[MUSIC] Hi, and welcome back. Today, we're going to continue discussing the modulus of elasticity and module five, which is part of unit one, material properties in design. So, the learning outcomes for today's module is, first, to become familiar with the values of the modulus of elasticity for typical engineering materials. Second, to understand the key differences between the modulus of elasticity and strength. And then, third, to understand when the modulus of elasticity becomes a key factor in material selection. So, just a quick review. Last time, we discussed how the modulus of elasticity is the slope of the linear elastic region of the stress strain curve. It's a property of the material, and it can be thought of qualitatively as a material stiffness. So, units and values. So, first off, again, in this course we're going to use capital E as our notation for the elastic modulus. In English the units are psi. And most metals are in the mega psi range. In metric units, the units are pascals, and most metals have a modulus of elasticity in the gigapascal range. So let's take a look and see the varying values of the modulus of elasticity for a number of different types of engineering materials. So, the first one we're going to start with is rubber, which has an elastic modulus of 0.01 mega psi. And then, the next one is ABS plastic. This is one of the more common plastics that's used in 3D printing, and it's stiffer with elastic modulus of 0.23 mega psi. Then we get into titanium, which is a common metal used in the aerospace industry, and it has an elastic modulus of around 16 mega PSI. And then, steel, which is commonly used in both the automotive and the aerospace engineering industries, is right around the 30 mega psi range. If you're more used to the metric units, they're on the right of the chart, there. And so, you can see from this chart that, obviously, plastics are easier to deform than metals, which I think we all knew. But that steel is common, it's commonly used in engineering because it's very difficult to deform or to deflect. If you wanted to see some super fancy kind of fun engineering materials graphing, kind of wins the elastic modulus prize with an elastic modulus of 152 Mpsi, so much much stiffer than steel. In specifically in the aerospace, the agriculture and the automotive industries, you tend to use certain metals over and over. And by far those are aluminum and steel. And then, especially in aerospace, you might see a little bit more titanium, and then some other industries you might see a little more cast-iron. So you can see aluminum is over here at the bottom. It's the easiest metal to deform out of these four with modulus of elasticity right in the 10 to 11 Mpsi range. And then, cast iron, slightly stiffer. Titanium is up in the 16 to 18 mega psi range. And then, steel is right around the 30 mega psi range. Okay, so it's important to understand the critical differences between the modulus of elasticity and the strength. So we talked about how the strength is a point of interest. It could be, the yield strength, where past that strength you get permanent deformation of the material, and that's capacity of the component and the material. With modulus of elasticity, it can really be thought of as a non-geometric stiffness, and it is the slope of the stress-strain curve. So, when you start going through and trying to pick materials for engineering design, you're going to notice some interesting things. One, that in the same material, the modulus of elasticity won't vary a lot depending on alloying, but the strength will. So, for example, 1025 steel that's been annealed has a modulus of elasticity of 29, and a strength of 36. But 4340 steel that's been quenched and tempered. So, different alloy different processing, has the same Young's modulus, or modulus of elasticity, of 29, but a significantly higher yield strength of 214. And so, then if we go down and we look at aluminum, aluminum has a Young's modulus, or modulus elasticity, of 10.5, and a strength of 54 KSI. So, when we look at the comparison down here on our left, we can see that for modulus elasticity, the aluminum is much lower than the steels, even though the steels are different alloys. But for the yield strength of aluminum versus steel, we see that 1025 steel is actually less strong than aluminum, which is significantly less strong than 4340 steel. So, you start to see variations in strength depending on the alloying of steel, but not these high variations in the modulus of elasticity. And that's important to keep in mind when you're designing components. The values for these material properties came from Mil Handbook 5J, which is a USA Department of Defense standard. So, when we look at the material selection in design, and we look at when is the modulus of elasticity important, it becomes really important when you'ree doing stress analysis and FEA because it's intrinsic to the material, so you need to make sure that your material properties are correct, especially when you're setting up your FEA. It's critical when you're trying to prevent deflection in a constrained geometry. And then, there's a couple of things called critical speed and buckling. And these are very, very dependent on the modulus of elasticity. So, critical speed is something we worry about, especially in shafts, which are rotating, so metal cylinders that connect let say a motor To a gear. And here, you can see a shaft connecting a generator with a turbine in the Boise River dam. And here's the shaft right here. And so, later in the course we'll learn about critical speed. Buckling, this is something you should have learned about in mechanics of materials. And you can see right here that buckling is dependent on the modulus of elasticity and the geometry. What's interesting about that is it's a failure mode that really doesn't have a lot to do with the strength of the material, and has everything to do with the geometry and modulus of the material. And then, another time it comes in really critical is to prosthetics and biomaterials. There's all sorts of different applications from how biological cells react to a material based off of its modulus, to things like stress shielding. And we'll get into that a little bit later in the class when we look at some case studies. So, we've covered the modulus of elasticity. Next module, we'll get into material selection. And I'll see you next time. [MUSIC]