Experimental investigation of the hardness, tensile, flexural, and impact properties of functionally graded glass fiber/epoxy/silica nanoparticles composites

In this study, the properties of functionally graded and non-graded hybrid nanocomposites were evaluated through hardness, tensile, three-point bending, and Izod impact tests. Four functionally graded samples with different silica nanoparticle concentrations across the thickness and one non-graded sample, all with a total nanosilica content of 6 wt% were fabricated in four layers using a hand lay-up technique. In addition, one sample without nanoparticles was also prepared. The results of the hardness tests conducted on the upper surface of the samples indicated that increasing the silica nanoparticles content led to higher hardness. Specifically, the average hardness of the top-surfaces of samples containing 3 wt% nanosilica was approximately 27% higher than that of the top-surfaces of samples containing 0 wt% nanosilica. Among the samples containing silica nanoparticles, Sample E (non-graded, homogeneous) exhibited the highest tensile strength and modulus, showing increases of 17% and 22%, respectively, compared with Sample D (3-0-0-3, functionally graded). In the three-point bending test, the flexural strength of sample B (3-2-1-0, functionally graded) loaded from the 3 wt% side, was 24.5% higher than that of sample A (0-1-2-3, functionally graded) loaded from the 0 wt% side. In the Izod impact test, samples with non-graded nanoparticle distribution demonstrated superior impact resistance relative to the functionally graded samples. Overall, the results confirm that nanoparticle distribution plays a critical role in composite performance. Non-graded silica nanoparticles dispersion enhances tensile, flexural, impact, and hardness properties, whereas stepwise grading may introduce interlayer mismatches that reduce overall performance.