抄録
Reliability analysis was conducted for the static fracture of circumferentially wound FRP flywheels. The carbon-epoxy and the glass-epoxy flywheels were considered. The probability of failure Pf was calculated assuming that both the longitudinal (circumferential) and transverse (radial) strengths have a two-parameter Weibull distribution and that failure obeys the maximum tensile stress criterion. Residual stresses were taken into consideration. The energy density ew (stored energy per unit weight) was evaluated as a function of Pf. The relation between Pf and the factor of safety was also examined. The principal results are summarized as follows.
(1) The energy density ew decreases with a decrease in the allowable value of Pf. This tendency gets stronger as the ratio of the inner radius to the outer radius λ decreases.
(2) The energy density ew for a specified value of Pf decreases as λ decreases. However, since the influence of λ is not large when λ_??_0.9, λ≅0.9 is close enough to satisfying the optimal design condition.
(3) The energy density ew for a specified value of Pf decreases with a decrease in mθ and mr, which are the shape parameters of the longitudinal and transverse strength distributions, respectively. The influence of mθ is remarkable when λ is large, and that of mr becomes stronger as λ decreases.
(4) When λ is small, the energy density ew of the glass-epoxy flywheel for a specified value of Pf can be higher than that of the carbon-epoxy flywheel. This is due to the presence of residual stress.
(5) The radial safety factor Sfr is considerably greater than the circumferential safety factor Sfθ when λ=0.9. Even though a state of Sfθ≅Sfr may be ensured for a smaller λ, such a λ will be far from satisfying the optimal design condition.
