Micromechanics-based thermoviscoelastic constitutive equations for rubber-like matrix composites at finite strains

Global constitutive equations that model the response of multiphase materials undergoing finite deformations in which any phases behaves as a rubber-like thermoviscoelastic material are derived. The monolithic thermoviscoelastic constituent is modeled by a free-energy function which is given by a sum of a long-term contribution, that is based on the entropic elasticity for thermoelastic polymers, plus a non-equilibrium part which characterizes the viscoelastic (dissipative) mechanism. The global constitutive relations that govern the behavior of the composite are derived by using a micromechanical analysis in conjunction with the homogenization technique. Applications are given that illustrate the response of a rubber-like thermoviscoelastic matrix reinforced by continuous elastic nylon fibers. Results exhibit the effect of the viscoelasticity on the response of the composite when it is subjected to thermal and mechanical loadings, as well as its creep and relaxation behavior at room and elevated temperature.