Effects of Cyclic Tensile Stress on Electrical Tree Growth in Epoxy Resin

Epoxy resin insulation is widely used on offshore power platforms and are subject to complex electromechanical stresses. This study investigates the impact of cyclic tensile stress on the electrical tree growth of epoxy resin composites under both pre-loaded and on-loading conditions. The results indicate that cyclic tensile stress not only induces the fatigue damage but also promotes the release of residual stress. When the stress amplitude is low, the fatigue damage dominates, accelerating the electrical tree growth as the stress frequency increases. In contrast, at higher stress amplitudes, the release of residual stress becomes more dominant, slowing down the electrical tree growth with the increasing frequency. Pre-loaded cyclic stress does not directly affect the electrical tree growth but enhances the residual stress release with the increasing stress amplitude, thus slowing down the electrical tree growth. Conversely, on-loading cyclic stress directly accelerates electrical tree growth, and as the stress amplitude increases, the growth rate of electrical trees also increases. Both the fatigue damage and the residual stress release effects are associated with the relaxation of physical and chemical crosslinks in epoxy resin. The strain energy density is used to quantitatively characterize the contribution of cyclic stress to electrical tree growth, with results aligning closely with experimental trends.