NONDIMENSIONAL ANALYSIS OF AN IDEALIZED THERMOSET COMPOSITES MANUFACTURE

Modeling the cure of thermoset composites has been the subject of many investigations in the literature. However, the studies have focused on specific composite systems and product specifications. Consequently, extending the results based on one combination of process and product parameters to another is not obvious, and the choice of cure cycles in practice remains predominantly heuristic-based. This work presents a generalized analysis of the cure, based on an idealized expression for the cure kinetics, in terms of four dimensionless groups formed of the process and product parameters-the Damkohler number (K(o)BAR), the dimensionless activation energy (E(o)BAR), the adiabatic reaction temperature (B(o)) and the Biot number (Bi). The non-dimensional approach reduces the large number of process and product variables involved, to the few dimensionless groups, and eliminates the need for a system-specific or product-specific modeling. Further, the article addresses the problem of selecting the best cure cycles for achieving a desired product quality. With regard to the manufacture of partially cured composite systems, optimal cure cycles which yield a homogeneous cure in the product, in the minimum possible time, are obtained as a function of the non-dimensional parameters. Design plots for the optimal cure temperature and duration are presented, and their use in practical situations is illustrated in the context of a commercially available graphite-epoxy prepreg from Hercules, which is widely used in the aerospace industry.