A methodology has been presented for deploying flexible, freeform structures with lattice skins as the deployment mechanism. In this paper, the focus has been primarily on the methodology for generating lattice structures and optimizing them so that the deployable structure maintains its profile after deployment. A ground structure approach for topology optimization of the lattice structure has been presented and applied to a representative, deployable UAV wing. By adjusting the lattice structure density and configuration, the topology optimization procedure resulted in a 78 percent improvement in maximum surface deviation when compared with a nonoptimized structure. The proposed ground structure approach penalizes lattice elements of non-manufacturable thicknesses, resulting in lattice structure topologies that meet manufacturabihty requirements while minimizing surface displacement as much as possible. A physical prototype of the structure was fabricated with SLS and Duraform FLEX material. It was successfully folded into a package with a maximum dimension of 120 mm, relative to a maximum dimension of 380 mm for the deployed wing. When coupled with prior feasibility studies, these results provide additional proof of concept for the use of lattice skins as deployment mechanisms. Opportunities for ongoing work include increasing the comprehensiveness of the topology optimization procedure and formalizing post-processing steps for infiltrating and rigidizing deployed parts. For the UAV airfoil, the topology optimization procedure is performed in two dimensions for cross-sections of the lattice skin and then periodically repeated in the span direction. In future work, the lattice skin needs to be designed in three dimensions with characteristics such as fold-ability taken into account. For large structures, it may be necessary to reduce computational complexity by continuing to design the lattice skin in spatial segments, but more systematic methods for decomposing the problem are needed. It would also be interesting to include shape optimization of the concentric skins and lattice structure, in addition to the topology design procedure. With respect to post-processing, repeated infiltration with polyurethane appears to provide adequate short-term air tightness for pneumatic inflation, but further work is needed to identify thermoset polymers or other spray-on materials for rigidization and long-term stability of the deployed structure. Finally, it would be interesting to explore the possibility of virtually collapsing parts and fabricating them in their collapsed form, as a replacement for the current process of decomposing large parts into manufacturable pieces.
Topology design and freeform fabrication of deployable structures with lattice skins
Rapid Prototyping Journal ; 17 , 1 ; 5-16
2011
12 Seiten, 15 Bilder, 5 Tabellen, 40 Quellen
Aufsatz (Zeitschrift)
Englisch
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