Investigation of interphase effect on the non-linear viscoelastic behavior of multiphase polymer composites

In this work, an analytical micromechanical model based on unit-cell approach is used to study the effect of interphase on the non-linear viscoelastic response of multiphase polymer composites. The representative volume element of composite consists of three phases including unidirectional fibers, polymer matrix and fiber/matrix interphase. Perfect bonding conditions are applied between the constituents of composites. The Schapery viscoelastic constitutive equation is used to model the nonlinear viscoelastic matrix. Prediction of the presented micromechanical model for the creep response of polymer material and two-phase composites shows good agreement with available experimental data. Furthermore, the predicted overall elastic behavior of three-phase composites demonstrates close agreement with other numerical results available. The effects of material and thickness of interphase on the creep-recovery strain curves of three-phase composites are studied in details. Results show that the interphase thickness and material properties have significant effect on the creep-recovery strain responses of the three-phase composites under transverse loading. According to micromechanical modeling results, it is found that the interphase negligibly affects the nano-linear viscoelastic behavior of three-phase composites under axial loading. Effects of the different stress levels and the variation of fiber volume fraction on the creep-recovery strain curves of three-phase composites are also investigated.