ON THE EQUILIBRIUM-THEORY OF 2ND-GRADE FLUIDS

THE CLASSICAL theory of fluids is not sufficiently general to include phenomena such as capilla6 rity and phase transitions. For this reason, among many, fluids of second grade were introduced; such a fluid is defined by a constitutive equation in which the stored energy depends not only on the density, but also on the density gradient. In this note we use the principle of virtual work to develop a consistent set of field equations and boundary conditions for such fluids. The theory shows the presence of surface tensions on the external boundary and gives a physically acceptable interpretation of the "hypertraction".