Multi-Die, Multi-Stage Pultrusion Process for Hybrid Composites: Degree of Cure and Temperature Profiles

Abstract

Fiber reinforced polymer (FRP) composites have been rivaling conventional structural materials for several decades and are now pervasive in innumerable applications due to many attractive properties. Even though FRPs can be manufactured by many methods, pultrusion process is the most cost-effective and common technique for manufacturing constant cross-section composites. In this work, a thermo-chemical modeling study on an untapped and enhanced pultrusion concept known as Multi-Die, Multi-Stage (MDMS) hybrid pultrusion process based on US patent No. 6007655 is presented. This study is unique and novel, and has never been presented in the literature. Two dimensional (2-D), steady state, finite difference models (FDM) are developed for modeling a conventional Single- Die, Single-Stage (SDSS) process and the MDMS process. Since the purpose of this study is to understand the thermochemical modeling results of the MDMS concept, only steady state approach is used. Different pultruded thicknesses with varying pull speeds are considered. Fiberglass/epoxy composite is used as pultruded part for the first stage, while carbon fiber/vinyl ester composite is used for the second stage. Steel is used as a die material for both stages. The Gauss Seidel iterative scheme is implemented in MATLAB R2013b to solve the energy and species equations for the pultrusion process model. Pultrusion process for a rectangular flat plate is considered as a validation case. Due to the symmetry, only a half of pultrusion domain is modeled. The proper boundary conditions are applied to match the actual manufacturing process. Multiple pull speeds (200 mm/min, 400 mm/min, and 500 mm/min) with different composite thicknesses (20 mm and 25 mm) are considered in the present analysis to investigate the effects of composite thickness and pull speed on degree of cure. It is clear from modeling results that the short and long SDSS fail to achieve even moderate degree of cure. However, the MDMS achieves a high and uniform degree of cure. The developed model can further be used as a design tool for developing hybrid composites employing MDMS pultrusion process.