Because of the relatively high specific mechanical properties of carbon fiber/epoxy composite materials, they are often used as structural components in aerospace applications. Graphene nanoplatelets (GNPs) can be added to the epoxy matrix to improve the overall mechanical properties of the composite. The resulting GNP/carbon fiber/epoxy hybrid composites have been studied using multiscale modeling to determine the influence of GNP volume fraction, epoxy crosslink density, and GNP dispersion on the mechanical performance. The hierarchical multiscale modeling approach developed herein includes Molecular Dynamics (MD) and micromechanical modeling, and it is validated with experimental testing of the same hybrid composite material system. The results indicate that the multiscale modeling approach is accurate and provides physical insight into the composite mechanical behavior. Also, the results quantify the substantial impact of GNP volume fraction and dispersion on the transverse mechanical properties of the hybrid composite while the effect on the axial properties is shown to be insignificant.
Mold preparation, material layup, and cure times for thermoset‐based composites often limit their use in high‐volume applications. As such, new rapid cure epoxy resins are being developed to achieve a complete cycle time within 3 min. In this research, calorimetry and rheometry are used to examine and model two novel rapid cure epoxy resin systems with internal mold release. The rapid cure epoxy resins followed an autocatalytic cure kinetic and William–Landel–Ferry diffusion model. The rapid cure epoxy resin was shown to achieve 94% cure in 2 min at 150°C. However, adding an additional 2.5 wt% internal mold release hindered the first step of the reaction, which delayed the second reaction step since the final degrees of cure were similar. Furthermore, the resin viscosity followed a modified William–Landel–Ferry equation and at 120°C could maintain a viscosity below 5 Pa s for 4.1 min. These models provided valuable insight into the range of processing conditions these novel resins could experience during impregnation and molding processes.
Efforts by manufacturers to produce more cost-effective carbon fibers have resulted in fibers with irregular cross-section often referred to as kidney-bean shaped fibers. In this research, compaction experiments were performed with a modified laser light section method to evaluate the compaction behavior of kidney-bean shaped carbon fibers. The kidney-bean shaped fibers followed a different compaction behavior compared to the Gutowski model for circular fibers. Additionally, these fibers required an order of magnitude larger force to compact than circular fibers to achieve similar fiber volume fraction, which has implications in infiltration and consolidation efficiency for composites manufacturing. A shape correction factor based on the fiber cross-sectional aspect ratio was proposed to extend the Gutowski model to fibers with irregular cross-sectional shapes. The modified Gutowski model provided an appropriate order of magnitude fit for the kidney-bean fibers. Furthermore, this modification to the Gutowski model recovered the original solution for circular fibers (cross-sectional aspect ratio = 1).
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