2008

Self-Deploying Trusses Containing Shape-Memory Polymers

Compacted structures can be used in shelters for hostile environments.

Composite truss structures are being developed that can be compacted for stowage and later deploy themselves to full size and shape. In the target applications, these “smart” structures will precisely self-deploy and support a large, lightweight space-based antenna. Self-deploying trusses offer a simple, light, and affordable alternative to articulated mechanisms or inflatable structures. The trusses may also be useful in such terrestrial applications as variable-geometry aircraft components or shelters that can be compacted, transported, and deployed quickly in hostile environments.

The truss technology uses high-performance shape-memory-polymer (SMP) thermoset resin reinforced with fibers to form a helical composite structure. At normal operating temperatures, the truss material has the structural properties of a conventional composite. This enables truss designs with required torsion, bending, and compression stiffness. However, when heated to its designed glass transition temperature (Tg), the SMP matrix acquires the flexibility of an elastomer. In this state, the truss can be compressed telescopically to a configuration encompassing a fraction of its original volume.

Image
Activation Sequence of an early prototype self-deploying truss shows one one-minute duration fromcompressed [2.5 in. (6.4 cm)] to deployed [28.5 in. (72.4 cm)].
When cooled below Tg, the SMP reverts to a rigid state and holds the truss in the stowed configuration without external constraint. Heating the materials above Tg activates truss deployment as the composite material releases strain energy, driving the truss to its original “memorized” configuration without the need for further actuation. Laboratory prototype trusses have demonstrated repeatable self-deployment cycles following linear compaction exceeding an 11:1 ratio (see figure).

While this new truss technology exhibits some functionality similar to that of cold hibernated elastic memory (CHEM) structures developed in other NASA-sponsored research (previously reported in NASA Tech Briefs), there are important distinctions. First, the CHEM SMP is based on a thermoplastic resin, while the new truss material’s high-performance SMP is a fully cured thermoset resin. The high-performance SMP molecular design has been implemented in a variety of resin systems, enabling resin selection for desired structural properties while enabling selection of a required Tg (e.g., 25–225 °C achievable in high-performance SMPs based on cyanate ester). Also, CHEM-based structures use unreinforced foam as the active component. In the new composite truss design, the high-performance SMP is integral to the structure, simplifying the design and increasing the savings in mass, cost, and system complexity. Structures employing high-performance SMP are fabricated using the same processes as conventional composites. The composite structure’s mechanical properties at temperatures below Tg are unaffected by repeated stowage-deployment cycles.

This work was done by Robert M. Schueler of Cornerstone Research Group, Inc. for Glenn Research Center. Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-17982-1.

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