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Published December 2020 | Submitted
Journal Article Open

Compliant morphing structures from twisted bulk metallic glass ribbons


In this work, we investigate the use of pre-twisted metallic ribbons as building blocks for shape-changing structures. We manufacture these elements by twisting initially flat ribbons about their (lengthwise) centroidal axis into a helicoidal geometry, then thermoforming them to make this configuration a stress-free reference state. The helicoidal shape allows the ribbons to have preferred bending directions that vary throughout their length. These bending directions serve as compliant joints and enable several deployed and stowed configurations that are unachievable without pre-twist, provided that compaction does not induce material failure. We fabricate these ribbons using a bulk metallic glass (BMG), for its exceptional elasticity and thermoforming attributes. Combining numerical simulations, an analytical model based on a geometrically nonlinear plate theory and torsional experiments, we analyze the finite-twisting mechanics of various ribbon geometries. We find that, in ribbons with undulated edges, the twisting deformations can be better localized onto desired regions prior to thermoforming. Finally, we join multiple ribbons to create deployable systems with complex morphing attributes enabled by the intrinsic chirality of our twisted structural elements. Our work proposes a framework for creating fully metallic, yet compliant structures that may find application as elements for space structures and compliant robots.

Additional Information

© 2020 Elsevier Ltd. Received 29 April 2020, Revised 3 August 2020, Accepted 21 August 2020, Available online 24 August 2020. This research was carried out at the California Institute of Technology and the Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration, and funded through the President's and Director's Fund Program. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement by the United States Government or the Jet Propulsion Laboratory, California Institute of Technology. PC and CD acknowledge support from the Foster and Coco Stanback Space Innovation Fund. This work was also supported by a NASA Space Technology Research Fellowship to CM. We thank Michael Mello for helping with material characterization and for fruitful discussions. We thank Basile Audoly and Paolo Ermanni for helpful suggestions, and Brian Ramirez, Sharan Injeti, Hao Zhou, Cristina Naify and Giordano Bellucci for useful discussions. CRediT authorship contribution statement: P. Celli: Conceptualization, Investigation, Methodology, Formal analysis, Supervision, Writing - original draft. A. Lamaro: Investigation, Methodology, Formal analysis, Writing - review & editing. C. McMahan: Investigation, Methodology, Formal analysis, Writing - original draft. P. Bordeenithikasem: Investigation, Methodology, Resources, Writing - review & editing. D.C. Hofmann: Conceptualization, Resources, Funding acquisition. C. Daraio: Conceptualization, Funding acquisition, Supervision, Writing - review & editing. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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