Evolution of Residual Stresses Induced during Curing Processing Using a Viscoelastic Micromechanical Model

Abstract

The effect of viscoelasticity of matrix material on the evolution of processing- induced residual stresses in [0/90] glass fiber/epoxy cross-ply laminate has been investigated by a finite element micromechanical model. The micromechanical model is based on a periodic array of continuous fibers embedded in an epoxy matrix. The epoxy matrix is represented by a nonlinear viscoelastic model. The finite element residual stress analysis indicates that a higher cooling rate results in higher initial residual stresses in the laminate. However, the residual stress relaxes with time and tends to an asymptotic small value independent of the cooling rate. The effect of free edge surface on the generation of residual stresses is also investigated, and it is found that they are significantly different from those in the interior region. Although the coefficients of thermal expansion (CTE) for the individual constituents (glass fiber and epoxy matrix) are constant, the CTE for composite, on the other hand, is initially time-dependent due to the mismatch constraint and approaches an asymptotic value after a long stress relaxation period.