Process-induced residual stress analysis of AS4/3501-6 composite material

The development of process-induced residual stresses in a typical graphite/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 that study are used to develop a cure-dependent viscoelastic material model for the composite system. A finite-element model is developed to solve the stress analysis problem. To overcome large memory storage requirements and lengthy calculation times, a recursive formulation is used in the finite-element analysis. Cure kinetic and heal transfer modeling are evaluated independently using the finite-difference method. Process-induced residual stresses in cross-ply laminates are calculated and the results are compared with elastic solutions. The results of the analysis indicate that in certain cases significant residual stresses are present during the cure cycle, even before final cool-down commences. Whether a material experiences significant curing stress before cool-down depends on many factors, including stress relaxation time, equilibrium modulus, the level of chemical shrinkage, and curing conditions.