Electric breakdown of a poly(ethylene terephthalate)/glass composite

Abstract The voltage lifetime of a poly(ethylene terephthalate)/glass composite is measured for two different orientations of short fiber with respect to the applied electric field (perpendicular and parallel). The difference in the voltage lifetime between two configurations is attributed to the microstructural features at the (fiber/matrix) interface, particularly microvoids. The morphological observations by scanning and transmission electron microscopy (SEM, TEM), and optical microscopy reveal the presence of microvoids as well as the crazed matrix and consequent erosion channel. The tree initiation site is identified and the nature of tree propagation is explained. A theoretical model based on such microstructural features is constructed, which explains the voltage lifetime vs fiber orientation in a relative framework. It is concluded that the graseous discharge at microvoids is the main mechanism for electrical breakdown and the site of such gaseous discharge is the (fiber/matrix) interface. Therefore, the orientation dependence of the electrical breakdown is the geometrical effect of the interface voiding with respect to the direction of the applied electric field.