Tech Briefs Magazine - August 2022 - 27

Materials & Coatings
Material Inspired by Chain Mail Transforms from Flexible
to Rigid on Command
Applications include a smart fabric for exoskeletons, an adaptive cast that adjusts its stiffness
as an injury heals, or a deployable bridge that could be unrolled and stiffened.
California Institute of Technology, Pasadena, CA
E
ngineers developed a material inspired
by chain mail that can transform
from a foldable, fluid-like state into
specific solid shapes under pressure. Materials
that change properties in similar
ways already exist; for example, coffee in
a vacuum-sealed bag. When still packed,
it is solid via a process called jamming.
As soon as the package is opened, the
coffee grounds are no longer jammed
against each other and can be poured as
though they were a fluid.
Individual coffee grounds and sand
particles have complex but disconnected
shapes and can only jam when compressed.
Sheets of linked rings, however,
can jam together under both compression
and tension (when pushed together
or pulled apart). The team tested a number
of particles to see which ones offered
both flexibility and tunable stiffness; the
ones that only jam under one type of
stress tended to perform poorly.
They designed a number of configurations
of linked particles, from linking
rings to linking cubes to linking octahedrons
(which resemble two pyramids
connected at the base). The materials
were 3D printed out of polymers and
even metals. Granular materials are an
example of complex systems, where
simple interactions at a grain scale can
lead to complex behavior structurally.
In the chain mail application, the ability
to carry tensile loads at the grain
scale is similar to having a string that
can carry compressive loads.
The engineers applied an outside
stress, compressing the fabrics using a
vacuum chamber or by dropping a
weight to control the jamming of the material.
In one experiment, a vacuum-locked
chain mail fabric was able to
support a load of 1.5 kilograms - more
than 50 times the fabric's weight. The
fabrics that showed the largest variations
in mechanical properties (from flexible
to stiff) were those with a larger average
number of contacts between particles,
Tech Briefs, August 2022
A material made from linked octahedrons. (Image: CalTech)
When stiffened, the material has the potential to act as a sturdy bridge. (Image: CalTech)
such as linked rings and squares, akin to
medieval chain mail.
These fabrics have potential applications
in smart wearable equipment.
When unjammed, they are lightweight,
compliant, and comfortable to wear; afwww.techbriefs.com
ter
the jamming transition, they become
a supportive and protective layer
on the wearer's body.
For more information, contact Emily
Velas co at evelasco@caltech.edu; 626-372
0067.
27

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Tech Briefs Magazine - August 2022

Table of Contents for the Digital Edition of Tech Briefs Magazine - August 2022

Tech Briefs Magazine - August 2022 - Intro
Tech Briefs Magazine - August 2022 - Sponsor
Tech Briefs Magazine - August 2022 - Cov1
Tech Briefs Magazine - August 2022 - Cov2
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