Evolution of residual stresses induced during curing processing using a viscoelastic micromechanical model

The effect of viscoelasticity of matrix material on the evolution of proces sing-induced residual stresses in [0/90] glass fiber/epoxy cross-ply lamina te has been investigated by a finite element micromechanical model. The mic romechanical model is based on a periodic array of continuous fibers embedd ed in an epoxy matrix. The epoxy matrix is represented by a nonlinear visco elastic model. The finite element residual stress analysis indicates that a higher cooling rate results in higher initial residual stresses in the lam inate. However, the residual stress relaxes with time and tends to an asymp totic 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 indivi dual constituents (glass fiber and epoxy matrix) are constant, the CTE for composite, on the other hand, is initially time-dependent due to the mismat ch constraint and approaches an asymptotic value after a long stress relaxa tion period.