First Report on Viscosity and Plasticity

Abstract

THE problem of flow has diverse aspects. We have the flow of gases, the mechanism of which is tolerably well understood, so that in the case of certain simple gases the viscosity, and its variations with temperature, can be calculated. We have liquids, of which the viscosity is precisely defined by a constant and can be accurately measured: the mechanism of the flow is imperfectly understood, but it is certainly quite different from that of gases, as the contrasting effect of temperature in the two cases abundantly demonstrates. When we come to the movement of solids under stress, where even the definition of constants which shall describe the experimental facts presents grave difficulty, we are confronted with a still more complex problem. In general, a finite stress is needed to produce permanent set, but this appears to be about the only common factor of the behaviour of such different classes of bodies as poly crystalline metals, metal single crystals, doughs, clays, glasses, gels, rubber and living protoplasm, and in certain cases matters are made still worse by the phenomenon known as thixo-tropy, a term applied to the marked decrease of viscosity caused by shaking or similarly disturbing certain colloidal substances. The evident complexity of the problems long kept investigators from this field, but, within the last twenty-five years or so, serious attempts have been made to systematise our knowledge. Imperfect as our general theories still are, the time is definitely ripe for a collected and critical account of the present state of the subject, and all workers in the wide field will welcome the enterprise and applaud the courage of our Amsterdam colleagues in issuing the “Report” under notice.

First Report on Viscosity and Plasticity

Prepared by the Committee for the Study of Viscosity of the Academy of Sciences at Amsterdam. (Verhandelingen der Koninklijke Akademie van Wetenschappen te Amsterdam, Afdeeling Natuurkunde, (Sectie 1), Deel 15, No. 3.) Pp. viii + 256. (Amsterdam: N. V. Noord-Hollandsche Uitgevers-Maatschappij, 1935.) 10 guilders.