Energy storage capabilities of rotating machines including a comparison of laminated disk and rim rotor composite designs

High speed rotating machines are being employed as energy storage devices to provide both pulsed and load leveling power to future electric weapon and/or electric drive vehicle systems. The ability to store as much energy as possible for the least weight is of paramount importance to these systems. The rotor configurations employed in these machines can vary greatly in shape, physical properties and stress distribution, as defined by the rotor's shape factor. This paper employs a unique approach to discriminate between vastly different rotor configurations based on a completely general derivation for the shape factor of constant thickness spinning rotors. The shape factor is used in conjunction with the rotor's maximum allowable operational stress and effective density to determine the maximum stored energy density of an individual rotating machine. These predictive techniques are then used to compare two composite rotor designs which have been built for electromagnetic pulsed power generation. These two machines are the laminated disk built by Kaman and the rim rotor built by CEM. Our analyses have determined that the true discriminator between these two designs is the allowable stress each can operate at since they both have about the same shape factor and composite density. The laminated disk design is limited by the interlaminar shear strength of the epoxy bond, while the rim rotor design is able to take full advantage of the strength limit of the composite fiber. These predictions are compared to test results for both machines.