Evolution and Failure Mechanism of Moisture Absorption, Mechanical, and Electrical Insulation Properties of Glass Fiber/Epoxy Resin (GF/EP) Composites Under Hygrothermal Aging

Glass fiber/epoxy (GF/EP) composites are widely used in high-voltage electrical equipment due to their excellent specific strength, durability and dielectric properties. However, long-term exposure to hygrothermal environments will lead to performance degradation of the material, which seriously threatens its service reliability. To solve this problem, accelerated aging tests were systematically carried out in this study by immersing GF/EP specimens in deionized water at room temperature and 80 °C. The performance evolution laws and failure mechanisms of the material were investigated through moisture absorption kinetic analysis, tensile property testing, scanning electron microscope (SEM) fracture observation and breakdown voltage testing. The results show that the initial moisture absorption behavior of the material follows the Fickian diffusion mechanism, and the water diffusion rate at 80 °C is 31.8 times that at room temperature. After 35 days of aging, the retention rate of the maximum tensile force is 86.6% for the room temperature group, while it decreases to 38.2% for the 80 °C group. SEM observations show that the failure mode of the material changes from ductile fracture to brittle fracture after aging at 80 °C, accompanied by serious interfacial debonding. Temperature is the dominant factor for insulation performance degradation: the breakdown voltage retention rate is above 91% at room temperature, while it decreases to about 37% at 80 °C, and the influence of 60% maximum tensile force (Fmax) preloading is relatively small. This study provides experimental data and theoretical support for the performance evaluation and life prediction of GF/EP composites in harsh hygrothermal service environments of high-voltage electrical equipment.