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Tire traction measurement on the road and in the laboratory
108
ABSTRACTS
62.
Army Test and Evaluation Command. Gradeability and side slope performance mobility. 7pp. (November 1965). The procedures given in the document concern determination of the braking ability and performance of vehicles on various grades and side slopes and related information regarding engine performance, transmission performance, and minimum fuel requirements. (U.S. Gov. Res. Dev. Rep., 10.4.71, AD-718 003.)
63.
Army Test and Evaluation Command. Drawbar pull. 10 pp. (August t965). The document sets forth the minimum data requirements for evaluation and comparison of drawbar pull characteristics of both wheeled and tracked vehicles on hard-surfaced roads; in adverse soils, and, for amphibious vehicles, in water. (U.S. Gov. Res. Dev. Rep., 10.4.71, AD-717 999.)
64.
Army Test and Evaluation Command. Testing wheeled, tracked, and special purpose vehicles 12 pp. (July 1970). The background document provides general testing background information relative to the testing of tactical land vehicles and certain vehicles. It applies to wheeled, tracked and special purpose vehicles used by the U.S. Army. (U.S. Gov. Res. Dev. Rep., 25.3.71, AD-874 023.)
65.
L. Barden and D. C. Proctor. The drained strength of granular material. Can. Geotech. J., 8 (3), 372 (1971). Using the stress dilatancy relation R = DK, the drained strength of granular material is separated into its dilatant and frictional components. The factors influencing the value of I ~ D ~ 2 and K~. ~ K ~< K~, are assessed theoretically, and experimental confirmation is provided from tests mainly on River Welland sand. These tests include five different sample geometries, and cell pressures up to 1000 psi (70.3 kg/cm~). The failure criterion is seen to be contained between two limiting types of behavior relevant to dense and loose assemblies. The main ambiguity exists in the case of axisymmetric extension when the strength is seen to be influenced by the sample boundary conditions. (Author's summary.)
66.
W. Bergman, H. R. Clement and N. J. Sheth. Tire traction measurement on the road and in the laboratory. (Ford Motor Co.). S.A.E. Paper No. 710630, Mid-Year Meeting (June 7-11 1971). The paper gives a comprehensive analysis of tyre traction. The nature of tyre/road traction is discussed in detail. In order to express traction characteristics in a manner applicable to all basic operating modes and their combinations, the traction-envelope concept was developed. The traction envelope is defined as a closed-loop path of travel of a point at the end of a variablemagnitude vector rotating about the geometrical centre of the area enclosed by the loop. The scalar value of this vector expresses the instantaneous value of the traction coefficient, and its direction describes the operating condition to which its value applies. The equation of an ellipse is used for the solution of the general traction-envelope equation. Comparison between measured and calculated values shows that the ellipse equation describes the traction envelope with sufficient accuracy. A universal traction coefficient, which is the average value of traction coefficients for all operating modes, is introduced in order to express traction properties for all operating conditions in a single numerical value. An extensive test programme is reported, aimed at establishing correlation between road and laboratory measurements. Laboratory tests were carried out on the internal-drum test-rig of the University of Karlsruhe, Germany. The drum has an internal diameter of 12.5 ft and is lined with a 3 M 80 grit abrasive surface. All tests were conducted with a constant water-film thickness of 0.2 mm and, except for the braking tests, at 30 m.p.h, and 1000 lb wheel load. The speeds for the braking tests were 30 and 60 m.p.h. Five operating modes were used. Road tests were conducted at the Ford Arizona Proving Ground and Truckee Airport, with the same vehicle and tyres. Test methods for road/laboratory correlation were the same for both sites and were, as far as possible, compatible with the laboratory-test procedure. Laboratory- and road-test data are presented. Cornering tests with and without power-application were conducted by two methods: the conventional constant-radius method and the new constant-speed method. It was found that the new method has significant advantages over the old one. Road/laboratory correlation-tests produced excellent correlation. A correlation evaluation based on the universal traction coefficient also gave very good results. (M.I.R.A.)
ABSTRACTS
62.
Army Test and Evaluation Command. Gradeability and side slope performance mobility. 7pp. (November 1965). The procedures given in the document concern determination of the braking ability and performance of vehicles on various grades and side slopes and related information regarding engine performance, transmission performance, and minimum fuel requirements. (U.S. Gov. Res. Dev. Rep., 10.4.71, AD-718 003.)
63.
Army Test and Evaluation Command. Drawbar pull. 10 pp. (August t965). The document sets forth the minimum data requirements for evaluation and comparison of drawbar pull characteristics of both wheeled and tracked vehicles on hard-surfaced roads; in adverse soils, and, for amphibious vehicles, in water. (U.S. Gov. Res. Dev. Rep., 10.4.71, AD-717 999.)
64.
Army Test and Evaluation Command. Testing wheeled, tracked, and special purpose vehicles 12 pp. (July 1970). The background document provides general testing background information relative to the testing of tactical land vehicles and certain vehicles. It applies to wheeled, tracked and special purpose vehicles used by the U.S. Army. (U.S. Gov. Res. Dev. Rep., 25.3.71, AD-874 023.)
65.
L. Barden and D. C. Proctor. The drained strength of granular material. Can. Geotech. J., 8 (3), 372 (1971). Using the stress dilatancy relation R = DK, the drained strength of granular material is separated into its dilatant and frictional components. The factors influencing the value of I ~ D ~ 2 and K~. ~ K ~< K~, are assessed theoretically, and experimental confirmation is provided from tests mainly on River Welland sand. These tests include five different sample geometries, and cell pressures up to 1000 psi (70.3 kg/cm~). The failure criterion is seen to be contained between two limiting types of behavior relevant to dense and loose assemblies. The main ambiguity exists in the case of axisymmetric extension when the strength is seen to be influenced by the sample boundary conditions. (Author's summary.)
66.
W. Bergman, H. R. Clement and N. J. Sheth. Tire traction measurement on the road and in the laboratory. (Ford Motor Co.). S.A.E. Paper No. 710630, Mid-Year Meeting (June 7-11 1971). The paper gives a comprehensive analysis of tyre traction. The nature of tyre/road traction is discussed in detail. In order to express traction characteristics in a manner applicable to all basic operating modes and their combinations, the traction-envelope concept was developed. The traction envelope is defined as a closed-loop path of travel of a point at the end of a variablemagnitude vector rotating about the geometrical centre of the area enclosed by the loop. The scalar value of this vector expresses the instantaneous value of the traction coefficient, and its direction describes the operating condition to which its value applies. The equation of an ellipse is used for the solution of the general traction-envelope equation. Comparison between measured and calculated values shows that the ellipse equation describes the traction envelope with sufficient accuracy. A universal traction coefficient, which is the average value of traction coefficients for all operating modes, is introduced in order to express traction properties for all operating conditions in a single numerical value. An extensive test programme is reported, aimed at establishing correlation between road and laboratory measurements. Laboratory tests were carried out on the internal-drum test-rig of the University of Karlsruhe, Germany. The drum has an internal diameter of 12.5 ft and is lined with a 3 M 80 grit abrasive surface. All tests were conducted with a constant water-film thickness of 0.2 mm and, except for the braking tests, at 30 m.p.h, and 1000 lb wheel load. The speeds for the braking tests were 30 and 60 m.p.h. Five operating modes were used. Road tests were conducted at the Ford Arizona Proving Ground and Truckee Airport, with the same vehicle and tyres. Test methods for road/laboratory correlation were the same for both sites and were, as far as possible, compatible with the laboratory-test procedure. Laboratory- and road-test data are presented. Cornering tests with and without power-application were conducted by two methods: the conventional constant-radius method and the new constant-speed method. It was found that the new method has significant advantages over the old one. Road/laboratory correlation-tests produced excellent correlation. A correlation evaluation based on the universal traction coefficient also gave very good results. (M.I.R.A.)