A new look on materials, geometry and manufacturing processes of flywheels is proposed. Our systems approach relies heavily on analytic modeling of stress analysis, interactive failure criteria, optimization, curing, resin flow, contolled failure progression and life prediction. In particular, the optimum ply stiffness and density variations along the radial direction can significantly reduce radial stress and improve rotor's strength; i.e., a steep increase in hoop stiffness and decrease in density. Addition of radial plies, on the other hand, will increase both radial stiffness and stress. The net effect is low strength and high cost - an approach that we do not recommend. Rotors can be manufactured by cigarette rolling and/or filament winding with prepreg, wet or dry tows. In the last case, a centrifugal resin infusion is a good solution. Instead of the conventional multi-step curing, a single-step cure can produce quality product at reasonable cost. A rotor with graded strength can lead to a controlled failure thus reduce the containment requirement. Only the outer rim of the rotor needs high fiber volume. The goal is to ensure safety while minimize the containment requirement. The ultimate product of this work is a set of guidelines and software to produce rotors with high energy, durability and competitive cost.
