A cure process model for resin transfer molding of advanced composites

Abstract

The resin transfer molding (RTM) process has been identified as a cost-effective fabrication technique for producing composite materials from geometrically complex reinforcements. Processing models can be used to determine the temperature and pressure cycles which will produce a finished part with the best properties in the shortest time. This work involved the development and verification of a processing model for RTM.

The processing model is based on the assumption that infiltration can be described as flow through a porous medium. Flow through porous media, as governed by D’Arcy’s law, depends on the viscosity of the fluid and the microstructure of the interconnected pores. Infiltration by thermosetting resin systems is assumed to behave as a Newtonian fluid with a time and temperature dependent viscosity. The kinetics of the resin can be described by mathematical expressions determined from standard thermal analysis techniques. The reinforcement is assumed to be a homogenous, anisotropic material which exhibits strain stiffening, hysteresis and plastic deformation. D’Arcy’s law describes the porous material in terms of the material permeability. Kozeny-Carman’s relationship is used to relate the porosity to the permeability. Solution of D’Arcy’s law is accomplished in a quasi-steady state manner by an evolving mesh finite element technique.

After infiltration is completed, the model continues to predict the temperature, degree of cure and viscosity of the resin. The equations governing the unsteady heat transfer are solved with an existing cure model by the finite difference method. Results of the processing model include estimates of infiltration, gel and cure times as well as the cured thickness and fiber volume fraction. Test laminates were fabricated, mechanically tested, and compared to prepregged laminate results. Construction of one of the test laminates was simulated with the processing model to verify the accuracy of the simulation.