The effects of cyclic pre-loading and thermal recovery on the viscoelastic response of carbon black-reinforced rubbers

Constitutive equations are derived for the time-dependent behavior of particle-reinforced elastomers at isothermal deformations with finite strains. A filled rubber is modelled as an equivalent network of strands bridged by junctions which can slide with respect to their reference positions under loading. The equivalent network is assumed to be strongly heterogeneous, and it is thought of as an ensemble of meso-regions where sliding occurs with different rates. Stress-strain relations are developed by using the laws of thermodynamics. For uniaxial tensile relaxation tests, these equations are determined by three adjustable parameters. To find the material constants, three series of tests are performed at longitudinal strains in the range from 100 to 250%. The study focuses on the effects of pre-loading and thermal recovery on the nonlinear viscoelastic response of natural rubber reinforced with carbon black.