Hysteresis Experiments in Rheology

Abstract

THE value of “normal” hysteresis experiments in rheology was recently discussed by Harris¹, who observed that hysteresis loops could be obtained even with Newtonian fluids and that steady oscillatory experiments were therefore to be preferred for materials which exhibit the effect of thixotropy because of the simpler analysis. It should be remembered, however, that steady oscillatory experiments cannot yield information on thixotropic fluids when their resistance to flow is near maximum. A thixotropic fluid is defined here as a fluid which exhibits an isothermal, time dependent resistance to flow at constant rate of shear. For the case when the fluid is contained between concentric cylinders the condition offering near maximum resistance to flow can be studied by the method of Billington and Huxley^2,3, in which a near instantaneous drive is applied to, for example, the outer cylinder, which is then maintained at constant angular velocity, and the resulting motion of the inner cylinder moving against the restoring couple of the measuring head is observed.