Composite Energy Storage Flywheel Design for Fatigue Crack Resistance

Composite flywheels can be a high density energy storage device because of the very high specific strength and strength per unit weight. The rotors are fiber reinforced in the circumferential direction to resist centripetal loads resulting from high speed rotation. A press-fit process is also used to induce pre-compression in the radial direction that improves mechanical strength by preventing radial separation of rotors. This design and fabrication process however leaves the radial and axial directions of rotor vulnerable to propagation of fatigue crack growth in the rotor. A semi-empirical approach is proposed to enhance the "crack growth" resistance of the rotor. Axial glass plies are incorporated to confine the crack growth through the radius and along the circumferential direction of rotor. The fracture properties of specific hybrid laminates are then measured to provide information required for an optimal rotor design.