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Phenomenological Interpretation of Energy Loss and Storage Mechanisms in Electrorheological Fluids

This work gives insight into the behaviour of an electrorheological (ER) fluid exposed to an oscillatory strain stimulus. Electrorheological fluids can have their behaviour modified by the application of an external electric field. Because an ER fluid consists of a liquid containing small particles, the oscillatory response of the material differs widely from a material subjected to a steady uni-directional shear, due to the effect of the oscillatory motion breaking down the structure formed within the material. The application of a three element model to the oscillatory behaviour of an electrorheological fluid is given. The model consisting of a mechanical three element analogy was proposed in order to provide a parametric description of the behaviour, suitable for use in the design of engineering systems, which will possibly utilise these materials in the future. This model consists of an irreversible yielding type element, a non-linear softening elasticity and viscous energy loss terms. The combination of the elastic, viscous and yielding type elements model the form of the stress-strain rate and stress-strain diagrams very well. These diagrams were obtained experimentally from an oscillatory electrorheometer. Application of the model is shown for a variety of strain amplitudes, oscillatory frequencies and electric field strengths. From these data the variation of energy storage (elasticity) and loss (yielding and Newtonian flow) mechanisms are shown to vary in a complicated manner, dependent for a given field strength on strain amplitude, frequency and hence strain rate.