System and Method of Quasi-Distributed Fiber Bragg Gratings Monitoring Brittle Fracture Process of Composite Insulators

Abstract

Brittle fracture of the composite insulator is a malignant accident. There is a lack of means to monitor the formation and expansion of stress corrosion cracking in rods, resulting in little understanding of the process of brittle fracture development. First, this article proposes a mechanical model for identifying cracks in rods by the wavelength shift trends of fiber Bragg gratings (FBGs). Second, several FBGs and FBG temperature compensation sensors are pasted on the 10-kV composite insulator rod's surface. Then an optical fiber monitoring system for the brittle fracture process of the rod is established. Finally, the model and system were validated by conducting stress corrosion testing with different tensions. The results show that the surface quasi-distributed FBGs can monitor the temperature and stress in the complete brittle fracture process of a glass-fiber-reinforced polymer (GFRP) rod, which verified the correctness of the mechanical model for wavelength shift identification of cracks in axial cross sections. A temperature difference of 1 °C and the wavelength shift of the FBG on two or more fibers reach 1.1 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">smin</sub> and 0.9 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">smin</sub> can be used as warning thresholds for corrosive heat release, crack initiation, and rapid development of cracks to fracture, respectively. This article provides a quasi-distributed FBGs' monitoring system and method to study brittle fracture of composite insulators in stress corrosion testing. It provides a technical means to evaluate and warn the mechanical properties of composite insulators.