Kind: captions
Language: en
this metal is about as close to Magic as
it is possible to find in nature I just
don't get it it can adjust its
arrangement of atoms to return to some
predefined shape but it also converts
between mechanical and thermal energy
and it can stretch up to 30 times more
than an ordinary metal and still spring
back to its original size I can feel it
in my hand shrinking back because of
these unique properties it's being used
in everything from Medical devices to
toys to bulletproof bike tires
go and it's allowing NASA to reinvent
the wheel for space
exploration this is the bones of a the
bones of the tire the bones of the tire
is a slinky so basically this is the the
slinky applied to the rim you just
wrapped a slinky around a rim yeah it
doesn't get any simpler than that right
here is a a bicycle that has slinkies
inside a polymer if you look inside
there this tire does not require air
pressure to work the structure and shock
absorption are all provided by that
metal Slinky so that's like around 100
PSI or what a normal road bike would
feel like which means you should be able
to puncture it with no loss of
performance so we're going to drive it
over a bed of nails but first we'll test
a traditional pneumatic tire just to
make sure these nails are Sharp
another puncture another flat tire this
one kind of expected so now I'm going to
put these airless tires to the test
driving over the same bed of nails here
we
[Applause]
go I heard a lot of Pops I must have hit
some Nails I don't feel anything
different
still rides
well going to get up some
speed and G that's definitely a nail
like the nail broke in it why is it
that's what it looks like Yeah The Nails
in the tire we're now going to try to
shoot a bullet into the tire and see
what happens 3 2 1
there it is there it is look at
that wow it's just it's a really clean
shot straight through yep barely even
see the mark on the tire looks like this
one actually hit the hit the uh alloy
yep it does to me yeah that's what it
feels like you can see we spliced off
some of the bullet before we even got to
the cardboard how's it ride yeah no
problems bulletproof bicycle
this bulletproof bike tire actually
comes out of NASA's Research into making
wheels for space
missions it is really hard to make good
wheels for other planets I mean a lot of
the places we want to send Rovers to
there is no or very low atmospheric
pressure we can't use rubber pneumatic
tires because of the extreme conditions
on the moon and Mars there's no
confining pressure outside of it it
could basically explode besides with
temperatures dropping to extreme lows
rubber becomes brittle if the were a a
flag pole the temperature facing the sun
would be
250° fah above zero in the shadow is
250° below zero let's uh put some rubber
on the moon 90 is the glass transition
temperature it's when the polymer goes
from being flexible to a rigid element
this is what happens when you dip rubber
in liquid nitrogen
[Music]
that's why you can't send rubber to the
moon this is why almost all the wheels
used for exploring other planets have
been made of hard metal this is actually
a spare for the Curiosity Rover made out
of aluminum a single Billet that gets
machined down so you don't have to worry
about Fasteners or welds or anything
like that that could potentially be a
failure point but with it being so
expensive to launch matter into space
the wheels have to be as lightweight as
possible it's it's lightish but it's
still heavy to meet those Mass
limitations they made this skin7 mm
thick thinner than a credit card yep
these structural members here which we
also call grousers they're there to give
the wheel strength but also help grab
onto obstacles and and help grab the
soil the problem is that because this
rub is so large and heavy and the
terrain is just so aggressive and nasty
they're actually seeing much higher Peak
loads kind of focused on areas between
these Growers than what was predicted
and this is the actual condition of the
wheels on Mars right now and as you can
see
got big holes and cracks where those
skin where that skin was now the wheel
still operates hasn't immobilized the
Rover it's still going to complete its
Mission but it does affect where it can
go and how how efficient it
is when you apply a force to a material
that is known as a stress and what
you're really doing is tugging on all
the atoms inside the object and as a
result their spacing changes a little
bit and so the material deforms for
example if you pull on an object it will
get slightly longer and the per unit
change in length is called strain now
for most materials under low stresses
strain is directly proportional to the
stress applied mean the more you stress
it the more it stretches and the
material is elastic if you remove the
stress the object goes back to its
original size so no atoms have moved
around and no bonds have been broken or
formed you've just made them Flex when
you applied that stress but if the
stress applied exceeds the yield
strength of the material well then this
strain is so great that the atoms can't
maintain their positions relative to
each other defects called Edge
dislocations can move through the
material the atoms are actually
rearranging themselves and so the
deformation is not reversible it's
plastic deformation so the object won't
go back to its original shape when the
stress is removed if enough stress is
applied the material can completely
fracture in the worst case scenario this
results in Holes like in the Mars rover
Wheels which reduced their performance
and ultimately could jeopardize the
mission ordinary metals can withstand a
strain of only around3 to 8% elastically
any more than that and they undergo
plastic deformation so they won't return
to their original shape ultimately they
could even
fracture there go right yeah and you
kinked it too kinked it and stretched it
that's why every component of a space
vehicle is designed never to stretch
more than that3 to 8% but that's a
significant
limitation there is a different type of
wheel that NASA has tried in space which
are those on the Apollo lunar roving
vehicle or lrv that particular structure
that they built is something that we
call a panograph all it is is it's a set
of wires that have been over under over
under woven and this this on the surface
here to get grip also to strengthen it's
primarily to to ensure that the tire
does not sink into the ground so they
did some studies with these tread strips
to figure out how much coverage they
needed and so they they found out that
roughly 50% was enough to keep the tire
kind of floating on the surface and
still uh maintain that flexibility the
lunar roving vehicle Wheels worked well
for the short distance Journeys traveled
on the Moon I mean the farthest this
vehicle ever went was 36 km but still
these wheels needed to be designed to
minimize plastic deformation of the
steel mesh and so they put put this
internal structure inside there we call
it a bump stop so as they hit a bump and
this is deformed when it hits that it
stops the deoration to keep it just
below that proportional limit where they
would induce
plasticity this wheel was good enough
for the short Apollo missions but for
longer Journeys a bump stop won't be
enough to prevent plastic deformation
building up over time mesh steel wheels
have been tried on Earth but their
performance does degrade over time this
was the Mars steel Spring tire we we
made and drove on that same test rig and
there's no fracture but you see a lot of
permanent deformation there what we need
is a material that is strong and durable
like steel but which can endure much
more strain without deforming
permanently and that is where this stuff
comes
in in 1961 the naval ordinance
laboratory was doing experiments with
different Alloys involving nickel and
titanium a sample that had been
repeatedly worked heated and cooled was
shown to one of the associate technical
directors who just happened to be a pipe
smoker so he decided to see what the
sample would do if he applied a bit of
heat from his lighter and when he did
that he found that the material changed
shape this shocked everyone and led to
more investigations into the material
which became known as nanl for its
components nickel and titanium and for
the naval ordinance laboratory where it
was discovered so why did n andol change
shape it's really because the Ally can
undergo a phase change in the solid
state in heated NL the atoms are
arranged in a cubic lattice Arrangement
and this phase is known as tinite but
upon cooling the atoms ease into a form
known as twined Martin site it's a
Messier lower symmetry arrangement of
the atoms and in this phase you can
apply stress to the material and deform
it but unlike in an ordinary metal this
deformation is not causing bonds between
atoms to break and Edge dislocations
moving throughout the material now in
this case the crystal structure is
changing once again to a detwinned form
of Martin site and now when you heat it
back up the material goes from Martin
site back to being austinite which means
all the atoms go back to their original
locations and so the material returns to
its original shape we can basically set
this shape as the parent known memory
shape that's why we call it shape memory
I can stretch this out I could if I
cooled it down I could stretch it out
even more but as soon as I heat it back
up it'll remember that original Parent
shape and that's why night andol is
considered a shape memory
alloy the shape is set at high
temperature when the material is in the
tinite phase then as the material is
cooled down it undergos a phase
transition into twined Martin site if
stress is now applied to the material in
this phase it can be extensively
deformed by changing the crystal
structure into detwinned Martin site
when the stress is released most of that
deformation remains but when the sample
is heated the atoms return to the tinite
phase which Returns the material to its
original shape
[Laughter]
it's like you're barely in the water no
and it's just as fast as you can conduct
heat to it or get heat away from it who
whoa I mean that's
cool this is the property of night all
that most people are aware of and one
that makes it useful for a lot of
applications so that's a stint they
slightly cool these down right below to
Martin site and then they crush it or
elongate it so you can see it gets real
thin and then they put in a catheter and
that catheter goes through the body to
the place where they want to deploy the
stent and then upon deploying it it
bounces right back increasing that outer
diameter and opening that artery nightl
is absolutely perfect for that shape
memory allo can actually generate
significant forces when they're heated
which means they can also be used as
actuators you're going to see a huge
amount of force and stress build up in
the wire which we can see with here
which how much it's pulling
6 lb 7 you can really see it Contracting
there 13 15 16
17 20
lb oh it's lifting it that's about 90
Newtons of
force scientists have even used shape
memory Alloys to fracture a
rock shape memory Alloys are being
investigated for use in aviation I made
a video before about Vortex generators
which are these little fins that stick
up out of the wing of a plane to trip
the air flow into turbulence this is
important for takeoff and Landing to
keep the flow attached to the wing so
you don't stall but when you're up at
cruise and you don't need need those
vortices being generated you want these
to Stow because they're a drag penalty
as the plane just climbs from takeoff to
cruise we go from some temperature on
the ground round to something close to
-50 -60 C at Cru the alloy is designed
in between those so that we can just
take advantage of the ambient
temperature change that happens in the
environment when we cool this one down
no controller no operator it
autonomously STS flat the temperature at
which the material transitions between
austinite and Martin site can be tuned
to be anywhere between -50 to positive 3
50° C this is done by changing the ratio
of the elements and using different heat
treatments and then as that would heat
back up coming into
landing comes right back
up this principle has been extended to
operate the main flaps on an aircraft
now the heating and cooling is not
passive but controlled by a heating
element so we've done demonstrations
where you have a 737 aircraft and no
hydraulic actuators on the wing box all
we have is a shuttle mechanism that's
driven by two tubes of nightl and we've
driven those aons and flap elements on
the wing box of a 737 in Flight 60° flap
angle down 30° flap angle up just by
Heating and Cooling two tubes of night
and all replaces all the Hydraulics the
shape memory effect is the main thing
people know about materials like n andol
but they have another unique property
which makes them ideal for making
durable wheels and you're just going to
take it and you're going to Loop it a
couple times around your hand like that
and you're just going to pull on that
wire and feel 6 to 8% strain in a piece
of metal oh that's really weird that's 6
to 8% strain which you can't do in other
wires right but what's weird about it is
that it feels a little crunchy it it
feel cuz you're feeling all of the
reorientations oh so weird so cool
though right yes very
cool can you hear that
yeah how weird is that that pinging is
20 shape memory Alloys can stretch up to
8% of their length and still spring back
to their original size this property is
known as super elasticity or pseudo
elasticity but they're kind of misnomers
because the material is not actually
operating in its elastic regime what's
actually happening is that this NL is in
the austinite phase its transition
temperature is lower than room
temperature but by applying a stress
even with no temperature change you can
force the crystal structure to change
from tinite into detwinned Martin site
and this rearrangement allows the nanl
to deform by that 8% and still it'll
snap back to its original configuration
once the stress is removed and the atoms
return to the tinite
phase that sound you're hearing is the
material undergoing a stressinduced
phase change in the solid state if you
want to think about it on a stress
strain curve now this transformation is
occurring entirely above the Martin site
transition temperature so the material
starts off in the tinite phase and then
the applied stress is what induces the
phase change from austinite to detwinned
Martin site and when that stress is
removed the atoms spring back to the
ight phase and so the material goes back
to its original size and
shape If This Were a normal tube I would
bend it to here and it would plasticize
if it was a brass tube which you know
has a plastic buckling mode it would go
like this and it would actually Buckle
the wall I would never take my hands and
bend them like this and have it
completely return to shape at the bend
the nightl is transforming from
austinite to Martin site and back when
we go from the higher symmetry phase the
tinite to the lower symmetry daughter
phase which one is it exothermic or
endothermic I feel like that should be
exothermic good job Science
Guy if you were to put your hand around
this tube you'll actually feel the heat
energy the enthalpy of that
transformation evolving as heat you
ready
yep oh yeah that's real hot oh ooh oh
that that actually is like burning like
I can't keep my hand on no keep your
hand on it it won't burn you that's when
the stress is removed and the material
goes back to being tinite that phase
change is endothermic it absorbs
heat right it's like you could use that
for a refrigerator so the it's exactly
right so another area where these
materials are being applied is in a
field called elasto calorics where we
use this transformation to do things
equivalent to heat pumping I want to
shoot this with our thermal camera we
got a Fleer with
us how's
that this dissipation potential can act
a little bit like the dissipation in the
shock absorber right so the tire itself
could actually perform some of that
dissipation potential on its own it
almost acts as a damper right to get rid
of that energy loss so then your your
tire actually has a potential of
becoming a complete suspension system
which obviously really simplifies
building vehicles for for space the
original Tire when I put load on it okay
you can see I'm only transferring a load
from the footprint to this little
section of the tire right by
tying these this Bump Stop element to
here when I go through a footprint you
can see now I'm transferring load 360°
around the tire right by by doing that I
have now increased my load carrying
capacity significantly without adding
any more
mass so to make a tire out of shape
memory alloy they weave night andol
Springs together into a mesh it's a
pretty tedious and timec consuming
process so you're going to take it like
so yep you're going to grab both ends no
and now take it you're not take it and
screw it in oh my my
goodness are you kidding me is this what
you do every day 684 times 684
times per tire but will these wheels
work on Rovers on the moon and
Mars well they test the wheels
extensively on a rotating Carousel of
different terrain types from Sand to
small rocks to bigger rocks so the
terrain endurance rig basically consists
of a a circular Carousel that is
independently driven the wheel tire
assembly is also independently driven so
we can create a force slip condition so
we can drive with zero
slip and this is about how slow a Mars
Rover would be traveling average speed
is about 6.7 cm/s that's a nominal speed
they don't go too fast
all right I'm going to go walk on
simulated Moon reguli it looks like
beach and it feels like beach this side
is meant to simulate the surface of the
Moon and this side is meant to be the
surface of
Mars it is uh very sinky sand wheel is
rolling along Rolling Along hits a rock
and I'm I just am I pushing into it or
do I want to get it on top I'd say get
on top and just put all your body weight
onto it
that's basically my full weight on it
the shape memory alloy is strong enough
to support the weight of a vehicle or
vehicle and crew but it's also
incredibly flexible so it can deform up
to 8% without being permanently damaged
and that's what's needed for long space
missions so that's a pretty good amount
of deoration right that's a great amount
of deformation and still not Beyond 8%
it's so gooey it's just walking back to
the car after the beach tricky for a
Rover right but these tires won't just
be for space they're also looking at
terrestrial
applications most aircraft the tires on
those aircraft they have to be
pressurized to really really high
pressurizations 300 400 PSI not the
conventional 30 to 60 PSI you do in a
car or truck tire right we have issues
where at those huge pressure
pressurizations they can explode the
other construct is is maintenance right
so if I'm a pneumatic tire and I'm
relying on that pneumatics for the
performance of the system I have to
always be checking the air pressure to
make sure that I'm at the right
inflation pressure so that I'm not
burning too much fuel or I'm not at a
place where I could potentially pop a
tire because of the loads by going to a
structural system that doesn't rely on
air and is designed specifically for the
application all of those things go away
they've tested one on a Jeep since it
doesn't rely on pressurized air for
support you just can't get a flat tire
plus it can never be underinflated which
significantly improves fuel economy with
a metal that works like magic you can
make airless tires that will take us
off-road on road into the air and across
other worlds
[Applause]
NASA's night and all tires are designed
to last the entire lifetime of a rover
mission even on a rough terrain of Mars
but here on Earth few products last a
lifetime from bike tires to phones to
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