Evaluation of Mechanical Properties of Hollow Particle Reinforced Composites and Analyses Aimed at Their Improvement
Hiroyuki TODA, Hisashi KAGAJO, Kazuo HOSOI, Toshiro KOBAYASHI, Yosuke ITO, Takashi HIGASHIHARA and Takashi GOHDA
Abstract:Hollow particle filled epoxy composites are fabricated by an ordinary molding technique. Young's modulus, tensile strength, fracture toughness and dielectric constant are measured as a function of density of the composites iI.e. wall thickness of the hollow particlesj. Specific strength is almost flat irrespective of the density, while specific modulus and the dielectric constant increase, and the fracture toughness simultaneously decreases with the decrease in the density. Fracture path varies from fractured particles in the case of particles with thinner shell to interfacial debonding in the case of thicker shell in the fracture toughness tests, while particle fracture is predominant in the tensile tests. In-situ observation of the material tests and finite element analyses are utilized to interpret the deformation and fracture behaviors and also to estimate the in-situ strength of silica. It is clarified by the observation that particles larger than 30ƒÊm in diameter are predominantly damaged and smaller particles less than 15ƒÊm are never fractured. Premature fracture of such coarse particles in early stage of loading is attributable to the strength properties. The in-situ strength of silica increases with the decrease in the particle diameter. According to the result of the finite element analysis, stress concentrates near inner surface along an equator under uni-axial loading, and this tendency becomes remarkable with the decrease in the wall thickness. On the other hand, interfacial stress decreases rapidly with the decrease in the wall thickness. The stress concentration along the equator is relaxed under multi-axial loading which is possible in the fracture toughness tests. All of these results indicate that elimination of the coarse particles is essential to improve the tensile properties, and that interfacial modification is effective only for toughness enhancement. SiCp reinforced Al2O3 and SiCp reinforced aluminum composites are also analyzed numerically to evaluate the efficiency of introducing hollow particles into ceramics and polymer materials. Key Words:composite, hollow particle, silica, epoxy, strength, modulus, dielectric constant, fracture toughness, finite element analysis, in-situ observation