Fracture toughness of nano- and micro-spherical silica-particle-filled epoxy composites

The effects of particle size and volume fraction on the mode I fracture toughness of epoxy composites filled with spherical silica particles were investigated through experiments and an analytical model. Spherical silica particles with various particle diameters ranging from 1.56 μm to 240 nm and volume fractions from 0 to 0.35 were added to epoxy resin. We found that the fracture toughness of the composites was approximately linear with respect to the reciprocal of the product of (i) the square root of the mean distance between the particle surfaces and (ii) the normalized mean stress in the matrix given by the equivalent inclusion method.