Experimental Study of the Effect of Carbon Nanotubes and Nano-Silica on the Impact Resistance of FML Sheets under low velocity Impact

Fiber-Metal Laminates (FMLs) are hybrid composites that combine the advantages of metals and fiber-reinforced polymers, offering superior fatigue resistance, excellent impact tolerance, and high strength-to-weight ratios. However, to further improve their impact performance and energy absorption capacity, the reinforcement of the polymer matrix with nanoparticles has emerged as a promising strategy. This study investigates the influence of carbon nanotubes (0%, 0.3%, and 0.6% wt) and nano-silica (0%, 3%, and 6% wt) on the mechanical behavior of aluminum/glass fiber-based FMLs under free-fall impact loading, using both experimental testing and finite element modeling. Specimens were fabricated by integrating varying weight percentages of CNTs and SiO₂ into the epoxy adhesive matrix. The results demonstrated that adding 0.3 wt% and 0.6 wt% CNTs increased energy absorption at 25 J impact energy to 22 J and 24 J, respectively—representing enhancements of 20% and 31% compared to the baseline sample without nanoparticles. Conversely, 3 wt% nano-silica yielded only modest improvements (5%–6.4%). Notably, the highest performance was achieved with a hybrid reinforcement of 0.3 wt% CNTs and 6 wt% SiO₂, leading to peak contact force improvements of up to 178% at 75 J impact energy. Finite element simulations using ABAQUS closely matched experimental observations, validating the numerical model's accuracy. These findings underscore the significant role of nanoparticle reinforcement in enhancing the impact resistance of FMLs and provide a foundation for the design of advanced, energy-absorbing structural materials.