PROCESS-INDUCED RESIDUAL-STRESS ANALYSIS OF AS4 3501-6 COMPOSITE-MATERIAL/

The development of process-induced residual stresses in a typical grap hite/epoxy composite material during cure is analyzed in this article. An extensive material characterization study of the resin system was reported in a previous article by the authors [1] and the results of t hat study are used to develop a cure-dependent viscoelastic material m odel for the composite system. A finite-element model is developed to solve the stress analysis problem. To overcome large memory storage re quirements and lengthy calculation times, a recursive formulation is u sed in the finite-element analysis. Cure kinetic and heal transfer mod eling are evaluated independently using the finite-difference method. Process-induced residual stresses in cross-ply laminates are calculate d and the results are compared with elastic solutions. The results of the analysis indicate that in certain cases significant residual stres ses are present during the cure cycle, even before final cool-down com mences. Whether a material experiences significant curing stress befor e cool-down depends on many factors, including stress relaxation time, equilibrium modulus, the level of chemical shrinkage, and curing cond itions.