FRP rods for brittle fracture resistant composite insulators

Brittle fracture of fibreglass reinforced polymer (FRP) rods can lead to mechanical failures of composite insulators even at low mechanical loads during operational service. Although this fact has been known for 20 years, it may still be a problem in some designs of composite insulators at the present time. In order to find countermeasures against brittle fracture, a study was carried out in the early eighties. It turned out that brittle fracture is a problem of FRP material and that material compositions exist, resistant to brittle fracture. A brittle fracture resistant FRP rod introduced in 1983 in one particular design of composite insulators resulted in a 15 year excellent service performance. This study deals with details of brittle fracture of FRP rods. Test setups were established to induce brittle fracture artificially. It was realized that brittle fracture is some kind of stress corrosion related to the composition of the FRP material. A broad variety of FRP materials was evaluated, showing the influence of the components of FRP material on the brittle fracture behavior of FRP rods as well as the effects of different manufacturing processes. The compositions of brittle fracture resistant FRP rods are disclosed. The results from artificial testing are compared with brittle fracture of FRP rods that occurred in composite insulators in operational service. Although no quantitative correlation could be established, the trend concerning the material behavior of FRP rods is similar.