature of Titanium Carbide. C. A. Brookes, Special Ceramirs 1962: Pruccedings of a Symposizr?x, British Ceramic Research Xssn. and Academic Press, New York, 1963. pp. 221x35. Recent work on the frictional properties, at high temperatures, of refractory compounds is reviewed and briefly discussed with reference to the adhesion theory of friction. Experiments on single crystals have revealed the onset of plastic deformation, due to frictional traction, and slip traces along the (I I I) planes of titanium carbide haxe been observed. .%lthough the bulk material undergoes a brittle-ductile transition the results indicate that no corresponding change in the coefficient of friction occurs. The mechanism of deformation and friction for polycrystalline specimens is discussed. Finally, a few comments are made on the possible “decoration”, by residual carbon, of lattice defects in titanium carbide crystals after etching.
Relative Influence of Various Factors on the Stick-Slip of Metals. G. Niemann and I<. Ehrlcnspiel, Lubrircc/io?z &zg., 21 (3) (1904) 84-86; 4 figs. Several of the essential factors which in fluence the stick-slip of metals have been investigated with test apparatus using a cylinder sliding on a plane. The relation between stick-slip and static friction is discussed. Jlethods for reducing stick slip and static friction are indicated.
The Friction of Clean Metals Immersed in Liquid Sodium. N. C. Balchin, But. J, Appl. P’hys., 13 (190~) .jk-5bg; g figs., r7 refs. hn apparatus for the measurement of friction is described, in which specimens are heated in a high vacuum (- 10-6 torr) to remove surface contamination such as oxide films and then immersed in liquid sodium. The friction between the specimens was mcasured both when they were dry and after immersion at temperatures from roe-r9o”C‘. In general, for specimens in liquid sodium, the frictional force was no longer proportional to load. Above a certain critical load, on the specimen, the I”-‘#0 g, depending coefficient of friction increased and asymptotically approached a higher constant value, about two-thirds of the dry friction. These results are consistent with the formation of a thin layer of a double oxide on thu surface of the specimen by a chemical reaction between the specimen, the liquid sodium and sodium nxidc dissolved in the latter.
The Effect of Angle between Direction of Sliding and Line of Contact on Friction and Wear of a Roller. F. Hirano and S. ‘isanabe, LL~~Y~CU~ZO?Z E~zg., 20 (2) (1904) 57-64; 7 figs., 7 tables, 9 refs. -\ flat plate was rubbed with a roller in sariens directions to investigate the effect of the angle between the direction of sliding and the line of contact of the roller on friction and xvear. The coefficient of friction and the amount of xear decrease with increase in angle. This directional effect is considerably affected by waviness of the plate. Surface roughness of the plate has littleinfluence upon the friction, but wear of the roller is apprcciably affcctcd by it. Grinding marks on the plate show a secondary effect on the friction. Coefficient of Friction as a Function of the Contact Temperature. (in Russian) N. AI. lilcment’cv, l’~st?zik .Ifas/rinosfi., 42
Friction of Greases and Grease Components during Boundary Lubrication. 1). Godfrey, ASLE Trms., 7 (1964) :4--31. Sleasurcments have been made of the cocffi3. LUBRICATION 3.1 Lztbviculim Approximate Methods for Time-dependent Gas-film Lubrication Problems. \V. A. Michael, ilSillE Trans., Swirs E, ,/_ ‘4ppl. Mech., jYJ (1963) 5og-j17.
EVENTS
(i9fi2) 43-45. For abstract see /fppZ. 203 .wn
‘7
(“9(‘4)
LUBRICANTS The pressure in a thin film of gas undergoing laminar, isothermal flow is given by the Reynolds equation, a nonlinear, second-order, parabolic-type partial differential equation. The Reynolds equation plays a central role in CT’eUY,j (1904)
460-~7.j