Further development of a data reduction method for the nonlinear viscoelastic characterization of FRPs

According to the well-known Schapery's formulation, the nonlinear viscoelastic response of any material is controlled by four stress and temperature dependent parameters, g(0) g(1), g(2) and a(sigma), which reflect the deviation from the linear viscoelastic response. Based on Schapery's formulation, a new methodology for the separate estimation of the three out of four nonlinear viscoelastic parameters, g(0), g(1) and a(sigma), was recently developed by the authors. In the present article, a further development of the previously developed methodology is attempted leading to an analytical estimation of the fourth nonlinear parameter, g(2), which additionally includes the viscoplastic response of the system. Thus, a full nonlinear characterization of the composite system under consideration is achieved. The validity of the integrated model was verified through creep-recovery experiments, applied at different stress levels to a unidirectional carbon fibre reinforced polymer. (C) 1999 Elsevier Science Ltd. All rights reserved.