Stress Relaxation Characteristics of Silicone Rubber Used in Cable Accessory Under Extreme Environment Temperature

Silicone rubber (SiR) is widely used as insulation material for cable accessories due to its exceptional dielectric and mechanical properties. In practical applications, cable accessories are maintained in an expanded state to ensure sufficient interface pressure. Cable accessories used in high-speed electric locomotive have experienced frequent failures under extreme environment temperatures, revealing reliability issues with accessory interface pressure. Therefore, this study investigated stress relaxation characteristics of SiR used in cable accessory under extreme environment (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-40^{\circ} \mathrm{C}$</tex> to 90° C). The stress relaxation characteristics of SiR under both constant temperatures and thermal cycling conditions were tested. The Kohlrausch function was used to analyze temperature-dependent stress relaxation behaviors. Two different temperature cycling profiles were developed to evaluate the effects of temperature cycling on stress relaxation behaviors. The results showed that the stress relaxation of SiR at constant temperatures conforms to the law of Kohlrausch tensile exponential function, and the activation energy of relaxation time at different temperatures is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E a=1154.9055 ~\text{mol} \cdot J^{-1}$</tex>. The stress of SiR under the tensile rate of 150 % during the temperature change process is positively correlated with the temperature, and the stress change is dominated by the Gough-Joule effect. The stress change of SiR at constant temperature is only caused by stress relaxation effect, and decrease slowly. The temperature cycling will lead to the cyclic change of the stress in SiR. In the two temperature cycling profiles in this study, the lowest value of normalized nominal stress in SiR is 0.761. The stress change of SiR during temperature cycling is an important cause of accessory failure. The findings are expected to provide critical insights for assessing interface pressure reliability of cable accessories in complex environments.