Showing papers on "Slip ratio published in 1972"

Diffusion Slip Velocity: Theory and Experiment

Abstract: Abstract A theoretical and experimental study of the phenomenon of diffusion slip in a binary gas mixture is presented. To provide some physical insight, a very general variational expression given earlier by Loyalka is rederived via the use of a method developed recently. The case of Maxwellian diffuse specular reflection is considered in some detail and the inadequacies of previous theoretical results based on the early arguments of Maxwell, kinetic models and simple intermolecular force laws are discussed. Although in general, the variational results (or the equivalent results given here) together with the assumptions of Lennard Jones potential and diffusive reflection give a satisfactory agreement with the available experimental data, it is found that for isobaric (isotopic) mixtures, in the choice of the intermolecular and gas-surface interaction parameters special care should be taken in that the results are quite sensitive to small variations in the values of these parameters.

Review of critical flow rate, propagation of pressure pulse, and sonic velocity in two-phase media

Abstract: For single-phase media, the critical discharge velocity, the sonic velocity, and the pressure pulse propagation velocity can be expressed in the same form by assuming isentropic, equilibria processes. In two-phase mixtures, the same concept is not valid due to the existence of interfacial transports of momentum, heat, and mass. Thus, the three velocities should be treated differently and separately for each particular condition, taking into account the various transport processes involved under that condition. Various attempts are reviewed to predict the critical discharge rate or the propagation velocities by considering slip ratio (momentum change), evaporation (mass and heat transport), flow pattern, etc. Experimental data were compared with predictions based on various theorems. The importance is stressed of the time required to achieve equilibrium as compared with the time available during the process, for example, of passing a pressure pulse.

Wear and related characteristics of an aircraft tire during braking

Abstract: Wear and related characteristics of friction and temperature developed during braking of size 22 x 5.5, type aircraft tires are studied. The testing technique involved gearing the tire to a driving wheel of a ground vehicle to provide operations at constant slip ratios on asphalt, concrete, and slurry-seal surfaces. Data were obtained over the range of slip ratios generally attributed to an aircraft braking system during dry runway operations. The results show that the cumulative tire wear varies linearly with distance traveled and the wear rate increases with increasing slip ratio and is influenced by the runway-surface character. Differences in the wear rates associated with the various surfaces suggest that runways can be rated on the basis of tire wear. The results also show that the friction coefficients developed during fixed-slip-ratio operations are in good agreement with those obtained by other investigators during cyclic braking, in that the dry friction is insensitive to the tire tread temperature is shown to increase with increasing slip ratio and, at the higher ratios, to be greater during braking on asphalt and slurry seal than on concrete.

Automatic brake controlling method and device

Abstract: Automatic brake controlling method and device therefor are provided, which are characterized by detecting an acceleration (or deceleration) of a moving vehicle to compute a vehicle speed by integrating by an integrator, simultaneously when a wheel speed is detected; by feeding back the electrical signal indicating the difference between the vehicle speed and the wheel speed to the integrator and a memory circuit so as to compute the vehicle speed signal equal to the wheel speed signal, whenever a brake is not applied; by opening said feedback circuit immediately after the application of the brake, and cancelling by the memory circuit drift, noise, the effect of a gravitational acceleration when said moving vehicle is travelling on an inclined road, and the like; and by controlling the brake force so as to maintain the application of the brake at the maximum value of the coefficient of friction and the lower slip ratio.

Wear of Steel Rollers under Rolling-Sliding Contact

Abstract: Wear of steel rollers has been investigated under unlubricated rolling contact with a small amount of sliding. A four-roller machine is used for the experiment; the velocity difference between the mating rollers is kept constant, while the slip ratio and the normal load are varied. A common feature is found in the wear characteristics when either the slip ratio or the load is varied. No appreciable wear takes place up to a certain critical value of each of the above parameters, and once this value is exceeded, wear begins to increase with the increase of the parameter. These wear characteristics are analyzed based on a microslip model, which was introduced for the interpretation of the frictional characteristics under such a rolling-sliding contact, by Soda and Watanabe. The extent of microslip region is determined and the macroscopic sliding wear law is applied there. The experimental and analytical results show a satisfactory agreement. It is concluded that the mechanism of the wear under rolling-sliding contact can be regarded as a usual sliding wear in the microslip region which appears in the contact area exceeding some critical running conditions.

Experimental investigation of elastic turbulence and boundary slip of elastomers over a broad temperature interval

Abstract: Ethylene-propylene copolymer, a typical stereo rubber, has been investigated by capillary viscometry. Ethylene-propylene copolymer possesses high thermooxidative stability, which has made it possible to study its viscosity properties, determine the onset of elastic turbulence and boundary slip, and measure the slip rate over a very broad temperature interval, from room temperature to 260° C. The flow of elastomers differs from that of thermoplastics in that at relatively low strain rates flow is complicated by the boundary slip effect. The mean boundary slip velocities of the copolymer at shear stresses above 106 dynes/cm2 are measured in tens of centimeters per second. As the temperature rises, they rapidly increase.