Viscoelastic behavior of composite flywheels

Composite flywheel energy storage technologies currently compete with advanced electrochemical batteries in applications that require high specific energy and power. Advances in a complete flywheel battery include weight reductions and efficiency improvements of bearings and power conditioning devices. Advances are also promised by a better understanding of the time-dependent stress/strain behavior in the composite flywheel rotor, and the ability to accurately predict such behavior under operational loads. Rotor models that account for time-dependent effects can be used to prevent creep rupture or undesirable levels of deformation, which both ultimately limit the amount of stored energy in a flywheel. The derivation and preliminary verification of a plane-stress time-dependent model of anisotropic multiple-ring assemblies under interference and rotational loads is described here. This model is based on the elastic-viscoelastic correspondence principle and is shown to match an accepted viscoelastic solution for an anisotropic ring under internal pressurization. A comparison of the viscoelastic model predictions with previous experimental results for press-fit pressure loss of several polymer composite ring pair assemblies is also presented.