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 τ 0 intervals) based on the theory of Arrhenius is presented in the following form: τ σ = τ 0 exp[( U 0 − γσ )/ RT ] (1) where τ is durability. τ 0 is a constant (10 −12 ‐10 −13 s) equal to period of vibrations of atoms around equilibrium position, U 0 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 = τ 0 exp[( W 0 − χE )/ RT ] (2) Here, τ E , W 0 and χ are analogous to τ σ , U 0 and γ , respectively. It is assumed that the following equation is valid under the simultaneous effects of E , σ and T : τ σ,E = τ 0 exp[( U 0 − ( γσ + χE ))/ RT ].(3) electric degradation