A VISCOELASTIC CONSTITUTIVE MODEL FOR PARTICULATE COMPOSITES WITH GROWING DAMAGE

A mechanical model which describes time- and temperature-dependent def ormation behavior of particulate composites with changing microstructu re, including growing damage, is described and then verified by experi mental study of a viscoelastic filled elastomer. An existing constitut ive model, which is based upon thermodynamics of irreversible processe s with internal state variables, is first reviewed and then used to de scribe 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 bel ieved here to be primarily microcracking. An elastic-viscoelastic corr espondence principle and the time-temperature superposition principle are used in modeling effects of the material's intrinsic viscoelastici ty and the effects of temperature changes. Laboratory tests of the str ess and dilatation responses of uniaxial test specimens under controll ed monotonically increasing axial extension and constant confining pre ssure 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.