Partial discharge analysis of prestretched and unstretched acrylic elastomers for Dielectric Elastomer Actuators (DEA)

Partial discharges (PD) occur in solid insulating materials when the insulating material is partially bridged by an electrical discharge in response to an applied voltage stress. PDs typically occur at localized points of high field stresses or at voids and other inhomogeneities within the insulator. The applied field's effect on the frequency of occurrence and intensity of PDs can be used to assess the electrical breakdown strength and aging characteristics of insulating materials. PD testing is therefore a promising characterization method to understand the insulating properties of the elastomers and geometries commonly used in DEAs. Prestretched (~100% and ~230% biaxial) and unstretched acrylic elastomers (3M VHB tapes) with solid metal electrodes have been tested. We have found the number and intensity of PDs increase with applied field, and that a significant number of PDs are detected before any actuation was visibly observed, implying that the fields required for actuation will cause material aging and degradation over time. Most interestingly, the number of PDs steadily increase as the applied voltage increases up to a sufficiently high voltage, where the PDs suddenly cease. Since internal voids can cause PDs, this may indicate that the Maxwell stress minimized the thickness of or eliminated these voids, which could explain how prestretching improves performance.