https://doi.org/10.3221/IGF-ESIS.78.03 Epoxy adhesives are known to have good strength and chemical resistance; however, they tend to be brittle, restricting their use in structural applications. This study examines the effect of low-concentration graphene and hybrid graphene–SiO₂ reinforcement on the mechanical and fracture behaviour of epoxy nanocomposites. Composites containing 0.1–0.4 wt.% graphene and hybrid systems with 0.05–0.2 wt.% graphene combined with SiO₂ were synthesised using in-situ polymerisation and ultrasonic dispersion to ensure uniform filler distribution. Tensile, flexural, and fracture tests were performed following ASTM standards. The mechanical properties of epoxy composites are significantly improved by adding nano fillers when used at optimal concentrations. From the single filler systems, epoxy with 0.3 wt. % graphene achieved the highest enhancement of tensile and flexural strengths compared to pure epoxy. Greater enhancement was also found in the hybrid composites with a combination of 0.15 wt.% graphene and 0.15 wt.%. SiO2 resulted in an increase of 53% and 22% for tensile strength and flexural strength, respectively. All nano composite specimens showed a higher fracture toughness, with the best improvement of 71.1% found for the composite mix containing 0.2 wt.% graphene and 0.2 wt.% SiO2. Scanning Electron Microscopy (SEM) images indicated stronger interfacial bonding, more crack deflection and less brittleness when the filler loadings were optimized. The excessive filler content caused agglomeration due to which the performance was lowered. The structural strength and fracture resistance of the epoxy nanocomposites were significantly improved when Graphene is combined with SiO2 and this combination created a strong synergistic effect. A finite element simulation was carried out to understand the impact of filler addition on the flexural strength of nanocomposites and results were compared with experimental outcomes.
