The Effect of Specimen Size on the Electric Breakdown of Unfilled and Filled Epoxy Polymers

Measurements are reported on the effect of specimen size and filler content on the electrical-impulse strength of epoxy polymer. For unfilled polymer, the strength was found to decrease more rapidly with increasing thickness than with increasing area. But the incorporation of as little as 1 percent by volume of filler removed the thickness effect and lowered the impulse strength. The area effect was, however, the same as for unfilled specimens. Since statistical time lags occur, it is concluded that breakdown is a random process occurring in an inhomogeneous material.