This course is an introduction to high-throughput experimental methods that accelerate the discovery and development of new materials. It is well recognized that the discovery of new materials is the key to solving many technological problems faced by industry and society. These problems include energy production and utilization, carbon capture, tissue engineering, and sustainable materials production, among many others. This course will introduce the learner to a remarkable new approach to materials discovery and characterization: high-throughput materials development (HTMD). Engineers and scientists working in industry, academic or government will benefit from this course by developing an understanding of how to apply one element of HTMD, high-throughput experimental methods, to real-world materials discovery and characterization problems. Internationally leading faculty experts will provide a historical perspective on HTMD, describe preparation of ‘library’ samples that cover hundreds or thousands of compositions, explain techniques for characterizing the library to determine the structure and various properties including optical, electronic, mechanical, chemical, thermal, and others. Case studies in energy, transportation, and biotechnology are provided to illustrate methodologies for metals, ceramics, polymers and composites. The Georgia Tech Institute for Materials (IMat) developed this course in order to introduce a broad audience to the essential elements of the Materials Genome Initiative. Other courses will be offered by Georgia Tech through Coursera to concentrate on integrating (i) high-throughput experimentation with (ii) modeling and simulation and (iii) materials data sciences and informatics. After completing this course, learners will be able to • Identify key events in the development of High-Throughput Materials Development (HTMD) • Communicate the benefits of HTMDwithin your organization. • Explain what is meant by high throughput methods (both computational and experimental), and their merits for materials discovery/development. • Summarize the principles and methods of high throughput creation/processing of material libraries (samples that contain 100s to 1000s of smaller samples). • State the principles and methods for high-throughput characterization of structure. • State the principles and methods for high throughput property measurements. • Identify when high-throughput screening (HTS) will be valuable to a materials discovery effort. • Select an appropriate HTS method for a property measurement of interest. • Identify companies and organizations working in this field and use this knowledge to select appropriate partners for design and implementation of HTS efforts. • Apply principles of experimental design, library synthesis and screening to solve a materials design challenge. • Conceive complete high-throughput strategies to obtain processing-structure-property (PSP) relationships for materials design and discovery.
Measurements using Indentation Methods
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Из курса от партнера Georgia Institute of Technology
Introduction to High-Throughput Materials Development
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High-Throughput Property Measurements
This module covers techniques to experimentally conduct property measurements suitable for high-throughput screening; optical, electronic, mechanical, chemical, and thermal properties are considered.
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Dr. Richard W. NeuProfessor
The George W. Woodruff School of Mechanical Engineering
Dr. J. Carson MeredithProfessor, Associate Chair for Graduate Studies, and J. Carl Pirkle Sr. Faculty Fellow
School of Chemical & Biomolecular Engineering
[MUSIC]
Hi, this is Rick Neu.
In this lesson we're going to look at ways to make
Mechanical Property Measurements using Indentation Methods.
The Learning Outcome is to explain the indentation methods for
measuring elastic modulus and strength in particular.
So first look at Elastic Modulus.
Now few things about Elastic Modulus we need to know.
One is relatively insensitive to microstructure,
so what that really means is it's possible to even use
1st principle calculations to determine some of the elastic constants.
In other words we can possibly use high throughput computational approaches
to learn a little bit about about the elastic modulus too.
So for example the VASP code could be used to determine this.
Using, it's a code to do Quantum Mechanical Molecular Dynamics analysis.
But there are exceptions and
there reasons why we need to be able to measure elastic modules.
For one we need to validate the results that we get from
these computation of codes.
But the other is the fact that
modules can be sensitive to microstructure in some cases.
If your microstructure's full of porosity,
it's not going to follow what a quantum mechanic code gives you.
If there's multiple phases that form,
they could interact in a way that's not predictable by first principles.
And anisotropy due to crystallographic texture and
other features from deformation or thermal processing can play a role.
So these things make it difficult to predict the elastic
modulus totally from first principles, so what do we do?
Well most viable high-throughput method for measuring elastic modulus are based on
indentation test, measuring the force-displacement response.
Because we can get fine spatial resolution, the rapid measurement as we
pointed out and you can automate the mapping of the surface.
So how might we do this?
Well we can use instrumented nanoindentation.
That's what we covered in a previous lesson.
That's pretty much a static measurement.
But because if you're just interested in determining elastic modulus, you're not
trying to apply a load to permanently deform the material you're probing.
You can use some methods that use lighter loads.
So it allows you to use atomic force microscopy methods.
And there's a couple ways you can do that.
There's this Dynamic Force Modulation method and
there's an Atomic Force Acoustic/Ultrasonic Microscopy method.
Just to explain the difference between these method you have to look at is basics
schematic of Atomic Force Microscopy basically consist of an indenter?
Tip, it's on a cantilever, end of the cantilever
there is some piece of electric oscillator that moves that cantilever up and down.
And there is someway to detect displacement at the tip.
And so that the cantilever could be in touch with the body below or
may be its not in touch but usually when we are doing these sorts of experiments.
We want the tip to be in touch with the body because we're looking at
the compliance of the tip with the body.
And so now we can look at, we can oscillate it into that body and
look at the compliance.
R, it turns out if the flexural resonance
of that cantilever is affected by the compliance of the body or
the stiffness of the body which of course relates to the modulus.
So you can measure the flexural resonance of a cantilever and
correlate that to the modulus.
And so there's a couple of ways you can do this and clearly,
this can be made high-throughput, so now let's turn to strength.
Now what do we mean by indentation strength?
And so here is some indentation stress strength curves that were
generated on a material library that had a thermal gradient.
And this particular material where it was cold and
a higher strength where it was hotter the strength went down.
And so there's three curve shown here.
The blue, the red, and the one near the bottom.
I think it's black and if you did a macroscopic tensile test,
a conventional ASTM ISO type test.
And compared the strength you get from that test to the indentation yield
strength measured using the methodology we explained in the previous lesson.
They aren't the same so here's a comparison that shows those three
different microstructures, the as-received.
Some intermediate temperature and one that was exposed to temperature 413 degrees C.
And what you see is the indentation yield strength is higher but
twice as high as the yield strength you measure in a macroscopic test.
And this is due to the fact that
it's a fairly complex data stress under the indentation test.
In fact, there's a scaling relationship that you can find if you understand
the mechanics of the material fairly well.
And you can see it's roughly a factor of two.
But the most important thing to note is the fact that they do scale,
materials that tend to be have higher strength and lower strength in
a tensile test will also scale the same way in the indentation test.
So you get the highest indentation yield strength
in the condition where it would have the highest yield strength.
And so we can use this still high through put measure
to tell us something about the relative strengths of the material.
Now the other aspect that you have to deal with when you're dealing with
metals in particular, is the microstructure and so the sampling size.
The thing with spherical indentation is you could actually
adjust the size of your indentor.
So this is a little schematic that illustrates this and
illustrates a microstructure.
So, at the bottom there's a metal, a polycrystal metal.
It could be some other material that has some distribution of grains or
other sorts of features, something that has a scale to it.
And so, on the left we have a microindentor,
it's bigger indentor, and on the right a nanoindentor.
Nanos hunt a thousand times smaller than a micro.
And so just to illustrate that that would be our large identer.
The large identor might be sampling many many many grains here.
But as you make the identor size smaller
you do this by making the radius smaller, you're sampling less grains.
You're smaller yet, almost sampling just one grain.
And you get down to the nanoscopic scale,
you may be just sampling essentially a single crystal.
Because your indentations all encompassed within that single grain.
And clearly you're going to have different responses, depending on this scale.
Or if you do nano indentation,
you have to relate that crystal response back to the macroscopic response.
And we have relationships and we know how these things do scale,
so we can make these connections.
So in this lesson, we've explained the indentation methods for
measuring elastic modulus and strength.
In particular, we focused on a few key things.
For elastic modules,
we explored different methods that can be used based on indentation.
Was either nano indentation or atomic force microscopy.
With strength we look at two issues that we have to deal with,
the issue of scale and the fact that you can use
different instruments that can indent at different scales.
And we learned a little bit about the meaning of this indentation strength and
how it compares to a traditional measure of yield strength.
So what's next?
We'll take a look at one other mechanical property and
that is Fracture Toughness, thank you.
[MUSIC]
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