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LORNA GIBSON: OK,
so what we're going

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to talk about in this
course are materials

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that have a cellular structure.

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So they're all very porous.

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And typically they have low
volume fractions of solids,

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like less than 30% solid.

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And we're going to talk
about different types

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of cellular solids.

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So one type are honeycombs.

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And this would be kind of your
standard hexagonal honeycomb,

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00:00:45,570 --> 00:00:46,630
something like that.

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We're going to talk about foams.

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And I'm sure you've
all seen polymer foams.

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Here's an aluminum foam.

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00:00:51,050 --> 00:00:53,570
We'll talk about other
sorts of foams as well.

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00:00:53,570 --> 00:00:56,520
We're going to talk about
some medical materials.

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00:00:56,520 --> 00:00:59,460
And I brought in some bone
samples, some trabecular bone

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00:00:59,460 --> 00:01:00,750
samples here.

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00:01:00,750 --> 00:01:03,211
I brought in a little tissue
engineering sample here.

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00:01:03,211 --> 00:01:05,710
And then, we're going to talk
about materials in nature that

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00:01:05,710 --> 00:01:07,362
have a cellular structure too.

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00:01:07,362 --> 00:01:09,320
So we're going to talk
a little bit about wood.

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00:01:09,320 --> 00:01:10,930
And I brought in a
piece of balsa wood.

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I'll pass these
around in a minute

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00:01:12,080 --> 00:01:13,200
so you can play with them.

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00:01:13,200 --> 00:01:14,283
This is the lightest wood.

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00:01:14,283 --> 00:01:15,900
And I brought in lignum vitae.

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This is the densest wood.

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00:01:17,403 --> 00:01:21,130
Lignum vitae is so dense
that it sinks in water.

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00:01:21,130 --> 00:01:23,915
And I have a couple of projects
right now on natural materials.

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00:01:23,915 --> 00:01:26,040
So I thought I'd talk a
little bit about those too.

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00:01:26,040 --> 00:01:29,010
We have one on bamboo and
making structural products out

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00:01:29,010 --> 00:01:29,510
of bamboo.

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00:01:29,510 --> 00:01:32,290
So this is like a beam
made out of bamboo.

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And this is a piece of
oriented strand board made out

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00:01:34,960 --> 00:01:35,880
of bamboo.

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00:01:35,880 --> 00:01:38,320
So the same way you have like
wood oriented strand board,

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00:01:38,320 --> 00:01:39,940
you can do the same
thing with bamboo.

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00:01:39,940 --> 00:01:40,982
And we have a project
that involves this,

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so I thought talk a
little bit about that

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later on in the course.

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So we'll talk a little bit about
the processing, how you make

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00:01:47,290 --> 00:01:49,960
these materials, the structure.

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00:01:49,960 --> 00:01:52,337
We'll talk a little bit
about how we do the modeling.

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00:01:52,337 --> 00:01:54,170
So we're going to start
with the honeycombs,

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00:01:54,170 --> 00:01:57,330
partly because they have
a nice, simple unit cell

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that you can repeat and you
can analyze fairly exactly.

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00:02:01,580 --> 00:02:04,290
And then we're going to talk
about modeling the foams.

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And then once we've got
the modeling background,

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so we're going to get
equations describing

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the mechanical properties, the
stiffness and the strength,

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once we've got that, then we
can apply it to lots of things.

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So we can apply it to
understanding the trabecular

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bone, the tissue
engineering scaffolds,

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or how cells interact
with scaffolds.

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We're going to look at
energy absorption in foams

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because they're good
for absorbing energy.

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We're going to look at a
lightweight sandwich panels

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as well.

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So we're going to look at
all these different things.

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And I have some slides I'm
going to go over today that have

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more pictures of all of this.

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And I'll pass this
around to a sec,

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but let me go through
the logistics first.

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So this first hand out has a
few of the kind of details.

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There's two books that I've
coauthored with colleagues.

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The one on cellular solids,
if you wanted to buy a book,

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is probably the most
relevant one to buy.

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00:02:54,060 --> 00:02:56,510
If you don't want to buy it,
you certainly don't have to.

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00:02:56,510 --> 00:02:58,820
I'm sure the library has
multiple copies of it.

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And the other more recent one
is called Cellular Materials

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in Nature and Medicine.

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And that's a little
more specialized.

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And again the library has that.

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So you don't need to
run out and buy that.

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00:03:08,264 --> 00:03:09,680
You can just get
it there, but let

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me just mention
there's that reference

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and it might be helpful.

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OK, so let me talk a little
bit about the projects.

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What we do in this class is
everybody does a project.

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And I like for you to do it
in pairs, just so that you

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have somebody to work with.

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I think it's nice to have
somebody to do it with.

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00:03:23,902 --> 00:03:25,360
And the project
has to be something

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on cellular materials,
but I really

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leave it pretty open
ended what the project is.

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00:03:29,480 --> 00:03:32,510
It's really up to you to
decide what you'd like to do.

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00:03:32,510 --> 00:03:34,510
And to give you some idea
what people have done,

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00:03:34,510 --> 00:03:37,050
people have done all kinds
of stuff in the past.

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So people have worked on
negative Poisson's ratio

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00:03:39,880 --> 00:03:40,695
honeycombs.

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00:03:40,695 --> 00:03:42,320
I didn't bring any
of those in with me,

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but you can design
these honeycombs

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so that they have this
property that when

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you push it this way-- instead
of if you make the strain

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smaller in this direction, it
gets wider in this direction

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00:03:54,340 --> 00:03:56,980
normally, but with negative
Poisson's ratio materials,

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it will contract
in that direction.

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So I've had people
do projects on that.

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00:04:01,410 --> 00:04:03,880
I've had people work
on osteoporosis.

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00:04:03,880 --> 00:04:06,620
I had a group once who
worked on elephant skulls

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00:04:06,620 --> 00:04:08,930
and I brought part of
their project with me.

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00:04:08,930 --> 00:04:13,060
So it turns out elephant skulls
have a sort of porous layer

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to them.

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00:04:13,982 --> 00:04:15,690
And this is-- they
have these large pores

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in the top of the skull.

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I don't have a whole skull,
but this is part of it.

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And what they did was they had
heard that elephant skulls have

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these pores and that
the pores somehow

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affect sound transmission
and how the elephant hears.

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And so they wanted to
do a project on that.

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And that was really all
they knew to start with,

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00:04:31,730 --> 00:04:33,979
elephants have pores and we
want to do a project on it

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because it's cool.

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So I helped them put
together this project.

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We went up to Harvard.

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We went up to the Museum
of Comparative Zoology

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where they have elephant skulls,
which are like about this big

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around, huge skulls.

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And some of them had the outer
part of the bone was broken

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and you could see
these big pores.

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So they got some nice
pictures of elephant skulls.

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And then they found that the
University of Texas at Austin

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has computer tomography
images of all sorts of bones

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of different animals.

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And sure enough, they
had elephant skulls.

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So they got the file
for the micro CT

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00:05:04,730 --> 00:05:08,410
image, which gives you the sort
of 3-D picture of the skull.

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And then they use
that to 3-D print

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small versions of the skull.

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So that's what this is, they
printed smaller versions.

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And these were just
a couple of slices

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00:05:16,890 --> 00:05:18,744
that I got from them
at the end project.

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And then what they did
with one of the skulls,

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they suspended it from a
wire, and they took speakers,

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00:05:22,940 --> 00:05:24,802
and they had sound that
vibrated the skull,

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00:05:24,802 --> 00:05:26,760
and then they put an
accelerometer on the skull

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00:05:26,760 --> 00:05:29,890
and they measured the vibration
response of the skull.

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And they also made, I think,
it was a dolphin skull,

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which did not have these
pores, and they kind of

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compared the vibration response
from the sound for these two

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skulls with two
different structures.

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So that was a project
for this class.

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People have worked on tissue
engineering scaffolds.

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Often there's people
who work on food foams.

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So one year, people
worked on bread.

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They did bread processing.

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They made bread by
having different amounts

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of yeast, different rise
times, different ingredients.

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And they made bread.

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And I have a little-- I like
these historical things.

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And I have a little thing
here I wanted to show you.

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So the people in 3032
last year, last fall,

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00:06:11,000 --> 00:06:13,130
will know that I went
to England in November.

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And I went to the Royal Society
for an editorial board meeting.

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But I also went and
looked at their archives.

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And one of the
things they showed

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me was this article, which is
in the sort of an original, sort

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of archives of the Royal
Society from 1600s.

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And it's by a guy
called John Evelyn.

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He's famous for writing
a book called Silva

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00:06:31,820 --> 00:06:33,202
about trees and wood.

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But he's written
this article here.

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And I love the title.

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It's "The Several Manors of
Making Bread in France, Where

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00:06:39,710 --> 00:06:42,940
by General Consent, the Best
Bread in the World is Eaten,"

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00:06:42,940 --> 00:06:45,090
by Mr. Evelyn.

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So here we have in the
Official Royal Society bread

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00:06:47,740 --> 00:06:48,800
making science.

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00:06:48,800 --> 00:06:51,390
And in fact, the article
was several pages long.

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00:06:51,390 --> 00:06:54,580
There was quite a lot on bread
and how you make it in France,

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00:06:54,580 --> 00:06:56,086
where the best bread is eaten.

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So if you want to do
something on food foams,

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00:06:57,960 --> 00:07:01,080
people have done meringue
before, various things.

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00:07:01,080 --> 00:07:04,330
They look at typically
changing something

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00:07:04,330 --> 00:07:07,620
about the recipe, or the
composition, or the processing,

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00:07:07,620 --> 00:07:08,399
or the baking.

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00:07:08,399 --> 00:07:09,690
And they look at the structure.

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00:07:09,690 --> 00:07:12,120
Sometimes they look at
mechanical properties too.

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00:07:12,120 --> 00:07:15,590
So anyway, there's a whole
list of things there.

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00:07:15,590 --> 00:07:17,080
You can think of other things.

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00:07:17,080 --> 00:07:18,496
If you look through
the books, you

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00:07:18,496 --> 00:07:21,010
might get some ideas
as well for projects.

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00:07:21,010 --> 00:07:22,810
So what I'd thought
I'd do next is

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00:07:22,810 --> 00:07:25,910
I wanted to just kind of
give an overview of what

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00:07:25,910 --> 00:07:27,450
we're going to talk about.

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00:07:27,450 --> 00:07:30,410
And I've got a bunch of slides.

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00:07:30,410 --> 00:07:35,730
Let's see I forgot some
things, because I do that.

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00:07:35,730 --> 00:07:39,160
Books, yeah, OK, let me
pass some of these things

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00:07:39,160 --> 00:07:43,310
around so you get to
play with them too.

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So here's some honeycombs.

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I don't know if we can pass
all these things around

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00:07:46,410 --> 00:07:47,701
because it's a little unwieldy.

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So this is an
aluminum honeycomb.

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00:07:49,770 --> 00:07:50,942
I like bringing toys in.

203
00:07:50,942 --> 00:07:52,400
These are little
rubber honeycombs.

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00:07:56,420 --> 00:07:58,210
This is a little
ceramic honeycomb.

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00:07:58,210 --> 00:08:00,053
This is a little
paper honeycomb.

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00:08:03,300 --> 00:08:06,210
And let's see, we
have some foams here.

207
00:08:06,210 --> 00:08:12,830
So here's a metal foam
and a ceramic foam.

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00:08:12,830 --> 00:08:15,150
And this is a sort
of, not quite a foam,

209
00:08:15,150 --> 00:08:17,620
it's made of hollow spheres
by centering hollow spheres

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00:08:17,620 --> 00:08:18,540
together.

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00:08:18,540 --> 00:08:20,809
So you can play with that.

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00:08:20,809 --> 00:08:21,850
And what else do we have?

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00:08:21,850 --> 00:08:24,080
We have little
lattice things here.

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00:08:24,080 --> 00:08:26,382
So here's a sort of
3-D lattice material.

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00:08:26,382 --> 00:08:28,090
So this has sort of
a cellular structure,

216
00:08:28,090 --> 00:08:29,300
but it's very, very regular.

217
00:08:29,300 --> 00:08:30,740
It's not like a foam.

218
00:08:30,740 --> 00:08:33,240
So that's called a 3-D
lattice material or sometimes

219
00:08:33,240 --> 00:08:34,770
a 3-D truss.

220
00:08:34,770 --> 00:08:37,230
And what else should
we pass around?

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00:08:37,230 --> 00:08:39,820
We need to do the bones.

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00:08:39,820 --> 00:08:40,809
Here's the wood.

223
00:08:40,809 --> 00:08:43,755
You can feel how different the
densities of the two woods are.

224
00:08:43,755 --> 00:08:45,130
I would like these
all at the end

225
00:08:45,130 --> 00:08:48,290
because I show these around
for different classes.

226
00:08:48,290 --> 00:08:51,780
Here's some bone, you can see
of the bone looks like the foam.

227
00:08:51,780 --> 00:08:56,250
And this is a tissue engineering
scaffold for generating skin.

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00:08:56,250 --> 00:08:59,260
All right, so while those
are getting passed around,

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00:08:59,260 --> 00:09:01,530
I'll talk a little
bit about what

230
00:09:01,530 --> 00:09:04,900
we're going to cover in
the class with some slides.

231
00:09:04,900 --> 00:09:07,114
OK, let's see, should
I dim the lights?

232
00:09:07,114 --> 00:09:09,530
Would that be a good thing,
Craig, if I dimmed the lights?

233
00:09:11,892 --> 00:09:14,100
CRAIG: They're kind of
preset, you can try maybe two.

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00:09:14,100 --> 00:09:16,880
LORNA GIBSON: OK.

235
00:09:16,880 --> 00:09:21,360
Doesn't seem to-- there we go.

236
00:09:21,360 --> 00:09:23,312
How about that?

237
00:09:23,312 --> 00:09:26,290
That OK?

238
00:09:26,290 --> 00:09:31,150
All right, so I like
these historical things.

239
00:09:31,150 --> 00:09:34,946
So this is a picture of
Robert Hooke's drawing of cork

240
00:09:34,946 --> 00:09:36,070
from his book Micrographia.

241
00:09:36,070 --> 00:09:39,530
And he was the first person
who used the word cell

242
00:09:39,530 --> 00:09:41,640
to describe a biological cell.

243
00:09:41,640 --> 00:09:43,610
And it comes from the
Latin cella, which

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00:09:43,610 --> 00:09:45,300
means a small compartment.

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00:09:45,300 --> 00:09:47,710
So you can think of the
cells as small compartments.

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00:09:47,710 --> 00:09:49,090
That kind of makes sense.

247
00:09:49,090 --> 00:09:51,860
And he kind of very
modestly says, "I no sooner

248
00:09:51,860 --> 00:09:53,930
to discerned these,
which were indeed

249
00:09:53,930 --> 00:09:56,940
the first microscopical
pours I have ever saw,

250
00:09:56,940 --> 00:09:59,500
but me thought I had with
the discovery of them

251
00:09:59,500 --> 00:10:02,790
perfectly hinted to me the true
and intelligible reason for all

252
00:10:02,790 --> 00:10:04,265
the phenomena of cork."

253
00:10:04,265 --> 00:10:06,390
So he's saying by looking
at the structure of cork,

254
00:10:06,390 --> 00:10:07,848
he thinks he
understands everything

255
00:10:07,848 --> 00:10:11,600
about the properties
of cork-- very modest.

256
00:10:11,600 --> 00:10:14,634
But in fact, this is kind of the
foundation of material science.

257
00:10:14,634 --> 00:10:16,300
So material science
is all about looking

258
00:10:16,300 --> 00:10:18,052
at the structure of
materials and trying

259
00:10:18,052 --> 00:10:20,260
to say something about the
properties of the behavior

260
00:10:20,260 --> 00:10:21,270
of the materials.

261
00:10:21,270 --> 00:10:23,160
And that sentence
kind of sums that up.

262
00:10:23,160 --> 00:10:25,724
So that's why I
like that sentence.

263
00:10:25,724 --> 00:10:27,890
So what we're going to do
is look at different kinds

264
00:10:27,890 --> 00:10:29,140
of cellular materials.

265
00:10:29,140 --> 00:10:31,220
We'll look at engineering ones.

266
00:10:31,220 --> 00:10:35,460
And these we typically refer
to as honeycombs or foams.

267
00:10:35,460 --> 00:10:39,400
Honeycombs have two
dimensional prismatic cells,

268
00:10:39,400 --> 00:10:43,070
while foams have three
dimensional polyhedral cells.

269
00:10:43,070 --> 00:10:46,150
And we'll look at applications
for the honeycombs and foams

270
00:10:46,150 --> 00:10:48,520
in things like lightweight
sandwich panels,

271
00:10:48,520 --> 00:10:50,870
in energy absorption
devices, and things

272
00:10:50,870 --> 00:10:51,890
like thermal insulation.

273
00:10:51,890 --> 00:10:54,290
We'll talk a little bit
about the thermal properties.

274
00:10:54,290 --> 00:10:57,530
We're also going to talk about
cellular materials in medicine,

275
00:10:57,530 --> 00:10:58,710
so trabecular bone.

276
00:10:58,710 --> 00:11:01,910
We'll talk about osteoporosis
and how loss of bone

277
00:11:01,910 --> 00:11:05,000
reduces the strength, and
how you might estimate that.

278
00:11:05,000 --> 00:11:07,480
We'll talk about tissue
engineering scaffolds,

279
00:11:07,480 --> 00:11:09,990
something about their
mechanical properties.

280
00:11:09,990 --> 00:11:12,380
You may think the mechanical
properties aren't probably

281
00:11:12,380 --> 00:11:13,797
the most important thing.

282
00:11:13,797 --> 00:11:15,380
But in fact, the
mechanical properties

283
00:11:15,380 --> 00:11:17,800
do have some effect on
how the cells interact

284
00:11:17,800 --> 00:11:18,780
with the scaffold.

285
00:11:18,780 --> 00:11:21,572
So we'll talk a little bit
about cell scaffold mechanics.

286
00:11:21,572 --> 00:11:23,780
And then we're going to talk
about cellular materials

287
00:11:23,780 --> 00:11:25,360
in nature at the
end of the course.

288
00:11:25,360 --> 00:11:27,290
So we'll talk a little
bit about honeycomb

289
00:11:27,290 --> 00:11:30,940
like materials, like wood and
cork, and foam like materials,

290
00:11:30,940 --> 00:11:32,520
like the trabecular bone.

291
00:11:32,520 --> 00:11:34,990
There's also a type of tissue
in plants called parenchyma

292
00:11:34,990 --> 00:11:36,510
that looks just like a foam.

293
00:11:36,510 --> 00:11:39,540
And there's some sponges that
have some interesting features.

294
00:11:39,540 --> 00:11:42,270
And often, in nature
the cellular material

295
00:11:42,270 --> 00:11:45,210
appears in combination
with some solid material.

296
00:11:45,210 --> 00:11:47,470
And so it's sort of a
structural component.

297
00:11:47,470 --> 00:11:49,050
And you can see
sandwich structures

298
00:11:49,050 --> 00:11:51,730
in nature, leaves and skulls.

299
00:11:51,730 --> 00:11:54,100
You can see materials that
have density gradients,

300
00:11:54,100 --> 00:11:56,830
palm stems and bamboo
are examples of that.

301
00:11:56,830 --> 00:12:00,230
And you can see materials
that have cylindrical shells

302
00:12:00,230 --> 00:12:02,400
with compliant cores, and
things like plant stems

303
00:12:02,400 --> 00:12:04,130
and animal quills are like that.

304
00:12:04,130 --> 00:12:06,600
So that's kind of the
range of materials

305
00:12:06,600 --> 00:12:07,964
that we're going to talk about.

306
00:12:07,964 --> 00:12:10,380
And one of the interesting
things about cellular materials

307
00:12:10,380 --> 00:12:12,460
is that you can make
cellular materials out

308
00:12:12,460 --> 00:12:13,780
of almost anything now.

309
00:12:13,780 --> 00:12:16,640
And this is really a huge
range of materials and lots

310
00:12:16,640 --> 00:12:19,650
of different
applications for this.

311
00:12:19,650 --> 00:12:22,100
So one of the fundamental
things we're going to do

312
00:12:22,100 --> 00:12:25,010
is look at the mechanisms by
which the materials deform

313
00:12:25,010 --> 00:12:26,370
and how they fail.

314
00:12:26,370 --> 00:12:28,260
And we'll use a
structural analysis

315
00:12:28,260 --> 00:12:30,800
to obtain the bulk mechanical
properties, so things

316
00:12:30,800 --> 00:12:33,290
like the stiffness, the moduli,
the strength, the fracture,

317
00:12:33,290 --> 00:12:34,320
toughness.

318
00:12:34,320 --> 00:12:36,480
We'll look at how
you can control

319
00:12:36,480 --> 00:12:39,370
the design of the microstructure
to get the properties that you

320
00:12:39,370 --> 00:12:42,440
might want, and also how you
might select for the best

321
00:12:42,440 --> 00:12:45,220
material for a given engineering
application in engineering

322
00:12:45,220 --> 00:12:46,290
design.

323
00:12:46,290 --> 00:12:48,070
So we're going to get
those three things.

324
00:12:48,070 --> 00:12:49,870
So let me start by showing
you some more examples

325
00:12:49,870 --> 00:12:52,320
of engineering cellular
solids, and in particular, some

326
00:12:52,320 --> 00:12:52,919
micrographs.

327
00:12:52,919 --> 00:12:55,210
So that you can see what it
looks like on a small scale

328
00:12:55,210 --> 00:12:56,214
too.

329
00:12:56,214 --> 00:12:57,380
So these are the honeycombs.

330
00:12:57,380 --> 00:12:59,796
These are the sorts of things
that I'm passing around now.

331
00:12:59,796 --> 00:13:03,400
The aluminum one, paper
resin, and the ceramic ones.

332
00:13:03,400 --> 00:13:05,650
The aluminum and
the paper resin ones

333
00:13:05,650 --> 00:13:08,190
are typically used in the
cores of sandwich panels.

334
00:13:08,190 --> 00:13:10,770
And the ceramic ones are used
in the catalytic converter

335
00:13:10,770 --> 00:13:11,920
in your car.

336
00:13:11,920 --> 00:13:16,080
So what they do is they block
off every other cell at one

337
00:13:16,080 --> 00:13:18,730
end and then the opposite
cells at the other end

338
00:13:18,730 --> 00:13:20,940
and exhaust gas from
your car is forced

339
00:13:20,940 --> 00:13:23,540
to go through those
channels in the honeycomb.

340
00:13:23,540 --> 00:13:27,380
And the walls, if you look
at that triangular one,

341
00:13:27,380 --> 00:13:29,780
those triangular walls
themselves are porous,

342
00:13:29,780 --> 00:13:33,020
and they're coated with the
catalyst, which is platinum.

343
00:13:33,020 --> 00:13:35,547
And that forces the exhaust
gas through the wall

344
00:13:35,547 --> 00:13:37,130
in contact with the
platinum, and then

345
00:13:37,130 --> 00:13:38,231
comes out the other end.

346
00:13:38,231 --> 00:13:40,480
And they're ceramic, obviously,
because the gas is hot

347
00:13:40,480 --> 00:13:43,470
and they need something that
has a high thermal resistance.

348
00:13:43,470 --> 00:13:45,580
So these are some
examples of honeycombs.

349
00:13:45,580 --> 00:13:47,910
These are some examples
of engineering foams.

350
00:13:47,910 --> 00:13:49,532
When I tell people
I work on foams,

351
00:13:49,532 --> 00:13:50,990
they always think
of polymer foams,

352
00:13:50,990 --> 00:13:52,884
like polystyrene or something.

353
00:13:52,884 --> 00:13:54,300
And there's lots
of polymer foams.

354
00:13:54,300 --> 00:13:56,320
But you can actually
foam any materials now.

355
00:13:56,320 --> 00:13:57,560
There's metal foams.

356
00:13:57,560 --> 00:14:01,200
There's ceramic foams, and
glass foams, carbon foams,

357
00:14:01,200 --> 00:14:02,620
all sorts of foams.

358
00:14:02,620 --> 00:14:04,840
So those are some examples.

359
00:14:04,840 --> 00:14:06,560
You can see when you
look at these images

360
00:14:06,560 --> 00:14:09,780
here that the foams have a
low volume fraction of solids,

361
00:14:09,780 --> 00:14:15,610
like if you look at say
this polyethylene one here.

362
00:14:15,610 --> 00:14:18,906
Say we look at this
guy up here, then

363
00:14:18,906 --> 00:14:21,280
you can see there's not much
solid, there's a lot of gas.

364
00:14:21,280 --> 00:14:23,210
So the volume
fraction of solids is

365
00:14:23,210 --> 00:14:25,094
fairly low on that foam there.

366
00:14:25,094 --> 00:14:27,010
So one of the things
we're going to talk about

367
00:14:27,010 --> 00:14:30,560
is how the volume fraction of
solids affects the properties.

368
00:14:30,560 --> 00:14:33,220
You can also see on the
top left and the top right,

369
00:14:33,220 --> 00:14:35,550
the top left one has
what we call open cells.

370
00:14:35,550 --> 00:14:37,770
There's just edges
along the polyhedra,

371
00:14:37,770 --> 00:14:39,940
there's no faces
over the membranes.

372
00:14:39,940 --> 00:14:42,700
And the right hand one
is a closed cell foam.

373
00:14:42,700 --> 00:14:45,680
So there's like membranes that
cover the faces of the cells.

374
00:14:45,680 --> 00:14:48,230
So we're going to talk a little
bit about the differences

375
00:14:48,230 --> 00:14:52,580
and the behavior of open cell
and closed cell foams too.

376
00:14:52,580 --> 00:14:53,530
These are food foams.

377
00:14:53,530 --> 00:14:54,820
So I've already
said you might want

378
00:14:54,820 --> 00:14:56,130
to do a project on food foams.

379
00:14:56,130 --> 00:14:59,340
And these are just some examples
of different kinds of foods

380
00:14:59,340 --> 00:15:00,810
that are in fact foams.

381
00:15:00,810 --> 00:15:02,340
And it turns out
the food industry

382
00:15:02,340 --> 00:15:04,370
spends quite a lot
of time and effort

383
00:15:04,370 --> 00:15:07,580
thinking about the mechanical
properties of food.

384
00:15:07,580 --> 00:15:11,140
And it turns out if the texture
of the food isn't right,

385
00:15:11,140 --> 00:15:14,260
then people don't like the
way it feels in their mouth.

386
00:15:14,260 --> 00:15:16,380
There's something they
actually called mouth feel.

387
00:15:16,380 --> 00:15:19,980
So it turns out if your
cereals too soggy, it's icky.

388
00:15:19,980 --> 00:15:21,610
If it's too crunchy, it's icky.

389
00:15:21,610 --> 00:15:23,500
So it's sort of a happy medium.

390
00:15:23,500 --> 00:15:25,850
And food companies spend
quite a lot of time and money

391
00:15:25,850 --> 00:15:29,897
worrying about the mechanical
properties of food.

392
00:15:29,897 --> 00:15:31,980
This is an example of
showing that the cells could

393
00:15:31,980 --> 00:15:36,180
be antisotropic, the cells could
be elongated in one direction.

394
00:15:36,180 --> 00:15:39,590
For instance, in the top one
on the polyurethane foam.

395
00:15:39,590 --> 00:15:41,470
And if they're elongated
in one direction,

396
00:15:41,470 --> 00:15:43,969
it's not too surprising, you
might have different properties

397
00:15:43,969 --> 00:15:47,140
in that direction from the
plane perpendicular to it.

398
00:15:47,140 --> 00:15:49,180
And then the bottom
images is of pumice.

399
00:15:49,180 --> 00:15:50,770
Pumice is a volcanic rock.

400
00:15:50,770 --> 00:15:53,890
And you can see how the pores
are kind of flattened out

401
00:15:53,890 --> 00:15:54,470
there.

402
00:15:54,470 --> 00:15:56,428
And they're flattened
out because that was once

403
00:15:56,428 --> 00:15:57,340
molten lava.

404
00:15:57,340 --> 00:15:58,960
And the molten lava
was flowing down

405
00:15:58,960 --> 00:16:00,710
a mountain side of a volcano.

406
00:16:00,710 --> 00:16:02,650
And as it flowed,
it got sheared.

407
00:16:02,650 --> 00:16:06,090
And the shape of those
pours reflects the shearing

408
00:16:06,090 --> 00:16:10,010
as the molten lava
flow down the volcano.

409
00:16:10,010 --> 00:16:15,815
And so this kind of sort
of stretched out cell shape

410
00:16:15,815 --> 00:16:17,690
is going to give you
antisotropic properties,

411
00:16:17,690 --> 00:16:20,320
different properties in
different directions.

412
00:16:20,320 --> 00:16:22,530
This is the 3-D truss
that I'm passing around.

413
00:16:22,530 --> 00:16:24,279
I don't know if it's
exactly the same one,

414
00:16:24,279 --> 00:16:25,410
but it's a similar one.

415
00:16:25,410 --> 00:16:27,820
And these trusses are
triangulated structures.

416
00:16:27,820 --> 00:16:32,090
And we'll talk a little bit
about their properties too.

417
00:16:32,090 --> 00:16:35,180
And then we also are going to
talk about some applications.

418
00:16:35,180 --> 00:16:37,590
So obviously, these
materials are mostly air.

419
00:16:37,590 --> 00:16:39,440
And that gives
them a low weight.

420
00:16:39,440 --> 00:16:41,890
And that means they're often
used in structural sandwich

421
00:16:41,890 --> 00:16:43,890
panels as the core of the panel.

422
00:16:43,890 --> 00:16:46,330
And these panels have
stiff faces separated

423
00:16:46,330 --> 00:16:47,629
by a lightweight core.

424
00:16:47,629 --> 00:16:49,920
And the idea is to make it
a little bit like an I-beam.

425
00:16:49,920 --> 00:16:51,836
So the way you have the
flanges on the I-beam,

426
00:16:51,836 --> 00:16:54,100
the faces are like the
flanges, and the porous core

427
00:16:54,100 --> 00:16:56,410
is like the web of the I-beam.

428
00:16:56,410 --> 00:16:58,800
They can also undergo
large deformations

429
00:16:58,800 --> 00:17:01,020
at relatively low stress.

430
00:17:01,020 --> 00:17:03,140
And that means they can
absorb a lot of energy.

431
00:17:03,140 --> 00:17:05,880
So if you think of the energy
as the area under the stress

432
00:17:05,880 --> 00:17:08,924
strain curve, if there's big
strains and big deformations,

433
00:17:08,924 --> 00:17:10,990
then there's going
to be a large area.

434
00:17:10,990 --> 00:17:13,130
And that sort of
energy absorption

435
00:17:13,130 --> 00:17:15,190
occurs at a fairly low stress.

436
00:17:15,190 --> 00:17:17,280
So typically, when you
want to absorb energy,

437
00:17:17,280 --> 00:17:19,672
it's not just how much
energy you want to absorb.

438
00:17:19,672 --> 00:17:21,880
You have to do it without
actually breaking the thing

439
00:17:21,880 --> 00:17:22,921
you're trying to protect.

440
00:17:22,921 --> 00:17:25,660
So you don't want to generate
high stresses as you go along,

441
00:17:25,660 --> 00:17:27,329
and foams are good at this.

442
00:17:27,329 --> 00:17:30,930
Foams are also good at
being thermal insulators.

443
00:17:30,930 --> 00:17:33,680
They have a low
thermal conductivity.

444
00:17:33,680 --> 00:17:35,680
And that's because they're
largely made of gas

445
00:17:35,680 --> 00:17:38,190
and the gas has a lower
conductivity than the solids.

446
00:17:38,190 --> 00:17:40,490
So that gives them a
lower conductivity.

447
00:17:40,490 --> 00:17:41,956
And they have a
large surface area.

448
00:17:41,956 --> 00:17:43,830
And the smaller the pore
size, the bigger the

449
00:17:43,830 --> 00:17:45,790
surface area per unit volume.

450
00:17:45,790 --> 00:17:47,520
And that makes them
good for things

451
00:17:47,520 --> 00:17:49,230
like carriers for catalysts.

452
00:17:49,230 --> 00:17:52,910
And that's why they're used for
these catalytic converters too.

453
00:17:52,910 --> 00:17:56,650
OK, so here's some examples of
cellular materials in medicine.

454
00:17:56,650 --> 00:18:00,410
So here's some examples
of trabecular bone.

455
00:18:00,410 --> 00:18:03,250
Trabecular bone exists at
the ends of your long bones.

456
00:18:03,250 --> 00:18:06,110
So say in your hip
or in your knee.

457
00:18:06,110 --> 00:18:09,770
It also exists in your vertebrae
in the middle of the spine

458
00:18:09,770 --> 00:18:11,125
in the vertebrae there.

459
00:18:11,125 --> 00:18:13,389
And it also exists
in your skull.

460
00:18:13,389 --> 00:18:15,180
And you can see it's
a porous type of bone.

461
00:18:15,180 --> 00:18:17,430
It looks very similar to
the foams and the sorts

462
00:18:17,430 --> 00:18:19,840
of mechanical models
we make for foams can

463
00:18:19,840 --> 00:18:21,829
be applied to the bone as well.

464
00:18:21,829 --> 00:18:23,370
And so that's one
of the things we're

465
00:18:23,370 --> 00:18:25,180
going to do later in the course.

466
00:18:25,180 --> 00:18:26,890
These are two slides
showing what happens

467
00:18:26,890 --> 00:18:28,680
when people get osteoporosis.

468
00:18:28,680 --> 00:18:32,330
The left hand slide is
from a 55-year-old female

469
00:18:32,330 --> 00:18:34,710
to the same bone,
the same slice.

470
00:18:34,710 --> 00:18:38,610
And the right hand one is
from an 86-year-old female.

471
00:18:38,610 --> 00:18:41,680
This thing here,
row star over row S,

472
00:18:41,680 --> 00:18:44,230
that's the relative density,
the density of the bone

473
00:18:44,230 --> 00:18:46,400
divided by the solid
that it's made from.

474
00:18:46,400 --> 00:18:49,300
That's the same as the
volume fraction of solids.

475
00:18:49,300 --> 00:18:52,880
And so on the normal bone on
the left it's about 17% solid.

476
00:18:52,880 --> 00:18:56,340
And on the osteoporotic bone
on the right it's, about 7%.

477
00:18:56,340 --> 00:18:59,666
So you can kind of see the
bone density has gotten lower,

478
00:18:59,666 --> 00:19:01,040
partly by thinning
of the struts,

479
00:19:01,040 --> 00:19:03,080
but partly by resorption
of the struts, as well.

480
00:19:03,080 --> 00:19:04,120
And obviously the
one on the right

481
00:19:04,120 --> 00:19:05,661
is going to have a
lot lower strength

482
00:19:05,661 --> 00:19:08,700
than the one on the left.

483
00:19:08,700 --> 00:19:10,980
These are micro
CT images of bone.

484
00:19:10,980 --> 00:19:12,890
And again, you can
see how the structure

485
00:19:12,890 --> 00:19:15,234
looks different at different
relative densities.

486
00:19:15,234 --> 00:19:17,650
The one on the left is sort
of in the middle at around 11%

487
00:19:17,650 --> 00:19:18,330
dense.

488
00:19:18,330 --> 00:19:21,460
The one in the middle
is the most dense 25%.

489
00:19:21,460 --> 00:19:23,170
And the one on the
right is 6% dense.

490
00:19:23,170 --> 00:19:25,470
So it's not too surprising
that the one on the right

491
00:19:25,470 --> 00:19:28,030
would have a much lower
strength from the other ones.

492
00:19:28,030 --> 00:19:30,430
And we'll look at how
we can model that.

493
00:19:30,430 --> 00:19:32,970
This is just showing
some deformation in bone.

494
00:19:32,970 --> 00:19:34,410
I have a colleague,
Ralph Mueller

495
00:19:34,410 --> 00:19:36,840
who's got a micro
CT machine, which

496
00:19:36,840 --> 00:19:39,720
allows you to do compression
tests in the micro CT.

497
00:19:39,720 --> 00:19:41,600
So he can make
these sort of images

498
00:19:41,600 --> 00:19:44,441
where he scans it
at zero strain.

499
00:19:44,441 --> 00:19:45,690
He compresses it a little bit.

500
00:19:45,690 --> 00:19:46,464
He scans it again.

501
00:19:46,464 --> 00:19:47,630
He compresses it a bit more.

502
00:19:47,630 --> 00:19:48,860
He scans it again.

503
00:19:48,860 --> 00:19:51,950
And he these are
stills from his images,

504
00:19:51,950 --> 00:19:53,910
but he makes
animations from this.

505
00:19:53,910 --> 00:19:56,000
And if you look at
the top right up here,

506
00:19:56,000 --> 00:19:57,510
you see these struts here.

507
00:19:57,510 --> 00:19:59,380
They're pretty
straight in this one.

508
00:19:59,380 --> 00:20:01,810
They're a little bent and
starting to buckle here.

509
00:20:01,810 --> 00:20:03,970
And then if you look at
that one strut there,

510
00:20:03,970 --> 00:20:05,660
you can see how it's
buckled right over.

511
00:20:05,660 --> 00:20:07,620
So you can look at the
deformation mechanisms

512
00:20:07,620 --> 00:20:12,570
by looking at the CT scans
and things like that.

513
00:20:12,570 --> 00:20:14,340
People are starting
to think about using

514
00:20:14,340 --> 00:20:17,700
metal foams for coatings
of orthopedic implants.

515
00:20:17,700 --> 00:20:19,270
So one of the
issues with implants

516
00:20:19,270 --> 00:20:22,300
is that say you have a hip
implant or a knee implant,

517
00:20:22,300 --> 00:20:26,237
you remove the bone
that's preexisting,

518
00:20:26,237 --> 00:20:28,320
and then you replace it
with some sort of implant.

519
00:20:28,320 --> 00:20:29,900
Typically, the
implant has a stem

520
00:20:29,900 --> 00:20:32,160
that fits into the
hollow part of the bone

521
00:20:32,160 --> 00:20:34,710
and then has a sort
of joint piece to it

522
00:20:34,710 --> 00:20:36,410
that fits into the joint.

523
00:20:36,410 --> 00:20:41,120
And you can get some loosening
of the stem in the remaining

524
00:20:41,120 --> 00:20:41,620
bone.

525
00:20:41,620 --> 00:20:46,011
And one idea is that you use
porous coatings to minimize

526
00:20:46,011 --> 00:20:46,510
that.

527
00:20:46,510 --> 00:20:49,120
And right now, typically
what they do is center beads,

528
00:20:49,120 --> 00:20:52,062
metal beads on to the stem.

529
00:20:52,062 --> 00:20:54,270
And another idea is maybe
you could use a metal foam.

530
00:20:54,270 --> 00:20:56,370
And these are some different
types of metal foams

531
00:20:56,370 --> 00:20:58,920
that people are looking at.

532
00:20:58,920 --> 00:21:02,150
Another type of cellular
material in medicine

533
00:21:02,150 --> 00:21:04,220
is a tissue
engineering scaffold.

534
00:21:04,220 --> 00:21:06,160
And this just shows
some different examples

535
00:21:06,160 --> 00:21:07,490
made by different processes.

536
00:21:07,490 --> 00:21:11,110
And we'll talk more about
these later on in the course.

537
00:21:11,110 --> 00:21:14,840
This one here at the
top left is a collagen

538
00:21:14,840 --> 00:21:17,416
based one made by a
freeze drying process.

539
00:21:17,416 --> 00:21:19,540
And I don't know if you
saw MIT's website yesterday

540
00:21:19,540 --> 00:21:22,250
and today, Ioannis Yannas was
the one who developed this.

541
00:21:22,250 --> 00:21:24,910
And he's just being inducted
into the National Inventors

542
00:21:24,910 --> 00:21:25,730
Hall of Fame.

543
00:21:25,730 --> 00:21:27,690
And this is what he
really was inducted

544
00:21:27,690 --> 00:21:32,850
for is he's invented
a skin-- well,

545
00:21:32,850 --> 00:21:34,890
he calls it a dermal
regeneration template

546
00:21:34,890 --> 00:21:38,920
for regenerating skin, mostly
in people with serious burns.

547
00:21:38,920 --> 00:21:42,880
Then these are some other
sorts of scaffolds that are

548
00:21:42,880 --> 00:21:44,690
made by different processes.

549
00:21:44,690 --> 00:21:47,914
This is by a sort of rapid
prototyping process here.

550
00:21:47,914 --> 00:21:49,830
The bottom two, these
are kind of interesting.

551
00:21:49,830 --> 00:21:52,210
These are actually the
extracellular matrix

552
00:21:52,210 --> 00:21:53,000
in the body.

553
00:21:53,000 --> 00:21:55,319
And they've had all the
cells removed from it.

554
00:21:55,319 --> 00:21:56,860
So these tissue
engineering scaffolds

555
00:21:56,860 --> 00:22:00,440
are really designed to mimic
the extracellular scaffold

556
00:22:00,440 --> 00:22:03,880
in your body or extracellular
matrix in your body.

557
00:22:03,880 --> 00:22:06,576
And you can see how when
you remove the cells,

558
00:22:06,576 --> 00:22:07,950
the structure of
those two things

559
00:22:07,950 --> 00:22:09,890
looks a lot like a
closed cell foam.

560
00:22:09,890 --> 00:22:13,570
So that's the kind of structure
you're trying to replicate.

561
00:22:13,570 --> 00:22:15,110
We'll look a bit
at cell mechanics.

562
00:22:15,110 --> 00:22:18,090
This is a cell
contraction of a scaffold.

563
00:22:18,090 --> 00:22:20,990
So here these sort of
very thin transparent bits

564
00:22:20,990 --> 00:22:24,520
of the collagen based scaffold,
and this is a fiber blast on it

565
00:22:24,520 --> 00:22:26,130
right here.

566
00:22:26,130 --> 00:22:28,040
And I had a student,
Toby [? Fryman, ?]

567
00:22:28,040 --> 00:22:30,246
who worked with me and
Ioannis Yannas on this.

568
00:22:30,246 --> 00:22:32,370
And you can see from the
video the cell is actually

569
00:22:32,370 --> 00:22:35,230
contract in the scaffolding
making it deform.

570
00:22:35,230 --> 00:22:37,410
And you can
calculate what forces

571
00:22:37,410 --> 00:22:40,360
the cell must be
imposing on the scaffold

572
00:22:40,360 --> 00:22:43,630
by knowing something about
the geometry of the struts

573
00:22:43,630 --> 00:22:45,510
and how the cells attached.

574
00:22:45,510 --> 00:22:47,770
And then it's going
a little bit more.

575
00:22:47,770 --> 00:22:50,170
So we'll talk more about that.

576
00:22:50,170 --> 00:22:52,400
And then there's a
final picture down here,

577
00:22:52,400 --> 00:22:54,930
where you can see these
two, the two points

578
00:22:54,930 --> 00:22:58,060
up here and down here have now
been brought pretty much right

579
00:22:58,060 --> 00:22:59,120
together.

580
00:22:59,120 --> 00:23:01,710
So we'll talk about
that in more detail.

581
00:23:01,710 --> 00:23:04,140
We've also done studies
on cell attachment

582
00:23:04,140 --> 00:23:08,410
and how that attachment rate or
the amount of cells that attach

583
00:23:08,410 --> 00:23:10,560
is related to the
surface area, the surface

584
00:23:10,560 --> 00:23:12,140
area per unit volume.

585
00:23:12,140 --> 00:23:13,780
So these are just
some tests from that

586
00:23:13,780 --> 00:23:17,570
done by [? Fergal ?] O'Brien,
a post-doc that worked with me.

587
00:23:17,570 --> 00:23:20,980
We've also done some
studies on cell migration.

588
00:23:20,980 --> 00:23:24,210
And Brendan Harley was
the student who did this.

589
00:23:24,210 --> 00:23:26,130
And he stained the
cells with one stain

590
00:23:26,130 --> 00:23:28,500
and he stained the scaffold
with something else.

591
00:23:28,500 --> 00:23:31,810
So red are the scaffold
and green are the cells.

592
00:23:31,810 --> 00:23:35,100
And then he used a confocal
microscope to track the cells.

593
00:23:35,100 --> 00:23:38,556
And he tracked the cells and
where they moved versus time.

594
00:23:38,556 --> 00:23:40,430
And if he has the location
at different times

595
00:23:40,430 --> 00:23:41,682
he can get the velocity.

596
00:23:41,682 --> 00:23:43,140
And one of the
things he did was he

597
00:23:43,140 --> 00:23:45,610
changed the stiffness
of the scaffold

598
00:23:45,610 --> 00:23:47,880
and he found that the
migration speed depended

599
00:23:47,880 --> 00:23:50,110
on how stiff the scaffold was.

600
00:23:50,110 --> 00:23:52,120
So he was looking at
sort of interactions

601
00:23:52,120 --> 00:23:55,760
between mechanical
properties of the scaffold

602
00:23:55,760 --> 00:23:59,074
and behaviors like
cell migration.

603
00:23:59,074 --> 00:24:01,240
And then we're going to
look at materials in nature.

604
00:24:01,240 --> 00:24:02,150
So here is wood.

605
00:24:02,150 --> 00:24:04,179
So you can see the
cellular structure of wood.

606
00:24:04,179 --> 00:24:05,470
It's a lot like the honeycombs.

607
00:24:05,470 --> 00:24:07,680
It has sort of a
prismatic structure.

608
00:24:07,680 --> 00:24:10,820
That one happens to be cedar,
but other woods look similar.

609
00:24:10,820 --> 00:24:11,850
Now, this is balsa wood.

610
00:24:11,850 --> 00:24:14,220
And this is showing just
how the balsa deforms.

611
00:24:14,220 --> 00:24:16,810
I think this was loaded
from top to bottom.

612
00:24:16,810 --> 00:24:18,340
And this is at zero load.

613
00:24:18,340 --> 00:24:20,860
And then this is more load,
and more load, and more load.

614
00:24:20,860 --> 00:24:22,350
And if you look
at that cell there

615
00:24:22,350 --> 00:24:24,920
with this little kind
of tear in it here,

616
00:24:24,920 --> 00:24:26,657
that's the same as
the cell down here,

617
00:24:26,657 --> 00:24:27,740
and that's the tear there.

618
00:24:27,740 --> 00:24:31,000
So you can see how the cell
walls bend and how they deform.

619
00:24:31,000 --> 00:24:34,880
And you can model that
using the honeycomb models.

620
00:24:34,880 --> 00:24:38,890
This is just another image
showing actual failure of wood,

621
00:24:38,890 --> 00:24:41,360
buckling of the cell walls.

622
00:24:41,360 --> 00:24:42,380
This is cork.

623
00:24:42,380 --> 00:24:45,185
So these are modern scanning
electron micrograph of cork.

624
00:24:45,185 --> 00:24:46,560
And one of the
interesting things

625
00:24:46,560 --> 00:24:48,644
is the cork cells have
these little corrugations.

626
00:24:48,644 --> 00:24:50,060
You see how they're
not flat, they

627
00:24:50,060 --> 00:24:51,900
have little kind of
wrinkles in them.

628
00:24:51,900 --> 00:24:54,510
And that gives rise to sort
of an interesting property

629
00:24:54,510 --> 00:24:55,010
of cork.

630
00:24:55,010 --> 00:24:56,660
If you take cork
and you load it.

631
00:24:56,660 --> 00:24:59,640
So here we were pulling it in
the direction of these arrows,

632
00:24:59,640 --> 00:25:02,240
pulling it like along
this direction here.

633
00:25:02,240 --> 00:25:04,490
And again, this is
the same set of cells.

634
00:25:04,490 --> 00:25:07,252
That tear there is the
same as that tear there.

635
00:25:07,252 --> 00:25:09,210
And you see all these
little corrugations here,

636
00:25:09,210 --> 00:25:12,010
they've all straightened out
when we're pulling on it.

637
00:25:12,010 --> 00:25:14,300
And the Poisson's ratio
of the cork is zero.

638
00:25:14,300 --> 00:25:16,169
It's kind of like a bellows.

639
00:25:16,169 --> 00:25:17,710
Like if you had an
old camera, or you

640
00:25:17,710 --> 00:25:19,140
have an accordion bellows.

641
00:25:19,140 --> 00:25:20,830
If you pull the
bellows in and out,

642
00:25:20,830 --> 00:25:22,600
it doesn't get any wider
this way or the other way.

643
00:25:22,600 --> 00:25:23,700
You're just sort of
opening the bellows

644
00:25:23,700 --> 00:25:24,744
and closing the bellows.

645
00:25:24,744 --> 00:25:26,910
And the cork cells are doing
kind of the same thing.

646
00:25:26,910 --> 00:25:28,881
And it gives them this
Poisson's ratio of zero.

647
00:25:28,881 --> 00:25:30,630
Which it happens is
one of the things that

648
00:25:30,630 --> 00:25:33,080
makes it easy to get the
cork into your wine bottle,

649
00:25:33,080 --> 00:25:35,530
because as you're pushing
on it, it's not pushing out

650
00:25:35,530 --> 00:25:36,401
in all directions.

651
00:25:36,401 --> 00:25:37,900
This is only for
this one direction,

652
00:25:37,900 --> 00:25:40,840
but it's not pushing
out in all directions.

653
00:25:40,840 --> 00:25:43,090
These are parenchyma
cells in plants,

654
00:25:43,090 --> 00:25:44,440
in carrots and potatoes.

655
00:25:44,440 --> 00:25:49,700
All those little blobs in the
potato, those are starch blobs.

656
00:25:49,700 --> 00:25:52,460
This is called a Venus
flower basket sponge,

657
00:25:52,460 --> 00:25:54,062
and Joanna Aizenberg,
at Harvard,

658
00:25:54,062 --> 00:25:55,270
has studied this quite a lot.

659
00:25:55,270 --> 00:25:56,900
This has a
hierarchical structure.

660
00:25:56,900 --> 00:25:59,410
If you look at
the overall sponge

661
00:25:59,410 --> 00:26:02,030
and then you look at each
of the sort of struts

662
00:26:02,030 --> 00:26:03,600
that make up the
lattice, that too

663
00:26:03,600 --> 00:26:05,607
has a hierarchical structure.

664
00:26:05,607 --> 00:26:07,940
And she's looked at the optical
properties of this glass

665
00:26:07,940 --> 00:26:08,440
sponge.

666
00:26:08,440 --> 00:26:09,731
It's kind of a beautiful thing.

667
00:26:12,140 --> 00:26:17,224
And then there's some cellular
structures in nature as well.

668
00:26:17,224 --> 00:26:18,390
There's sandwich structures.

669
00:26:18,390 --> 00:26:19,473
There's density gradients.

670
00:26:19,473 --> 00:26:21,690
And there's tubes
with a cellular core.

671
00:26:21,690 --> 00:26:23,130
So here's some examples of that.

672
00:26:23,130 --> 00:26:25,350
Here's the iris leaf,
you know the iris plant

673
00:26:25,350 --> 00:26:28,340
has these long kind of leaves
that stand up like this.

674
00:26:28,340 --> 00:26:30,080
And it's just like
a sandwich panel.

675
00:26:30,080 --> 00:26:32,910
The parenchyma are kind of
like a foam in the middle here.

676
00:26:32,910 --> 00:26:34,930
And there's very
dense fibers called

677
00:26:34,930 --> 00:26:37,690
sclerenchyma that run up and
down the length of the leaf.

678
00:26:37,690 --> 00:26:40,190
And they're like fibers
in a fiber composite.

679
00:26:40,190 --> 00:26:42,940
And here's a bull rush
or a cat tail leaf.

680
00:26:42,940 --> 00:26:44,720
And they're like
little I-beams almost.

681
00:26:44,720 --> 00:26:46,511
It's like a whole series
of little I-beams.

682
00:26:46,511 --> 00:26:49,360
And again that's sort
mechanically efficient.

683
00:26:49,360 --> 00:26:52,680
These are examples of sandwich
structures in bird skulls.

684
00:26:52,680 --> 00:26:54,370
Some of you know I'm a birder.

685
00:26:54,370 --> 00:26:58,166
So I sort of sneak in bird
stuff from time to time.

686
00:26:58,166 --> 00:27:00,790
But you can see how these birds
skulls are all sandwich panels,

687
00:27:00,790 --> 00:27:03,640
and obviously birds want
to minimize their weight

688
00:27:03,640 --> 00:27:04,720
for flight.

689
00:27:04,720 --> 00:27:08,070
And this is one of the
ways that they do that.

690
00:27:08,070 --> 00:27:10,690
This is a horseshoe crab,
sort of similar kind of thing.

691
00:27:10,690 --> 00:27:13,040
This is from Mark
Myers in San Diego.

692
00:27:13,040 --> 00:27:16,420
He did a study on the crab
in its shell as a sandwich.

693
00:27:16,420 --> 00:27:19,040
And this is the ever
so handsome cuttlefish.

694
00:27:19,040 --> 00:27:21,500
And the cuttlefish has something
called a cuttlefish bone.

695
00:27:21,500 --> 00:27:23,390
This is the bone
here and the bone

696
00:27:23,390 --> 00:27:26,350
is made up of these kind of
sandwich type structures.

697
00:27:26,350 --> 00:27:30,170
The cuttlefish is related to
octopus and squid and things

698
00:27:30,170 --> 00:27:31,110
like that.

699
00:27:31,110 --> 00:27:33,070
And it's hard to see
in this picture here,

700
00:27:33,070 --> 00:27:35,736
but these little things here are
actually like little tentacles.

701
00:27:35,736 --> 00:27:38,180
There's several tentacles
that it eats stuff with.

702
00:27:38,180 --> 00:27:40,340
The cuttlefish is
actually a mollusk.

703
00:27:40,340 --> 00:27:42,410
All those things are mollusks.

704
00:27:42,410 --> 00:27:45,460
It's called a fish, but
it's not really a fish.

705
00:27:45,460 --> 00:27:47,490
And here's an example of
a natural material that

706
00:27:47,490 --> 00:27:49,817
has a radial density gradient.

707
00:27:49,817 --> 00:27:51,650
Have you ever noticed
if you look at a palm,

708
00:27:51,650 --> 00:27:54,627
like you see those pictures of
Hollywood in LA, and the palm

709
00:27:54,627 --> 00:27:56,210
trees, you know,
they line the street.

710
00:27:56,210 --> 00:27:57,834
But they're all about
the same diameter

711
00:27:57,834 --> 00:27:59,452
from the bottom to the top.

712
00:27:59,452 --> 00:28:01,910
And when you think of like an
oak tree, it's not like that.

713
00:28:01,910 --> 00:28:04,990
It's big diameter at the bottom,
skinny diameter at the top.

714
00:28:04,990 --> 00:28:09,282
So when wood grows, the wood has
more or less the same density

715
00:28:09,282 --> 00:28:10,490
in the bottom and at the top.

716
00:28:10,490 --> 00:28:13,040
So as it's growing, the density
is more or less the same.

717
00:28:13,040 --> 00:28:15,800
And it resists the bigger
loads from getting taller

718
00:28:15,800 --> 00:28:17,201
by adding circumference.

719
00:28:17,201 --> 00:28:19,450
So it gets wider and wider
as it gets older and older.

720
00:28:19,450 --> 00:28:20,730
But palms don't do that.

721
00:28:20,730 --> 00:28:22,840
They come out of the
ground a certain diameter.

722
00:28:22,840 --> 00:28:25,480
And most palms just
grow that same diameter.

723
00:28:25,480 --> 00:28:27,107
As they get taller
and taller, you

724
00:28:27,107 --> 00:28:29,690
can imagine there's wind forces,
and different kinds of forces

725
00:28:29,690 --> 00:28:32,160
are on it, the stresses
get bigger and bigger.

726
00:28:32,160 --> 00:28:34,430
And the way they resist
those is that the cell walls

727
00:28:34,430 --> 00:28:36,220
get thicker, and
they preferentially

728
00:28:36,220 --> 00:28:38,170
get thicker on the outside.

729
00:28:38,170 --> 00:28:40,320
And if you think of
moment of inertia,

730
00:28:40,320 --> 00:28:42,300
remember moment of
inertia is increased

731
00:28:42,300 --> 00:28:46,050
more with the material
on the outside of a beam.

732
00:28:46,050 --> 00:28:48,160
And that's kind of
what the palm is doing.

733
00:28:48,160 --> 00:28:51,940
So if you look at young cell
walls and old cell walls,

734
00:28:51,940 --> 00:28:53,780
here's some SCM
pictures of young ones

735
00:28:53,780 --> 00:28:55,110
and it's sort of skinny.

736
00:28:55,110 --> 00:28:57,780
And SCM pictures of older
ones, and the cell wall

737
00:28:57,780 --> 00:28:58,600
has gotten thicker.

738
00:28:58,600 --> 00:29:00,080
So we're going to talk
a little bit about that.

739
00:29:00,080 --> 00:29:02,288
And it turns out, this is
an incredibly efficient way

740
00:29:02,288 --> 00:29:09,660
to deal with getting taller and
needing to resist bigger loads.

741
00:29:09,660 --> 00:29:11,920
Another material that has
a radial density gradient

742
00:29:11,920 --> 00:29:13,610
is bamboo.

743
00:29:13,610 --> 00:29:17,090
So this again shows these sort
of dense sclerenchyma fibers.

744
00:29:17,090 --> 00:29:19,120
Do you see these kind
of dense parts here?

745
00:29:19,120 --> 00:29:20,840
And you can see there's
not very many of them here.

746
00:29:20,840 --> 00:29:23,464
And there's more and more as you
get towards the outside there.

747
00:29:23,464 --> 00:29:25,700
So there's a density
gradient there.

748
00:29:25,700 --> 00:29:27,410
So we'll talk about that.

749
00:29:27,410 --> 00:29:30,560
And some plant materials
have a cylindrical shell

750
00:29:30,560 --> 00:29:31,950
with a compliant core.

751
00:29:31,950 --> 00:29:33,930
Plant stems or commonly like.

752
00:29:33,930 --> 00:29:35,507
This is a milkweed stem.

753
00:29:35,507 --> 00:29:37,590
And you can see it's got
these sort of fibers that

754
00:29:37,590 --> 00:29:39,380
are almost completely dense.

755
00:29:39,380 --> 00:29:41,470
And then a sort of
lower density core,

756
00:29:41,470 --> 00:29:44,350
cellular core, here, and
a void in the very middle.

757
00:29:44,350 --> 00:29:47,310
And you can show that that core
helps prevent local buckling.

758
00:29:47,310 --> 00:29:49,310
So if you take a drinking
straw and you bend it,

759
00:29:49,310 --> 00:29:51,380
you get that kinking
kind of failure.

760
00:29:51,380 --> 00:29:53,490
You can show that
having this sort of foam

761
00:29:53,490 --> 00:29:55,870
like core in the middle
helps to resist that.

762
00:29:55,870 --> 00:29:57,245
Imagine you have
a drinking straw

763
00:29:57,245 --> 00:29:58,370
and now you put
foam in the middle.

764
00:29:58,370 --> 00:30:00,536
It's going to be harder to
get it to kink like that.

765
00:30:00,536 --> 00:30:02,370
So that's what the
plants are doing.

766
00:30:02,370 --> 00:30:03,980
Animal quills do the same thing.

767
00:30:03,980 --> 00:30:07,150
That's a porcupine
and a hedgehog quill.

768
00:30:07,150 --> 00:30:09,910
And all of this stuff
is in these two books.

769
00:30:09,910 --> 00:30:12,912
So it doesn't really
matter to me if you go out

770
00:30:12,912 --> 00:30:13,620
and buy the book.

771
00:30:13,620 --> 00:30:15,661
I don't make very many
much money on these books.

772
00:30:15,661 --> 00:30:18,302
So this is not an
income producing thing.

773
00:30:18,302 --> 00:30:20,260
But those are the books
that all these pictures

774
00:30:20,260 --> 00:30:21,850
have been taken from.

775
00:30:21,850 --> 00:30:24,680
All right, so I
think that's my sort

776
00:30:24,680 --> 00:30:27,060
of introduction to the class.

777
00:30:27,060 --> 00:30:29,880
Are there any questions
about how we're organized

778
00:30:29,880 --> 00:30:31,940
or what we're going to be doing?

779
00:30:31,940 --> 00:30:34,152
Are we good?

780
00:30:34,152 --> 00:30:35,270
It's OK?

781
00:30:35,270 --> 00:30:36,029
OK.

782
00:30:36,029 --> 00:30:38,570
So then I think what I'm going
to do for the rest of the time

783
00:30:38,570 --> 00:30:42,830
is start the next section of the
course which is on processing

784
00:30:42,830 --> 00:30:44,980
of cellular materials.

785
00:30:44,980 --> 00:30:46,845
Now, I have another
little hand out here.

786
00:30:49,307 --> 00:30:51,890
So I don't know if I'll remember
to do this for every lecture,

787
00:30:51,890 --> 00:30:54,260
but I like to have a
little outline, that

788
00:30:54,260 --> 00:30:56,540
partly makes me be organized.

789
00:30:56,540 --> 00:30:58,844
So it's just a little
outline for the lecture.

790
00:31:02,484 --> 00:31:03,400
AUDIENCE: [INAUDIBLE].

791
00:31:07,900 --> 00:31:11,939
LORNA GIBSON: You
asked me to do what?

792
00:31:11,939 --> 00:31:13,480
AUDIENCE: Put the
room light back up.

793
00:31:13,480 --> 00:31:14,190
LORNA GIBSON: Put the what up?

794
00:31:14,190 --> 00:31:14,290
AUDIENCE: Lights.

795
00:31:14,290 --> 00:31:15,498
LORNA GIBSON: Oh, the lights.

796
00:31:15,498 --> 00:31:18,350
I'm going have another
set of slides though.

797
00:31:18,350 --> 00:31:21,745
So let me get out
of the intro slides.

798
00:31:25,340 --> 00:31:28,250
I know I have another
set of slides.

799
00:31:28,250 --> 00:31:30,280
So I'm going to just
leave the screen up.

800
00:31:30,280 --> 00:31:32,728
And kind of put stuff
on the board and talk

801
00:31:32,728 --> 00:31:33,436
about the slides.

802
00:31:33,436 --> 00:31:34,230
AUDIENCE: That's fine.

803
00:31:34,230 --> 00:31:35,313
LORNA GIBSON: You're good?

804
00:31:35,313 --> 00:31:36,420
OK.

805
00:31:36,420 --> 00:31:37,799
OK.

806
00:31:37,799 --> 00:31:39,840
So I wanted to talk a
little bit about processing

807
00:31:39,840 --> 00:31:42,420
of cellular solids and
then, next time we'll

808
00:31:42,420 --> 00:31:44,050
start talking about
the structures.

809
00:31:44,050 --> 00:31:45,841
It seemed good to talk
about the processing

810
00:31:45,841 --> 00:31:47,330
before we got to the structure.

811
00:31:47,330 --> 00:31:49,080
So I'm going to talk a
little bit about honeycombs

812
00:31:49,080 --> 00:31:50,955
and how they make
honeycombs, and then foams,

813
00:31:50,955 --> 00:31:52,120
and then lattice materials.

814
00:31:52,120 --> 00:31:53,242
Yeah?

815
00:31:53,242 --> 00:31:57,090
AUDIENCE: The slide you're
showing with the the shell

816
00:31:57,090 --> 00:31:59,014
with the foam
inside it, are there

817
00:31:59,014 --> 00:32:00,938
techniques for analysis of it?

818
00:32:03,005 --> 00:32:04,380
LORNA GIBSON:
Well, I don't think

819
00:32:04,380 --> 00:32:05,890
we're going to get into
all the gory details,

820
00:32:05,890 --> 00:32:07,230
but I can certainly
give you references.

821
00:32:07,230 --> 00:32:09,797
That's something that one of
my students did at one point.

822
00:32:09,797 --> 00:32:11,880
And in fact, I've been
collaborating with Jennifer

823
00:32:11,880 --> 00:32:14,060
Lewis up at Harvard
and she has a student

824
00:32:14,060 --> 00:32:17,160
who's making sort of
cylindrical shells

825
00:32:17,160 --> 00:32:19,080
with foams out of ceramic foam.

826
00:32:19,080 --> 00:32:24,180
So he's 3-D printing sort
of with coaxial nozzles

827
00:32:24,180 --> 00:32:26,610
a cylindrical shell
that's pretty solid.

828
00:32:26,610 --> 00:32:28,480
And then a ceramic
foam on the inside.

829
00:32:28,480 --> 00:32:29,940
And that's one of the things
he's playing around with.

830
00:32:29,940 --> 00:32:31,523
So he's looking at
ways you might make

831
00:32:31,523 --> 00:32:34,820
engineering versions of that.

832
00:32:34,820 --> 00:32:38,350
So I wanted to start with
looking at honeycombs

833
00:32:38,350 --> 00:32:40,360
and how they make honeycombs.

834
00:32:40,360 --> 00:32:42,515
And I thought what I'd do
is I've got some slides.

835
00:32:42,515 --> 00:32:44,140
And I'm going to talk
about the slides.

836
00:32:44,140 --> 00:32:46,681
And then I'll put some notes on
the board to kind of describe

837
00:32:46,681 --> 00:32:48,000
what we're doing, OK?

838
00:32:48,000 --> 00:32:51,570
So this is the first sort
of slide on the honeycombs.

839
00:32:51,570 --> 00:32:53,240
And the two main
techniques that they're

840
00:32:53,240 --> 00:32:55,720
made by, especially
those aluminum honeycombs

841
00:32:55,720 --> 00:32:58,670
and paper honeycombs that I
passed around, one technique

842
00:32:58,670 --> 00:33:00,590
is an expansion process.

843
00:33:00,590 --> 00:33:04,750
So what they do is they take
flat sheets of some metal,

844
00:33:04,750 --> 00:33:08,680
say aluminum, and they put
little stripes of glue on it

845
00:33:08,680 --> 00:33:09,520
in different places.

846
00:33:09,520 --> 00:33:11,186
So these little kind
of specialty things

847
00:33:11,186 --> 00:33:12,520
are where the glue goes.

848
00:33:12,520 --> 00:33:14,410
And then they
stack those guys up

849
00:33:14,410 --> 00:33:17,140
in a sort of
particular arrangement.

850
00:33:17,140 --> 00:33:19,700
And then what they do is
they pull it all apart, kind

851
00:33:19,700 --> 00:33:20,700
like a paper doll thing.

852
00:33:20,700 --> 00:33:23,190
They pull it all apart and
when they pull it apart,

853
00:33:23,190 --> 00:33:25,960
they get the hexagonal shape.

854
00:33:25,960 --> 00:33:28,721
So let me just show on the
board how you do the gluing

855
00:33:28,721 --> 00:33:29,512
and how that works.

856
00:33:51,290 --> 00:33:53,200
So they would start
with some sheets.

857
00:33:53,200 --> 00:33:56,860
Say we start with
two sheets like that.

858
00:33:56,860 --> 00:33:58,850
They'd put some glue
down, say there.

859
00:33:58,850 --> 00:34:00,250
And then there's a gap.

860
00:34:00,250 --> 00:34:02,720
And then they put glue on
the opposite side over there.

861
00:34:02,720 --> 00:34:04,050
And then there's another gap.

862
00:34:04,050 --> 00:34:05,680
And then they put glue there.

863
00:34:05,680 --> 00:34:08,170
And then they do
the same positions

864
00:34:08,170 --> 00:34:10,830
but the opposite sides
on the next sheet.

865
00:34:10,830 --> 00:34:12,520
So they do that.

866
00:34:12,520 --> 00:34:14,710
And then if you glue
those together-- well,

867
00:34:14,710 --> 00:34:16,620
let me do another one.

868
00:34:16,620 --> 00:34:18,199
Maybe do a couple more.

869
00:34:18,199 --> 00:34:22,440
So then if I do one like
that, it's glued there,

870
00:34:22,440 --> 00:34:25,330
and there, and there.

871
00:34:25,330 --> 00:34:28,550
That guy gets there,
and there and there.

872
00:34:28,550 --> 00:34:31,139
And when glue that-- when
you push that together

873
00:34:31,139 --> 00:34:38,536
and then take it
apart, you've got

874
00:34:38,536 --> 00:34:39,827
something that looks like this.

875
00:34:43,850 --> 00:34:47,110
So say I call that one,
two, three, and four.

876
00:34:47,110 --> 00:34:49,239
Then this would be 2 and 3.

877
00:34:49,239 --> 00:34:51,739
OK, so this thing here is that.

878
00:34:51,739 --> 00:34:54,530
Where it's not glued,
you get them doing that.

879
00:34:54,530 --> 00:34:57,310
And then it's glued
again down here.

880
00:34:57,310 --> 00:35:00,430
And so you get this
kind of pattern.

881
00:35:00,430 --> 00:35:02,390
And one of the things
about these honeycombs

882
00:35:02,390 --> 00:35:06,500
that are made by the expansion
process is these inclined walls

883
00:35:06,500 --> 00:35:08,500
have a thickness t.

884
00:35:08,500 --> 00:35:10,850
And because there's
two sheets up here,

885
00:35:10,850 --> 00:35:13,850
the vertical walls
have a thickness 2t.

886
00:35:13,850 --> 00:35:19,130
So that's typically what you
see in the commercial honeycombs

887
00:35:19,130 --> 00:35:21,110
that are made by this way.

888
00:35:21,110 --> 00:35:29,390
And this process is used
for aluminum honeycombs,

889
00:35:29,390 --> 00:35:36,110
for paper resin honeycombs,
for Kevlar honeycombs.

890
00:35:40,830 --> 00:35:45,360
And I'll just say note that the
inclined walls have a thickness

891
00:35:45,360 --> 00:35:50,285
t, and the vertical
walls are 2t.

892
00:35:57,040 --> 00:35:59,190
So that's the expansion process.

893
00:35:59,190 --> 00:36:02,920
And the process that's
commonly used for honeycombs

894
00:36:02,920 --> 00:36:04,621
is called a corrugation process.

895
00:36:12,010 --> 00:36:13,700
And for the corrugation
process, it's

896
00:36:13,700 --> 00:36:17,490
just like the lower
schematic here shows.

897
00:36:17,490 --> 00:36:18,860
You take a flat sheet.

898
00:36:18,860 --> 00:36:21,700
So you've got a roll
of a flat sheet.

899
00:36:21,700 --> 00:36:24,600
And you've got some rollers
that have the right shape

900
00:36:24,600 --> 00:36:27,490
to give you the corrugated
profile that you want.

901
00:36:27,490 --> 00:36:29,340
You pass the sheet
through the rolls

902
00:36:29,340 --> 00:36:31,490
and you get
individual sheets out.

903
00:36:31,490 --> 00:36:33,901
And each sheet is kind
of a half hexagon.

904
00:36:33,901 --> 00:36:35,400
And then you put
the sheets together

905
00:36:35,400 --> 00:36:37,560
and that forms
the whole hexagon.

906
00:36:37,560 --> 00:36:39,200
So you have a flat
sheet that's fed

907
00:36:39,200 --> 00:36:42,902
through a shaped wheel to
form half hexagonal sheets,

908
00:36:42,902 --> 00:36:44,110
which you then bond together.

909
00:37:28,150 --> 00:37:30,410
And it's the same kind of
thing that the inclined

910
00:37:30,410 --> 00:37:33,090
walls have thickness t
and the vertical walls

911
00:37:33,090 --> 00:37:34,304
have thickness 2t.

912
00:37:45,190 --> 00:37:46,880
And this corrugation
process, you

913
00:37:46,880 --> 00:37:48,730
can only really
use it in materials

914
00:37:48,730 --> 00:37:51,510
that you can deform
a fairly large amount

915
00:37:51,510 --> 00:37:52,890
to get the corrugations.

916
00:37:52,890 --> 00:37:55,930
So typically, this
is for metals.

917
00:37:55,930 --> 00:38:01,170
And aluminum is probably
the most common metal

918
00:38:01,170 --> 00:38:02,213
that this is used for.

919
00:38:06,095 --> 00:38:08,720
AUDIENCE: How are the corrugated
sheets attached to each other?

920
00:38:08,720 --> 00:38:11,190
LORNA GIBSON: I think they're
just bonded with epoxy.

921
00:38:11,190 --> 00:38:14,250
Yeah, so obviously if you wanted
to use it for high temperature

922
00:38:14,250 --> 00:38:17,100
performance-- you know,
all of these things

923
00:38:17,100 --> 00:38:19,796
are bonded with some sort of
epoxy or some sort of resin.

924
00:38:19,796 --> 00:38:21,170
So there's an
issue if you wanted

925
00:38:21,170 --> 00:38:23,960
to use it higher temperatures.

926
00:38:23,960 --> 00:38:27,890
So another process that's used
to make ceramic honeycombs

927
00:38:27,890 --> 00:38:30,160
is an extrusion process.

928
00:38:30,160 --> 00:38:32,260
And you just take
a ceramic slurry

929
00:38:32,260 --> 00:38:34,520
and you pass it through a die.

930
00:38:34,520 --> 00:38:37,700
And you can make a ceramic
honeycomb by doing that.

931
00:39:03,884 --> 00:39:05,300
And I believe
that's how they make

932
00:39:05,300 --> 00:39:07,550
the ceramic honeycombs
I passed around,

933
00:39:07,550 --> 00:39:10,410
the catalytic converter ones.

934
00:39:10,410 --> 00:39:13,860
Other techniques involve
rapid prototyping.

935
00:39:13,860 --> 00:39:16,220
You can 3-D print honeycombs.

936
00:39:16,220 --> 00:39:18,950
And Jennifer Lewis has a
project on 3-D printing

937
00:39:18,950 --> 00:39:20,804
of honeycombs up at Harvard.

938
00:39:20,804 --> 00:39:22,970
And one of the interesting
things they're looking at

939
00:39:22,970 --> 00:39:25,650
is not just printing with an
ink, but printing with a fiber

940
00:39:25,650 --> 00:39:26,510
reinforced ink.

941
00:39:26,510 --> 00:39:28,780
So they're making cell
walls of the honeycomb that

942
00:39:28,780 --> 00:39:30,160
are fiber reinforced.

943
00:39:30,160 --> 00:39:32,980
And one of the tricks is trying
to orient the fibers in the way

944
00:39:32,980 --> 00:39:34,810
that you want them
to be oriented.

945
00:39:34,810 --> 00:39:37,570
So there's rapid prototyping
techniques as well.

946
00:39:47,870 --> 00:39:50,240
You can use also
selective laser centering.

947
00:40:05,990 --> 00:40:07,750
Let's call it selective
laser scanning.

948
00:40:07,750 --> 00:40:09,910
So you can have a
photosensitive polymer

949
00:40:09,910 --> 00:40:14,350
and use a laser to cure that
and build up a honeycomb type

950
00:40:14,350 --> 00:40:15,430
structure.

951
00:40:15,430 --> 00:40:19,494
And you can also cast
honeycomb structures.

952
00:40:19,494 --> 00:40:21,660
So those rubber honeycombs
that I pass around, those

953
00:40:21,660 --> 00:40:23,350
are made by casting.

954
00:40:23,350 --> 00:40:26,360
You take a liquid silicone
rubber and you add a hardener

955
00:40:26,360 --> 00:40:27,610
and you pour it into a mold.

956
00:41:22,910 --> 00:41:26,874
Another kind of interesting way
that people have made-- well

957
00:41:26,874 --> 00:41:28,540
here's another example
of the honeycombs

958
00:41:28,540 --> 00:41:30,940
that are 3-D printed.

959
00:41:30,940 --> 00:41:33,070
And this is an example
of-- or a couple

960
00:41:33,070 --> 00:41:36,500
of examples of looking
at a bio carbon template.

961
00:41:36,500 --> 00:41:39,110
So what that means is
that these materials are

962
00:41:39,110 --> 00:41:42,240
based on the wood, but none
of them are actually wood.

963
00:41:42,240 --> 00:41:45,577
So what they do is they take
wood, like they take pine,

964
00:41:45,577 --> 00:41:46,910
or they take beech or something.

965
00:41:46,910 --> 00:41:49,550
They take some kind of
wood and they carbonize it.

966
00:41:49,550 --> 00:41:51,490
So that they do the
same processes as

967
00:41:51,490 --> 00:41:53,100
used for making carbon fibers.

968
00:41:53,100 --> 00:41:56,450
So you put the wood in
an inert atmosphere.

969
00:41:56,450 --> 00:41:59,140
And you pyrolyze it.

970
00:41:59,140 --> 00:42:01,940
You heat it up to I
think 800 degrees C.

971
00:42:01,940 --> 00:42:04,580
And all you're left
with is the carbon.

972
00:42:04,580 --> 00:42:06,017
And it preserves the structure.

973
00:42:06,017 --> 00:42:07,350
And you replicate the structure.

974
00:42:07,350 --> 00:42:08,802
You just get the same structure.

975
00:42:08,802 --> 00:42:09,760
There's some shrinkage.

976
00:42:09,760 --> 00:42:11,640
The shrinkage is about 30%.

977
00:42:11,640 --> 00:42:14,250
But you get the same
structure as the wood.

978
00:42:14,250 --> 00:42:17,240
So this material up here
is actually all carbon.

979
00:42:17,240 --> 00:42:19,640
It's just replicating
the wood that was used,

980
00:42:19,640 --> 00:42:21,180
the pine that was used.

981
00:42:21,180 --> 00:42:22,700
An then what people
have been doing

982
00:42:22,700 --> 00:42:26,110
is using that carbon structure
and then infiltrating

983
00:42:26,110 --> 00:42:29,070
that with gaseous silicon.

984
00:42:29,070 --> 00:42:30,920
And they form silicon carbide.

985
00:42:30,920 --> 00:42:34,540
So these structures down
here are all silicon carbide

986
00:42:34,540 --> 00:42:36,990
replicas of wood.

987
00:42:36,990 --> 00:42:41,100
And they're thinking about
using that for things

988
00:42:41,100 --> 00:42:44,840
like filters for
high temperatures

989
00:42:44,840 --> 00:42:46,584
or for catalyst carriers.

990
00:42:46,584 --> 00:42:48,000
And one of the
attractive features

991
00:42:48,000 --> 00:42:49,720
is wood has fairly small cells.

992
00:42:49,720 --> 00:42:52,370
The cells around
50 microns across.

993
00:42:52,370 --> 00:42:54,310
And so you get a
large surface area.

994
00:42:54,310 --> 00:42:55,730
And this is a
similar thing here.

995
00:42:55,730 --> 00:42:58,407
These two are the
carbon template.

996
00:42:58,407 --> 00:43:00,490
And here they've used
silicon and they've actually

997
00:43:00,490 --> 00:43:01,560
filled in the voids.

998
00:43:01,560 --> 00:43:03,740
And so they've got
silicon carbide

999
00:43:03,740 --> 00:43:05,500
where the cell walls used to be.

1000
00:43:05,500 --> 00:43:08,587
And they've got silicon
where the void used to be.

1001
00:43:08,587 --> 00:43:10,170
So people are playing
around with this

1002
00:43:10,170 --> 00:43:12,790
is another way of making a
honeycomb type of structure.

1003
00:43:12,790 --> 00:43:15,610
And they use other kinds of
plants besides wood as well.

1004
00:43:15,610 --> 00:43:18,030
But that's the kind
of general idea.

1005
00:43:18,030 --> 00:43:20,370
So the idea is that wood has
a honeycomb like structure.

1006
00:43:30,980 --> 00:43:32,730
And the cells are fairly small.

1007
00:43:36,290 --> 00:43:40,680
the cells are in the order of
50 microns sort of in diameter

1008
00:43:40,680 --> 00:43:44,390
and maybe a few
millimeters long.

1009
00:43:44,390 --> 00:43:47,906
And this bio carbon template
replicates the wood structure.

1010
00:44:08,690 --> 00:44:14,100
So the wood is pyrolized
at 800 degrees C

1011
00:44:14,100 --> 00:44:16,421
in an inert atmosphere.

1012
00:44:21,870 --> 00:44:24,650
So say an inert gas.

1013
00:44:24,650 --> 00:44:27,230
And that gives you the
bio carbon template.

1014
00:44:35,460 --> 00:44:38,480
And you maintain the
structure, although there's

1015
00:44:38,480 --> 00:44:39,385
some shrinkage.

1016
00:44:55,870 --> 00:45:15,099
structures

1017
00:45:15,099 --> 00:45:17,640
And then this carbon structure
can then be further processed.

1018
00:45:31,260 --> 00:45:32,950
So for example, you
can infiltrate it

1019
00:45:32,950 --> 00:45:34,405
with a gaseous silicon.

1020
00:45:40,520 --> 00:45:42,935
And you end up with a
silicon carbide wood replica.

1021
00:45:58,800 --> 00:46:01,490
So possible applications are
things like high temperature

1022
00:46:01,490 --> 00:46:09,058
filters, or catalyst carriers.

1023
00:46:34,638 --> 00:46:36,497
I think that's it
on the honeycombs.

1024
00:46:40,460 --> 00:46:42,955
Are we good with all
sorts of methods?

1025
00:46:46,020 --> 00:46:48,179
And my little talk
here on processing

1026
00:46:48,179 --> 00:46:49,470
is certainly not comprehensive.

1027
00:46:49,470 --> 00:46:52,430
I'm sure there's other
ways people have developed.

1028
00:46:52,430 --> 00:46:53,568
These are some main ways.

1029
00:47:27,980 --> 00:47:30,880
All right then, I want to
talk about foams as well.

1030
00:47:30,880 --> 00:47:33,280
People have developed
different types of processes

1031
00:47:33,280 --> 00:47:36,140
for different types of solids,
so polymers, and metals,

1032
00:47:36,140 --> 00:47:37,140
and ceramics.

1033
00:47:37,140 --> 00:47:39,870
So I just go through each class
of solid and talk about that.

1034
00:48:09,240 --> 00:48:11,350
So the idea with
polymer foams is

1035
00:48:11,350 --> 00:48:13,700
that you want to
introduce gas bubbles

1036
00:48:13,700 --> 00:48:17,370
into either a liquid
monomer or a hot polymer.

1037
00:48:17,370 --> 00:48:19,620
And then you want
the bubbles to grow.

1038
00:48:19,620 --> 00:48:22,020
And then you want to
stabilize them and solidify it

1039
00:48:22,020 --> 00:48:26,239
by other cross linking or
by cooling the hot polymer.

1040
00:48:26,239 --> 00:48:28,030
So there's a variety
of ways of doing that,

1041
00:48:28,030 --> 00:48:29,700
but let me just put that down.

1042
00:49:17,190 --> 00:49:19,690
So there's a few ways to
get the bubbles in there

1043
00:49:19,690 --> 00:49:20,620
in the first place.

1044
00:49:20,620 --> 00:49:23,340
One, is just by
mechanical stirring.

1045
00:49:23,340 --> 00:49:25,304
So if you've ever
made meringue, you

1046
00:49:25,304 --> 00:49:26,970
know what that is,
you just take a whisk

1047
00:49:26,970 --> 00:49:29,260
and you beat egg
whites and bubbles.

1048
00:49:29,260 --> 00:49:31,860
The air will get enveloped
in the egg whites.

1049
00:49:31,860 --> 00:49:33,750
They also do that with polymers.

1050
00:49:33,750 --> 00:49:35,720
Or you can use a blowing agent.

1051
00:49:35,720 --> 00:49:37,740
And there's several
varieties of blowing agents.

1052
00:50:08,190 --> 00:50:09,880
So the blowing
agents are divided

1053
00:50:09,880 --> 00:50:13,280
into physical and
chemical blowing agents.

1054
00:50:13,280 --> 00:50:16,440
And the physical ones,
they force the gas

1055
00:50:16,440 --> 00:50:18,490
into solution under
high pressure,

1056
00:50:18,490 --> 00:50:19,900
and then you reduce
the pressure,

1057
00:50:19,900 --> 00:50:23,010
and the gas bundles expand.

1058
00:50:23,010 --> 00:50:25,600
So you can use physical
blowing agents.

1059
00:51:13,130 --> 00:51:18,290
Or you can introduce
liquids that, if you're

1060
00:51:18,290 --> 00:51:21,450
using a hot polymer, that at the
temperature of the hot polymer,

1061
00:51:21,450 --> 00:51:22,290
they form a gas.

1062
00:51:22,290 --> 00:51:24,684
So that the liquid
just turns into a gas.

1063
00:51:24,684 --> 00:51:26,100
And that would
form vapor bubbles.

1064
00:52:01,250 --> 00:52:02,806
And then the chemical
blowing agents.

1065
00:52:02,806 --> 00:52:04,930
There's a couple of different
ways that those work.

1066
00:52:11,040 --> 00:52:13,000
You can either use
chemical blowing agents

1067
00:52:13,000 --> 00:52:15,920
where you have two parts that
react together to form a gas.

1068
00:52:15,920 --> 00:52:17,950
And so that gas
then blows the foam.

1069
00:52:17,950 --> 00:52:19,580
Or you can have a
chemical blowing

1070
00:52:19,580 --> 00:52:21,040
agent that reacts
with the polymer

1071
00:52:21,040 --> 00:52:24,100
to form a gas and
that blows the foam.

1072
00:52:24,100 --> 00:52:25,360
So either way.

1073
00:52:25,360 --> 00:52:27,780
And you can have them
decompose on heating.

1074
00:52:27,780 --> 00:52:28,890
So the same kind of thing.

1075
00:52:28,890 --> 00:52:31,430
Evolved the gas when it
gets into the hot polymer.

1076
00:53:04,390 --> 00:53:07,960
So there's these different
ways of blowing the foams.

1077
00:53:07,960 --> 00:53:11,110
And there's many, many different
types of these blowing agents.

1078
00:53:11,110 --> 00:53:13,920
But, these are kind of
the general techniques.

1079
00:53:13,920 --> 00:53:17,200
And whether or not the foam
forms an open cell or a closed

1080
00:53:17,200 --> 00:53:19,080
cell structure depends
on the rheology

1081
00:53:19,080 --> 00:53:21,580
of the polymers, so
the viscosity of it,

1082
00:53:21,580 --> 00:53:22,980
and also the surface tension.

1083
00:53:52,580 --> 00:53:54,620
Another way to make a
foam is to make something

1084
00:53:54,620 --> 00:53:56,065
called a syntactic foam.

1085
00:53:59,770 --> 00:54:01,590
A syntactic foam
is made by taking

1086
00:54:01,590 --> 00:54:04,350
thin walled hollow
spheres and then using,

1087
00:54:04,350 --> 00:54:06,950
say a resin, like an epoxy
resin, to bond them together.

1088
00:54:06,950 --> 00:54:09,210
So you end up with
something that's porous.

1089
00:54:09,210 --> 00:54:11,779
And you've got the void
from the hollow sphere,

1090
00:54:11,779 --> 00:54:13,320
but you don't foam
it in the same way

1091
00:54:13,320 --> 00:54:15,460
that you blow bubbles
through it in some way.

1092
00:55:17,302 --> 00:55:18,760
One other thing
about polymer foams

1093
00:55:18,760 --> 00:55:21,110
is they sometimes have
a skin on the surface.

1094
00:55:21,110 --> 00:55:23,430
So when you blow them,
say you've got a mold,

1095
00:55:23,430 --> 00:55:26,020
there will be a skin that
forms against the mold,

1096
00:55:26,020 --> 00:55:29,230
and sometimes the process
is designed in a way

1097
00:55:29,230 --> 00:55:31,120
that the skin is
thick enough that it

1098
00:55:31,120 --> 00:55:33,160
acts like a skin in
a sandwich panel.

1099
00:55:33,160 --> 00:55:36,530
So they control the mold in
a way and the blowing process

1100
00:55:36,530 --> 00:55:39,794
so that they get a foam in
the middle and thicker skins

1101
00:55:39,794 --> 00:55:41,210
on the top and the
bottom surface.

1102
00:55:41,210 --> 00:55:42,460
And that forms a sandwich panel.

1103
00:55:42,460 --> 00:55:43,880
Those are called
structural foams.

1104
00:56:46,080 --> 00:56:47,050
Let's see.

1105
00:56:47,050 --> 00:56:50,030
So I think what I'm going to
do next is the next section's

1106
00:56:50,030 --> 00:56:50,850
on metal foams.

1107
00:56:50,850 --> 00:56:52,347
And I've got a few
slides on that.

1108
00:56:52,347 --> 00:56:54,430
So I think I'm going to
run through the schematics

1109
00:56:54,430 --> 00:56:55,320
and just talk about it.

1110
00:56:55,320 --> 00:56:56,980
But, I'll put the notes
on the board next time.

1111
00:56:56,980 --> 00:56:58,500
And there is one thing I
forgot to do at the beginning.

1112
00:56:58,500 --> 00:57:00,302
I like to tell you
a little about me.

1113
00:57:00,302 --> 00:57:01,510
And I want to hear about you.

1114
00:57:01,510 --> 00:57:03,900
So I wanted to leave a
few minutes for that.

1115
00:57:03,900 --> 00:57:06,030
So let me just wait
until people are

1116
00:57:06,030 --> 00:57:07,380
finished writing stuff down.

1117
00:57:07,380 --> 00:57:09,426
And I'll go through
these in a few minutes,

1118
00:57:09,426 --> 00:57:11,550
and then we'll through it
in more detail next time.

1119
00:57:11,550 --> 00:57:14,045
And I'll write notes down.

1120
00:57:14,045 --> 00:57:14,545
OK?

1121
00:57:14,545 --> 00:57:16,930
Are we good?

1122
00:57:16,930 --> 00:57:21,622
So there's a whole variety of
ways of making foamed metals.

1123
00:57:21,622 --> 00:57:23,580
And most of them have
been focused on aluminum.

1124
00:57:23,580 --> 00:57:27,800
But you could in theory do them
with other types of metals.

1125
00:57:27,800 --> 00:57:29,440
So this was one of
the first processes

1126
00:57:29,440 --> 00:57:31,610
and it just involved
taking a molten aluminum,

1127
00:57:31,610 --> 00:57:34,420
so here's the aluminum
down here in a crucible.

1128
00:57:34,420 --> 00:57:37,390
They added silicon
carbide powder to it

1129
00:57:37,390 --> 00:57:39,350
and then they just
used a stirring paddle,

1130
00:57:39,350 --> 00:57:43,120
like they just stirred it up
and mixed gas in that way.

1131
00:57:43,120 --> 00:57:45,615
And they found that they
got bubbles that rose up.

1132
00:57:45,615 --> 00:57:46,990
And then they used
conveyor belts

1133
00:57:46,990 --> 00:57:49,076
to just kind of
pull the foam off.

1134
00:57:49,076 --> 00:57:50,700
And the thing about
the silicon carbide

1135
00:57:50,700 --> 00:57:52,860
was that if you
didn't have that,

1136
00:57:52,860 --> 00:57:54,610
then the bubbles
wouldn't be stable enough

1137
00:57:54,610 --> 00:57:55,380
that you could do this.

1138
00:57:55,380 --> 00:57:56,921
The bubbles would
collapse before you

1139
00:57:56,921 --> 00:57:58,290
got to be able to pull them up.

1140
00:57:58,290 --> 00:58:02,650
But the silicon carbide I think
makes the aluminum melt more

1141
00:58:02,650 --> 00:58:05,920
viscous and it helps prevent
sort of drainage and collapse

1142
00:58:05,920 --> 00:58:07,000
of the bubbles.

1143
00:58:07,000 --> 00:58:08,320
And so that's one way.

1144
00:58:08,320 --> 00:58:10,750
And there's a type
of foam called Cymat,

1145
00:58:10,750 --> 00:58:12,510
and this is an example
of the foam that's

1146
00:58:12,510 --> 00:58:13,900
made with that process.

1147
00:58:13,900 --> 00:58:17,210
Maybe I'll bring it next time
and we can pass it around.

1148
00:58:17,210 --> 00:58:21,810
Another method is to use a metal
powder and titanium hydride

1149
00:58:21,810 --> 00:58:22,680
powder.

1150
00:58:22,680 --> 00:58:24,460
Then you can consolidate that.

1151
00:58:24,460 --> 00:58:27,000
So here's-- it's hard
to see the writing,

1152
00:58:27,000 --> 00:58:28,400
but this is a aluminum powder.

1153
00:58:28,400 --> 00:58:30,150
This would be the
titanium hydride powder.

1154
00:58:30,150 --> 00:58:32,600
You mix them together and
then you compact them.

1155
00:58:32,600 --> 00:58:34,190
You press them together.

1156
00:58:34,190 --> 00:58:37,180
And the titanium hydride
decomposes and forms

1157
00:58:37,180 --> 00:58:39,350
the hydrogen gas
at a temperature

1158
00:58:39,350 --> 00:58:41,080
at which the aluminum
is not really

1159
00:58:41,080 --> 00:58:45,460
quite molten but it's kind of
viscous-y, kind of softening.

1160
00:58:45,460 --> 00:58:48,850
And so when the aluminum is
soft like that and the titanium

1161
00:58:48,850 --> 00:58:51,910
hydride decomposes and
forms the hydrogen gas,

1162
00:58:51,910 --> 00:58:54,190
you get a foam
from that process.

1163
00:58:54,190 --> 00:58:56,830
And I think, somewhere,
yeah, this foam here

1164
00:58:56,830 --> 00:59:00,260
I think was made
by that process.

1165
00:59:00,260 --> 00:59:02,730
Then in a similar thing, you
can just put titanium hydride

1166
00:59:02,730 --> 00:59:07,080
powder into molten aluminum,
and again the titanium hydride

1167
00:59:07,080 --> 00:59:11,050
powder evolves the hydrogen
gas and you get foamed aluminum

1168
00:59:11,050 --> 00:59:12,370
from that.

1169
00:59:12,370 --> 00:59:15,550
And I think this foam here
was made with that process.

1170
00:59:15,550 --> 00:59:18,100
They all look kind of similar.

1171
00:59:18,100 --> 00:59:21,800
Another method is by replicating
an open cell polymer foam.

1172
00:59:21,800 --> 00:59:24,860
So I think I passed an open
cell polymer foam around.

1173
00:59:24,860 --> 00:59:28,440
And that's made by taking an
open celled-- an open cell

1174
00:59:28,440 --> 00:59:31,330
aluminum foam-- it's made by
taking an open cell polymer

1175
00:59:31,330 --> 00:59:34,120
foam, you fill up all
the voids with sand.

1176
00:59:34,120 --> 00:59:36,230
You then burn off the
polymer, but now you've

1177
00:59:36,230 --> 00:59:40,090
got sand in all the sort of
places where there were voids.

1178
00:59:40,090 --> 00:59:42,840
And then you infiltrate
molten metal into that.

1179
00:59:42,840 --> 00:59:44,290
And then you get
rid of the sand.

1180
00:59:44,290 --> 00:59:46,110
And then you're left
with an aluminum

1181
00:59:46,110 --> 00:59:49,670
foam that replicates the polymer
that you started off with.

1182
00:59:49,670 --> 00:59:52,170
So this replication technique.

1183
00:59:52,170 --> 00:59:55,110
There's a vapor
deposition technique.

1184
00:59:55,110 --> 00:59:57,790
And this was developed by
Inco to make nickel foams.

1185
00:59:57,790 --> 00:59:59,680
So they take again an
open cell polymer foam,

1186
00:59:59,680 --> 01:00:05,000
that's kind of this thing here
is, and they infiltrate into it

1187
01:00:05,000 --> 01:00:07,780
nickel CO4.

1188
01:00:07,780 --> 01:00:10,420
The only teeny detail that's
a problem with this process

1189
01:00:10,420 --> 01:00:13,280
is that happens to
be highly toxic.

1190
01:00:13,280 --> 01:00:15,010
So they put this
gas through here.

1191
01:00:15,010 --> 01:00:19,070
And then they get nickel
depositing on the polymer

1192
01:00:19,070 --> 01:00:21,450
and they burn the polymer
out and they center it.

1193
01:00:21,450 --> 01:00:23,390
So it is possible to do this.

1194
01:00:23,390 --> 01:00:24,310
They have done this.

1195
01:00:24,310 --> 01:00:27,060
But it's not that
practical because

1196
01:00:27,060 --> 01:00:29,520
of the toxicity of the gas.

1197
01:00:29,520 --> 01:00:32,810
Now another method is something
called entrapped gas expansion.

1198
01:00:32,810 --> 01:00:37,940
And here, what you do is you
take a can, like a metal can.

1199
01:00:37,940 --> 01:00:40,360
This one's titanium,
a titanium alloy.

1200
01:00:40,360 --> 01:00:43,310
And then you put a
titanium powder in here.

1201
01:00:43,310 --> 01:00:44,980
You evacuate the can.

1202
01:00:44,980 --> 01:00:47,590
So the can has a little valve
on it, so you can evacuate it.

1203
01:00:47,590 --> 01:00:49,640
And then you backfill
it with argon gas

1204
01:00:49,640 --> 01:00:51,420
and you pressurize
the argon gas.

1205
01:00:51,420 --> 01:00:54,050
So you've got a powder with
sort of pressurized gas

1206
01:00:54,050 --> 01:00:55,720
inside of a can.

1207
01:00:55,720 --> 01:00:57,840
And then you hot
isostatically press it.

1208
01:00:57,840 --> 01:01:00,040
So you heat it up and
you press it uniformly

1209
01:01:00,040 --> 01:01:01,520
in all three directions.

1210
01:01:01,520 --> 01:01:03,700
And you compact it.

1211
01:01:03,700 --> 01:01:05,390
And then, if you
want you can roll it.

1212
01:01:05,390 --> 01:01:06,730
Sometimes people
roll it because they

1213
01:01:06,730 --> 01:01:07,980
want to make sandwich
panels, and they

1214
01:01:07,980 --> 01:01:09,354
want to have a
certain thickness,

1215
01:01:09,354 --> 01:01:11,447
and they want to have
faces on the panel.

1216
01:01:11,447 --> 01:01:12,530
But then you heat that up.

1217
01:01:12,530 --> 01:01:14,810
And as you heat it up,
the gas evolves again.

1218
01:01:14,810 --> 01:01:17,890
And the thing expands and
you get a foam that way.

1219
01:01:17,890 --> 01:01:20,210
So that's another method.

1220
01:01:20,210 --> 01:01:22,760
Another method is by
making hollow spheres

1221
01:01:22,760 --> 01:01:25,150
and then bonding the
spheres together.

1222
01:01:25,150 --> 01:01:27,690
And in this process-- this
was developed at Georgia Tech.

1223
01:01:27,690 --> 01:01:29,940
They used the titanium
hydride again.

1224
01:01:29,940 --> 01:01:32,120
They made a slurry of
the titanium hydride

1225
01:01:32,120 --> 01:01:34,330
in an organic
binder in a solvent.

1226
01:01:34,330 --> 01:01:36,250
And then they had a
little kind of needle

1227
01:01:36,250 --> 01:01:37,550
that they injected gas.

1228
01:01:37,550 --> 01:01:42,470
And so they had this slurry
and they were blowing gas

1229
01:01:42,470 --> 01:01:45,860
through this needle and they got
hollow spheres of the titanium

1230
01:01:45,860 --> 01:01:46,817
hydride.

1231
01:01:46,817 --> 01:01:49,400
And then they heated it up, and
again evolved the hydrogen gas

1232
01:01:49,400 --> 01:01:49,570
off.

1233
01:01:49,570 --> 01:01:51,570
But now they're just left
with titanium spheres.

1234
01:01:51,570 --> 01:01:54,220
And then they bonded
the spheres together.

1235
01:01:54,220 --> 01:01:55,550
And these aren't titanium.

1236
01:01:55,550 --> 01:01:57,770
This is an iron
chromium, like it's not

1237
01:01:57,770 --> 01:01:59,480
quite a stainless steel.

1238
01:01:59,480 --> 01:02:00,740
But this is the same thing.

1239
01:02:00,740 --> 01:02:02,460
I can pass that
around next time too.

1240
01:02:02,460 --> 01:02:04,870
Those are the little
beads that they make.

1241
01:02:04,870 --> 01:02:07,950
And then there's also
fugitive phase technique.

1242
01:02:07,950 --> 01:02:11,490
So you can take say salt
particles, put them in a mold

1243
01:02:11,490 --> 01:02:14,220
and pour a liquid
metal into that,

1244
01:02:14,220 --> 01:02:17,810
and then, leach the salt away.

1245
01:02:17,810 --> 01:02:20,777
And I think that's it
for the metal foams.

1246
01:02:20,777 --> 01:02:22,610
So I think I'm going
to stop there for today

1247
01:02:22,610 --> 01:02:23,830
in terms of the lecture.

1248
01:02:23,830 --> 01:02:25,280
I'll go over that
again next time.

1249
01:02:25,280 --> 01:02:26,710
And I'll write
stuff on the board.

1250
01:02:26,710 --> 01:02:28,230
But I wanted to tell
you a bit about me.

1251
01:02:28,230 --> 01:02:29,688
So the people in
3032, they already

1252
01:02:29,688 --> 01:02:31,970
know me because they
had me in the fall.

1253
01:02:31,970 --> 01:02:33,850
But I see some unfamiliar faces.

1254
01:02:33,850 --> 01:02:35,850
So I thought I would tell
you a little about me.

1255
01:02:35,850 --> 01:02:41,230
So I grew up in Niagara Falls
in Canada, big power station.

1256
01:02:41,230 --> 01:02:43,890
Lots of big civil engineering
works in Niagara Falls.

1257
01:02:43,890 --> 01:02:46,340
And my father worked at
an engineering company

1258
01:02:46,340 --> 01:02:48,780
that specialized in the
design of hydroelectric power

1259
01:02:48,780 --> 01:02:49,330
stations.

1260
01:02:49,330 --> 01:02:51,663
It was founded by the guy who
designed the Niagara Falls

1261
01:02:51,663 --> 01:02:52,490
power station.

1262
01:02:52,490 --> 01:02:56,210
And then I went to
university in Toronto.

1263
01:02:56,210 --> 01:02:58,990
And I did a degree in civil
engineering in Toronto.

1264
01:02:58,990 --> 01:03:01,494
And then when I finished my
degree in civil engineering,

1265
01:03:01,494 --> 01:03:03,410
I wasn't really sure
what I wanted to do next.

1266
01:03:03,410 --> 01:03:05,710
And I applied for some jobs, and
I applied to graduate school.

1267
01:03:05,710 --> 01:03:06,640
I applied to MIT.

1268
01:03:06,640 --> 01:03:09,270
And I didn't get in-- ouch.

1269
01:03:09,270 --> 01:03:11,730
But I did OK, it turns out.

1270
01:03:11,730 --> 01:03:13,950
And I ended up-- I
had an advisor when

1271
01:03:13,950 --> 01:03:16,330
I was in Toronto who had taken
a sabbatical in Cambridge,

1272
01:03:16,330 --> 01:03:16,830
England.

1273
01:03:16,830 --> 01:03:20,180
And he said he thought I might
enjoy Cambridge, England.

1274
01:03:20,180 --> 01:03:22,040
And I ended up going
to Cambridge, England

1275
01:03:22,040 --> 01:03:24,350
to doing my PhD there.

1276
01:03:24,350 --> 01:03:26,855
And I worked on the
cellular solids for my PhD.

1277
01:03:26,855 --> 01:03:28,480
And it was a nice
combination because I

1278
01:03:28,480 --> 01:03:30,800
was interested in material
behavior and mechanics,

1279
01:03:30,800 --> 01:03:33,192
but I had a background in
me in civil engineering.

1280
01:03:33,192 --> 01:03:35,400
And these are just like
civil engineering structures,

1281
01:03:35,400 --> 01:03:37,530
but they're on a little
teeny weeny scale,

1282
01:03:37,530 --> 01:03:39,770
not like big buildings
or bridges or something,

1283
01:03:39,770 --> 01:03:41,880
like little teeny things.

1284
01:03:41,880 --> 01:03:44,490
And really all of
this has come out

1285
01:03:44,490 --> 01:03:47,240
of doing that PhD in Cambridge.

1286
01:03:47,240 --> 01:03:49,090
But when I was there,
I never even thought

1287
01:03:49,090 --> 01:03:50,250
about being an academic.

1288
01:03:50,250 --> 01:03:53,220
And I never applied
for any academic jobs.

1289
01:03:53,220 --> 01:03:54,970
I didn't think I wanted
to be an academic.

1290
01:03:54,970 --> 01:03:58,890
And I went and got a job in
Calgary in the oil business.

1291
01:03:58,890 --> 01:04:00,760
And I was working at
a consulting firm that

1292
01:04:00,760 --> 01:04:02,270
did work for the oil business.

1293
01:04:02,270 --> 01:04:02,990
I hated it.

1294
01:04:02,990 --> 01:04:03,730
I just hated it.

1295
01:04:03,730 --> 01:04:04,850
It was like I had a boss.

1296
01:04:04,850 --> 01:04:06,810
I hated having this boss.

1297
01:04:06,810 --> 01:04:09,789
And, you know, the projects
were too short term.

1298
01:04:09,789 --> 01:04:11,830
The winter in Calgary--
if you think this is bad,

1299
01:04:11,830 --> 01:04:13,670
you've seen nothing.

1300
01:04:13,670 --> 01:04:15,120
Like less snow, but cold.

1301
01:04:15,120 --> 01:04:18,140
I mean like 30, 40
below, everyday, cold.

1302
01:04:18,140 --> 01:04:19,400
Real cold.

1303
01:04:19,400 --> 01:04:21,010
So I stayed there one winter.

1304
01:04:21,010 --> 01:04:22,510
And somewhere along
the way there, I

1305
01:04:22,510 --> 01:04:25,600
decided maybe the academic
job thing would be good.

1306
01:04:25,600 --> 01:04:28,835
And I just sent my CV out to a
bunch of Canadian universities.

1307
01:04:28,835 --> 01:04:31,210
And I ended up getting a job
at the University of British

1308
01:04:31,210 --> 01:04:32,550
Columbia in Vancouver.

1309
01:04:32,550 --> 01:04:34,390
And I lived in
Vancouver for two years.

1310
01:04:34,390 --> 01:04:35,630
And I probably would
have stayed there,

1311
01:04:35,630 --> 01:04:37,230
except there was a
gigantic recession,

1312
01:04:37,230 --> 01:04:39,580
and it was all very depressing,
and there was no money.

1313
01:04:39,580 --> 01:04:41,650
And that the
universities in Canada

1314
01:04:41,650 --> 01:04:43,900
are almost all run by the
provincial governments.

1315
01:04:43,900 --> 01:04:45,233
And the government had no money.

1316
01:04:45,233 --> 01:04:47,109
It was all, you
know, frustrating.

1317
01:04:47,109 --> 01:04:48,900
And I sort of thought,
oh, I'll look around

1318
01:04:48,900 --> 01:04:49,700
and see what else I can get.

1319
01:04:49,700 --> 01:04:52,270
And I answered a little ad
in Civil Engineering Magazine

1320
01:04:52,270 --> 01:04:53,600
for a job at MIT.

1321
01:04:53,600 --> 01:04:54,695
And I got the job at MIT.

1322
01:04:54,695 --> 01:04:56,570
And I was in the civil
engineering department

1323
01:04:56,570 --> 01:04:57,580
for about 12 years.

1324
01:04:57,580 --> 01:04:59,700
And then I moved over to
the materials department.

1325
01:04:59,700 --> 01:05:01,658
Because my work started
off on sort of sandwich

1326
01:05:01,658 --> 01:05:02,990
panels and structural things.

1327
01:05:02,990 --> 01:05:05,000
And then it kind of became
more biomedical stuff

1328
01:05:05,000 --> 01:05:06,822
and had less and less
to do with civil.

1329
01:05:06,822 --> 01:05:09,030
And I've been in the materials
department since then.

1330
01:05:09,030 --> 01:05:11,071
And this is kind of what
I do, this kind of work.

1331
01:05:11,071 --> 01:05:13,900
So that's kind of my
little five minute story.