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.
Comparison of Ultrasonic Methods for Detecting Defects in Unidirectional Composite Material
