Electrically induced local creep in dielectric polymers: Experiments and modeling

Abstract

Dielectric polymers such as biaxially oriented polypropylene (BOPP) are widely used in capacitors for electric energy storage and pulse power. Under working conditions, they are subjected to high voltage as well as cyclic charging and discharging, resulting in significant Maxwell strain that evolves due to viscoelasticity. Such creep behavior has important implications to the reliability, aging, and breakdown failure of dielectric polymers, and we seek to understand it with the goal to predict the long term strain evolution using short term experimental data. We established a digital image correlation based experimental setup to monitor field induced deformation in-situ, observing significant strain concentration as well as creep. We carried out systematical analysis using Burgers model and find that it is incapable of predicting long term local creep of BOPP at strain concentration, despite its success in capturing mechanical creep as well as the evolution of average strain under an electric field. We thus developed a modified Burgers model that accounts for the evolution of concentrated electric field and accurately predicted long term local creep under either constant or cyclic voltage. In particular, we successfully predicted the evolution of concentrated local strain up to 10⁶ s using the experimental data in the first 10³ s, demonstrating the power of our modified Burgers model. We expect that the modified Burgers model will play an important role in analyzing aging and failure behaviors of dielectric polymers and capacitive devices.