Compliant morphing structures from twisted bulk metallic glass ribbons. (December 2020)

• Record Type: Journal Article
• Authors: Celli, P.; Lamaro, A.; McMahan, C.; Bordeenithikasem, P.; Hofmann, D.C.; Daraio, C.
• Is Part Of: Journal of the mechanics and physics of solids. Volume 145(2020)
• Publication Date: 2020-12
• Subjects: Ribbons -- Bulk metallic glass -- Deployability -- Compliant structures -- Morphing structures -- Torsion -- Shells; Mechanics, Applied -- Periodicals; Solids -- Periodicals; Mechanics -- Periodicals; Mécanique appliquée -- Périodiques; Solides -- Périodiques; Mechanics, Applied; Solids; Periodicals; 531.05
• DOI: 10.1016/j.jmps.2020.104129
• Languages: English
• ISSNs: 0022-5096

Abstract

Abstract: 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.