Effects of mechanical and thermal stresses on electric degradation of polyolefins and related materials

Degradation under the simultaneous effects of mechanical stress and temperature in polyolefins (PE, PP), composites on their basis (PE+PP fibre, PP+PP fibre, PP+glass fibre) and radiation low-density polyethylene (X-LDPE) used in high-voltage cables obeys the thermofluctuation theory of Zhourkov (in certain σ and τ₀ intervals) based on the theory of Arrhenius is presented in the following form: τ_σ = τ₀ exp(U₀ − γσ)/ RT] (1) where τ is durability. τ₀ is a constant (10⁻¹²-10⁻¹³s) equal to period of vibrations of atoms around equilibrium position, U₀ is the activation energy of the mechanical destruction process (at σ = 0), γ is a structure-sensitive parameter, T is absolute temperature and R is universal gas constant. Electric degradation under the effects of electric field and temperature in the materials mentioned above obeys the equation: τ_E = τ₀ exp(W₀ − χE)/ RT] (2) Here, τ_E, W₀ and χ are analogous to τ_σ, U₀ and γ, respectively. It is assumed that the following equation is valid under the simultaneous effects of E, σ and T: τ_σ,E = τ₀ exp(U₀ − (γσ + χE))/ RT]. (3) electric degradation