An Electrorheological Fluid in Squeeze Mode

Electrorheological (ER) fluids may be regarded as smart materials, in the sense that their mechanical properties can be affected by an applied electrical field. This paper describes experiments performed in a unit containing circular plates which are placed in parallel, with an ER fluid (silicone oil with dispersed plastic spheres) between them, so that the fluid is forced in the radial direction when plates move towards each other. This is termed “squeeze mode operation.” Force obtained is at least one order of magnitude larger than in shear mode (plates moving parallel to each other). Results show that damping as well as stiffness are affected by the electrical field. A constitutive equation is derived, describing the force as a function of displacement and velocity of plates. Models of the micro-mechanical behaviour of the ER fluid are proposed. They provide an efficient tool for interpreting test results and their predictions are shown to agree well with these. Only DC fields were studied. The response to harmonic motion of plates was analysed for frequencies below 50 Hz.