An investigation of brittle fracture of composite insulator rods in an acid environment with either static or cyclic loading

The effect of static and cyclic roading conditions on the stress corrosion cracking of unidirectional glass reinforced polymer (GRP) rods used in comp osite high voltage insulators has been investigated. A series of stress cor rosion experiments has been performed on unidirectional E-glass/modified po lyester composite rods. The rods have been subjected to mechanical tensile static and cyclic stresses in the presence of a nitric acid solution. The s tress corrosion fracture process in the rods was monitored using acoustic e mission techniques. The experimental loading conditions simulated possible in-service loads for composite suspension insulators. The results obtained in this study showed that the brittle fracture process can be generated in the rods when subjected to relatively tow tensile stresses in the presence of a nitric acid solution. The morphology of the experimentally generated b rittle fracture cracks in the rods closely resembles those from in-service failed composite suspension insulators. It has also been shown in this rese arch that low frequency, low amplitude vibrations in tensile loads can sign ificantly accelerate the fracture process. It appears that the brittle frac ture cracks in the rods generated under cyclic loads are less planar in nat ure in comparison with the cracks formed under static conditions. It has al so been found that the acoustic emission generated during the stress corros ion fracture process in the rods is sensitive to the placement of the trans ducers. However, a reasonably good correlation between the stress corrosion crack growth rates and acoustic emission has been attained. (C) 2000 Kluwe r Academic Publishers.