Monday, 19 October 2020 Speaker: Dr. Emmanuel Siéfert The Racah Institute of Physics, Hebrew University of Jerusalem Inflating to shape: from soft architectured elastomers to patterned fabric sheets

Abstract

Shape-morphing structures are at the core of future applications in aeronautics, minimally invasive surgery and smart materials. In this talk, I will present two strategies consisting in programming slender morphing inflatables structures. A first strategy consists in manufacturing elastomeric plates embedding a network of channels, which expand when inflated mainly perpendicular to their local orientation, similarly to simple elastic tubes. Playing with both the orientation and density of channels, the direction and intensity of the in-plane homogenized “growth” may be programmed, in general incompatible with a flat geometry. The structure spontaneously buckles and adopts a shape, which minimizes its elastic energy. In the case of very thin plates, an analytic method is proposed to solve the general inverse problem. In a second part, I will present structures made of two superimposed inextensible thin sheets, sealed together along a specific line network. Starting with flat curved ribbons, i.e the case of the popular mylar balloon letters, we observe and rationalize the surprising overcurvature upon inflation, as well as the wrinkle pattern. Extending the system to two-dimensional patterned structures, the local in-plane contraction upon inflation may be oriented along a director field, similarly to liquid crystal elastomers. We program the morphing of such stiff inflatable structures and investigate their mechanics.

Biography

Dr. Emmanuel Siéfert is currently a Lady Davis postdoctoral researcher at the Hebrew University of Jerusalem, in the Racah Institute of Physics, working with Prof. Eran Sharon on the shape selection and fracture of geometrically frustrated sheets. Prior to that, he did his PhD in Mechanics in the PMMH laboratory under the supervision of José Bico and Benoît Roman, studying the geometry and mechanics of architectured sheets actuated by inflation. He was awarded from Sorbonne Université in 2019. He studied solid and fluid mechanics in Polytechnique and at the Technical University of Munich and did his master research at MIT on bouncing droplets under the supervision of Prof. John Bush.

Notes

• In this work, a different actuation method is developed based on the inflation of cavities inside the structure.


• These new kind of prototyping technologies open new posibilities to design and manufacture engineering structures that have interesting applications in the future e.g. soft medical applications, shape-morphing furniture and architecture.


• Baromorph elastomers presented in this study are pneumatic shape-morphing structures made of stretchable material embedding a specific network of channels that encodes the target 3D shape by means of localized, anisotropic in-plane deformation by applying pressure.


• A different strategy to produce shape-morphing inflatables has been investigated, based on the constrained volume optimization of quasi-inextensible fabric sheets to program complex and stiff quasi-1D and 3D shapes.

Suggested readings

• Siéfert, E., Reyssat, E., Bico, J., & Roman, B.
  Bio-inspired pneumatic shape-morphing elastomers.
  Nature materials 18(1), 24-28, 2019.


• Siéfert, E., Reyssat, E., Bico, J., & Roman, B.
  Programming curvilinear paths of flat inflatables.
  Proceedings of the National Academy of Sciences 116(34), 16692-16696, 2019.


• Siéfert, E., & Warner, M.
  Inflationary routes to Gaussian curved topography.
  Proceedings of the Royal Society A 476(2240), 20200047, 2020.


• Siéfert, E., Reyssat, E., Bico, J., & Roman, B.
  Programming stiff inflatable shells from planar patterned fabrics
  Soft Matter 16(34), 7898-7903, 2020.


• Guseinov, R., McMahan, C., Pérez, J., Daraio, C., & Bickel, B.
  Programming temporal morphing of self-actuated shells.
  Nature communications 11(1), 1-7, 2020.


• Bauhofer, A. A., Krödel, S., Rys, J., Bilal, O. R., Constantinescu, A., & Daraio, C.
  Harnessing photochemical shrinkage in direct laser writing for shape morphing of polymer sheets.
  Advanced Materials 29(42), 1703024, 2017.

LMS seminars on related topics

• 25/06/2020, Prof. Paolo Celli, From patterned sheets to functional morphing structures