Rheological Properties of Plastic Clay Body

Abstract

In order to study the rheological preperties of plastic clay body, cyclic tortion test method by Astbury was examined on a plastic mass for electrical insulators. Thin hollow cylindrical tubes, 10φ-20φ×100, were formed by extruding. One end of specimen was fixed, and the other free end was oscillated torsionally, while the rotating angle was changed in a sinusoidal way. By analyzing the hysteresis loops of the stress-strain curves, the following results were obtained. (1) By the sinusoidal torsional motion, S-S curve was constricted in a steady hysteresis loop, showing that the phenomenon of the “Memory” was lost. (2) The remanent sterin depended markedly on the maximum strain (torsional strain amplitude). (3) The coercive force and the maximum stress much decreased on the increase of the moisture content. (4) The ratio of the coercive force to the maximum stress was constant regardless of experimental conditions. (5) The energy absorbed during one cycle was directly proportional to the maximum strain, and was reduced with increasing moisture content. (6) If the torsional strain amplitude and the frequency of sinusoidal oscillation were taken as the same condition, the ratio of energy lost during one cycle to the one for the perfectly plastic body was equal to the ratio of the coercive force to the maximum stress, which was constant, irrespective of experimental conditions. (7) The critical value of the strainen ergy, which determines the ratio of the number of the elastic elements to the that of viscous elements was not constant.The writers, on the basis of the results, pointed out, (1) the plastic property should be added to the Astbury's model as one of the mechanical components, (2) the assumption that the elastic elements would be changed to the same number of the viscous elements due to the increase of strain energy, shoud be modified, (3) the term which gives the effect of moisture content on the behaviour of plastic clay body must be added in the fundamental rheological equation, (5) the model by Astbury should be revaluated after determining more precisely the model parameters.