The performance changes of silicone rubber cables under tension are the result of the combined effects of material properties, structural design, and the operating environment, primarily manifested in three dimensions: mechanical properties, electrical properties, and aging resistance. These changes not only affect the short-term reliability of the cable but also directly determine its long-term service life. Especially under complex conditions of combined dynamic and thermal stress, the performance degradation law becomes a key indicator for assessing cable safety.
From a mechanical perspective, tension significantly weakens the tensile strength of silicone rubber. Tensile strength and elongation at break are the core parameters for measuring its tensile deformation capacity. Under static conditions, high-quality silicone cables can achieve a tensile strength of 8-12 MPa and an elongation at break exceeding 300%. However, when the cable is under tension, the slippage and orientation of molecular chains lead to the gradual destruction of the internal structure. In the initial stage of tension, the molecular chains align along the stress direction, and the material exhibits elastic deformation. As the stretching rate increases, irreversible slippage of the molecular chains occurs, and cross-linking points break, resulting in a simultaneous decrease in tensile strength and elongation at break. For example, under the combined effects of 200℃ heat aging and 50% tensile elongation, the tensile strength of silicone rubber may drop to below 50% of its initial value, the elongation at break may decrease by 70%, the material gradually hardens and becomes more brittle, and ultimately loses its flexibility and impact resistance.
Deterioration of electrical properties is another important effect of tensile conditions. The insulating properties of silicone rubber depend on the stability of its molecular structure and the density of cross-linking. During stretching, the slippage of molecular chains expands the free volume, increases carrier mobility, and leads to increased dielectric losses. Simultaneously, the disruption of the cross-linking system reduces the breakdown field strength, making cables more susceptible to partial discharge or insulation breakdown under high-voltage environments. For example, the breakdown field strength of unaged silicone rubber can reach 20-30 kV/mm, but under the combined effects of stretching and heat aging, this value may drop to below 10 kV/mm, significantly shortening the electrical life of the cable. Furthermore, micro-cracks caused by stretching can become channels for moisture and impurities to penetrate, further accelerating the aging process of the insulation layer.
Regarding aging resistance, tensile stress exacerbates the thermo-oxidative aging and mechanical fatigue of silicone rubber. The main chain of silicone rubber is composed of silicon-oxygen bonds, whose bond energy is higher than that of carbon-carbon bonds, allowing the material to remain stable at high temperatures. However, tensile stress disrupts the equilibrium of the crosslinking reaction, accelerating the degradation of molecular chains.
For example, in a 200℃ thermal aging test, the crosslinking density of unstretched silicone rubber increases over time, while the crosslinking density of stretched specimens decreases due to stress resistance, leading to faster hardening and embrittlement. Simultaneously, long-term stretching causes mechanical fatigue in silicone rubber, resulting in molecular chain breakage and the formation of microcracks.
These cracks propagate under thermal stress, eventually leading to macroscopic cracking. For example, in dynamic tensile cyclic testing, the crack propagation rate of silicone rubber cables is 3-5 times faster than under static conditions, significantly shortening their service life.
The influence of material formulation and structural design on tensile properties cannot be ignored. By adjusting the substituent groups on silicon atoms, the temperature range adaptability and tensile strength of silicone rubber can be optimized. For example, the introduction of phenyl groups into phenyl silicone rubber improves its high-temperature oxidation resistance and reduces its low-temperature brittleness, making it more suitable for extreme environments. Fluorosilicone rubber, through the introduction of fluorinated alkyl groups, enhances oil resistance while maintaining wide-temperature performance and reduces chemical corrosion under tension. Furthermore, the addition of reinforcing fillers (such as fumed silica) can construct a three-dimensional network structure, inhibiting molecular chain slippage and improving tensile strength and abrasion resistance. Metal oxides (such as iron oxide) enhance heat dissipation through thermal conductivity pathways, preventing material degradation caused by localized overheating.
In practical applications, the tensile state of silicone rubber cables needs to be properly controlled through structural design. For example, the conductor uses a loose stranding process (pitch ratio 12-16 times) to allow space for thermal expansion and prevent insulation layer cracking due to rigid compression; the insulation layer uses a thick-walled structure (thickness ≥1.5mm), and either pure silicone rubber or filled silicone rubber can be used to disperse tensile stress; the "grip force" at the interface between cable accessories and the main insulation needs to be controlled within the range of 0.1-0.25MPa to ensure electrical strength while avoiding material damage due to excessive pressure. These design measures can effectively slow down performance degradation under tensile conditions and extend the cable's service life.
