background image
We turned this approach around and used a spatially
uniform temperature which is easier to apply and
then exploited the ability of different materials to
internally control their rate of shape change through
their molecular design.ˇ±
The team demonstrated the approach with a series
of examples including a mechanism that can be
switched from a flat strip into a locked configura-
tion as one end controllably bends and threads itself
through a keyhole. They also demonstrated a flat
sheet that can fold itself into a 3-D box with inter-
locking flaps. These examples all require the precise
control of the folding sequence of different parts of
the structure to avoid collisions of the components
during folding.
ˇ°We have exploited the ability to 3-D print smart
polymers and integrate as many as ten different
materials precisely into a 3-D structure,ˇ± said Martin L. Dunn, a professor
at Singapore University of Technology and Design who is also the director
of the SUTD Digital Manufacturing and Design Centre. ˇ°We are now extend-
ing this concept of digital SMPs to enable printing of SMPs with dynamic
mechanical properties that vary continuously in 3-D space.ˇ±
The team used companion finite element simulations to predict the re-
sponses of the 3-D printed components, which were made from varying
ratios of two different commercially-available shape-memory polymers. A
simplified reduced-order model was also developed to rapidly and accu-
rately describe the physics of the self-folding process.
ˇ°An important aspect of self-folding is the management of self-collisions,
where different portions of the folding structure contact and then block
further folding,ˇ± the researchers said in their paper. ˇ°A metric is developed
to predict collisions and is used together with the reduced-order model
to design self-folding structures that lock themselves into stable desired
configurations.ˇ±
The research team envisions a broad range of applications for their tech-
nology. For example, an unmanned air vehicle might change shape from
one designed for a cruise mission to one designed for a dive. Also possible
would be 3-D components designed to fold flat or be rolled up into tubes so
they could be easily transported, and then later deformed into their intend-
ed 3D configuration for use.
In addition to those already mentioned, the research also involved co-au-
thor Yiqi Mao, and three other Georgia Tech collaborators: Kai Yu, Michael
Isakov and Jiangtao Wu. (Article continued on page 3 >>>)
4-D Printing Technology Comes To Life
Smart shape memory polymers enable self-folding of complex objects
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Using components made from shape-memory
materials with slightly different responses to
heat, researchers have demonstrated a four-
dimensional printing technology allowing cre-
ation of complex self-folding structures
September 21, 2015, Atlanta, GA: Technology,
developed by researchers at the Georgia Institute of
Technology and the Singapore University of Tech-
nology and Design (SUTD), could be used to create
3-D structures that sequentially fold themselves
from components that had been flat or rolled into a
tube for shipment. The components could respond
to stimuli such as temperature, moisture or light in
a way that is precisely timed to create space struc-
tures, deployable medical devices, robots, toys and
a wide range of other structures.
The researchers used smart shape memory poly-
2015 OCTOBER #6-9
mers (SMPs) with the ability to remember one shape and change to an-
other programmed shape when uniform heat is applied. The ability to create
objects that change shape in a controlled sequence over time is enabled
by printing multiple materials with different dynamic mechanical properties
in prescribed patterns throughout the 3-D object. When these components
are then heated, each SMP responds at a different rate to change its shape,
depending on its own internal clock. By carefully timing these changes, 3-D
objects can be programmed to self-assemble.
The research was reported September 8 in the journal Scientific Reports,
which is published by Nature Publishing. The work is funded by the U.S. Air
Force Office of Scientific Research, the U.S. National Science Foundation
and the Singapore National Research Foundation through the SUTD DManD
Centre.
The research creates self-folding structures from 3-D printed patterns con-
taining varying amounts of different smart shape-memory polymers. The
patterning, done with a 3-D printer, allows the resulting flat components
to have varying temporal response to the same stimuli. Earlier methods
required application of differential heating at specific locations in the flat
structure to stimulate the shape changes.
ˇ°Previous efforts to create sequential shape changing components involved
placing multiple heaters at specific regions in a component and then control-
ling the on-and-off time of individual heaters,ˇ± explained Jerry Qi, a profes-
sor in the George W. Woodruff School of Mechanical Engineering at Georgia
Tech. ˇ°This earlier approach essentially requires controlling the heat applied
throughout the component in both space and time and is complicated.
Image shows the self-folding process of smart
shape-memory materials with slightly different
responses to heat. Image credit: Qi Laboratory