[MUSIC]

Hello, everyone.

Welcome to the Materials Data Science and Informatics class.

I'm Surya Kalidindi, the instructor for this class.

The title for today's lesson is Material Property, Material Structure, and

Manufacturing Processes.

The expected outcomes for today's lessons are to understand the meanings of this

comes in the title in the context of materials development efforts.

And then in the process we also learned that materials design and

process design are in worst problems that are very difficult to solve.

Let's start. With the word property.

Properties are usually defined and measured.

A typical standard test for problem measuring, mechanical properties,

is the tension test and this tension test is described in the ASTM standard E8.

In the tension test, one typically starts with a cylindrical sample and

I place a load along the axis of the sample.

As you apply the load, the cylindrical sample stretches, and when it stretches,

for a while it actually undergoes uniform deformation in the sense that the cross

section remains constant throughout the length of the sample.

And after a while you get what is called as nicking, or localized deformation.

Eventually the sample breaks.

One recourse the load displacement or load extension.

And extension is defined as L minus L nought, the change in length.

And then define the stress and strain, where the stress is defined as load

divided by the initial cross-sectional area.

And strain is defined as Extension divided by initial cross section area.

And the extension is L minus L not.

So once one has the load and the extension you normalize

it by the geometric parameters of the sample and define the stress and strain.

Once you have the stress/strain curve,

you can now define properties on the stress/strain curve.

So the first property of interest might be yield strength.

Yield strength is defined as the stress at which elastic deformation or

inelastic deformation sets in the sample.

So in design it's an important property because you want to design your

You're component [INAUDIBLE] that there's no permanent defamation or

inelastic defamation.

Another property of [INAUDIBLE] is the ultimate tensile strength.

Ultimate tensile strength is also very useful property, because it tells

you how much stress you can apply on the sample without breaking the sample.

A third property from that is apparent here from this curve

is called the total elongation.

It's percentage strain at which the sample breaks.

That falls in extremely useful property because you want to design

your conference.

Such a way that they don't break to give you enough strain before they break,

they give you enough warning before they break.

So, these are three of the properties you can define on the stress strain

from a tension test.

There are more,

but this hopefully will give you some idea of examples of properties.

Let's now define property in a little bit more general way.

The property refers to a physical property of interest.

which means that you are imposing some sort of a physical

loading condition on the sample and you're measuring it's response.

It is defined as a characteristic of the materials' response to the applied load

and it is always normalized, suitably normalized.

And what we mean by that is exactly what I described in the previous slide,

where we took the load and the extension, and normalize it by area and

length to get stress and strain.

Without normalization, if you define a property it is

likely to be sensitive to small changes in the geometry of the sample.

That you use for the test.

So the normalization gets rid of that sensitivity and

makes the property more useful.

In structural applications, there are many properties of interest.

These include things such as elastic stiffness,

elastic modulus, yield strength, fracture toughness, fatigue strength.

And so on so forth.

In reality, we're often interested in property combinations.

We seldom are interested in individual properties but

interested in property combinations

as an example as a specific example of a property combination of interest.

Let's look at this combination, Elongation versus Tensile strength.

In the previous light we have defined these properties again to remind you.

Tensile strength tells you something about how much load you can apply on the sample

before the sample.

Under those plastic deformation or sometimes breaks.

And the elongation you see an indicator of

how much we can stretch the sample before it breaks.

These are both very useful and ideally you would want a combination that has

high tensile strength and high elongation.

In a plot like this, high tensile strength and high elongation are in these areas.

In fact if you look at all the property combinations,

the values of property combinations that you can get in a very broad

range of steels I think that at about a few thousand steels the percentage.

Even in this plot.

You see that, that particular combination the high strength and

high elongation is not that easily achievable.

At least it's not achievable in the known materials so far.

It doesn't mean it cannot be attained in any material, but it just means that in

the steals that have produced and tested so far, that combination has been elusive.

That's one of the observation you can make.

The second observation that becomes clear from a plot like this

Is that even in a single steel, if you look at one of these ellipses,

that ellipses represents a single grade of steel.

That means that the chemical composition is reasonably well controlled.

So even when you control the chemical composition of the particular steel,

you still get a substantial variance.

In the properties and

if you look at the ranges of these properties these are substantial.

And therefore, the challenge and

design because you don't know whether you can design for the property here or

can you design for the property there or somewhere in between.

Ideally what we would like to do is to do two things.

One is we want to control the property variance such whether.

Properties are more tightly controlled.

And we would like to get access to properties,

combinations that are of value in engineering design.

So we would like to produce new materials that would exhibit properties in

this area.

So if we want to do that, the next logical question is, what do properties depend on?

And if you think about it the properties depend on material internal structure.

That should be rather obvious because the material internal structure has to

control the properties.

However, the difficulty is the material internal structure is

extremely complex and in fact it spans many many land scales.

If you look at the smallest land scales and

in particular pay attention to the hale bars here.

So if you look at the scale of the nanometer below,

you'll see that the atomic structure is fairly well organized,

at least in metals, which are polycrystalline.

So in the crystalline solids or polycrystalline solids,

the atomic structure is rather well organized.

However, if you start looking at this area indicated as A and

B, you'll start seeing that there are defects.

Although it is crystal in and although it is ordered with a large extent,

it's by no means perfect and these defects are extremely important.

Here in this particular graph, you see another defect between the two arrows and

that's another kind of defect and that is a denominator length scale.

Now if you actually go to the micron lens care, which is

three orders of magnitude larger than a nanometer, you get other kinds of effects.

What you see here as lines are essentially what are called dislocations.

These dislocations represent defects that are missing half planes

within the crystal structure.

Within the three dimensional crystal structure.

And you can see that these locations

are arranged in very complicated ways at a much higher length scale.

Now we are talking about a 100 micron length scale which is still much,

much smaller than a macro scale material sample that you can hold in your hand.

At this length scale that is still yet

detail of the material Polycrystalline structure.

What you are seeing as individual creatures here, anyone of this creatures,

or you're seeing as those creatures, those are called grains or individual crystals.

So basically in anyone of this grains you have a crystalline structure

that may look like that.