3. On the statistical analysis of linear vehicle dynamics

3. On the statistical analysis of linear vehicle dynamics

ABSTRACTS Rao. The Response of Soils to Dynamic Loadings. Report No. 24: Wave Velocities Through Partially Saturated Sand-Clay Mixtures. Massachusetts...

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ABSTRACTS Rao. The Response of Soils to Dynamic Loadings. Report No. 24: Wave Velocities Through Partially Saturated Sand-Clay Mixtures. Massachusetts Inst. of Tech., Cambridge. Dept. of Civil Engineering. Investigations concerning the velocity of dilatational and shear waves through compacted specimens of kaolin& and kaolinite-sand mixtures at different moisture contents have been described. The delay time between the input and output signals from piezoelectric crystals located at the two ends of compacted samples has been utilized to evaluate the wave velocity. The results reveal that there are two important parameters involved in the propagation of dilatational waves: confining stress and moisture content. An increase in confining stress tends to increase the dilatational wave velocities. An increase in the moisture content also tends to increase the dilatational wave velocity, particularly at high saturation. The magnitude of wave velocity measured in various mixtures is similar to those in dense sand. The results of shear wave tests show a reduction of shear wave velocity with increase in moisture content. The decrease is attributed partly to the decrease in the rigidity of the fabric and partly to addition of mass which contributes to the inertia force. For a constant dry density, the presence of sand tends to decrease the wave velocity, apparently because differing amounts of sand required different compactive efforts. (Author’s Summary.) H. A. Balakrishna

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L. Barden and A. J. Khayatt. Incremental Strain Rate Ratios and Strength of Sand in the Triaxial Test. GCofechniacte 16. No. 4 (1966). Certain design problems in soil ‘mechanics should’ be treated as deformation rather than failure problems and to this end incremental stress-strain relations must be developed for different types of soil. The incremental strain rate ratio given by the stress-dilatancy relation may prove valuable in such studies. A short account is given of the stress-dilatancy theory with particular reference to the concepts of the upper c6,., and lower +,@hmits. The main object of the Paper is to investigate the conditions under which these hmtts are approached employing stress paths involving both loading and unloading in triaxial compression and extension. A major part of the Paper is devoted to a critical discussion of errors involved in drained triaxial tests on sand and to certain modifications developed to minimize these errors. The peak or failure points in the various tests have been studied to assess the failure criteria commonly applied to soils. It is shown that the extended Von Mises and Tresca criteria are inapplicable to sands for theoretical reasons alone. (Author’s Summary.)

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J. L. Bogdanoff and F. Kozin. On the Statistical Analysis of Linear Vehicle Dynamics. Army Tank Automotive Center, Warren, Mich. Land Locomotion Lab. Statistical analyses of the dynamics of some two-dimensional linear vehicles travelling on a rough track are performed to determine the influence on two aspects of vehicle ride of a set of parameters which include wheel base length, idealized tire imprint length, speed, and damping constant. It is assumed that the vehicles move with constant horizontal velocity on a second order, weakly stationary and mean square continuous random track with contact maintained at a11 times between the idealized tires and the track. The two aspects of vehicle ride used as measures of the ride roughness are peak value of power spectral density and variance of frame acceleration, the frame acceleration being either vertical at the c.g. of frame, vertical at the point over idealized wheel, or angular (pitching). For the same speed, damping, power spectral density for the track, and two particular vehicles, the idealized tire imprint length was a relatively unimportant parameter over a fairly large range of values. On the other hand, one parameter which included the wheel base length was found to be important under the same conditions. Four sets of parameter values were found which at the same speed produced best or optimal rides for vertical acceleration at the frame c.g. and over the wheel, depending upon which measure of ride roughness was employed. The influence of speed was then examined on vehicles having these sets of parameter values. In all cases, increasing speeds produced sharp increases in ride roughness. (US. Govt. Res. Dev. Reports.) 99