Nonlinear Viscoelastic Analysis of Composites using Competing Micromechanical Models

Abstract

Micromechanical models for a study of nonlinear viscoelastic (NVE) response of composite laminae are developed and their performance compared. A single integral constitutive law proposed by Schapery and subsequently generalized to multiaxial states of stress is utilized in the study for the matrix material. This is used in conjunction with a computationally facile scheme in which hereditary strains are computed using a recursive relation suggested by Henriksen. Composite response is studied using two competing micromodels, a simplified square cell model (SSCM) and a finite element based self-consistent cylindrical model (FECM). The algorithm is developed assuming that the material response computations are carried out in a module attached to a general purpose finite element program used for composite structural analysis. It is shown that the SSCM as used in investigations of material nonlinearity can involve significant errors in the prediction of transverse Young’s modulus and shear modulus. The errors in the elastic strains thus predicted are of the same order of magnitude as the creep strains accruing due to viscoelasticity. The FECM on the other hand does appear to perform better both in the prediction of elastic constants and the study of creep response.