Mechanical and diffusion behavior of nano-silica filled multi-layer bidirectional E glass/epoxy composites: Experimental and FEM study

E-glass fiber reinforced epoxy composites were fabricated by the hand lay-up technique with varying fiber layers (2, 3, and 4) under constant matrix content to investigate the influence of fiber weight fraction. Nano-silica fillers (2, 4, and 6 wt.%) were incorporated within each laminate to investigate their effects on mechanical properties, post-aging mechanical performance under neutral (pH 7) conditions, and moisture absorption behavior in acidic, neutral, and alkaline environments. Increasing the number of E-glass fiber layers significantly enhanced the tensile, flexural, and hardness properties of the composites due to the higher fiber reinforcement content, while the 4-layer E-glass/epoxy composite reinforced with 4 wt.% nano-silica demonstrated the best overall mechanical performance among all developed composite configurations. Post-aging in pH 7 medium for 55 days resulted in moderate reductions in mechanical properties across all composite variants. Finite element analysis (FEA) was employed to validate the experimental tensile and flexural results, demonstrating good agreement between numerical and experimental findings. Fracture surface morphology analyzed by scanning electron microscopy (SEM) showed fiber pull-out, matrix cracking, and filler dispersion, which correlated well with the observed mechanical performance, while energy-dispersive X-ray spectroscopy (EDS) verified the elemental composition of the composites. XRD analysis identified crystalline α- quartz nano silica within an amorphous epoxy/glass matrix in the composite, corroborated by FTIR functional group retention. Water absorption over 55 days followed Fickian diffusion, with acidic medium (pH 3) exhibiting the highest uptake, followed by alkaline (pH 8), then neutral (pH 7).