Design and spin test of a hybrid composite flywheel rotor with a split type hub

A study is conducted on lowering the radial tensile stresses and increasing the performance of the fiber wound composite flywheel rotor by applying pressure on the inner surface of the rotor using a split type hub that spreads in the radial direction due to the centrifugal force. A conventional solid or ring type hub in most cases produces tensile stresses within the rotor, possibly causing delamination and eventually lowering the maximum speed of the rotor. The relationship between the stresses of the rotor and the thickness of the hub is derived and applied to the single and hybrid rotors. A hybrid composite rotor of 180mm inner diameter and 340mm outer diameter is designed and fabricated, which reaches only the strength ratio of 0.58 at the maximum rotating speed of 40,000 rpm. A spin test was conducted to show the improved performance of the rotor with the split type hub by measuring the mechanical strains from the rotor. The radial and circumferential strains at four different locations are measured up to 30,000 rpm using a wireless telemetry system, and they are in good agreement with the analytical calculations. The rotor has survived a spin test of up to 40,000 rpm, which corresponds to the usable energy of at least 500 Wh with the safety factor of 1.7.