Electromechanical strain at dielectric interfaces

Mechanical strains at liquid- and polyethylene-metal electrode interfaces were detected using an interferometric method. The results indicate that the mechanical stresses at the interfaces can be expressed in terms of the Gibbs adsorption equation. Measurements on a variety of dielectric-metal systems suggest that all dielectric interfaces under electrical stress normal to the interface will be subjected to tangential mechanical stress and subsequent strain. Under alternating applied fields the stresses are cyclic and, in solid dielectrics in particular, could lead to stress cracking and other fatigue phenomena. The processes might be particularly significant in the strong fields encountered in high-voltage cables. Moreover, since similar processes operate at liquid-dielectric interfaces, these Gibbsian electrocapillarity effects can be expected to have an important role in water-tree inception and growth in cables