Influence Mechanism of Low-Temperature Environments on the Mechanical Reliability of Silicone Rubber Insulation in Cable Accessory

The recurrent failures of cable accessories under low-temperature environments highlight critical uncertainties in their interfacial mechanical reliability. To address this issue, this study elucidates the influence mechanism of low-temperature environments on the mechanical properties of silicone rubber (SiR) used for accessory insulation. The crystallization behavior at low temperature is investigated using differential scanning calorimetry (DSC). The stress relaxation behaviors under constant temperatures and variable temperatures are tested. The effects of temperature and tensile ratio on the stress relaxation of SiR are analyzed. A calculation formula for the entropy-elasticity stress of SiR at low temperature is established utilizing the rubber state equation. The results show that, at constant temperatures, the stress variation in the stretched SiR is exclusively governed by stress relaxation effect. The higher the tensile ratio and the temperature the faster the relaxation rate. When the temperature decreases, the stress in the stretched SiR changes linearly, essentially resulting from the entropic elastic stress variation induced by the combined effects of thermal expansion, the Gough-Joule effect, and stress relaxation. The stress in the stretched SiR under low tensile ratio of 110 % is mainly dominated by the thermal expansion effect, exhibiting a gradual increase. At tensile ratios between 125 % and 400 %, the Gough-Joule effect becomes the predominant mechanism, driving progressive stress decrease with the decrease of temperature. And it is precisely the reason for the unreliability of the interface pressure between cable and accessory under low-temperature environments. At extremely low temperatures, the strain-induced crystallization (SIC) effect in the stretched SiR can lead to a sharp increase in stress and an elevated crystallization temperature. These results can be used for evaluating the mechanical reliability of cable accessories in the cold environments.