Analyses of composite insulators with crimped end-fittings: Part II - Suitable crimping conditions

In this research the mechanical behavior of composite suspension insulators with crimped end-fittings manufactured by NGK has been evaluated. Two issues have been addressed in this study. Insulators crimped with the standard, high, reversed and constant high stress conditions have been analyzed for their crimping deformations, and the two and three dimensional compression profiles for the four different crimping conditions have been determined. Second, a series of mechanical tests has been performed by subjecting the insulators to excessive tensile axial loads until failure. Acoustic emission (AE) was also monitored during the tests. It has been found that the shape of the compression profiles is dependent on the manufacturing crimping process. The magnitudes of compression for the standard, high, reversed and constant high stress conditions are almost the same, with the distribution of compression along the fitting being noticeably different for each stress condition. The results from the pull-out tests clearly demonstrate that the crimping process can significantly effect the mechanical strength of the insulators. The insulators with the standard controlled stress conditions failed by rod pull-out whereas the other crimping conditions resulted in rod fracture. It has been shown in this study that the mechanical strength of crimped insulators can be optimized to avoid both crushing of the glass reinforced polymer (GRP) rods due to crimping and rod fracture under excessive tensile loads.