Cure Cycle Effect on High-Temperature Polymer Composite Structures Molded by VARTM

This paper presents an analytical and experimental investigation of cure cycle effect on carbon-fiber reinforced high-temperature polymer composite structures molded by vacuum assisted resin transfer molding (VARTM). The molded composite structure consists of AS4-8 harness carbon-fiber fabrics and a high-temperature polymer (Cycom 5250-4-RTM). Thermal and resin cure analysis is performed to model the cure cycle of the VARTM process. The temperature and cure variations with time are determined by solving the three-dimensional transient energy and species equations within the composite part. Several case studies were investigated by the developed analytical model. The same cases were also experimentally investigated to determine the ultimate tensile strength for each case. This study helps in developing a science based technology for the VARTM process for the understanding of the process behavior and the effect of the cure cycle on the properties of the molded high-temperature polymer composites. 1. Introduction Nonautoclave molding technology, such as vacuum assisted resin transfer molding (VARTM), offers a more cost effective manufacturing process for composite materials than the resin transfer molding (RTM) and autoclave/prepreg technique. However, its potential for fabricating high-temperature polymer composites needs to be explored. Process variables, including the maximum cure temperature, cure time, and postcure cycles have significant effects on the resulting composite [1–7]. Golestanian and El-Gizawy [1] presented results on cure-dependent properties of resin transfer molded thin composites with woven fiber mats. In their study, resin properties are assumed to change from viscoelastic liquid to properties of the solid as the part cures. Khattab and El-Gizawy [4] developed an analytical model to determine the cure-dependent mechanical properties as functions of degree of cure for high-temperature polymer composites molded by VARTM. Kim and Daniel [5] conducted an experimental study to investigate the cure cycle effects on residual stress and residual strain on composite material structures fabricated by resin transfer molding process. Three different cure cycles with different peak temperature and different heat rates were used. The study showed that the residual stress developed at high cure temperature was lower than that developed at a lower cure temperature due to the constraint induced strain. The effect of different heat-up rates was not that clear. Liu et al. [6] experimentally investigated the effects of cure cycles on void content and