| The incorporation of inorganic particles into polymeric matrices is a widely used method for toughening and stiffening polymers, but is poorly understood at a mechanistic level. By using glass bead filled epoxies, the effects of various material parameters, such as volume fraction, size, surface treatments of glass beads, and inherent matrix toughness, on the fracture toughness of composites were studied. To understand the relationship between the fracture toughness and the various material parameters, the micro-deformation processes occurring during fracture are identified and their contributions to toughening evaluated. Among these processes, micro-shear banding within the matrix was found to play a major role. By promoting this process through changes in the matrix ductility, the fracture energy of composites has been increased by as much as 340% over that of the unmodified epoxy using just 10 vol% of glass beads. Moreover, a possible explanation is also given for the lack of success of previous efforts to toughen these materials by changing interfacial strength. In addition to the study on glass bead filled epoxies, hybrid-particulate composites based on glass beads, rubber particles, and epoxy resin were prepared and their fracture behavior was investigated. An increase in fracture toughness by the incorporation of glass beads and rubber particles could be explained by combining the micro-shear banding mechanism of glass beads and the cavitation/matrix shear yielding mechanism of rubber particles. |
