Failure analysis of a field brittle fracture composite insulator: Characterization by FTIR analysis and fractography

A field brittle fracture composite insulator was examined and analyzed in detail in terms of chemical property and fractography with the purpose of obtaining the cause and mechanism of the failure as well as providing more detailed information on acid source and classification of fracture surface feature responsible for brittle fracture. The Fourier transform infrared spectroscopy (FTIR) analysis was employed to investigate the chemical properties of the rust on the surface of high voltage end fitting and fractured FRP rod. Furthermore, the scanning electron microscopy (SEM) was employed to obtain microscopic pictures of fractured FRP rod with a high magnification. The results showed that the acid source responsible for the initial failure of seal were sulfuric acid and nitric acid from acid rain. The acid source responsible for the development of crack within the FRP rod was the nitric acid generated by the discharge in the presence of moisture. In addition to the classical appearance of mirror, mist and hackle zones on the fracture surface of individual glass fiber, the appearance of mirror and wedge (or wedges) zones was also a common feature of fracture surface of individual glass fiber and can be used as an indication of brittle fracture. The crack propagation directions at micro scale showed some extent of irregular, this was caused by the local variation in acid environment as well as the resin wrapping of fiber and may resulted in the appearance of matric scarp on the fracture surface. An axially perforative defect was detected on the fracture surface of FRP rod, this indicated an insufficient resin infiltration process in the production of FRP rod. The results of this research provide the experimental basis for the further understanding of brittle fracture.