Study on the Static and Dynamic Tensile Behavior of Epoxy Composites Reinforced with Nano-Alumina

Epoxy resins suffer from inherent brittleness, limiting their reliability in impact-resistant structures. This study addresses the dispersion–performance trade-off in nano-alumina (Al₂O₃)/epoxy composites by fabricating specimens with 0–15 wt% filler loadings using an optimized ultrasonic-mechanical dispersion strategy. Quasi-static and dynamic tensile behaviors (600–1600 s⁻¹) were evaluated using a universal tester and a split Hopkinson tensile bar (SHTB) system equipped with high-sensitivity semiconductor strain gauges. Results identify a critical agglomeration threshold at 3 wt%. The 1 wt% composite exhibited optimal quasi-static strength (44.76 ± 0.25 MPa), a 4.0% improvement over the neat epoxy (43.04 ± 0.33 MPa). While all composites showed positive strain-rate sensitivity, nano-Al₂O₃ incorporation generally reduced dynamic strength, except for the 5 wt% composite at intermediate rates. Notably, the 15 wt% composite recovered to 78.49 ± 0.48 MPa at 1600 s⁻¹ due to high-rate energy dissipation mechanisms. Microstructural analysis revealed a transition from brittle cleavage to a hybrid fracture mode dominated by microvoids and localized plastic tearing. This work quantitatively defines the optimal loading window for nano-Al₂O₃/epoxy composites in protective engineering.