A PROCEDURE TO DETERMINE THE MATERIAL CONSTANTS AND THE VISCOSITY FUNCTION FOR A FLUID WITH YIELD SHEAR-STRESS

This paper is concerned with the theoretical and experimental study of a fluid with yield stress. The viscometric motion of SKF-LGMT Li 3/04 grease in a cone-cone (plate) configuration is studied. A procedure f or the determination of the upper and tower shear yield stress is laye d down. The material behaviour of the sample is modelled as a Maxwell fluid exhibiting yield stress; therefore, three material constants mus t be experimentally determined: the yield stress tau(0), the viscosity coefficient eta(0), and the relaxation time lambda(1). An analytical solution for the velocity distribution of this fluid in the cone-cone creep motion is obtained and, consequently, the real strain rate and t he viscosity function are computed.