A virtual containment strategy for filament-wound composite flywheel rotors with damage growth

This paper presents a method for setting a safe operating speed for a filament-wound composite flywheel with an idealized delamination-type flaw. Fracture mechanics concepts were used to establish the severity and growth rate of such a flaw. The strain energy release rates of various-sized delaminations were evaluated using a 2-D finite element method, and the effects of flaw radial location and press-fitting were investigated. Once a flaw attains a certain size, the strain energy release rate is found to decrease, thus stabilizing further growth. Flaw growth rates under cyclic loading were estimated using the Paris law. Several virtual containment strategies were also investigated. Once a flaw is detected during flywheel operation, the maximum operating speed can be reduced to prevent catastrophic failure, achieve a specific design life, and maximize energy storage capacity over the remaining life. With a speed control strategy for energy maximization following the detection of damage, a numerical example showed an improvement of more than four times the energy capacity over a system without virtual containment.