A viscoelastic constitutive model for particulate composites with growing damage

A mechanical model which describes time- and temperature-dependent deformation behavior of particulate composites with changing microstructure, including growing damage, is described and then verified by experimental study of a viscoelastic filled elastomer. An existing constitutive model, which is based upon thermodynamics of irreversible processes with internal state variables, is first reviewed and then used to describe the mechanical behavior of elastic and viscoelastic media with changing microstructure. A rate-type equation is successfully employed in describing the evolution of microstructural changes, which are believed here to be primarily microcracking. An elastic-viscoelastic correspondence principle and the time-temperature superposition principle are used in modeling effects of the material's intrinsic viscoelasticity and the effects of temperature changes. Laboratory tests of the stress and dilatation responses of uniaxial test specimens under controlled monotonically increasing axial extension and constant confining pressure at different temperatures were performed. The effects of strain level, strain rate, confining pressure, and temperature on the stress and dilatation are described and compared to the theoretical model. (C) 1997, Elsevier Science Ltd.