Viscoelastic micromechanical modeling of free edge and time effects in glass fiber/epoxy cross-ply laminates

A viscoelastic finite element analysis has been carried out to investigate the free edge and time effects in a [0/90]_ns glass fiber/epoxy cross-ply laminate, subjected to mechanical loads. The analysis is based on a three-dimensional micromechanical model that predicts the stress/strain field at the fiber and matrix levels near the free edge surface of the cross-ply laminate. The epoxy matrix is represented by a nonlinear viscoelastic constitutive model. In addition, two different damage criteria for the matrix cracking and interface debonding have been introduced into the model, which were incorporated into the finite element analysis program, adina, through the user-defined subroutine. Damage initiation as well as damage growth in the cross-ply laminate is predicted by the present model. It is found that the edge effect is more dominant in the damage initiation process and its influence on the global properties of cross-ply laminate, is not significant. Under a constant load, it is possible for the damage to grow further due to the viscosity of the matrix and the stress/strain redistribution in the cross-ply laminate.