Characterization of the fracture behavior of epoxy reinforced with nanometer and micrometer sized aluminum particles

The effects of particle size and silane treatment on the fracture toughness are experimentally evaluated for epoxy reinforced with nanometer and micrometer sized rigid particles. These nano- and micro-composites are fabricated using two different sizes of spherical aluminum particles: 20–100 nm and 3–4.5 μm in diameter. The volume fraction of particles is fixed at 2% and the particles are dispersed using ultrasonication. In order to investigate the effect of particle–matrix adhesion on the failure process, composites are fabricated using both as-received and silane treated aluminum particles. The adhesion properties are controlled by using 3-glycidoxypropyltrimethoxysilane as an organofunctional coupling agent. Two different methods are employed to carry out the silane treatment process. In a direct approach, the coupling agent is directly added to the epoxy–particle mixture; in a more involved approach, the particles are first coated with the coupling agent and then dispersed in the epoxy resin. The fracture toughness is characterized in terms of the critical values of the mode-I stress intensity factor, KIc, and also by the work-of-fracture. Additionally, fractured surfaces are observed under a scanning electron microscope to investigate both particle dispersion and evidence of extrinsic toughening mechanisms. It is observed that particle size, dispersion and silane treatment, all play an important role in determining the enhancement of fracture toughness. In general, it is observed that both improved particle dispersion and appropriate silane treatment lead to an increase in toughness. With regards to particle size, the composites with nanometer sized aluminum particles lead to a greater work-of-fracture while the micrometer sized aluminum particles lead to a greater initiation toughness.