Hello and welcome to our second lesson in our course on material selection using Ashby charts.
In today's lesson, we're going to focus on using our material property charts from lesson 1
to visually select materials for various applications.
But before we begin using our charts, we need to think about what we're trying to achieve
when performing a material selection. Well we're trying to choose the best material for our design.
This involves identifying material properties of interest based on how our product should perform
during use. We go over this in more detail in our basic systematic material selection course,
but once these key material properties have been identified, we can begin comparing materials with
one another to make the optimal choice. This often involves maximizing or minimizing various material
properties depending on my design criteria, think minimizing cost, maximizing strength, etc.
In lesson one, we saw that we can compare materials with one another using tables like the one shown
here. But we also saw that this can be challenging, comparing hundreds of materials with one another
just using these tables. So instead, let's use our property charts. We'll start with a bar chart like
the one shown here. Now we want to introduce the subject of ranking, I just said that often we're
trying to optimize our material selection by maximizing or minimizing some property.
I can do this with ranking with my bar chart. I can rank the materials from best to worst based on
my design criteria. So when looking in a chart of young's modulus. Perhaps we're interested in a very
stiff material for an application like a dinner plate. I know I don't want a floppy dinner plate.
Therefore, we want a material with a high young's modulus or to maximize young's modulus, so we focus
on the upper portion of our chart. But what if I'm instead designing a material for
the bottom of a running shoe. I want some amount of stiffness, but in order to protect my joints,
I need something with a lower stiffness than my dinner plate. Therefore I'm going
to shift my focus lower on this bar chart and look to optimize my property in this region.
Once again, using a logarithmic scale here instead of linear is very useful to help make the ranking
process easier to visualize. Well comparing one property is just fine, but design usually
requires considering more than one property. We can use our bubble charts to compare two material
properties against one another. Here things are a little more complex than with our bar charts.
Our example here is a young's modulus versus density bubble chart. Remember the small ovals
and circles represent individual materials while the larger envelopes show material families.
We can think about this chart in four quadrants.
So if we start in the lower left corner we can see materials that have low stiffness and low
density. Makes sense we're seeing our foams, particularly polymeric foams in this corner.
Again depending on our design criteria, we either want to focus on this quadrant or avoid it.
Next, we have the lower right corner, where we have low stiffness but high density. Notice how there
aren't a lot of materials in this quadrant. We have some elastomers and and that's mostly it.
This is okay as generally a structural design doesn't need a heavy yet not very stiff material.
Next, we move to our upper right hand corner, where we have high density and high stiffness materials.
Our technical ceramics and metals can be found here with composites
sitting right at the edge. Finally we have the upper left-hand corner. Once again, it's mostly
empty apart from our composites. Many engineers and designers consider this quadrant filled with
the ideal materials- high stiffness but low density. Perfect for aerospace and automotive applications.
While no materials really exist up here, especially in the middle, our property charts can help us pick
materials close to this ideal as possible. It also allows material scientists and designers
to see how brand new materials can fit within the landscape of existing engineering materials.
So we've now seen how we can use our property charts to help us rank our materials based on our
design criteria, but the charts I showed you only have about 100 engineering materials. In reality,
we have thousands of engineering materials so our chart should really look something like this.
This is so much more information to sort through. Is there some way that we could simplify this?
Well we can go back to our design criteria. Maybe there are some material families that I just
don't need to consider. Or maybe I have a minimum acceptable value for a specific material property,
so I can simply toss out the materials that don't meet that minimum. This process is called screening.
It actually occurs before ranking. Screening means I'm tossing out unsuitable materials
and then I rank the materials that are left over. So we can see this example in a bar chart.
Here I have a bar chart of yield strength on my y and I've split the x axis based on material family.
Based on my design criteria, I know that I don't need to consider polymers and elastomers, so
I can just get rid of them and now I can focus on ranking my materials that are left over to
maximize my yield strength. So I'm focusing up here in my chart. I can also do this with bubble charts.
Here we're really focusing on which of these four quadrants. I want to have my material reside
in. So let's say I'm shooting for this optimal upper left hand corner, so I'm simply going to
focus all my attention in this direction. And with that, we've come to the end of our lesson.
We've shown how we can take our material property charts and visually select materials
using screening and ranking based on design criteria. In the final lesson for this course,
we're going to take our material property charts and our visual material selection
strategy and apply it to a real world example an airplane wing. So join us, as
we explore how to use our charts to select materials with multiple design criteria.
My name is Kaitlin Tyler, thank you so much for joining me and I'll see you in the next one!