Improving Radial Integrity of Flywheel Composite Rotors: Numerical Analysis of Designs and Experimental Evaluation of Reinforcements

ABSTRACT The present study focused on improving the radial integrity of flywheel composite rotors, which is a critical parameter in flywheel design. Four different rotor designs—consisting of different resins, concentric elastomer composite interlayers, gradient fiber volume fraction and radial reinforcement were numerically analyzed. The rotor with radial reinforcement was found the most promising due to its significantly high radial integrity and practical feasibility. Subsequently, two reinforcement approaches were experimentally studied for the first time: the incorporation of milled carbon fiber (MCF) for multidirectional reinforcement and the unique stitching pattern, specifically for radial reinforcement. The incorporation of MCF improved the radial tensile strength and energy density by a maximum of 37% and 15%, respectively. The fracture analysis showed cohesive failure involving residual resin attachments, MCF pull outs and remnant impressions of fibers confirming additional reinforcement by MCF. The unique radially stitched rotor did not delaminate completely and sustained higher loads under mechanical tests. Under multi‐step loading tests, it retained almost 100% stiffness without any stiffness loss due to the delamination propagation resistance provided by the stitches. The findings provided promising methods for improving the radial integrity of flywheel composite rotors.