59,166 research outputs found
Programming complex shapes in thin nematic elastomer and glass sheets
Nematic elastomers and glasses are solids that display spontaneous distortion
under external stimuli. Recent advances in the synthesis of sheets with
controlled heterogeneities have enabled their actuation into non-trivial shapes
with unprecedented energy density. Thus, these have emerged as powerful
candidates for soft actuators. To further this potential, we introduce the key
metric constraint which governs shape changing actuation in these sheets. We
then highlight the richness of shapes amenable to this constraint through two
broad classes of examples which we term nonisometric origami and lifted
surfaces. Finally, we comment on the derivation of the metric constraint, which
arises from energy minimization in the interplay of stretching, bending and
heterogeneity in these sheets
Patterning nonisometric origami in nematic elastomer sheets
Nematic elastomers dramatically change their shape in response to diverse
stimuli including light and heat. In this paper, we provide a systematic
framework for the design of complex three dimensional shapes through the
actuation of heterogeneously patterned nematic elastomer sheets. These sheets
are composed of \textit{nonisometric origami} building blocks which, when
appropriately linked together, can actuate into a diverse array of three
dimensional faceted shapes. We demonstrate both theoretically and
experimentally that: 1) the nonisometric origami building blocks actuate in the
predicted manner, 2) the integration of multiple building blocks leads to
complex multi-stable, yet predictable, shapes, 3) we can bias the actuation
experimentally to obtain a desired complex shape amongst the multi-stable
shapes. We then show that this experimentally realized functionality enables a
rich possible design landscape for actuation using nematic elastomers. We
highlight this landscape through theoretical examples, which utilize large
arrays of these building blocks to realize a desired three dimensional origami
shape. In combination, these results amount to an engineering design principle,
which we hope will provide a template for the application of nematic elastomers
to emerging technologies
Porous composite with negative thermal expansion obtained by photopolymer additive manufacturing
Additive manufacturing (AM) could be a novel method of fabricating composite
and porous materials having various effective performances based on mechanisms
of their internal geometries. Materials fabricated by AM could rapidly be used
in industrial application since they could easily be embedded in the target
part employing the same AM process used for the bulk material. Furthermore,
multi-material AM has greater potential than usual single-material AM in
producing materials with effective properties. Negative thermal expansion is a
representative effective material property realized by designing a composite
made of two materials with different coefficients of thermal expansion. In this
study, we developed a porous composite having planar negative thermal expansion
by employing multi-material photopolymer AM. After measurement of the physical
properties of bulk photopolymers, the internal geometry was designed by
topology optimization, which is the most effective structural optimization in
terms of both minimizing thermal stress and maximizing stiffness. The designed
structure was converted to a three-dimensional STL model, which is a native
digital format of AM, and assembled as a test piece. The thermal expansions of
the specimens were measured using a laser scanning dilatometer. The test pieces
clearly showed negative thermal expansion around room temperature.Comment: 11 pages, 4 figure
On the consistency of Fr\'echet means in deformable models for curve and image analysis
A new class of statistical deformable models is introduced to study
high-dimensional curves or images. In addition to the standard measurement
error term, these deformable models include an extra error term modeling the
individual variations in intensity around a mean pattern. It is shown that an
appropriate tool for statistical inference in such models is the notion of
sample Fr\'echet means, which leads to estimators of the deformation parameters
and the mean pattern. The main contribution of this paper is to study how the
behavior of these estimators depends on the number n of design points and the
number J of observed curves (or images). Numerical experiments are given to
illustrate the finite sample performances of the procedure
The kinematics of hyper-redundant robot locomotion
This paper considers the kinematics of hyper-redundant (or “serpentine”) robot locomotion over uneven solid terrain, and presents algorithms to implement a variety of “gaits”. The analysis and algorithms are based on a continuous backbone curve model which captures the robot's macroscopic geometry. Two classes of gaits, based on stationary waves and traveling waves of mechanism deformation, are introduced for hyper-redundant robots of both constant and variable length. We also illustrate how the locomotion algorithms can be used to plan the manipulation of objects which are grasped in a tentacle-like manner. Several of these gaits and the manipulation algorithm have been implemented on a 30 degree-of-freedom hyper-redundant robot. Experimental results are presented to demonstrate and validate these concepts and our modeling assumptions
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