CRITICAL MECHANICAL-BEHAVIOR IN THE FLUID SOLID TRANSITION OF SUSPENSIONS

Velocity and attenuation measurements of compressional waves at 3 and 5 MHz, as a function of solid volume concentration, are reported for d ifferent suspensions. The suspensions were made of 1 mu m size particl es of kaolinite or glass beads in water or light oil, At a volume conc entration of 40%, a sharp peak in attenuation accompanied by a change in velocity is observed. The volume concentration at which this peak o ccurs is independent of frequency and particle geometry, The observed critical change in attenuation around 40% is consistent with an excess attenuation induced by the fluid-shearing processes between neighbori ng particles, and corresponds to the jamming point concentration predi cted by particle packing simulations. (C) 1995 American Institute of P hysics.