Analyses of composite insulators with crimped end-fittings: Part I—non linear finite element computations

Abstract The purpose of this research has been to design an advanced numerical model that can be used to evaluate the mechanical behavior of composite insulators with crimped end-fittings subjected to axial tensile loads. Two issues have been addressed in this study. First, examples of insulator failures due to improper crimping have been shown and discussed. Second, comprehensive non-linear two- and three-dimensional finite element simulations of crimped insulator ends have been performed. The effects of uniformly and linearly distributed crimping deformations as well as external tensile loads on mechanical stress in the insulator end have been examined. Numerical results have been compared with the experimental data obtained by performing tensile strength tests on crimped insulators supplied by NGK. It has been shown in this research that the type of crimping can significantly affect the mechanical strength of crimped composite insulators. For the same magnitude of crimping and the friction coefficient at the rod/fitting interface, the load/displacement diagrams are strongly dependent on the crimping profiles generated during the manufacturing process. The highest radial and tangential stress concentrations in the composite rods exist due to crimping. However, the stresses are reduced if a crimped composite insulator is subjected to axial tension. At the same time, the normal stresses along the rod are significantly increased when the rod is being pulled out of the fitting. The concentration of the normal stress along the rod is significantly affected by the magnitudes of applied compression and axial tensile loads as well as the type of compression profile on the rod surface generated during manufacturing. It has been clearly shown in this research that the mechanical behavior of crimped composite insulators can be evaluated by performing finite element computations considering the actual crimping deformations and the geometrical and physical properties of the insulator end.