Failure Analysis of Brittle Fracture in Nonceramic Insulators

Abstract

Time dependent transverse cracking of the glass reinforced polymer (GRP) core rod in nonceramic insulators (NCI) under low mechanical loads, commonly referred to as brittle fracture, has been investigated. Tension tests were performed on GRP core rods with E glass, ECR glass as well as epoxy and polyester matrices using nitric and oxalic acid environments in order to obtain the relationship between applied stress and the time to rupture. While both E glass and ECR glass remain prone to brittle fracture, ECR has a substantially superior resistance to stress corrosion cracking than E glass. Scanning electron microscopy of fracture surfaces has produced a quantitative relationship between the stress history and the fracture mirror size on the fibers. Results of an epoxy cone insulator end fitting are presented, and the mechanism of brittle fracture is discussed.