San Diego Composites Inc. (SDC, San Diego, Calif., USA) reports that it has developed a lightweight composite toroidal pressurant tank using an automated fiber winding process. SDC has been working on an MDA-funded Phase II SBIR effort, overseen by Eddie Japzon, to develop lightweight composite toroidal tanks to provide coolant for next-generation missile defense seekers.

The program has successfully demonstrated the design, analysis, material and process development, prototype fabrication and burst strength of a small-diameter composite toroidal tank. The tank tested was approximately the size of a bagel and burst at a pressure of more than 20,000 psi. The SDC composite toroidal tank design represents a 55 percent weight reduction compared to the baseline metal design for the application. As part of this effort, SDC designed and fabricated an automatic fiber winding machine that improves producibility and quality of the tank by controlling the winding process parameters such as fiber tension and indexing. SDC has also developed the various other materials and processes required to fabricate the tank, such as thin-walled liners, fill tubes, EB welding and resin transfer molding (RTM) curing to make the project successful

On Oct. 5 the first prototype was tested at SDC's high-pressure burst facility to a failure pressure of 21.1 ksi, or 5.5 percent above the design pressure of 20 ksi.

Program Manager Dan Jacobson believes that a key to the programs success included SDC's ability to work through the detailed design and analysis of the composite toroidal tank while in parallel developing the unique automated fiber winding machine. The automated approach resulted in a more producible and lower cost product compared to a hand-wound tank. Hand winding approaches are not desirable due to repeatability differences between tanks which results from variation in winding tension and fiber placement; this adversely affects the tolerances, thicknesses, and performance of the tank. The automated toroidal fiber winding machine solves these problems and produces a consistent product that is more reliable and provides mission assurance to the critical hardware.

The company says the technology is applicable to other applications and scalable. SDC is confident that this winding method can be used for geometries ranging from 4 inches/102 mm to more than 24 inches/610 mm. SDC proposes to leverage this work to apply the technology to multiple applications in the aerospace and commercial markets.