Optimizing flexural performance of 3D fibre-reinforced composites with hybrid nano-fillers using response surface methodology (RSM)

This study presents the flexural performance and damage mechanism of three-dimensional orthogonal woven E-glass/epoxy composites (3DOWC) modified with an innovative toughened epoxy resin using different weight percentages of Nanostrength® (NS: up to 7.5 wt%) and graphene nanoplatelets (GNP: up to 1.5 wt%). The Central Composite Design (CCD)-based Response Surface Methodology (RSM) was developed to optimize input parameters for maximum flexural strength, failure initiation load, and energy absorption. For single fillers, the composite with 0.5 wt% GNP showed an increase in flexural strength of up to 48.4% (warp), while with 7.5 wt% NS it increased by 39.3% (weft). The optimal weight percentages of hybrid nano-fillers in 3DOWC increase the flexural strength, along the warp and weft directions respectively, by up to 77.3% and 18.0% at 4.1 wt% NS and 0.5 wt% GNP; the failure initiation load by up to 42.5% and 28.9% at 4.7 wt% NS and 0.5 wt% GNP; and energy absorption by up to 13.4% and 9.6% at 7.5 wt% NS and 1.5 wt% GNP. Scanning electron microscopy (SEM) of damaged samples revealed that crack reconnection by GNP, fibril formation and plasticization by NS, and the combined effect of crack reconnection and plasticization by hybrid fillers improved the overall flexural performance of 3DOWC. This study significantly enhances the flexural performance of 3DOWC, making them ideal for high-strength, lightweight applications in the aerospace, automotive, and construction industries.