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Nonlinear geometric effects in mechanical bistable morphing structures

zichen's picture


Bistable structures, exemplified
by the Venus flytrap and slap bracelets, can switch between different
functional shapes upon actuation, and have important applications in
mechanical/electro-mechanical devices ranging from bio-inspired robots to
deployable aeroplane wings. Despite numerous efforts in modeling such large
deformation of shell structures, the roles of mechanical and nonlinear geometric
effects on bistability remains elusive. Closely related, emerging challenges
include modeling the spontaneous curving and buckling of thin objects such as
leaves, flowers, nanoscrolls, nanohelices, and film-on-substrate electronics.


This study investigates, through
both theoretical analysis and table-top experiments, the geometric and mechanical
conditions for bistability due to geometric nonlinearity (nonlinear behavior
due to geometric effects). Two dimensionless parameters (one related to both
the mechanical forces and geometry, and the other associated with forces)
control bistability; the aspect ratio also plays a key role (i.e., via edge
effects) in determining the energetic preferences between the two locally
stable states.  This
work classifies the
conditions for bistability, thus defining the design space for bistable
morphing structures, and extends the theory of plates and shells with large
deformation. These results provide a mechanical framework for studying
morphogenesis associated with growth and instability, and facilitate the design
of multi-stable functional structures, from artificial muscles and bio-inspired
robots to deployable, morphing structures in aerospace applications.

This work is to appear in Phys. Rev. Lett. (http://arxiv.org/abs/1206.4739v5)

 

In addition, a movie of such bistable morphing structure can be found at http://youtu.be/m8Opdw7AQUI


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zichen's picture

In addition, a movie of such bistable morphing structure can be found at http://youtu.be/m8Opdw7AQUI.

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