International Journal of Solids and Structures (Impact Factor: 2.21). 01/1995; 32(2):165-172. DOI: 10.1016/0020-7683(94)00142-J
ABSTRACT The thermodynamic analysis of viscoelastic constitutive laws makes itpossible to estimate the class of admissible creep-relaxation functions. This set of functions turns out to be larger than it was traditionally supposed. Except for the well known positive definite, monotone decreasing functions, the new class also includes the so-called non-traditional functions, such as locally non-monotone and even non-positiveones, hence involving the effect of the so-called negative viscosity. It is shown that generalized creep-relaxation functions turn out to be effective in the phenomenologic modelling of the complicated materials behaviour, like that in homogenization of heterogeneous bodies and in modelling of the wave propagation and of the negative Poisson ratiophenomena in composites. New directions for fundamental and applied research, that are considered with the thermodynamic admissibility of viscoelastic models, are discussed. Examples of the application of generalized creep-relaxation functions are given, in particular for the dynamics of composites and for the thermomechanical modelling of wood.