Fracture mechanisms of epoxy-based ternary composites filled with rigid-soft particles

Epoxy composites filled with different amounts of aggregate-free silica nanoparticles and phase-separated submicron rubber particles were fabricated to study the synergistic effect of multi-phase particles on mechanical properties of the composites. Compared with binary composites with single-phase particles, the ternary composites with both rigid and soft particles offer a good balance in stiffness, strength and fracture toughness, showing capacities in tailoring the mechanical properties of modified epoxy resins. It was observed that debonding of silica nanoparticles from matrix in the ternary composites was less pronounced than that in the binary composites. Moreover, the rubber particles became smaller and their shape tends to be irregular, affected by the presence of rigid silica nanoparticles. The toughening mechanisms in the epoxy composites were evaluated, and the enlarged plastic deformation around the crack tip, induced by the combination of rigid and soft particles, seems to be a dominant factor in enhancing fracture toughness of the ternary composites.