Burst failure prediction of composite flywheel rotors: A progressive damage approach via stiffness degradation

Over the past decade, interest and research in the flywheel energy storage system has been renewed because of improvements in the material properties of composites, and because of the continued need for an alternative high performance energy storage system that is more efficient, environmentally friendly, and economic than traditional electrochemical batteries.; The flywheel energy storage system is an electromechanical battery in which energy is stored via the kinetic energy of the rapidly spinning rotor. The high rate of rotation experienced by the rotor induces high levels of stresses that must be analyzed and used to accurately predict the burst failure speed.; During the course of this study, experimental testing of the composite flywheel rotors revealed that they are capable of reaching speeds much higher than initially predicted by the analysis. Upon closer inspection of the test specimens, it was discovered that they suffered from multiple instances of epoxy failure but were still able to reach unexpectedly high speeds. Hence the composite rims showed signs of durability where epoxy failure (or damage) could be tolerated to allow the rotor to reach the high rotational speeds observed during the experiments.; The research presented here is motivated by the need for an analysis method where the epoxy failure(s) can be simulated as damage, thus leading to burst failure speed predictions that correlate well with the experimental results. In addition to the analysis and spin testing of the rotors, this study also involved manufacturing and supplemental experiments to determine the material properties. The results of the failure prediction method that was developed matched well with the available spin test results.