§1. Course logistics and the history of engineering education [00:05]
Tomorrow I'll do an hour, maybe a little more than an hour of lecture, and then we'll have the two presentations. Next week we'll plan on probably a couple of presentations a day. I might have to cancel a day next week or two, which means we run into the next week. Whoever's in charge of the catering, we'll figure that out as I find out what my schedule is. We should still finish before July 4th, or actually by June 26 — that's my last day before vacation.
We're going to start metallurgy today. We'll do some more on corrosion later. People asked earlier — the presentations can be on anything with redeeming academic value. I'd rather you do something you're interested in than something you're not interested in. A lot of you already have some of these things, you just have to pull them together.
So the question is, why metals? In fact, the history of this department was that when MIT started, it was the Department of Mining Engineering. Let me tell you a little about the history of engineering. The first engineering school in the world was probably École Polytechnique in France, in the 1700s. The first engineering school in the United States, about 1797, was West Point. Until 1845 the commandant of West Point had to come out of the Corps of Engineers. The word engineering comes from a French word which means maker of war machines. So an engineer was someone who built catapults and bridges and breastworks. That's what they taught at École Polytechnique, that's what they taught at West Point.
The first engineering school in the United States that was not military engineering was Rensselaer Polytechnic in 1823 in Troy, New York. Anybody from Rensselaer? Near Albany. In 1823, what was going on in New York State that required engineering? The Erie Canal. They needed to dig canals and build bridges, so they needed engineers. And to distinguish it from military engineering, they called it civil engineering. So now you know — we're civil engineers. You should all be civil, anyway.
Michigan claims they have an engineering school in the 1840s. I don't know if all the students were bears or what — there wasn't a whole lot in Michigan in the 1840s, but nonetheless. MIT started officially in 1861. They had no money. But then there was the Morrill Act. Anybody from University of Illinois? In the middle of University of Illinois Urbana-Champaign, they have a cornfield — they built the library underneath it, it's a submerged library. And this cornfield has been in continuous planting since the 1840s. It's called the Morrill Plot. Morrill was the guy who in 1863 put through the Land Grant College Act.
Congress wanted to encourage all the people going west, even during the Civil War, to start colleges of agriculture and mining. The government didn't have any money, so they could give away land. There was a big fight between Harvard and William Barton Rogers, who was trying to start MIT. Barton Rogers won — some people at the state house didn't like Harvard, I guess, even though half of them probably graduated from Harvard. He won the fight, and MIT became the land grant college for Massachusetts — the only state in the nation where a private university is the land grant college.
What's the second richest school in the country, in terms of endowment, after Harvard? It's University of Texas. They gave them some land in east Texas, which is nice rolling hills — gets a little hot in the summer but it's very pleasant, very beautiful. And the settlers, after they formed that, decided why should we be giving all this good land to the university. We're going to give them a bunch of land out near Lubbock and Amarillo, which is all desert. And now it's called little Kuwait. They gave them all the oil. They didn't know about oil back the time they made this transfer. So the University of Texas became very wealthy. However, the state legislature got involved, and now it's not just the University of Texas — all the Texas state colleges have to share the wealth. They can use it for buildings or equipment but not people. So it's like a neutron bomb: beautiful buildings, nice equipment, no people.
MIT came along, and Course One is civil engineering. MIT was really one of the first schools that started separating engineering into disciplines. Course Two is mechanical engineering. Course Three was mining engineering. Course Four was architecture. Course Five was chemistry — maybe. Course Six obviously wasn't electrical engineering, that didn't come along until the 1880s — I think Course Six was geology, which merged with mining later. Eventually metallurgy came in there somewhere, and finally they changed Course Three to the Department of Metallurgy in 1888. When I was a freshman it was metallurgy and material science — and it was 75% metallurgy. By the time I graduated six years later, it was probably 60% metallurgy, and now they were doing electronic materials, ceramics, and polymers as other materials.
§2. Why structural materials are still mostly metals [07:18]
Structural materials are still generally metals. That's my introduction to why we want metals. Does anyone know why structural materials are still mostly metals, as opposed to ceramics?
It's mostly because metals can be elasto-plastic — they can deform without breaking. Actually, the largest use of structural materials is ceramics. It's called portland cement, or stone. People have been using it for millennia. The Romans used portland cement and some of their portland cement is still around, still in good shape after thousands of years. But it is a little brittle. And a lot of times you don't like to have things that are brittle.
The definition of ductile is, it deforms beyond the yield point. [Tom points to a stress-strain curve on the slide.] I probably should have asked the first day, what are your undergraduate disciplines? How many mechanical engineers? Electrical engineers? Physics? Chemists? — I already figured that one out, I looked at the blank stares when I started talking about chemistry. Nuclear engineers? One. Naval architecture? Aerospace? Any others?
We actually have a number of ocean engineers, marine scientists, naval architects. We used to have a Department of Ocean Engineering and Naval Architecture, but it got merged into mechanical engineering. The reason was, they had lots of graduate students, most of whom were from Greece or Korea or Japan. They had almost no undergraduates. MIT really does care about undergraduate education, more so than graduate education. That's another story we can talk about sometime.
So the point is, metals can deform, bend before they break. This is the yield point of materials. If you had any mechanical engineering, or even if you were in some of the other fields, you've learned about stress-strain curves in some course of mechanics. Over here where it's colored red, this is brittle behavior — and these are all steels. Intergranular fracture, which is a type of fracture you get with hydrogen embrittlement, with stress corrosion cracking in some steels, is very brittle. The metal doesn't deform, it just snaps. Not quite as brittle as cast iron, and certainly not anywhere near as brittle as glass, but it's still brittle.
Cleavage fracture — if you look in a lot of books they'll call it brittle, but in fact it's a three and a half percent strain. There are some textbooks that define this transition between brittle and ductile as anything above half a percent strain being ductile. In general you like to design with at least three to five percent strain, because you have some flexibility. You'd love to design with twenty or thirty percent strain. And you get ductile dimples — it pulls like taffy.
§3. Silly Putty and paper: ductile vs. brittle demonstrations [11:01]
[Tom produces Silly Putty.] There is an example which most of you played with as children — Silly Putty. This is actually a double dose, so it can be large enough. I can take Silly Putty and pull on it and it stretches and it's ductile. Actually it's a near-Newtonian fluid. But I can take the same Silly Putty — now I have to get it a little thinner because I'm not that strong — and I pull it like that, and it's brittle. Remember doing that as a child? [Tom hands the Silly Putty around the class.] You can pass that around, everyone can do their own experiment.
I can talk about brittle and ductile in other terms. If I take a piece of paper — paper is brittle, and I will prove it to you in just a second — I can pull on the edge of a piece of paper with several pounds of force. If I put a notch in it, a brittle material is notch-sensitive: takes ounces, not pounds. That is the basis of the science of fracture mechanics. If you put a notch into something that's brittle, it will be notch-sensitive. And you can tell it's brittle because when you put it back together, it matches — there is no significant deformation in the paper.
If I try that with a piece of rubber, which is a ductile material — I pull this piece of rubber many times — I've got a great big notch and I can't extend that crack in the rubber. The rubber actually deforms. You can actually see where it's all wrinkled at the tip. Someday I'll have to use a new piece — it's not wrinkled at the tip on a fresh one.
§4. The Liberty ships and the brittle-fracture problem [12:52]
There are two things that are important in fracture mechanics. This was all discovered, or studied extensively, at three places in the world just after World War II. And it had something to do with a naval problem during World War II. Anybody know what the brittle fracture problem was in World War II? Liberty ships.
[Tom produces a bound report.] MIT's library 15 years ago was throwing this out. They were selling it for two dollars, and one of my graduate students picked it up for me. This is the report of an investigation on the design and methods of construction of welded steel merchant vessels, from July 1946. Just for you Coast Guard folks — the first signature is a rear admiral, U.S. Coast Guard engineering chief. Down here we have the vice admiral, chief of the Bureau of Ships. And there's a guy James Forrestal, if you've ever heard of him — Secretary of the Navy at the time.
If you look at the data: 4,694 welded steel merchant vessels were built by the Maritime Commission. These were not all Liberty ships, some were T1 and T2 tankers. 970 suffered casualties involving fractures. By casualty I mean a metal casualty, not a person casualty — though some of them probably suffered the other type too. 24 sustained a complete fracture of the strength deck, one vessel sustained a complete fracture at the bottom, eight vessels were lost, four broken in two, and four were abandoned after fracture occurred. 26 lives were lost in these structural failures.
The most famous picture is this one — the Schenectady lying at dock. View of SS Schenectady after splitting in two at her outfitting dock. Just been built, hadn't been out to sea, and they got two ships for one. Here's the SS Manhattan, taken at sea — not a good day for the people on the SS Manhattan. You can see the blimp up there, one of two blimps it says. There are a number of pictures in here you don't usually see. A completely split-in-two ship.
It turns out they failed for two reasons. The steel was somewhat brittle, so it was like paper as opposed to rubber. And they had notches, and the notches were due to welding defects. The welds weren't necessarily bad — they weren't perfect, actually. Sometimes during World War II, people would take the stick electrodes — if you've ever seen a stick electrode, that's what they welded the ships together with in World War II, mostly — and after a tired long day on a big thick weldment, they would throw a bunch of these electrodes into the groove and weld over them. And no one was doing X-rays to see that they had just put a huge defect into a piece of armor plate.
§5. Battleship armor weld and the lost art of heavy welding [16:27]
[Tom produces a thick weld sample.] Speaking of armor plate — we'll pass this one around, it's a little heavier. Let me put it up here first. It's not dirty, I just don't like to scratch everything up. This is a weld that came out of a forging press. It's about an 18-inch thick weld. This is the type of weld they would have been making. I counted once — somewhere between 400 and 600 passes. There are some sharp edges on this, so be careful, don't cut yourself. [Tom hands the weld sample around the class.] That's how they welded battleship armor, which could be 14, 16, in some cases 18 inches thick.
We no longer know how to do that. I'll tell you the story of how we tried to weld that together unsuccessfully when the forging press broke after 60 years of service and some guys came in to try to weld it. They were very good welders — no defects in that weld — but lots of residual stresses. The first time they welded it, they didn't do the proper welding procedure, and it cracked before they even got it off the welding platform. The next time they did a better job, they got it back onto the press. The first time they tried to forge a truck wheel — this was at one of the two big plants that make aluminum truck wheels for big semi-trailers and tractors, this was not Alcoa, it was the other plant, I think an 8,000-ton press — the first one they hit, they got another crack because of residual stresses and improper welding procedures.
§6. The three postwar studies: Weck, Pellini, and MIT [18:25]
Because of the Liberty ships, a lot of people were very concerned, and three places in the world did big studies in the late 1940s and early 1950s to understand brittle fracture in welded steel ships. One was a guy, Richard Weck, who when I was starting out as a young welding engineer in the mid-70s became the director general of the British Welding Institute. He was at Cambridge University, and as a young man in his 20s he got on his bicycle and rode out to Abingdon, near Cambridge in England. He found a nice field, went back, and convinced the British government to start the British Welding Institute, which now is one of the biggest and best known welding institutes in the world. They've done excellent research over the years. Richard Weck became Sir Richard Weck — one of the most arrogant men you will ever meet. But you won't meet him, he's dead now. That was one place where they studied brittle fracture of welded steels, and he convinced the British to do it because the British Admiralty wanted to know about these ships too.
The other place was the Naval Research Laboratory, and a guy William S. Pellini, who wrote this little monograph. He was formerly superintendent of the Metallurgical Division of the Naval Research Lab. Whose laboratory is the Naval Research Lab? [pause for student response] NAVSEA is Carderock. Office of Naval Research — right. So the 6.1 money: the research lab is NRL. NRL covers aviation, NAVAIR, NAVSEA, everything else — the whole Navy — because it's the basic research laboratory of the U.S. Navy. Carderock is the applied research.
Carderock has a little bit of 6.1 money, and NRL has 6.2 money and other things. Do you know what 6.1 and 6.2 money is? 6.1 is basic research — basic scientific research. The Naval Research Lab has produced at least one Nobel laureate, Jerome Karle, who won the Nobel Prize in chemistry 40 years ago. They've done a lot of things. They did a lot of the basic work for the whole GPS system of the world. It's a very prestigious scientific laboratory.
The applied laboratories — NAVSEA and NAVAIR — have 6.2 money. These are pots that Congress puts in the budget. They're line items in the budget. So when the Secretary of Defense says I want this much money for 6.1, the Navy will get this much basic research, the Army will get this much. If you're a Marine, you're in there with the Navy. 6.2 is applied research, where they might be looking at corrosion science under 6.1, but corrosion applied to aluminum for lightweight vessels under 6.2. Then there's 6.3 and 6.4, a lot of which is done at Carderock, which is exploratory development and advanced development. And then you get into the seven numbers, where they actually are building prototypes.
So if they built the Sea Cliff submarine, or earlier built the Alvin submersible back in the 60s — just last week the Alvin had its 50th anniversary, which is sort of a joke because it's not the same Alvin. It's been reborn twice, most recently about five years ago as a completely from-the-ground-up new vessel. That would be bigger money — tens of millions of dollars to build something like the Alvin. The new Alvin, I think, cost about $40 million.
So Pellini started out doing research and developed things where you make sure you got nice ductile steel when it was welded. [Tom advances the slide.] You weld a steel plate — this one is brittle. They found that steel, when it gets cold, can become very brittle. And cold just happens to be around room temperature. So there's this ductile-brittle transition temperature that people really learned to worry about — they actually knew about it before this, but they didn't really worry about it. It's measured in energy in foot-pounds. Since Pellini was interested in submarines, he basically started the explosion bulge test. You have this big cavity with rounded edges, you put a plate on. Here's your test plate in this 14-inch diameter test specimen. These are expensive tests — an explosion bulge nowadays might run you $50,000 or $100,000. They go to some place like White Oak — they used to have White Oak, now they probably go somewhere out even further away from the world, like Aberdeen or somewhere. I don't know if they go to Aberdeen, that's an Army lab. They set an explosive charge off, actually several charges, and they keep on deforming this test plate by different amounts.
Sometimes they get brittle fractures, sometimes they get a bulge before the thing fractures all the way, sometimes they get great big nice ductile things before it finally starts to tear. They can correlate that to other things. Pellini did all kinds of work on figuring out how to weld ship steels. Along with that came, in the mid-50s, the building of the Nautilus nuclear submarine out of HY-80, which was also a program started at U.S. Steel by the Navy to develop a higher strength steel. The submarines in World War II were probably 50 ksi steel. HY-80 was 80 ksi yield. So you had a big improvement in depth capability. And then Rickover developed the nuclear reactor so they could stay under, go underneath the pole and everything.
The third place where they did work — Welding Institute in Britain, Naval Research Laboratory — was MIT, in the Metallurgy Department. Morris Cohen and Ben Averbach were two people who had a nice gravy contract from ONR for 10 or 15 years to look at brittle fracture. They were doing really the science aspect as opposed to the more applied things.
§7. Bessemer steel, English deforestation, and Saugus Ironworks [26:22]
So what people learned was — back in the 1860s and 70s, people sort of learned, if you were going to try to build a bridge or something out of steel — and remember, they didn't make things out of steel before the 1870s. Anybody know why? They made swords, but steel cost almost as much as gold to make before the 1870s. [pause] Yes — the Bessemer process. Henry Bessemer came along in 1854 and taught people how to make steel. You cannot melt steel with a normal hydrocarbon flame. You can use coal, you can use oil, you can use methane, but you can't melt steel in air. You can get about two or three hundred degrees from the melting point. In my welding course, when you watch on video, you'll see me bring in some propane torches and MAPP gas torches and put a steel wire in there — and I can't melt it.
But Bessemer learned how to preheat the air coming in and get hotter combustion, and showed people that with the proper design of a Bessemer converter, he could preheat the incoming air and melt steel. So now they had a way to melt steel. Before that they had wrought iron, which was basically a process of taking iron ore and putting it into a reducing gas atmosphere and making solid porous chunks of iron. That was wrought iron, and that was easy to work. Before that they also had cast iron — we'll talk about what cast iron is. Cast iron was one of the first industries brought from the old world to the new world.
In England in the 1500s they had an energy crisis. The energy crisis was, they were running out of trees. There were three uses of trees. One was to make charcoal to make glass, which was a very expensive thing to have in your home — glass in the windows. Another was to make charcoal to make cast iron, because you needed to make cannon and things like that for the military. And the third use of big trees was to make ships. In fact, I read from this book called Out of the Fiery Furnace — they passed laws that you could not cut down trees anywhere within three miles of the Thames River, because if you wanted a big mast for your ship, you needed a big tree. It took like a whole forest to build a man-of-war. They were running out of trees to make charcoal to make iron. And what do they have in the new world? They had forests.
So they brought over Saugus Ironworks. If you've got some time this summer — actually they will give you a day off later — go up to Saugus, Massachusetts and go through the national park, which is the Saugus Ironworks, and learn about how to make iron.
What they knew from the 1850s, 60s, and 70s is, you could measure the force of fracture of a bar of steel, and that would allow you to calculate — because they had developed beam theory — how strong something would be. That way you could size the parts, rather than just making things ten times larger than they needed to be, which is what they did out of stone and brick — the cathedrals and the Roman aqueducts. They actually could calculate to use the least amount of material. They still had safety factors of five and ten because cast iron was sort of brittle, and they knew that.
They got to steel that wasn't brittle most of the time, and they could start to build railroads. Andrew Carnegie was richer than Bill Gates or Warren Buffett in his day and time, on an equivalent basis. He was the richest man in the world because he took over the steel mills. So steel was king. But what they had learned, even though they had the science of fracture mechanics since 1925, in the 1950s they learned that you needed not just the force of fracture, you needed to know the energy of fracture.
§8. Ashby plots and why steel still wins [31:18]
I could have had a piece of rubber that would fracture at a force like a rubber band — smaller cross section — that might fracture with less force than the piece of paper. But the rubber band at least would be ductile and stretch before it finally snapped, whereas the piece of paper might break suddenly at the dock. So if you build paper boats, don't float them in water. Paper's not very good in water. What we have today is, we look at fracture toughness versus strength.
[Tom pulls up an Ashby plot.] This is what's called an Ashby plot, by this guy Mike Ashby. Used to be at Harvard, now he's retired from Cambridge in the UK, which is where he started. One of the great material scientists, mechanical engineers of my generation.
He plots fracture toughness — which is like an energy of fracture, related by the fracture mechanics to the energy of fracture, has funny units, megapascals per square root of meter, we can talk about that later if you want — versus strength in megapascals. You can put all the materials in the world in certain classes. The metals are up here. What you want is something that's very tough and very strong — the metals are up here. The ceramics are over here. They might be reasonably strong but they're not very tough. The iso lines, of equal strength and toughness — ratio of K₁c squared over pi times the fracture strength — these are ratios, and that comes right out of the fracture mechanics formula. You'd love to have something way over there. But nature sort of keeps strength and toughness, energy and force of fracture, aligned, except for ceramics and pottery and bricks, which is what people used to use.
Here are your woods, your plastics — there's low-density polyethylene. Plastics and woods are in here. Foams and polymers are down here. I don't usually use foams and polymers for structural materials. Balsa wood should be on here somewhere, but it's way down. Here's balsa wood, way down here. Here's perpendicular to grain and parallel to grain, if we're talking woods. So here are the woods, there's balsa, these are the plastics. Rocks, ice. You can see where everything is. What's at the top? Steels, nickel alloys, titanium alloys. Aluminum is actually not so good, magnesium's not so good, among the metals. But they're a heck of a lot better than everything else.
So I've now spent a half an hour telling you about the history of engineering and telling you about why we use metals. We haven't even gotten started — but that's the first part of welding metallurgy: why do we use metals. And why is Tom Eagar going to spend most of the next four hours of lecture over the next few days talking about steels?
The answer is quite simple. There's a paper written by one of my favorite authors — at least I understand what he writes, me — called "The Future of Metals." A paper I wrote, that has this plot I stole from somebody, from 23 years ago. Out of 100 pounds of metal made in the world, 95 is steel. That's partly because of the previous plot — what has the highest toughness and strength? It's the steels. That outer boundary is exactly the same as the steels. Nickel and titanium are almost as good. But you can probably guess, why don't we make everything out of nickel and titanium? [pause] It's expensive. There's also not enough of it.
If I look at how much of these things we have — we make one and a half billion tons of steel a year in the world. We make 45 million tons of aluminum. People are talking about using more aluminum and more magnesium in cars. One of the problems is, 40% of all that aluminum goes to beverage cans. [Tom produces a beverage can.] We'll do a demonstration with that later. So if the automotive guys really started using lots of aluminum, there's not enough aluminum in the world. There could be, but who's going to put the billions and tens of billions of dollars into aluminum production unless they know the market is there? So it's a chicken-and-egg problem.