Temperature and Cure in Pultruded Composites Using Multi-Step Reaction Model for Resin

Abstract

A numerical model has been developed to analyze the temperature and degree of cure profiles in pultruded composites. In pultruded composites the resin plays an important role in holding the fibers together in a structural unit and also transferring and distributing the applied load to the fibers. The degree of cure of the pultruded composite is an important phenomenon in the manufacturing process since it can be related to the mechanical properties. Therefore, the degree of cure of the resin plays a crucial role in the pultrusion process. The chemical reaction of the resin determines the degree of cure as well as the exothermic energy released by the resin. A one-step reaction model has been employed for the resin system in most of the previous research. For some resin systems, a one-step model may not produce good results; therefore, it was decided to pursue a multiple-independent-step reaction model that more closely follows the actual behavior of the resin. In this research, the effect of an approximate multiple-independent-step reaction model for the thermoset epoxy resin SHELL EPON 862/W was studied. The numerical model utilized a fixed control volume based finite difference approach [1]. This technique was used to solve the coupled, non-linear, three-dimensional steady-state energy and species equations for a cylindrical geometry. The species equation(s) utilized both a one-step Arrhenius reaction rate model as well as a multiple-independent-step Arrhenius reaction rate model for the resin. The kinetics parameters of the resin for a one-step reaction model were obtained from the differential scanning calorimeter (DSC) scans and for the multistep model a regression fit was made to obtain the kinetic parameters from the DSC scans. The numerical model was used to predict the temperature and degree of cure for the pultruded composite both inside the die and in the post-die region. These numerical results were compared with experimental measurements. The processing variables examined in this study were die-wall temperature setting, pull speed and fiber volume fraction.