Fabrication and analysis of nanoparticle-infused natural fibre honeycomb core in sandwich structures
Authors:   , Govender Sumeshan 
Published: September 2024

his study investigates the feasibility of employing natural fibre materials to fabricate honeycomb core structures, addressing concerns over the environmental impact associated with conventional cores composed of aluminium, Nomex, and petroleum-based materials. The research process involves the fabrication of honeycomb cores utilizing a 3D printed moulding technique, followed by the adhesion of these cores to flax and glass fibre facings, thereby augmenting structural durability. Through the incorporation of cellulose and nanoclay as additives to the adhesive, the investigation reveals a substantial enhancement in flexural strength and impact resistance, surpassing the performance of structures bonded solely with epoxy. However, a notable reduction in compressive strength is observed upon the introduction of these additives to the adhesive. Quantitatively, the study demonstrates that the addition of 3wt% cellulose to the epoxy adhesive results in a remarkable 7.43% increment in flexural strength, a 4.09% increase in yield stress, a 0.17% rise in flexural modulus, a 6.45% enhancement in core shear ultimate strength, a 7.17% increase in facing bending stress, and a 7.94% elevation in absorbed energy. Similarly, the addition of 3wt% nanoclay to the epoxy leads to a significant enhancement, with a 10.48% rise in flexural strength, a 4.09% increase in yield stress, a substantial 20.92% augmentation in flexural modulus, a 10.75% improvement in core shear ultimate strength, a 10.5% increase in facing bending stress, and an elevated absorbed energy by 14.37%. Furthermore, in out-ofplane oriented structures, ultimate compressive strength experiences an increase of 7.32% and 20.1% for cellulose and nanoclay additives, respectively, while compression modulus rises by 6.6% and 29.65%. Nevertheless, it is noteworthy that the structures bonded with nanoclayfilled epoxy exhibit the most favourable overall performance, boasting an ultimate compressive strength of 7.72 MPa and a compression modulus of 7.77 MPa, outperforming their in-plane counterparts due to the larger compressive area of the out-of-plane samples. In terms of tensile properties, the study establishes that hybrid face sheets display an impressive 33.65% higher ultimate tensile strength compared to plain flax fibre samples. Additionally, the hybrid face sheets manifest a 69.45% increase in tensile strength and a substantial 58.73% enhancement in yield stress and Young's modulus, respectively, in contrast to exclusively flax fibre facings. Moreover, the research indicates that hybrid face sheets lead to significantly reduced moisture absorption, with structures employing solely flax fibre face sheets experiencing a mass increase of 11.88% after 168 hours of exposure, while structures utilizing hybrid face sheets encounter a substantially lower mass increase of 6.31%. This corroborates the effectiveness of hybrid face sheets in enhancing the water resistance properties of the composite. In summation, the study underscores the potential of natural fibre honeycomb composite structures to perform comparably to traditional honeycomb materials such as Nomex and aluminium, while being constructed from environmentally sustainable materials. The integration of an efficient additive manufacturing process further bolsters the prospects of these structures, enabling customization and scalability for diverse applications across industries, including aerospace, automotive, and marine sectors.