On the non-linear viscoelastic behaviour of polymer-matrix composites

The non-linear viscoelastic response of a unidirectional carbon-fibre-reinforced polymer composite has been studied. For the needs of the present study, creep and recovery tests in tension for different stress levels were executed while measurements were made of the creep and recovery strain response of the composite system. For the description of the viscoelastic behaviour of the material, Schapery's non-linear viscoelastic model was used. For the description of the non-linear viscoelastic response of the material and the determination of the non-linear parameters, an analytical method, based on a modified version of Schapery's constitutive relationship where a viscoplastic term was added, has been developed. The method has successfully been applied to the current tests and an estimation of the non-linear parameters was successful. Useful results and conclusions for the applicability of the new method were also extracted.