Nonlinear Viscoelastic Analysis of a Unidirectional Composite Material

The single-integral nonlinear viscoelastic constitutive equations developed by Schapery from thermodynamic theory have been adapted to analyze the time-dependent response of a unidirectional composite material. This viscoelastic analysis has been combined with an existing time-independent elastoplastic micromechanics analysis, to permit the study of nonlinear time-dependent response of materials loaded beyond their elastic limit. Literature values as well as a brief series of creep-recovery tests on a typical epoxy resin were used to characterize the nonlinear viscoelastic response of the matrix constituent of a composite material. Composite response under transverse loading at various stress levels was then predicted, and the results compared with actual composite creep data.