Electro-rheology is the phenomenon in which the rheology of fluids is modified by the imposition of electric fields. In this Review the nature of the fluids active in this role are presented and the influence of important variables such as shear rate, field strength, field frequency, temperature and fluid composition are described. Also discussed are the dielectric behaviour of dispersions in flow since this is of direct bearing on the phenomenon of electro-rheology. Various models for electro-rheology are presented and assessed. The authors also describe how recent developments in new classes of electro-rheological fluids have resulted from a clearer understanding of the probable electrodynamic origins of the effect. The Review concludes with an overview of the practical applications that electro-rheology has and may have in the future.

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Twenty-four foods (encompassing fruits, vegetables, meat, bread, cheese and rice) were tested in the Allo Kramer Shear Press at various weight levels ranging from those needed to cover the bottom of the cell to those required for a complete fill. The relationship between maximum force values and sample weight was found to be different for different foods. Products could be grouped into three general categories: those exhibiting a constant force to weight ratio (e.g. white bread, sponge cake), those exhibiting a continuously decreasing force to weight ratio (e.g. raw apples, cooked white beans), and those exhibiting a constant force, independent of sample weight, beyond a certain cell fill level (e.g. canned beets, canned and frozen peas). Fitting the observed behavior into mathematical models allows to infer that extrusion, in addition to the previously recognized shear and compression, plays an important role in the behavior of foods in the standard cell of the Shear Press, and that most foods are subject to various combinations of these forces. The contribution of extrusion was confirmed by actual extrusion tests. Peak areas showed an exponential relationship to sample weight following the equation A = l0 W . Some evidence was obtained that exponents a and b are related to the amount and the general type of resistance offered by the food.