Effect of inclusion size on mechanical properties of polymeric composites with micro and nano particles

The effect of the particle size on the mechanical properties of polymeric composites reinforced with spherical particles was investigated. The size of particles varied from macro (0.5 mm) to nano (15 nm) scale. It was found that particle sizes at micro scale have little influence on the Young’s modulus of the composite and that Young’s modulus increases as the size of particles decreases at nano scale. It was also observed that tensile strength of the composite is significantly dependent on particle size. At 1 vol% loading, the tensile strength increased as the particle size decreased. However, the trend for the composite with alumina nanoparticles of 3% volume fraction was found to be opposite. TEM and SEM micrographs showed higher likelihood of poor dispersions in the composite with 3 vol% nanoparticles than that with 1 vol%. To understand the effect of the particle size in micron scale on the failure process, finite element analyses showed that total strain energy release rate for particle/matrix debonding growth decreases as particle size decreases and that sliding fracture mode becomes dominant as the debonding grows. It was found that interfacial fracture toughness does not depend on particle size but increases substantially when the sliding fracture mode prevails.