Methods for Making Reinforced Composite Flywheels and Shafts

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The maximum safe operating speed of flywheels and shafts made of low tensile strength material is often determined by the speed at which radial tensile stress exceeds stress limit for the material. In the field of electrical pulsed power generation, generators with increased power and energy storage capability are needed to satisfy a host of new applications. Laboratory electromagnetic accelerator experiments, such as impact fusion studies, require reliable high energy sources, while other concepts, such as space launchers, demand stored energies in the gigajoule range. Conventionally used steel flywheels, while improving the performance of generators, are limited due to their weight and relatively low maximum permissible tip speeds.

Flywheels are attached to the rotors of pulsed power generators to increase energy storage capabilities. Flywheels function as reservoirs which store rotational kinetic energy. As energy is withdrawn from a spinning flywheel, its angular speed decreases; as energy is being supplied to a spinning flywheel, its angular speed increases. Composite materials, such as epoxy-reinforced graphite fibers, have specific strengths about ten times greater than steel. Due to the high flywheel rim velocity and the impulsive nature of the flywheel deceleration, the construction of the flywheel is of critical importance to achieving the maximum energy density and discharge speed for the generator.


  • Spun at higher speeds than conventional flywheels
  • Achieve higher specific energy storage
  • Achieve higher power generation capabilities
  • Require little machining prior to use
  • Last longer, work harder, and are more efficient
  • Have uniform stress distribution (pressure uniform along contact length)


  • The outer ring is assembled onto the inner ring and dimensioned for a tapered interference fit to provide radial compressive pre-stress
  • Assembled from radially thin concentric rings of fiber composite material with bonding agent under pressure until the agent solidifies
  • Possible to obtain a radial compressive stress in all of the rings and a tangential compressive stress in all but the outer ring (preferred for safest possible operating speed)

Market Potential/Applications

Invention may be used to pre-stress other low tensile strength material for example, ceramics for use in a flywheel or shaft. It can be used as support banding for weak underlying structures.

For further information please contact

University of Texas,
Austin, USA
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