Fracture Properties of Glass Filled Polyphenylene Oxide Composites

Abstract

The phenomological fracture properties of glass bead filled polyphenylene oxide composites were investigated. Yield strength and Young's modulus were obtained as a function of volume fraction of filler using standard microtensile testing techniques. Fracture toughness was measured using double edge notched tensile bars. The effects of adhesion were studied by using untreated and A-1100 silane-treated glass beads. The nature of the fracture surfaces was observed by use of an optical microscope, a scanning electron microscope and a transmission electron microscope. It was found that the fracture toughness of these materials de creased by increasing the filler content and by improving the adhesion. In general, an increase in strength and stiffness was accompanied by a decrease in toughness. The fractographic studies gave a detailed mapping of the frac ture front as it propagated through the material. Fracture occurred in two stages. The initial stage was a region of stable crack growth accompanied by, crazing, heat generation and viscous flow in the resin matrix. At a well defined condition, the cracks became un stable and catastrophic failure ensued. The fracture mechanism in the unstable region was distinctly different than in the stable region. The exact mechanism was strongly dependent on the degree of adhesion between the phases. It is felt that a reasonably clear picture has been presented of how filled polyphenylene oxide polymers fail and how some of the variables affect the resistance to castastrophic failure.