this isn't an illusion or a magic trick
although it's often passed off as one
it's nitinol
a bizarre metal known as a shape memory
alloy that can be trained to remember
any shape it's been slowly gaining
popularity over the past few decades
but it's about to be put through one of
its biggest tests
yet but shape memory is one of those
things that i really believe
is going to create a paradigm shift for
the world
nitinol is an alloy made of nickel and
titanium and was first discovered by dr
william j buehler in 1959
as he was looking for different alloys
to use in the nose cones of missiles
but he noticed that nitinol had a very
peculiar response to temperature
and stress so shape memory alloys are
governed by this principle of phase
transformation
othman benafon works with shape memory
alloys at nasa's glenn research center
he talked us through what's going on
within the metal basically
he says all matter moves through
different phases as it heats or cools
from solid to liquid to gas but some
materials can also go through different
phases and remain a solid under extreme
temperature or pressure
the elements are the same but the
arrangements of the atoms change
so you really don't change the matter
from solid to another liquid
it's a solid to solid phase
transformation
lots of materials have this property but
in nitinol
the process can be controlled and the
key to shape memory alloys
is that this phase transformation is
reversible
that is the key that is why we have that
name memory
so you can heat and cool and go back and
forth there's always a path to go from
one state
to another
to train the nitinol you heat treat it
at 500 degrees celsius in your desired
shape
then quench it in cold water now
whenever the alloy's temperature reaches
a threshold
known as its transformation temperature
it reverts back to the shape you trained
it to remember
and there's more to nitinol than just
the shape memory effect it can also be
super elastic
if the alloy is created to have a low
transformation temperature
say below room temperature then it's
already in that phase of its final shape
so when we try to deform it it bounces
right back
by altering the ratio of nickel to
titanium scientists can choose from a
broad range of transformation
temperatures for these reactions to
occur
that way nitinol can reshape or bend
predictably in a variety of applications
or
environments shortly after its discovery
scientists and engineers created a
nitinol heat engine
which rapidly heated and cooled the
nitinol wire to drive a pulley system
and generate energy
soon nitinol showed up in everything
from the f14 fighter jet
to flexible eyeglass frames and in the
medical field
nitinol is widely used in stents that
can easily fit inside a blood vessel
and then expand to help treat heart
disease since shape memory alloys can
sense temperature and react to it
they could take the place of temperature
sensors or even motors
they've been used to automatically pop
open greenhouse windows if the
temperature rises too high
or restrict the flow of hot water and
shower heads to prevent scalding
in short a lot of people have benefited
from shape memory alloys
even if they don't realize it but this
is only the beginning
according to othman they're starting to
find their true calling
in space every inch of a spacecraft
is so valuable where these smas become
very important they buy you weight
they buy you space and they buy you
sometimes
simplicity of the design the metal
itself
is a sensor the metal itself is the
actuator so you can take
multiple functions and bundle it into a
piece of metal
now just by saying that i i work in the
field of shape memory alloys
and every time i say that a piece of
metal does these things i go
this is this is kind of cool shaped
memory alloys are finding lots of work
on mars missions like mars global
surveyor
to pathfinder and more recently on
insight to help with everything from
deploying antenna
to moving solar panel covers one of
offman's colleagues at nasa
santa padula has even been working on
using shape memory alloys in rover
wheels
they've been working for quite a while
um and had
developed this you know really great
technology called spring tire
but the one limitation that they always
ran into was
when they tried to design for high
enough load they would permanently
deform the systems and it would no
longer
return to its original shape and still
act like a
nicely rolling wheel but by
incorporating shape memory alloys with
super elastic properties
when everybody saw the performance of
that they said
we need this thing shape memory alloy
wheels are slated to debut
on the second leg of the mars sample
return mission following perseverance's
path
and picking up the sample tubes it
dropped along the way future rovers are
going to move in this direction
compliant wheels have a lot of
advantages
over rigid wheels and other
architectures
one of the things that this has shown me
is that
we have the ability with a lot of these
emerging technologies
to step back and to reassess entire
systems and say if we could wipe that
dry erase board clean and just start
over with design
how would we do it differently now that
we have this new construct to leverage
that's where we're going to see this
enormous
shift in terms of new design
a new innovation spurring the future of
technology