From Materials Selection in Mechanical Design, Third Edition

6.6 Materials for Flywheels

Flywheels store energy. Small ones the sort found in children's toys are made of lead. Old steam engines have flywheels; they are made of cast iron. Cars have them too (though you cannot see them) to smooth power-transmission. More recently flywheels have been proposed for power storage and regenerative braking systems for vehicles; a few have been built, some of high-strength steel, some of composites. Lead, cast iron, steel, composites there is a strange diversity here. What is the best choice of material for a flywheel?

An efficient flywheel stores as much energy per unit weight as possible. As the flywheel is spun up, increasing its angular velocity, ?, it stores more energy. The limit is set by failure caused by centrifugal loading: if the centrifugal stress exceeds the tensile strength (or fatigue strength), the flywheel flies apart. One constraint, clearly, is that this should not occur.

The flywheel of a child's toy is not efficient in this sense. Its velocity is limited by the pulling-power of the child, and never remotely approaches the burst velocity. In this case, and for the flywheel of an automobile engine we wish to maximize the energy stored per unit volume at a constant (specified) angular velocity. There is also a constraint on the outer radius, R, of the flywheel so that it will fit into a confined space.

The answer therefore depends on the application. The strategy for optimizing...

Products & Services
Flywheels have a high mass and are connected to a rotating shaft that smoothes the delivery of torque, or turning power, from a motor or engine. The inertia of flywheels allows them to absorb and release energy with little change in speed.
Flywheel Power Systems
Flywheel power systems are flywheel rotors with integrated motor / generators contained inside a housing. They store energy mechanically in the form of kinetic energy.
Mechanical Brakes
Mechanical brakes convert kinetic energy to other energy forms, primarily heat. They decelerate shafts and linked components via friction between a rotating body and wear-resistant material.
Alternative Power Generators
Alternative power generators produce electricity from renewable energy sources, such as wind, flowing water, solar energy and biomass, which create less environmental damage and pollution than fossil fuels.
Power Take-offs (PTO)
Power take-offs (PTOs) are extensions of a vehicle's drive train that can be engaged to power auxiliary equipment such as plows, augers, winches, and many other material handling, construction, and agricultural implements.

Topics of Interest

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A flywheel is an energy storage device. It absorbs mechanical energy by increasing its angular velocity and delivers energy by decreasing its angular velocity. Commonly, the flywheel is used to smooth...

After years of being billed as the next great revolutionary means of propulsion, flywheels may finally be ready for prime time. Prototype flywheels for space missions are under study at NASA's Glenn...

Introduction Kinetic energy from flywheels has been in use for a variety of stabilizers and UPS units in the past. Stabilizers with a short ride-through period consisting of a motor flywheel and...

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