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Oak Ridge Center Claims World-Record For Highest Composite Hoop Strength

OAK RIDGE, Tenn., Sep. 5, 1997 — A composite cylinder believed to hold the record for having the highest recorded hoop tensile strength for its class of materials has been fabricated by the Center for Composites Manufacturing at the U.S. Department of Energy's (DOE)'s Oak Ridge Centers for Manufacturing Technology and the Oak Ridge National Laboratory (ORNL).

The wet-filament wound cylinder formed from carbon fiber and a polycyanate resin achieved an average hoop (circumferential) tensile strength of 673 Ksi (4,640 Mpa) with a 4.3 percent coefficient of variation.

Three of the ten test rings from the cylinder had individual strengths greater than 700 Ksi (4,826 Mpa). This compares with the ultimate tensile strength of ultra-high strength steel which is only 311 Ksi (2,144 Mpa). In addition, the density of the carbon fiber composites is nearly one-fifth that of the steel's density.

The cylinder had a nominal inner diameter of 24-in. (610 mm) and a wall thickness of 0.125-in. (3.18 mm). Ring testing was accomplished using "split-D" tensile fixtures and procedures that are based on the ASTM D2290 (NOL) method.

The measured hoop strengths are considered conservative. The true material strength of the cylinder may actually be higher because of the additional bending stresses the D-fixtures impose on the ring during testing, according to Barbara Frame, a member of the development staff at the Center for Composites Manufacturing.

Applications for strong, lightweight composite cylinders and rings include high speed rotating hardware such as energy storage flywheels. Higher hoop strength materials are important because they enable flywheels to be operated at higher rotational speeds.

Increasing the flywheel's speed increases its energy density, or the amount of energy that can be stored and recovered per its unit weight, thereby increasing the efficiency and cost effectiveness of the flywheel, Frame said.

The polycyanate resin matrix provides high temperature stability, low outgassing, low water absorption and radiation resistance. Potential applications for these composite materials include flywheel energy storage systems for space and satellite structures.

ORCMT integrates the manufacturing expertise of the Oak Ridge Y-12 Plant and the research and development activities of Oak Ridge National Laboratory and is a major national resource for manufacturing and prototyping technologies. The Y-12 Plant is managed by Lockheed Martin Energy Systems for the DOE. Oak Ridge National Laboratory is managed by Lockheed Martin Energy Research Corporation.