Contribution to the study of the coefficient of friction of wet tyre treads. (in German)

likely that vapor lubrication applies to lame&r solids only wbcn relatively high specific forces arc acting between the layers. Developments in High-temperature, Ultrahigh-vacuum Friction Studies. L. G. Kellogg, L$&icatdon Eng., zz (2) (1966) 57-66; rG figs., 2 tables, 13 refs. The Frictional Behavior of Materials in JP-4 Fluid. K. H. Krueger, Lubrication Eng., 21 (12) (1965) 501-505; 7 fig%, 2 tables, 6 refS. A laboratory apparatus was used to measure friction of materials sliding in JP-4 fluid in order to predict the performance of a particular type of hydraulic pump. Only cemented tungsten carbide gave low friction. Lowest coefficients of friction were obtained with cermets containing uniform rounded tungsten-carbide particles, 3 to 16% cobalt, and no apparent oxides or voids. Friction increased with increasing surface roughness of tungsten carbide. Repetitive testing of different tungsten carbide materials did not significantly change the coefficient of friction in Jr-4 at 300°F. Metal-PTFE compacted materials gave low friction in JP-4 but were not satisfactory because of a small amount of wear. contribution to the Study of the Coefficient of Friction of Wet Tyre Treads. (in German) W. F. Kern, Kautschtik Gumwzi, zg (2) (1966) 91; 20 figs., g tables, ro refs. A systematic analysis of materials properties contributing to an increase in the coefficient of friction. Skidding on Wet Roads at High Speeds. G. Grime, Chartered Mech. Eng., rg (2) (1966) 82-84; I fig., 2 tables, r ref. Two papers recently presented to the Automobile Division draw attention to a motoring danger which is particularly prominent i.e., that of skidding on wet roads. 3. LUBRICATION

AND LUBRICANTS

3.1. Lubricatiosa On the Determination of Friction Forces in Turbulent Lubrication. V. N. Constantinescu and S. Galetuse, ASLE Trans., 8 (1965) 367-380. The mixing length theory, used previously for the determination of the velocity profiles and pressure distributions in turbulent films is now employed in order to determine the friction stresses ~0, ra on the two lubricated surfaces and their dependence on the Reynolds number and on the pressure distribution. Thus, it results that the curves %(B,) and -fn(Bz) are antisymmetric and that the Wear, 9 (r966) 398-409

tlrrivativcs &&&,, af,jau,s :tt U, -- 0 IMIX’ constant values, independent of the I