MULTISCALE CARBON FILLER REINFORCED EPOXY COMPOSITE FOR STRUCTURAL APPLICATIONS

Abstract

Carbon fiber reinforced polymer composites (CFRPs) are gaining enormous research interest in the composites industry, particularly for aerospace and automotive structural applications, owing to their stiffness, strength, and low specific weight. Generally, the presence of in-plane high-performance fibers provides suitable mechanical properties (such as tensile, impact and fatigue tests) for various structural applications. However, these composites are prone to anisotropic behavior, and the brittle nature of the matrix, leading to premature failures, like, delamination and fiber pullout, limits their use in critical applications. Anisotropic materials exhibit direction- dependent properties. In CFRP composites, anisotropic behavior arises from challenges in achieving uniform fiber dispersion in the matrix. The carbon fibers provide high strength and stiffness in the direction of the fibers, while the polymer matrix provides toughness and ductility in other directions. In contrast, the through-thickness characteristics are influenced by the interaction between the fiber-matrix interface. Hence, it is important to enhance the out-of-plane and transverse performance while maintaining the in-plane mechanical properties and lightweight characteristics. To achieve this, it is essential to have a strong interfacial interaction between carbon fiber (CF) and epoxy. The interfacial interaction between carbon fiber (CF) and epoxy has to be strong to achieve this. To address this, incorporating easily available nanofillers, such as silica, aluminium oxide, titanium oxide, nanoclay, graphene and carbon nanotubes etc, which have high mechanical and thermal properties have been employed. Among these nanofillers, carbon-based nanofillers (GNPs and CNTs) possess excellent mechanical, thermal and electrical properties, making them potential reinforcement to enhance the mechanical behavior and interfacial adhesion of the CFRP composites. Nanofillers can be incorporated into the CF-epoxy structure in two ways, namely, nanoengineering the surface of the carbon fibers and/or dispersing them within the composite matrix. Hence, this study aims to reinforce the epoxy matrix and modify the carbon fiber using carbon nanofillers, as they have similar surface chemistry and properties as CF. To understand these modifications, the fabrication of a multiscale fiber-reinforced epoxy laminate composite is taken up. The first part of the study focuses on fabricating graphene nanoplatelets (GNPs) reinforced epoxy matrix based multiscale carbon fiber-epoxy laminated composite. In the initial stage, the incorporation of GNPs into the epoxy matrix is achieved through probe sonication to ensure homogenous dispersion. Following this, the fabrication of the carbon fiber-epoxy composites laminated composite is carried out using a vacuum-assisted resin infusion method. The addition of 0.2 wt % GNPs in carbon fiber-reinforced epoxy composite (GNP CF EP) significantly improves the ultimate tensile strength and fracture toughness by ~ 22% and ~ 35%, compared to carbon fiber epoxy composite (CF EP), respectively. This improvement can be attributed to enhanced fiber-matrix interaction. Thorough fiber-matrix interfacial characterization provided a ~ 42% increase in fiber pull-out strength from the matrix, ~ 38% more energy absorption during delamination, and an improved modulus gradient across the interface.