Static and Dynamic Compressive Properties of Nano-Al2O3-Reinforced Epoxy Matrix Composites

This study investigates the influence of nano-alumina (nano-Al2O3) on the compressive properties and damage mechanisms of epoxy matrix composites across a wide strain rate range. Composites with varying nano-Al2O3 contents (0, 1, 3, 5, 10, 15 wt%) were tested under quasi-static (0.001~0.1 s−1) and dynamic (2500~4800 s−1) conditions using a universal testing machine and a Split Hopkinson Pressure Bar, respectively. The phase, the microstructure, and their effects on macro-mechanical performance and micro-damage were characterized by XRD, SEM, and TEM. Results indicate that the incorporated nano-Al2O3 is highly crystalline, single-phase lamellar α-Al2O3. Its addition significantly modulates the compressive properties, with effects dependent on both content and strain rate. Under quasi-static compression, yield strength increased monotonically with nano-Al2O3 content at 0.1 and 0.01 s−1, reaching a maximum increase of ~9.5% at 15 wt%. However, at 0.001 s−1, optimal strength occurred at 10 wt%, beyond which agglomeration caused degradation. Dynamic tests revealed a positive strain rate effect. The 10 wt% composite exhibited optimal overall performance, combining high peak stress and a stable stress plateau, whereas the 15 wt% sample showed higher peak stress but poor post-peak load-bearing capacity. Microstructural analysis showed that 10 wt% nano-Al2O3 dispersed uniformly, enhancing toughness by inhibiting crack propagation via interfacial bonding and microstructural refinement. In contrast, at 15 wt%, particle agglomeration induced interfacial defects, promoting debonding and brittle fracture. This work provides insights into the wide-strain-rate mechanical behavior of nanoparticle-reinforced polymers and supports the design of high-performance, impact-resistant epoxy composites.