Void formation and electrical breakdown in epoxy resin

The long term behaviour of epoxy resin subjected to high alternating electrical stress was studied using optical magnifications of up to 1500, a scanning electron microscope, and a high sensitivity discharge detector. The formation of voids in initially void-free specimens was investigated when voltages of duration between ten seconds and several thousand hours were applied using a pin-plane configuration. Defects in epoxy resins, mechanisms of their electrical aging, and their long term dielectric strength are discussed in relation to the phenomenon of void growth.