Evaluation and enhancement of radial tensile strength of composite rotors for energy storage

Abstract This study focused on the measurement and improvement of the radial tensile strength of composite rotors for flywheel energy storage. Filament wound carbon/epoxy composite rotors were fabricated and the radial tensile strength was measured using uniaxial tensile testing of coupons extracted from a thick rotor and diametric tensile testing of C‐rings. Compared to the uniaxial tensile test, the C‐ring test resulted in a reasonably accurate measurement of the radial tensile strength due to the absence of the effect of the curved fibers. Numerical analyses of C‐ring tests were also performed. The results matched well with the experiments and confirmed the failure of C‐rings purely because of the radial stress. The incorporation of multi‐walled carbon nanotubes in the composite rotor resulted in cohesive failure of fiber and matrix and increased the radial tensile strength by a maximum of 50%. The findings provided unique insights for accurate measurement and improvement of the radial tensile strength of composite rotors. Highlights Composite rotors were filament wound and radial tensile strength was measured. Radial tensile strength of C‐ring was accurate than that of tensile coupon. FEA of the C‐ring test validated the experimental radial tensile strength. Incorporation of MWCNT increased the radial tensile strength by 50%. Fractography showed cohesive failure indicating strong reinforcement by MWCNT.