Design and optimization of a material property distribution in a composite flywheel

The material properties of a fiber reinforced plastic laminate can be tailored for a given structure and loading by continuously varying the direction of the fiber through-out the plies. Here, it is shown that adding such a material property distribution to a thick-radius, composite flywheel can improve performance. A flywheel made from alternating plies of purely circumferential and purely radial reinforcement is designed as the performance benchmark. A second flywheel, substituting plies with a continuous fiber angle variation for the purely radial plies, is investigated. It is shown that the design of the fiber angle distribution can be formulated as an optimal control problem incorporating Classical Lamination Theory to describe the constitutive behavior and the Tsai-Wu failure criteria to predict failure of the flywheel laminate. The effects of the matrix properties on performance are also investigated. Numerical simulation indicates a 13% increase in energy density for the optimized flywheel over the benchmark flywheel. To demonstrate the feasibility of manufacture, automated ply layup machines are developed that are capable of producing the necessary carbon fiber plies. Experimentally determined material properties are used to re-run the optimization routine then prototype benchmark and optimized flywheel are constructed. Tangential strain measurements confirm that the separate flywheels have different material properties suggestive of those found in the analysis.