Use of non local equilibrium theory to predict transient temperature during non-isothermal resin flow in a fibrous medium

Liquid composite molding processes generally involve injection of a polymeric resin in a fibrous preform previously placed in a closed mold. Resin kinetics largely depend on the temperature cycle applied and, as far as thick composites parts are concerned, they can greatly impact on the temperature profile, especially in the core of the part where high temperature range can be reached, affecting the part mechanical properties. Thermal analysis of the system is usually done at the macro-scale level. However, at micro level and because of resin flow across the fibrous preform, local thermal effects have to be considered. A heat dispersion coefficient for instance will account for the hydrodynamic effects so as to improve significantly the accuracy of the temperature profile prediction at steady state. To improve prediction of transient temperature profiles, local heat transfer between resin and fibers needs to be considered. The characterization of this coefficient is conducted following an inverse method, numerical solutions parametered by this coefficient being derived from a non local thermal equilibrium (or two-equation model) and compared with experimental temperature profiles drawn for several injection velocity cases in a sensored mold. Significant improvement in the prediction of transient temperature profile is then obtained. Correlation between the injection velocity and the local heat exchange coefficient is also shown.