Exotic Materials in NASCAR Engines?

I was at a panel discussion some years ago at a motorsports engineering meeting about materials allowed on the car by different racing series. They had the tech people for IMSA, F1, Indy and NASCAR up there answering questions from the audience.

NASCAR gets a lot of ribbing because compared to, say, F1, we are sort of in the dark ages. See, NASCAR (in attempts to keep cost reasonable) frowns on “exotic materials”. Tubes in the chassis are steel, not titanium or titanium alloys. Exotic is usually a code word for “expensive”.

Someone asked the panel what exactly was meant by “exotic materials”. Robin Pemberton replied

“If you have to ask, it’s exotic.”

Lots of people think that NASCAR requires that all engine blocks be made of cast iron.  That’s actually not written anywhere.  The engine blocks have to be from the manufacturer’s original castings. There is an explicit rule that the engine blocks can’t be aluminum.

Why would you want aluminum?  Aluminum is much lighter. Newton’s Law says that the force the engine provides is equal to the product of mass times acceleration (F=ma). Don’t let people tell you NASCAR is about speed. It’s really about acceleration.

Newton’s law says that if you want a big acceleration, you need a big force and/or a small mass. So anything you can do to lighten up the engine (which sits relatively high in the car) will help your acceleration and your handling.

Ford’s new F-150, for example, replaces steel with aluminum to save weight and thus improve gas mileage. Aluminum has it’s challenges, but since NASCAR doesn’t allow it to be used in the engine block, let’s look at what you might do.

Crystal Structure

Get yourself a pencil and a diamond.  I’ll wait.

The pencil lead is grey, opaque and soft. The diamond is clear, shiny and very hard. But they’re both nothing more than Carbon atoms, with the atoms arranged differently.

This is graphite (pencil lead). Ignore the colors, they’re just there to show you that graphite is sheets upon sheets of carbon atoms arranged in a hexagonal pattern.  Every ball there represents a carbon atom.

Diamond is a little more complicated. Exact same atoms, but different arrangement (below).

 

Two big differences here to notice. First, each carbon atom in graphite is connected to three other carbon atoms, but in diamond, each carbon atom is connected to four other carbon atoms. This is the reason for the second thing to notice:  Graphite is made of planes of atoms with no connection between those planes. That means that it’s easy to shear (slide off) entire planes of atoms. That’s what happens when you write. The diamond planes are interconnected, which makes it much harder to remove one layer.

Yeah, But What’s That Got to Do with Engines?

NASCAR engine blocks are indeed made from cast iron, but not the cast iron you’re probably used to. A brief lesson on how you make cast iron. You start with iron, which is a very malleable (meaning easily deformed) material. Through millions of years of experimentation, people realized that you could change the properties of cast iron depending on what you added.

In face, if you put small amounts of Carbon in with the iron and heat treat it in a very specific way, the Carbon freezes in graphite flakes, like the picture on the left below. The flakes give the iron a lot of strength, but they also make it brittle. The sharp points on those graphite flakes are very high-stress points, which means it’s easier to start a crack there. If you’ve ever cracked an engine block or a frying pan, you know how that works. Once the crack starts, it keeps cracking. So gray iron, which is what this type is called, is strong, but brittle.

Then some enterprising soul figured out that if you add some magnesium, the Carbon doesn’t form flakes, it forms globs. (Yes, globs is the technical term.) Since there are no sharp points, there’s less stress and less cracking, which is why this type of cast iron is called ductile iron. Ductile being the opposite of brittle. This solves the problem of cracking, but ductile iron is nowhere near as strong as gray iron.

Sometime in the 1960’s, someone Baby Bear’ed cast iron. They found that if you added Mg anywhere from 0.007% to 0.015%, you get something spectacular, which is shown in the bottom-most picture. (Credit for the pictures: http://www.atlasfdry.com/graphite-iron.htm)

To set the scale, the bar shown is 50 micrometers. Micro just means millionth. Most human hairs are between 50 and 100 micrometers in diameter. The picture you’re looking at is three or four hair-widths wide.

If I had found this, I would have called it “micro-coral”. You get some of the flat flakes of gray iron, which provides the strength, but the edges of the flakes are round (like ductile iron). This cast iron is just right. It’s not as strong as gray iron, but it also doesn’t crack as easily as ductile iron.

This is called Compacted Graphitic Iron or, if you’re German, Gusseisen mit Vermiculargraphit.  I’ll abbreviate it CGI.

And CGI is the “exotic material” NASCAR teams use for engine blocks. You can have a comparable strength with less weight. CGI engine blocks are especially useful in V-shaped engines because that area between the two cylinder banks (the two edges of the ‘V’) has to take a lot of stress.

You may wonder why, if we knew about this material in the 1960’s, it’s taken so long to use it for engines. The reason is because of the very fine control over the amount of Magnesium added. It has to be controlled to within a few thousandths of a percent. A change of just one one-hundredth of a percent can drop the tensile strength by 25%. A person in a lab can exert this much control, but if you’re going to make this in a production facility, you need computers and computerized manufacturing.

This Week’s Semi-Gratuitous Colorful Picture for Moody

The pictures I’m showing you are Scanning Electron Micrographs. Instead of using light waves, we use electrons to make the image. Light can be thought of as a particle or a wave. So can things like electrons, protons, neutrons, etc.

Electrons have a much smaller wavelength than visible light, which means electrons can “see” things our eyes have no chance of seeing. Color doesn’t really mean anything when you’re talking electrons because color refers to a range of wavelengths that our eyes are capable of seeing.

But, of course, that doesn’t stop scientists from artificially coloring their images to make them clearer to explain or, sometimes, just because you can. So here, from The Telegraph, is an artificially colored scanning electron micrograph of a flea done by a gentleman named Steve Gschmeissner. He’s got everything from cells to bugs to plants.

And yes, there are a lot of scientists who buy images like this to frame and put on their walls. I have x-ray images of calla lilies and eucalyptus in my living room.

But no bugs.