Thermodynamic restrictions on constitutive functions for fiber suspensions

Abstract

The constitutive properties of fiber suspensions are investigated with the methods of thermodynamics. Fiber orientation, orientation change velocity and gradient of orientation are considered as relevant variables for the constitutive functions, and the Second Law of Thermodynamics in the form of the dissipation inequality is exploited by a method introduced by I-S. Liu [Arch. Rat. Mech. Analysis 46 , 131 (1972)]. The restrictions on the constitutive functions show, that the fiber suspension is a micropolar continuum with non-vanishing couple stresses. In addition it is shown that the classical relation of entropy flux being heat flux over temperature holds only in the special case that the free energy density does not depend on the orientation change velocity, otherwise there exists an extra entropy flux.