Resin transfer molding (RTM) process of a high performance epoxy resin. II: Effects of process variables on the physical, static and dynamic mechanical behavior

Abstract

The effects of processing variables on the mechanical behavior and the void content of one‐part epoxy based glass fabric composites produced by resin transfer molding (RTM) were investigated. The variables studied included injection pressure, injection temperature, and fabric structure. Image analysis was used to measure the void content in the composites. Variations in injection pressure and temperature were found to have a significant effect on the quality and the mechanical performance of composites. The optimized physical and mechanical performance of the composites was obtained by processing the resin at 160°C under 392 kPa pressure. Molding of highly permeable EF420 fabric required a shorter mold filling time, but resulted in reduced flexural strength and storage modulus in the resulting composites as compared with that of the composites containing 1581 fabric.

Effect of Injection Rate and Post-Fill Cure Pressure on Properties of Resin Transfer Molded Disks

“…Chang and Hourng developed a model predicting that vacuum assistance would cause voids formed in the transverse impregnation of unidirectional fibers to shrink and disappear [6]; while Lundstro¨m and Gebart actually observed a decrease in measured void content in composites molded with vacuum assistance, with very few voids observed at the largest vacuum levels [7]. Similarly, the effects of injection pressure and injection rate or local velocity have been observed by both Patel and Lee [8], and Lee and Wei [3]. Patel and Lee used flow visualization to investigate flow patterns for several fiber mat architectures at different injection rates, while Lee and Wei investigated the effect of these variables on void formation in a radially expanding flow.…”

“…However, the variation in local mat architecture seems to affect the statistical variation of the data. Another potential explanation of the increase in strength at flow rate of 1 cm 3 /s is that shear thinning resins may penetrate into fiber bundles more easily, thus reducing void formation [3].…”

“…Most of the studies on mechanical characterization of RTM parts focus on the effect of the reinforcement type and properties such as the weave pattern. Studies attempting to correlate mechanical properties with the process parameters such as injection rate and packing pressure are limited [3][4][5].…”

“…Poor wetting and air entrapment during molding lead to voids that degrade mechanical properties and surface finish in the final part, while thermal gradients can cause the part to deform or buckle as it cures [2]. Parameters such as injection rate [3][4][5], gate and vent locations, molding or packing pressure [6][7][8], and preform microstructure [9][10][11] are commonly known to contribute to void formation. Quantitative details about how individual process parameters lead to void formation, and the resulting change in mechanical performance are vital to understanding and design of effective RTM processes.…”

Porosity Reduction in the High-Speed Processing of Glass-Fiber Composites by Resin Transfer Molding (RTM)

“…Notwithstanding the physical barriers imposed by the surface and viscous forces, there have been successful attempts to overcome void formation at high-speed molding. Among such strategies, the change of the inlet location [23,24] and the utilization of higher injection pressures [5,25] have demonstrated a significant reduction both in mold filling times and void inclusions. Further, other alternatives that can be readily implemented like preheating the preform to remove volatiles from the sizing system prior to resin injection [26]; and also, applying a ''postfill'' cure pressure or ''packing pressure'' after the mold fill operation, have been also shown to be effective in superseding fluid front influences which otherwise would trigger void formation [13,26,27].…”