THE STRENGTH OF ELECTRORHEOLOGICAL (ER) FLUIDS

The definition of the strength of an ER fluid is discussed. Studies on the electrorheology of ER fluids containing zeolite particles in various oils indicate that the order of magntiude difference between the measured values of the yield stress and those calculated based on the axial force of interaction between particles in a single-row chain can be explained by an enhancement of the force due to the observed clustering of particles into multi-row chains. The force enhancement factor varied with the shear rate and the concentration of particles, but was relatively independent of the electric fleld, temperature and host fluid. Reasonable agreement existed between the predicted and the measured shear stress-shear strain curves and the concentration dependence of the yield stress when the appropriate force enhancement factor was taken into account. The present theoretical-experimental considerations suggest that ER fluids may attain a yield strength of approximately 50 kPa.