Mechanics Research Communications, Volume 24, Number 2, 1 March 1997, pp. 167-177(11)

ABSTRACT Separation of the storaged and dissipated energies in viscoelastic deformation is considered. This is a key problem for the construction ofviscoelastic minimum principles and for the micromechanics of heterogeneous materials with memory. The notion of the viscoelastic free energy functional is discussed, thermodynamic admissibility conditions areestablished. An engineering analysis is realized through the method of harmonic strain regimes, influence of the loss and the storage moduli on the dissipation rate is studied. For the Volterra-Frechet integral expansion approach, necessary conditions on the general form of a free energy viscoelastic functional are formulated. The obtained resultsare used to examine the thermodynamic validity of certain classic viscoelastic models, like that of Staverman-Schwarzl. Through the spectral method, this energy representation is shown to correspond to a generalized Maxwell model. (C) 1997 Elsevier Science Ltd.