Effects of combined UV-tensile aging on structural and electrical properties of high temperature vulcanized silicone rubber in composite insulators

High-temperature vulcanized silicone rubber (HTV-SR) in composite insulators undergoes performance degradation under prolonged ultraviolet (UV) exposure and mechanical stress in plateau environments, posing risks to power grid reliability. To investigate the aging behavior and mechanism of HTV-SR under coupled UV and tensile stress conditions, accelerated aging tests are conducted for 500 hours under constant UV irradiation combined with varying tensile stresses. Surface morphology, structure, mechanical and electrical properties of HTV-SR samples before and after aging are systematically characterized to analyze the synergistic and competitive effects of UV and tensile aging. The results show that UV irradiation induces chain scission and oxidative crosslink, increasing surface crosslink density while deteriorating the mechanical and electrical performance. In contrast, tensile stress alone causes minor structural disturbances due to the inherent elasticity of the material, with limited impact on electrical properties. Under combined aging, tensile stress reduces the effective surface crosslink density and inhibits UV-induced oxidative crosslink. As the tensile ratio increases, molecular chains exhibit more pronounced stress relaxation and filler debonding, further accelerating UV-induced structural and electrical degradation. This study provides theoretical support for the weathering assessment of composite insulators and highlights the importance of maintaining an appropriate crosslink density of HTV-SR to enhance structural and electrical stability in service environments.