Application of fracture mechanics to dielectric breakdown in air, silicone oil and silicone rubber

Fracture Mechanics have been well developed to predict the fracture of materials with crack or any feature where stress concentration exists. On the other hand, internal electrodes have widely been adopted in electronic and electromechanical devices. At a sharp tip of an electrode, high electric field concentration is induced, which may lead to premature dielectric breakdown. Due to these similarities, researchers developed concepts of electrical fracture toughness KE and electrical toughness JE analogous to fracture toughness KM and mechanical J-integral JM respectively to predict the premature dielectric breakdown of materials due to electric field concentration. In the past, validity of this approach has been proved on piezoelectric materials by Prof. Zhang’s research group using CT samples under combined mechanical and electrical loading. This study aims to extend the developed methodology to investigate whether the concepts of fracture mechanics can also be applied to dielectric breakdown in dielectrics, including gaseous, liquid and solid dielectrics, or in other words, to examine whether the electrical fracture toughness and the electrical toughness exist in these materials. Air, silicone oil and silicone rubber were chosen as each kind of dielectrics in this study. By utilizing a tailor-made device and commercial software, ANSYS, experiments and finite element analysis have been conducted. It was found that, under some conditions, the concept of fracture mechanics can be applied to dielectric breakdown in these three dielectrics and the corresponding electrical fracture toughness are obtained