Condition monitoring and virtual containment for composite flywheels

This paper presents a health monitoring technique for advanced composite flywheels. Flaws of primary interest, such as delamination and debonding of interfaces, are those unique to composite flywheels. Such flaws change the balance state of a flywheel through small, but detectable, motion of the mass center and principal axes of inertia. The proposed technique determines the existence and the severity of such flaws by a method similar to the influence-coefficient rotor balancing method. Because of the speed-dependence of the imbalance caused by elastic flaws, normalized vibrations and imbalance change are defined. The normalized imbalance change not only permits the use of vibration readings at multiple speeds to increase the technique's accuracy, but also is a direct measure of the flaw severity. To account for the possibility that flaw growth could actually improve the balance state of a rotor, a new concept of "accumulated imbalance change" is also introduced. Laboratory tests show the proposed method is able to detect small simulated flaws that result in as little as 2-3 microns of mass center movement. Virtual containment software was also developed and demonstrated.