The brittle fracture of composite insulators is a malignant fracture accident.Therefore

we investigated the brittle fracture monitoring of composite insulators. Four optical fibers were pasted on the surface of the fiber-reinforced plastic（FRP） rod of a 10 kV composite insulator

one of which has 2 fiber Bragg gratings（FBGs） to measure temperatures

and the others have 5 FBGs to measure stresses. Temperature calibration tests

tension calibration tests

and stress corrosion tests were carried out on the rod with surface-encapsulated FBGs. The results showed that three cracks appeared in the stress corrosion tests of the rod

of which crack 1 developed into a brittle fracture

and

the other two did not. The temperatures and the stresses in the entire brittle fracture process of the rod were monitored by the FBGs on the rod surface. It is found that the stress corrosion process can be divided into four stages as follows:no change in the initial stage

corrosive heat release in the second stage

crack initiation in the third stage

and finally

the cracks developing rapidly until the rod break. From the second stage

the heat begins to emit in the corrosion zone

and the maximum difference between the corrosion zone temperature and the ambient temperature reaches 2.46 ℃

thus a temperature difference of 1 ℃ can be used as an early warning for the second stage in the brittle fractures of composite rods. The stress FBGs can detect a crack with an axial distance of 20 mm between them

and a wavelength shift 1.1λ

wmax

or 0.9λ

wmin

of the stress FBGs can be used as an early warning for a crack initiation or a serious crack in the brittle fracture process of composite insulators

respectively. By the FBGs monitoring method in this paper

a technical means can be provided to investigate fracture mechanisms and materials against brittle fracture/decay-like fracture of composite insulators.