Heterogeneity-induced mesoscale toughening in polymer nanocomposites

We report a mesoscale toughening mechanism in polymer nanocomposites that is distinct from previously reported ones. Fractography analysis of epoxy composites with nano-silica additives reveals a stochastic dispersion of nanofiller clusters which creates mesoscale stiffness heterogeneity as confirmed by nanoindentation testing. To analyze the effect of heterogeneity, a finite element model where a crack grows through heterogeneous material was created. Simulations and experimental results indicate that inducing stiffness heterogeneity increases toughness by modification of the crack tip fields. Our results indicate that mesoscale toughening (induced by the nanoparticle additives) plays a significant role in influencing fracture toughness in nanocomposite materials. [Display omitted]