Void growth and resin transport during processing of thermosetting — Matrix composites

Abstract

The fabrication of composite laminates having a thermosetting resin matrix is a complex process. It involves simultaneous heat, mass, and momentum transfer along with chemical reaction in a multiphase system with time-dependent material properties and boundary conditions. Two critical problems, which arise during production of thick structural laminates, are the occurrence of severely detrimental voids and gradients in resin concentration. In order to efficiently manufacture quality parts, on-line control and process optimization are necessary, which in turn require a realistic model of the entire process. In this article we review current progress toward developing accurate void and resin flow portions of this overall process model.

Void stability as a function of temperature and pressure is first considered at equilibrium as a bounding behavior for the actual cure cycles. If sufficient moisture is present in the resin, notably high void pressures are possible. Next, the time-dependent stability and growth of voids containing pure water vapor and air/water mixtures is described for a typical commercial curing cycle. The resin pressure early in the cycle and the initial resin moisture content are critical considerations in producing a void-free laminate. A pressure-temperature-humidity stability map is described which identifies conditions for void growth or dissolution throughout the cure cycle.

A generalized 3-dimensional resin flow model is summarized, which employs soil mechanics consolidation theory to predict profiles of resin pressure, resin flow velocity, laminate consolidation, and resin content in a curing laminate.