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

Abstract

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 sigma and tau(0) intervals) based on the theory of Arrhenius is presented in the following form: tau(sigma) = tau(0) exp[(U-0 -gamma(sigma))/RT] (1) where tau is durability. tau(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 sigma = 0), gamma 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: tau(E) = tau(0) exp[(W-0 - chiE)/ RT] (2) Here, tau(E), W-0 and chi are analogous to tau(sigma), U-0 and gamma respectively. It is assumed that the following equation is valid under the simultaneous effects of E, sigma and T: tau(sigma,E) = tau(0) exp[(U-0 -(gamma(sigma) + chiE))/ RT]. (3).