A Symmetric Angle-Ply Composite Flywheel for High-Speed Energy Storage

This study was conducted to investigate the stress, strain, and strength ratio distributions in the composite flywheel rotor for high-energy density storage applications. Symmetric laminate design was used to avoid shear and extension-bending coupling and to minimize torsion coupling. The rotor studied consists of four anisotropic unidirectional plies. The continuity conditions of the radial stresses and displacements between plies were used to obtain a local stiffness matrix for each ply and develop the global stiffness matrix for the rotor due to the different ply orientations. The Tsai-Wu three-dimensional (3D) quadratic failure criterion in stress space was used to evaluate the strength ratio of the rings. Analysis was done for ply orientations between [65 deg] S and [685 deg] S. Three specific ply orientations were reported for discussion. The results show how the stress, strain, and safe rotational speed of the flywheel change as the ply orientations are varied. The circumferential stress was found to be the dominant stress. It increases as the ply angle increased in the circumferential direction while the axial stress decreased. Due to significant improvements in composite materials and technology, the results from this study will contribute to further development of the flywheel which has recently reemerged as a promising application for energy storage.