University of Texas System

Elvin Estes

John H Gully

W Alan Walls

Steve M Manifold

Michael L Spann

The maximum safe operating speed or flywheels and shafts made of low tensile strength material is often determined by the speed at which radial tensile stress exceeds a radial tensile stress limit for the material. Circumferentially wound fiber composite material, for example, has a relatively low tensile strength along the radial direction perpendicular to the fibers. To increase the maximum safe operating speed, it is therefore desirable to form a fiber composite flywheel or shaft with radial compressive prestress. Such a prestressed flywheel or shaft has an outer annulus and an inner cylinder disposed in the outer annulus, and an annular layer of solidified bonding agent within an annular region between the outer annulus and the inner cylinder, wherein the outer annulus and the inner cylinder include substantial radial prestress induced by the bonding agent. The rim portion of a flywheel, for example, is formed from an outer ring (the annulus) and an inner ring (the cylinder, which is hollow in this case). Large, thick flywheels preferably have multiple cylindrical sections joined by such layers of bonding agent, and a plurality of the cylindrical sections each including an outer layer of relatively stiff fiber-composite material, and an inner layer of relatively compliant fiber-composite material within an integral matrix material.

Reinforced composite flywheels and shafts

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 a radial tensile stress limit for the material. Circumferentially wound fiber composite material, for example, has a relatively low tensile strength along the radial direction perpendicular to the fibers. To increase the maximum safe operating speed, it is therefore desirable to form a fiber composite flywheel or shaft with radial compressive prestress. Such a prestressed flywheel or shaft is made by placing a cylinder within a fiber composite annulus, injecting a bonding agent under pressure into the interface between the annulus and the cylinder, and maintaining the bonding agent under pressure while the bonding agent solidifies. Preferably, the cylinder and annulus are aligned in a concentric relationship during solidification by a chamber into which the cylinder and annulus are placed. The rim portion of a flywheel, for example, is formed from an outer ring (the annulus) and an inner ring (the cylinder, which is hollow in this case). The chamber is defined by a pair of plates which abut opposite faces of the rings, and by two concentric cylinders which limit the radial movement of the rings as the rings expand or contract, respectively, in response to the pressure of the bonding agent. The bonding agent is preferably a mixture of epoxy resin and chopped fiber or other randomly oriented epoxy reinforcing material.

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Austin, TX, United States of America

Elvin Estes