Fatigue performance of electrical insulator bolted connection with an unintended gap

The bolted connections are important components in overhead power distribution network systems, fixing the insulator to the cross-arm. This connection is subjected to various loads, such as the self-weight of the conductor, wind, and thermal, which induce cyclic stresses that can lead to fatigue failure. The presence of separation gaps, resulting from non-compliances with dimensional tolerances in insulator connections, increases stress concentrations at the thread roots and promotes the initiation of cracks. Therefore, the role of gap size in the fatigue performance of the insulator connection is investigated in this study. The fatigue performance of a commonly used bolted connection (i.e., M24x3.0p stud) in a distribution power network having controlled gap sizes was experimentally tested under reverse cyclic flexural load using a test rig specifically developed for this purpose. The experimental results were used to develop a probabilistic fatigue life model for bolted connections with gaps. Furthermore, the probability of failure was estimated considering the effect of both gap size and load level of the connection. Also, the Miner's linear cumulative damage theory was employed, together with Monte Carlo simulation, to enable the inclusion of wind load variation to describe variable in-service loading and used for life expectancy estimation of the in-service connection. It was observed that fatigue life is reduced by approximately 80% as the gap distance increases from 1 mm to 3 mm. Finally, probabilistic life expectancy curves were developed to provide a quantitative assessment tool to assist the asset owners, in performing risk-based asset management.