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 www.nasatech.com/tsp 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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Overview
The document discusses the development of lightweight, inflatable tubular structural components reinforced with tape-spring technology, primarily for applications in outer space. The innovation aims to enhance the load-carrying capabilities of aluminum or composite tubes, which are limited in thickness and diameter due to the requirements for inflation. Traditional designs focused solely on the tube itself, which restricted their ability to support significant loads.
The key innovation involves embedding axial and circumferential tape-springs within the aluminum or composite tubes. Axial tape-springs are thin-wall elastic strips with a curved cross-section, while circumferential tape-springs have a flat cross-section. This combination allows the structure to resist buckling more effectively. The tape-springs provide reinforcement in both longitudinal and circumferential directions, dramatically increasing the buckling load capacity of the tubes.
The document highlights that the behavior of tape-springs is highly non-linear; they are easy to roll up when bent but resist buckling when straight. This unique property makes them ideal for reinforcing inflatable structures, as they can maintain structural integrity while being lightweight. Additionally, the use of damping materials between the tube and the tape-spring can help control the dynamic behavior of the structure, further enhancing its performance.
The invention does not require stretching the aluminum beyond its yielding point, which means that the inflation pressure needed is significantly lower than in previous designs. The gas used in this system is primarily for controlling deployment and eliminating wrinkles, making the overall design more efficient and practical for use in space.
The document also emphasizes the potential applications of this technology in constructing inflatable structures in space, where traditional materials and methods may not be feasible. By combining tape-spring reinforcements with advanced materials, this innovation represents a significant advancement in the field of aerospace engineering and structural design.
Overall, the document outlines a promising approach to creating robust, lightweight, and inflatable structures that could be utilized in various challenging environments, particularly in space exploration and construction.
