Graphene films for enhancing through thickness conductivity and fracture toughness of carbon fiber-based aerospace composites

P. Lamichhane, D.R. Dhakal, S. Chaudhari, R. Vaidyanathan (presenter)
Oklahoma State University,
United States

Keywords: graphene nano-particles, conductive polymers, through thickness electrical conductivity, inter laminar fracture toughness, lightning strike mitigation

Summary:

Carbon fiber-reinforced polymer (CFRP) have many potential applications as primary and secondary structures in the aerospace, automobile and wind energy industries. However, for many of these applications, poor electrical conductivity on the surface and in the through the thickness direction of the composites limits its capabilities and necessitates additional secondary manufacturing operations to improve the electrical conductivity. This is because the composite resistivity (thermal and electrical) is dominated by the lamina resistivity, which is further controlled by the interlaminar fiber-fiber resistivity. CFRP typically has very low through thickness conductivity in comparison to conductivity in the fiber direction. The study of through-thickness conductivity could also be important because delamination activity in CFRP can be monitored with the change in electrical resistance in through thickness direction. Poor electrical conductivity on the surface and through the thickness of CFRP in the thickness direction further results in the degradation and delamination of the composite materials due to lightning strikes during service. Therefore, understanding and minimizing lightning strike damage and delamination cracks in CFRP are extremely valuable to maintain and improve their reliability and performance. Previous research from our research group has demonstrated that the interlaminar fracture toughness can be improved by more than 100% while maintaining the flexural strength and modulus through the addition of less than 0.2% by weight nano-additives. In this study, a conductive polymer such as Polyaniline (PANI) has been doped with graphene nano-platelets (GNP) and polyvinylpyrrolidone (PVP) as a binder resulting in a thin film as shown in Figure 1 and 2. The through-thickness conductivity of CFRP fabricated (shown in schematic in Figure 3) with these thin films between each lamina was studied. Further, the effect of using a PANI/PVP: GNP film in the mid-plane of the composite on the delamination of the CFRP composite was also studied. It was observed that the through thickness conductivity was improved by ~250% with the addition of ~11 wt% GNP as a function of the composite. The use of the GNP in the mid-plane was found to result in an improvement of 50% in the interlaminar fracture toughness. The advantage of this method is that these improvements were obtained with very small levels of addition of the graphene into the composite. Scanning Electron Microscopy (SEM) Thermogravimetric Analysis (TGA) FTIR as well as Raman spectroscopy analysis were done to analyze the composite behavior and generally supported the conclusions. References: 1. D. Dhakal, M. Subramanian, and R. Vaidyanathan, “High thermal and electrical conductivity polymer composites,” US Patent Application No. 62/627059, February 6, 2018.