Lightweight, inflatable tubular structural components containing tape-spring reinforcements are undergoing development. The basic (without tape-spring reinforcement) tubular components are made, variously, of aluminum laminates or composite materials and are under consideration for use in erecting structures in outer space. They could also be used to erect structures for terrestrial applications in situations in which a greater value is placed in light weight than on strength.

Two types of tape-spring reinforcements have been conceived for this purpose: longitudinal and circumferential. Longitudinal tape-spring reinforcements are made from strips of spring steel or other high-modulus materials with curved cross sections, such as the type of spring strips used commonly in compactly stowable carpenters' measuring tapes. The reinforcements would exploit the well known nonlinear mechanical responses of such tapes, namely: (1) high resistance to buckling while they are straight, (2) the ease with which they can be rolled up once they have been initially flattened, and (3) much stronger resistance to bending or buckling toward the concave-side-out configuration than toward the concave-side-in configuration.

Usually, a thin-wall tube buckles inward first. If one attaches longitudinal curved-cross-section tape springs to the inside of a thin-wall tube at several circumferential positions and orients them with their concave sides facing toward the interior, then the tape-springs help to restrain the tube against inward buckling while the tube helps to restrain the tapes against outward buckling. The net effect is a large increase in the load-bearing capacity of the reinforced tube.

Because the stiffness of a tape-spring decreases as its length increases, it has been proposed to add circumferential reinforcing tape-springs, or other forms of circumferential reinforcement, to long tubes for certain applications. Circumferential reinforcing tape-springs would be fabricated as straight, thin, flat strips. They would be attached to the insides of the tubes. The circumferential reinforcements would also serve as hard attachment points for tubes subjected to lateral loading.

This work was done by Houfei Fang and Michael Lou of Caltech for NASA's Jet Propulsion Laboratory . For further information, access the Technical Support Package (TSP) free on-line at  under the Mechanics category. NPO-20615

This Brief includes a Technical Support Package (TSP).
Tape-Spring Reinforcements for Inflatable Structural Tubes

(reference NPO-20615) is currently available for download from the TSP library.

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This article first appeared in the July, 2000 issue of NASA Tech Briefs Magazine.

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