Investigation of mechanical characteristics of decay-like degraded FRP rods and residual life prediction

Abstract

Decay-like fracture accidents have posed significant threats to the safe operation of the power transmission lines, and the time interval between the intermediate stage of decay-like degradation and final fracture remains challenging to predict. The present work investigated the residual mechanical strengths of several 500 kV composite insulators that exhibited decay-like degradation, and their degradation extent was quantified by analyzing the cross-sectional degradation areas of the fiber reinforced polymer (FRP) core rods using parallel light illumination method. A clear negative correlation was observed between the cross-sectional decay-like degradation areas and the residual mechanical strengths. Moreover, visual examination and microscopic observation of the fracture spots were conducted, and the fracture modes of different samples were classified as either decay-like fractures or splitting fractures. The macroscopic and microscopic morphologies of the fracture spot of individual sample reflected its unique fracture cause (pure mechanical fracture or stress corrosion fracture), which is directly related to the mechanical strength exhibited by the sample. Additionally, acoustic emission (AE) technique was employed during the tensile fracture test, and the signals were categorized via clustering algorithm. Finally, the correlation between the farthest heating location and the residual mechanical strength was analyzed. It was proposed that a farthest heating location exceeding the 4th large shed can significantly increase the risk of fracture for the in-service decay-like degraded composite insulators.