Prestressed thick flywheel rims

A homogeneous fiber composite flywheel rim has a radial tensile stress distribution when spinning about its axis of cylindrical symmetry. A circ-wound rim is ideally suited to support the very high hoop stresses, but it can only support very low radial tensile stresses. This limits the allowable rim inside-to-outside radius ratio so that the energy stored per unit volume is low. It would be desirable to have relatively thicker rims with no radial tensile stresses at the ultimate design speed for hoop stress failure. The methods for calculating the prestress produced by a given schedule of winding tensions are given. The significant parameters to be controlled in the fabrication process are presented. Some tension schedules for balancing the radial rotational stress in rims of a specific size and material are also presented. Experimental development of prestress conditions in small scale test ring demonstrates the capability to achieve prestress levels that can effectively eliminate radial tensile stress in the composite thick rim. Successful experimental development led to the fabrication of a full scale prestressed flywheel rim and utilization of that rim in the Oak Ridge Y-12 Plant FY 1977 flywheel test package.