SOME FUNDAMENTAL ASPECTS OF POWDER BEHAVIOUR

A phenomenological theory of powder behaviour is developed in which the powder is considered to exist in three states, elastic, consolidating or flowing, depending on the stresses acting upon it. Each state and the transition from one state to another is characterised by the appropriate stress-strain relation, equation of state and rate equations. In terms of the (γo, σ, τ)-space transition betwen states is represented by incipient yield, incipient consolidation and steady flow surfaces which intersect in one line, called the triple state line. The relation between the steady flow surface and the steady flow curve, the critical state line, which has been used in previous work on powder behaviour, is discussed. A statistical mechanical method is used to derive the equation of state for the unstressed density of the powder in the elastic state and to show that it is directly related to the interparticle forces and can therefore be used as a state variable. Another particulate approach based upon a simplified mechanical model yields the general form of the equations for the incipient yield and incipient consolidation loci at constant density. Examples are given of power behaviour under constant normal and under constant shear stress. © 1968.