Condition monitoring of filament-wound composite flywheels having circumferential cracks

A condition monitoring technique for advanced composite flywheels is presented. Flaws of primary interest, such as delamination and debonding of interfaces, are those unique to filament-wound 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, a normalized imbalance change is 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 a 2-3 μm of mass center movement. A virtual containment system, which is a condition monitoring system plus additional logic to adjust the flywheel speed when a flaw is detected, was also demonstrated.