Fracture toughness of spherical silica-filled epoxy adhesives

Crack propagation in epoxy adhesives filled with spherical silica was investigated using double cantilever beam (DCB) specimens. In particular, to clarify the effect of particle size and particle/matrix adhesion upon the fracture toughness, silica particles were prepared with mean particle sizes in the range of 6–30 μm, where the particles were treated with γ-aminopropyl methyldiethoxysilane and hexamethyl disilazane. The former and latter treatments demonstrated well- and poorly-bonded interfaces between the particle and matrix, respectively. The experimental results showed that the fracture toughness of DCB specimens increases with particle size and with interfacial strength of silica/matrix depending on the particle content. The behavior has been interpreted in terms of crack pinning and crack blunting.