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136. The adhesion of vehicle tyres on icy surfaces
ABSTRACTS
79
134.
J. W. Terriil and J. E. Shea. Soil compaction investigations. 68 pp. (November 1969). The interim report covers tests conducted to evaluate the soil compacting efficiency of the Cemco flat-iron, pneumatictired road roller, and an experimental 3-wheel tandem 12- to 18-ton vibrating roller built by the Buffalo-Springfield Roller Company, by comparison with densities obtained by standard compaction equipment. (Author's Summary. U.S. Gov. Res. Rep., 25.7.71, AD-800022.)
135.
V. J. Virehis and J. D. Robson. Response of an accelerating vehicle to random road undulation. J. Sound Vibr. 18, No. 3,423-427 (October 1971). Work was undertaken to investigate the primary effect of forward acceleration of a vehicle on its response to randomly undulating road surfaces. Consideration was restricted to the case of uniform acceleration and a particularly simple vehicle model. Care was taken to ensure that the essential parameters of the system were typical of those in practice. The vehicle was replaced by a linear, dapped spring/mass system, a displacement being imposed at the lower end of spring and damper by the surface traversed. Variation of road-displacement as a function of distance was assumed to be that of a member function of an ergodic random process. Mean square relative displacement was taken to be a suitable response parameter. Basic theory is discussed, and various equations are derived including a final equation for mean square response. Earlier investigations are then mentioned in connection with a Sunbeam Imp car for which physical parameters were available; these investigations had suggested a one-degree-of-freedom system with a damping ratio of 0.35 and an undamped frequency of 1 "58 Hz as a suitable model. The surface was assumed to be traversed at constant acceleration. The profile autocorrelation function used was computed from data taken in a survey of a country road. A computing technique based on some of the equations derived was evolved to determine mean-square response under various conditions. Results are presented. Mean-square response for the system considered at speeds and accelerations usual for road vehicles is shown to differ little from that with zero acceleration. As a first approximation, such non-stationary effects can be neglected in the prediction of vehicle response. The simplification may be applicable to both uniform and non-uniform accelerations. (M.LR.A.)
136.
R. Weber. The adhesion of vehicle tyres on icy surfaces. Auto. lndustrie 16, No. 3 (September 1971). The author discusses the experimental results obtained when tyres ~ith and without studs and with snow-chains are run on the surface of smooth ice provided by the test rig described in the first part of the article. The influence of ice-surface temperature and of vehicle speed on side, tractive and braking forces was first investigated with unstudded tyres having at least 80 per cent tread-depth. With the rolling tyre, temperature is found vitally to affect adhesion--the maximum adhesion coefficient from side-force is twice as great at - - 5 as at 0°C. On wet ice at about 0°C, no sideforce maxima occur; the side-force does not decrease with increasing slip-angle. The first maxima are recorded between - - 0 . 5 and - - 1.5°C, depending on vehicle speed. Maximum cornering force decreases steeply with rising vehicle-speed, and maximum values occur at lower side-slip angles with rising speed. With the braked wheel, sliding coefficients rise much less steeply than do the maximum adhesion coefficients with falling ice-temperature at all vehicle-speeds--probably because the severe frictional effect considerably warms up, or even melts, the ice in the contact patch of the sliding tyre. The effect of vehicle speed on the sliding coefficient is examined. The relationship between circumferential force and percentage slip is largely determined by the side-slip angle. The circumferential forces attainable decrease with increasing slip angle, their maxima simultaneously shifting towards ever larger slip coefficients. When cornering force is plotted against braking and tractive forces for various slip angles, it is seen that the differences in behaviour found between cross-ply and radial tyres on dry surfaces do not occur on smooth ice. Diagrams providing three-dimentional representation of braking and side forces respectively versus percentage slip and side-slip angle show that the forces longitudinal and lateral to the tyre are built up according to the same laws. Tests with winter tyres fitted with studs protruding 1.3 and 1.9 mm respectively indicated that temperature has no influence on the sliding coefficient of studded tyres--this is attributed to the presence of ice fragments in the contact patch and the decreasing stud-penetration depth as the ice hardens with falling temperatures. When sliding coefficient is plotted against vehicle speed, minimum values are found between 10 and 20 km/hr, and values rise as speeds approach 60 km/hr. At 20 km/hr on ice at - - 5°C, the sliding coefficient of the locked wheel fitted with a tyre having studs protruding less than I mm was no greater than that of a wheel with unstudded
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ABSTRACTS tyre, but thereafter, sliding coefficient increased steeply with stud length. Tests with tyres fitted with chains or sprayed with a commercial preparation designed to improve grip on snow or ice did not yield satisfactorily reproducible results. Comparison of the experimental results with those obtained on icy roads, or even on an ice-rink, is difficult because of differences in the moisture-content, surface structure, degree of contamination, etc., of the ice and in tyre cleanliness and temperature. The test-rig results become invalid at temperatures below --5"C. (M.I.R.A.)
137.
R. V. Whitman. Response of soils to dynamic loading. Contract Report No. 3 26, Massachusetts Institute of Technology (May 1970). Since 1957 a series of reports has been prepared covering the results of laboratory tests of dynamic loading of soils. This 26th report in this series summarizes all the research performed under the basic contract and contributions by other investigators, assesses the state-ofitbeart as of 1967, and provides abstracts of the 25 earlier reports issued. In addition the report deals with the role of soil mechanics with regard to weapons effects prediction and protective construction design. Results from field experiments and theoretical analyses are interpreted so as to show the relation between soil properties and such phenomena as crater size and shape ground motions, and response of buried structures. Chapters deal specifically with the evaluation of dynamic uniaxial strain and dynamic shear strength, and with the relation between seismic wave velocity and soil properties. An extensive bibliography is included.
These abstracts have been collected by A. D. Trapp of the Department of Agricultural Engineering, The University of Newcastle-upon-Tyne. The following is a list of publications searched: (1) British Technology Index, The Library Association, London. (2) Monthly Summaries, Motor Industry Research Association, Lindley. (3) Applied Mechanics Review, Am. Soc. Mech. Eng., New York. (4) U.S. Govt. Research Development Reports, Dept. of Commerce, Springfield. (5) J. Soil Mech. and Found. Div., Am. Soc. Civil Eng., New York. (6) Geotechnique, Inst. Civil Eng., London. (7) Civil Eng. and Public Works Review, London. (8) Soils and Fertilizers, Commonwealth Bureau of Soils, Harpenden. (9) J. Agric. Eng. Res., NIAE, Bedford. (10) Civil Engineering, Am. Soc. Civil Eng., New York. (11) Soil Science Proceedings, Am. Soc. of Soil Science, Washington. (12) J. Engng Education, Am. Soc. Eng. Education, Washington. (13) Materials Research and Standards, Am. Soc. Testing Materials. (14) J. Strain Analysis, Inst. Mech. Eng., London. (15) Agricultural Engineering, Am. Soc. Agric. Eng., Michigan. (16) Soviet Soil Science (Trans. of Poehovedeniye), Soil Sci. Soc. of Am., Wisconsin. (17) Canadian Geotechnical J., National Res. Council of Canada.
79
134.
J. W. Terriil and J. E. Shea. Soil compaction investigations. 68 pp. (November 1969). The interim report covers tests conducted to evaluate the soil compacting efficiency of the Cemco flat-iron, pneumatictired road roller, and an experimental 3-wheel tandem 12- to 18-ton vibrating roller built by the Buffalo-Springfield Roller Company, by comparison with densities obtained by standard compaction equipment. (Author's Summary. U.S. Gov. Res. Rep., 25.7.71, AD-800022.)
135.
V. J. Virehis and J. D. Robson. Response of an accelerating vehicle to random road undulation. J. Sound Vibr. 18, No. 3,423-427 (October 1971). Work was undertaken to investigate the primary effect of forward acceleration of a vehicle on its response to randomly undulating road surfaces. Consideration was restricted to the case of uniform acceleration and a particularly simple vehicle model. Care was taken to ensure that the essential parameters of the system were typical of those in practice. The vehicle was replaced by a linear, dapped spring/mass system, a displacement being imposed at the lower end of spring and damper by the surface traversed. Variation of road-displacement as a function of distance was assumed to be that of a member function of an ergodic random process. Mean square relative displacement was taken to be a suitable response parameter. Basic theory is discussed, and various equations are derived including a final equation for mean square response. Earlier investigations are then mentioned in connection with a Sunbeam Imp car for which physical parameters were available; these investigations had suggested a one-degree-of-freedom system with a damping ratio of 0.35 and an undamped frequency of 1 "58 Hz as a suitable model. The surface was assumed to be traversed at constant acceleration. The profile autocorrelation function used was computed from data taken in a survey of a country road. A computing technique based on some of the equations derived was evolved to determine mean-square response under various conditions. Results are presented. Mean-square response for the system considered at speeds and accelerations usual for road vehicles is shown to differ little from that with zero acceleration. As a first approximation, such non-stationary effects can be neglected in the prediction of vehicle response. The simplification may be applicable to both uniform and non-uniform accelerations. (M.LR.A.)
136.
R. Weber. The adhesion of vehicle tyres on icy surfaces. Auto. lndustrie 16, No. 3 (September 1971). The author discusses the experimental results obtained when tyres ~ith and without studs and with snow-chains are run on the surface of smooth ice provided by the test rig described in the first part of the article. The influence of ice-surface temperature and of vehicle speed on side, tractive and braking forces was first investigated with unstudded tyres having at least 80 per cent tread-depth. With the rolling tyre, temperature is found vitally to affect adhesion--the maximum adhesion coefficient from side-force is twice as great at - - 5 as at 0°C. On wet ice at about 0°C, no sideforce maxima occur; the side-force does not decrease with increasing slip-angle. The first maxima are recorded between - - 0 . 5 and - - 1.5°C, depending on vehicle speed. Maximum cornering force decreases steeply with rising vehicle-speed, and maximum values occur at lower side-slip angles with rising speed. With the braked wheel, sliding coefficients rise much less steeply than do the maximum adhesion coefficients with falling ice-temperature at all vehicle-speeds--probably because the severe frictional effect considerably warms up, or even melts, the ice in the contact patch of the sliding tyre. The effect of vehicle speed on the sliding coefficient is examined. The relationship between circumferential force and percentage slip is largely determined by the side-slip angle. The circumferential forces attainable decrease with increasing slip angle, their maxima simultaneously shifting towards ever larger slip coefficients. When cornering force is plotted against braking and tractive forces for various slip angles, it is seen that the differences in behaviour found between cross-ply and radial tyres on dry surfaces do not occur on smooth ice. Diagrams providing three-dimentional representation of braking and side forces respectively versus percentage slip and side-slip angle show that the forces longitudinal and lateral to the tyre are built up according to the same laws. Tests with winter tyres fitted with studs protruding 1.3 and 1.9 mm respectively indicated that temperature has no influence on the sliding coefficient of studded tyres--this is attributed to the presence of ice fragments in the contact patch and the decreasing stud-penetration depth as the ice hardens with falling temperatures. When sliding coefficient is plotted against vehicle speed, minimum values are found between 10 and 20 km/hr, and values rise as speeds approach 60 km/hr. At 20 km/hr on ice at - - 5°C, the sliding coefficient of the locked wheel fitted with a tyre having studs protruding less than I mm was no greater than that of a wheel with unstudded
80
ABSTRACTS tyre, but thereafter, sliding coefficient increased steeply with stud length. Tests with tyres fitted with chains or sprayed with a commercial preparation designed to improve grip on snow or ice did not yield satisfactorily reproducible results. Comparison of the experimental results with those obtained on icy roads, or even on an ice-rink, is difficult because of differences in the moisture-content, surface structure, degree of contamination, etc., of the ice and in tyre cleanliness and temperature. The test-rig results become invalid at temperatures below --5"C. (M.I.R.A.)
137.
R. V. Whitman. Response of soils to dynamic loading. Contract Report No. 3 26, Massachusetts Institute of Technology (May 1970). Since 1957 a series of reports has been prepared covering the results of laboratory tests of dynamic loading of soils. This 26th report in this series summarizes all the research performed under the basic contract and contributions by other investigators, assesses the state-ofitbeart as of 1967, and provides abstracts of the 25 earlier reports issued. In addition the report deals with the role of soil mechanics with regard to weapons effects prediction and protective construction design. Results from field experiments and theoretical analyses are interpreted so as to show the relation between soil properties and such phenomena as crater size and shape ground motions, and response of buried structures. Chapters deal specifically with the evaluation of dynamic uniaxial strain and dynamic shear strength, and with the relation between seismic wave velocity and soil properties. An extensive bibliography is included.
These abstracts have been collected by A. D. Trapp of the Department of Agricultural Engineering, The University of Newcastle-upon-Tyne. The following is a list of publications searched: (1) British Technology Index, The Library Association, London. (2) Monthly Summaries, Motor Industry Research Association, Lindley. (3) Applied Mechanics Review, Am. Soc. Mech. Eng., New York. (4) U.S. Govt. Research Development Reports, Dept. of Commerce, Springfield. (5) J. Soil Mech. and Found. Div., Am. Soc. Civil Eng., New York. (6) Geotechnique, Inst. Civil Eng., London. (7) Civil Eng. and Public Works Review, London. (8) Soils and Fertilizers, Commonwealth Bureau of Soils, Harpenden. (9) J. Agric. Eng. Res., NIAE, Bedford. (10) Civil Engineering, Am. Soc. Civil Eng., New York. (11) Soil Science Proceedings, Am. Soc. of Soil Science, Washington. (12) J. Engng Education, Am. Soc. Eng. Education, Washington. (13) Materials Research and Standards, Am. Soc. Testing Materials. (14) J. Strain Analysis, Inst. Mech. Eng., London. (15) Agricultural Engineering, Am. Soc. Agric. Eng., Michigan. (16) Soviet Soil Science (Trans. of Poehovedeniye), Soil Sci. Soc. of Am., Wisconsin. (17) Canadian Geotechnical J., National Res. Council of Canada.