Abstract
The flow properties of some kinds of granular masses have been investigated with a double cylinder type viscometer which, in principle, is a Couette viscometer. Recently, observing the behavior of coarse sands in this viscometer, the present authors found that a flow pattern was expressed in a very simple form. In the present paper, is a report made of the experiments performed of the plastic yield stress of a few samples of sand of various particle diameter, and also of the functional dependence of the plastic yield stress on the rate of revolution of the inner cylinder and other variables. The following results have been obtained.
(1) When the diameter of the outer cylinder is larger than about 20cm, the torque T∞ does not depend upon the diameter of the cylinder, but upon the particle diameter of dry sand.
(2) The final torque decreases with the increasing rate of revolution of the inner cylinder in the range of rate of revolution, 30∼400rpm, but takes almost constant value at lower rates of revolution than about 30rpm.
(3) The plastic yield stress S0 is related to the vertical pressure P of packed sand by the equation
S0=cP+K
where c is a constant depending upon the coefficient of internal friction, μ, and K is a constant accounting for the intergranular cohesion-like forces.
(4) Using the constant value c obtained experimentally, the coefficient, μ can be calculated by the equation (4). The coefficient, μ decreases with the increasing rate of revolution. Then, at lower rates of revolution the coefficient, μ increases with the decreasing particle diameter of sand, but it can be considered that there is no effect of the diameter of the particle on the coefficient, μ at higher rates of revolution. The cohesion-like force increases with the decreasing internal friction, and depends on the wetting fluid saturation, but the physical problem of these phenomena has yet been left unsolved.
