WM_Su2015_02

Okay, yesterday I started out. Today we're going to talk about materials, but we're going to talk about metals. And what about polymers? Why do we talk about ceramics? Why are we talking about ceramics as structural materials? Ceramics are brittle, very useful for many things, higher melting temperatures than metals in general. Polymers, why don't we use polymers and special materials? We do use them in structural material — trash cans, little toys, all kinds of things, but really critical things.

So metals have this same force property called ductility, and there's a whole bunch of metals. And I listed these metals for a particular reason — they are the ones that show up on this graph, which is in a handout that will show up on Stellar. Turns out 95 pounds out of every 100 pounds of metal made in the world is steel, okay. And aluminum is less than two percent. Copper's over one percent, 6.80 percent [?]. Most of the zinc is used to coat the steel for protection, because the second Achilles heel of steel, aside from the first, which we'll get to — duh, steel's heavy. Steel stops [in] their current systems. But you have to use lots of zinc, millions of tons of zinc, to protect the hundreds of millions of tons of steel.

Zinc is a byproduct of copper. But we have a lot of uses for lead in the roof. Christiania, [thorium?] is lead, okay. Lead has tremendous atmospheric corrosion resistance. The first water pipes in England, well, lead does it easy. The Romans, okay. But now we don't even allow it to be in the solder of our joints that are plumbing, but we used to make our plumbing out of lead, okay. Nickel is expensive but it's critical, and we use it in places where other common materials [won't do]. Magnesium, titanium — most of them goes into aluminum, but anyway.

So I put those across here. There's lots of different types of metals. And which ones — if we take iron, or any one of these, I could draw the line down here — you have strength, ductility, toughness, and cost. These are properties of a better metal. Those are the mechanical properties in particular, except cost, which is an economic property. And steel has — remember the slope. They actually straights up this plot, steel's right out there at the top, along with cobalt alloys, copper and nickel, okay. But all those others have much higher cost. The closest one to steel is copper, which costs about eight [times more], okay.

So steel has little cost plus the strength, the ductility, the toughness, that's why it's [used]. But it also has — in terms of processing, we can fabricate steel lots of different ways and relatively easily compared to a lot of metals. Recyclability — steel is easy to recycle. Availability is one of the most abundant elements of the earth's crust. Abundance is a little better. And there's a bunch of other properties you could list here, and these are — we have performance properties. Corrosion, steel's not so great. Were fracture, fatigue — steel is actually pretty good. In fact, the [later tested?]. Regardless of [that], some people define materials science and engineering as processing, structure, properties, and performance, okay. So here are three of the four things that define material science. And for structural materials, iron actually just rises to the top, and not by a small percentage — it's 95 percent of all metals made.

So my overall life summary of yesterday, maybe this isn't what you got, but we use metals for structures because of fracture resistance. [Tom appears to drop or fumble something.] Chuck. A chocolate shop. Okay, we use steel the most because of the combination — string [strength], which is another important point. Materials are not chosen because of a single property, okay. It's actually a sweep of properties.

And one of the biggest fallacies in the area of people overselling materials is that they say, oh, I just got the lightest material in the world. The lightest material in the world is an aerogel. Anyone ever heard of aerogel before? Yeah, so what's an aerogel?

Student: [Inaudible response about silicon-oxygen bonds.]

Yeah, it's a silicon oxygen bond. It's actually made in a — we call sol-gel process. And it's a cellular material. Go look right in the end of the [infinite] corridor. You turn down to go to building 16, so let's play case across from Professor Gibson's office. She's the world's expert in cellular materials, and she's done this play case there. She's got this little cube of aerogel. You have to protect it from the atmosphere because the moisture in the air will dissolve it. It's sort of like lightweight Jell-O without the work, okay. You know, Jell-O is just protein cellular structure with water in between.

So an aerogel is the lightest material. It has about 10 percent of the density of water, or even less in some cases. Thing is, if you blow on it, it'll collapse. So it's not exactly a structural material, but it's the lightest of the world. And because people found something that was lightweight, one of the folks — I think people started spending millions of dollars on aerogels as if they had an application for it, okay. Today, twenty-five years later, they still don't have an application for it. It's just — materials, so why not go spend millions of dollars doing research on something useless? Does have good insulation properties, as long as you're working in the Atacama Desert in Chile, okay, where there's no moisture in the air. Or maybe up in space, in some — it's probably very good [against] radiation in space, you know. Yeah, okay, you can think of that. Okay, you can find that's what people [do].

Joe Williams, Jim Williams — that a lot of state, Jim was head of [the] aircraft engines for General Electric in Cincinnati, and he calls them boutique materials, okay. They have an application, or maybe even three applications, but they're not high volume materials, okay. And when you're talking about lots of things, [you] work with what you have. We are talking about things you'd like to have, a pipeline.

I said that, of steel is heavy. Give you an idea, this is a piece of one-inch steel made about thirty years ago. It's 85-89 across Connecticut. [Tom holds up a steel sample.] This is a piece of two inch thick titanium electroslag weld made at our graduate center when we were looking at trying to build a titanium submarine. Why have we not [built a] titanium submarine? A long time ago the Soviets done that also. The main source of titanium — it's like aluminum, it's like fifth most abundant in the Earth's crust. And titanium, it's not five, but it's not [scarce].

Well, we use lots of titanium dioxide. All the room in this room, the white side then. But it takes a lot of energy to refine titanium to metallic state. It also doesn't have very good fracture toughness. It's a [hairy CC?], okay. It's okay, but it is lightweight, and they never been a fighter — the first one had titanium skin, because at the [time], when you're flying at a hundred thousand feet at Mach three or whatever this thing was, the skin temperature is above the temperature at which aluminum will maintain its strength. In fact, the Concorde supersonic jet — Concorde didn't fly on speed, [it] flew on skin temperature. Colder day, fly better across the Atlantic.

I [flew] the Concorde once. I paid the extra three thousand dollar super first class ticket just — said this — was twenty years ago, and it was the filthiest plane I've ever been on. They didn't have any extra aircraft so they didn't have maintained it very well. Small seats, everybody was in the super first class, everybody was bored at once. It's a long story.

But there are — so steel, this is a piece of the X-33 space plane liquid hydrogen tank. Carbon-carbon composite, Nomex honeycomb. It's a long story, but that material cost twelve thousand dollars a pound. It's a light, though, right? When it's only twelve thousand the [pound]. And as fabricated, a titanium submarine's only about a hundred times the cost of an HY-100 submarine. And what are you paying for the [hull on] an HY-100 submarine right now? Probably twenty-five or thirty dollars a pound. So you want to start paying three thousand bucks a pound protecting our subs up? You can do it.

But there were other reasons. Why did the Soviets [build their] titanium subs? They had funny money. It was all funny [money]. No, because they had cracks. One of the problems they had — they were worried about it, it was Soviet subs. And I was involved with — my first research project at MIT in 1977 was Office of Naval Research. It's a — well, [I went to a meeting], I came [back]. So I remember coming back from Europe, and then I got involved in a number of things that David Taylor [Naval Ship R&D Center] — Congress was really upset about, that the Soviets [were doing a] leapfrog again right in technology. And [at the] time, they were concerned because this sub could go faster underwater than our destroyers could go on the surface, okay. So Chase Utley [chips chasing] aircraft range. And then the other thing is, they could dive deeper than the collapse — the collapse depth of [our] depth charges. Well, you can always design [around that], okay. But people thought we'd never be able to subtract them.

Well, it turns out they developed cracks. There's something called the fatigue interaction. I remember guys [at] the Naval Research Laboratory at one of these conferences, and they're meeting — how do they solve the [Greek Kooks] fatigue interactions? I said I don't know, okay. Well, it turns out they did, okay. The Naval Research Laboratory had done all kinds of studies on this. It was one of the reasons why they couldn't recommend, even if you had the money, to go build the titanium submarine. But that's the difference between a political decision in the former Soviet Union — they wanted to leapfrog, even though, you know what, no one's going to tell the top brass that even if we build it, the doggone three personal defense is full of cracks, okay. That's why they could confuse them, okay. They were full of cracks, you know what, had nothing to do with economics. They had an economic system they could never justify what they did, okay.

There are lots of joining technologies for other things. This is a piece of friction stir welded aluminum. [Tom holds up a friction stir weld sample.] Student came to me, wants to work for NASA. And this is how they put together part of the Space Shuttle main tank — was a longer [weld]. But nonetheless, distortion-free, relatively distortion-free friction stir weld. Boeing went out and spent ten million dollars building a friction stir welding machine for some of their structures, because a welded joint is always lighter than a bolted joint.

But we're supposed to talk about welding and welding metallurgy. There's other technologies that around today, hear about additive manufacturing. This is something that I did twenty years ago. One of my students did her thesis when peace broke out in the early 90s with [the] former Soviet Union. And I apologize [for the digression].

During the Star Wars build-up in the mid 80s, there was lots of money for lots of things. And the US Navy, White Oak, Maryland, was developing — spent a quarter billion dollars developing a particle beam weapon. Now this was to be a relativistic electron beam, millions of electron volts, that if there was a cruise missile or an Exocet missile coming in to attack the ship, this was [to take it out]. Two meters [before], after Falklands War, where the Exocet — French Exocet missile — hit the British carrier Sheffield, our [HMS] Sheffield, [destroyer], and destroyed the ship. And the reason that destroyed [the] ship had nothing to do with the explosive charge of the Exocet or setting off the charges. It was the fact [it had an] aluminum superstructure, and the superstructure caught on fire, okay, and you can't put out the fire, and they just burned the whole thing.

You might say, oh, those silly [British]. Well, it turns out before that, the original JFK — was on the new [Forrestal-class?] carrier — and then [a] destroyer, [the] Belknap ran into it. They had like a Belknap pole mount on the carrier, so they can see the aspect changes — this is this random little pole before you know, [a] seeing-eye [thing] when an aircraft carrier — that the destroyer Belknap's random ran into the JFK on maneuvers. And he was right underneath one of the aircraft elevators, and some jet fuel [dropped] down on top of the [Belknap] that ignited the superstructure, wiped out the Belknap. And the joke at the time was the gallon of jet fuel beat the Exocet [missile].

And I was around at David Taylor in the 1980s when they were trying to go from aluminum superstructures, doing waffle steel construction, for cellular superstructure that would be lightweight. And the problem of steel is heavy, and it corrodes. And I've been looking for my [Lulu] steel transition joint bonding and stuff. But the Navy uses a steel-aluminum transition joint. So all this stuff is part of [it]. This is just sort of an introduction of why we get to study welding metallurgy.

I told you have to study it because Nancy says so. Okay, but in fact, supposed to be welding metallurgy, and these are the books I took off my shelf on welding metallurgy, okay. [Tom displays a stack of books.] This is the oldest, actually. It's fourth edition 1783 — but the original edition was the nineteen forties — [The] Weldability of Steels. Bob Stout was [my] — sort of fabulous professor at Lehigh University, when I worked about [Bethlehem] Steel. But they wrote a book on weld steel — supposed turns out John Gross was [head of?] research, you will see, he's been back. Remember Levi and John Gross at the steel used to call aluminum a near-metal, because aluminum doesn't have the same fracture toughness and things like that.

See, this is the [next textbook]. George Linnert — George was passed by long time. And this is from the 1960s, two whites — Welding [Metallurgy]. Guess how many volumes? Two volumes. This is sold since the nineteen sixties, as of ten years ago, four hundred thousand copies, okay. Hey, you want to make some money, right? I'm welding metallurgy, that type of coverage. This is the latest one, 2015. Chocolate Bowl [Sindo Kou?], the professor at Ohio State.

And almost any book founded by — just passing. [Tom searches through books.] Let's show you. This is most recent book, [connectivity] at dry docks. Almost any book on steel fracture will have a picture of the Schenectady. I can't find it.

But I'll given — I'll show you where it came from. This is a [July] 1346 [1946?] report on of an investigation on the design of methods of construction on welded steel merchant vessels, and the Schenectady. [Tom searches.] Here's the Schenectady, an [anchor] that pictures — you would never seen that picture before us. Yeah, brittle fracture.

Turns out this is a final report of the board of investigation convened by Order of the Secretary of the Navy. What happened? [Long pause as Tom looks through document.] Final report, [Board] of investigation. We thought the men might be [at] libraries. One [time], my graduation was over Christmas, I [was] over [at the] MIT library book sale of books that were going to get rid of. He bought this for two bucks, and [it's] been sort of one of my prized possessions. But it is the final report. Was in the MIT libraries from 1947 until just a few years ago. But during the war — [Tom continues searching.] James Forrestal, Secretary, but they had structural failure history.

Anyway, I've got — six thousand ships, the number that had serious structural problems was huge. But like a thousand, eleven hundred ships and major structural failures. Six or seven broke up completely in two. There's the picture of the Schenectady, but there's also the picture of the SS Manhattan, which is right here. This happened, not at dry dock, but out in the middle of the ocean. Exact[ly] the number — [Tom flips pages.]

Anyway, how am I going to go through all these books? But I guess the reason I bought these is because there is no single course on a lot of [welding] networking. NAFSA [?] — this is sort of like my little questions about what to meet, which is the long term [DEAs?] up. They say you're supposed to have a course in welding metallurgy, but they don't tell you what's supposed to be in the course.

And I'll tell you, of all these books, there are about half a dozen different ways to think of welding metallurgy. For example, [Sindo Kou?] — very knowledgeable guy, who received more awards from American Welding Society than any person alive or dead, and basically [Sindo Kou] — I'll show you that actually have — [Tom searches.]

Anyway, John has a list of the problems of weldability of steels, or [welding] in general. And the interesting thing to me when I looked at this just last week, the first time, was to look at topics. And the topics, okay — so he's got fabrication-related topics, and these done some other topics over here which he calls service-related effects. The fabrication-related defects are hot cracking, warm cracking, cold cracking, [Hayden?] decision, process control, and others. And he goes through the book — goes through these things in some detail.

But, you know, I've been doing this stuff for forty years, and looking at that, most of these I have never seen a real service [problem]. No, it turns out when we were developing — when Johnston's [doc savage?] was coming up in the 1950s, 1960s, and we're developing all kinds of new ways for jet engines, a lot of these types of cracking were very prevalent fifty, sixty years ago, but they're not prevalent today. [Doc's?] off the problems. No, you know, just a big seal, but you choose the compositions properly, okay.

But people are developing new — [Long pause; Tom moves to phase diagram.] Phase diagram is just plotting temperature versus composition of a metallic alloy. I'm going to show you one for [steel in] a little bit. But for alloys, almost — this is called eutectic, it's the lowest melting alloy, and it's about four percent copper, okay. But four percent copper in aluminum — it dissolves in, lowers the melting point by over a hundred degree centigrade, okay. By 2024 alloy is somewhere over here, and it starts to solidify, something carolluma [around here], when it's what we call the liquidus line. And in this region I have liquid plus solid. Over here I have liquid plus another solid. We might call this alpha and we might call this solid theta — of n different crystal structures and things like that. But this one's actually probably aluminum-free copper, you know.

But the problem is, it starts to solidify here and it doesn't finish solidifying till here. Things solidify over a range of [temperatures]. You're familiar — if you've ever made homemade ice cream with the old fashioned crank, and crank, use salt and water — use salt and ice. Both of [those] are solids at room temperature, but you put them together and the salt will melt the ice. That's what we do on the sidewalks in the winter, right? Because when they alloy together, the salt plus the ice will form a low melting salt water, okay, which melts below zero degrees [Celsius]. Same thing with aluminum and copper.

Well, if you have something that melts over a long range of temperature, this is called the mushy zone. It's like a Slurpee, okay. And if I now have the thermal contraction stresses — as the whole thing is cooling down, that Slurpee just pulled apart, end up with cracks.

Student: Please demonstrate. That sounds like — [unclear question about what was just said].

You just said it. As it cools, it pulls apart and cracks. That's — I thought about the restart of my question. You said that was a different kind of welding [at] the top of your list.

Well, I said this — I said most of these things that John is going to talk about [in] this book. It has a whole chapter on hot crack — okay, well, solidification cracking, then on heat effects on [cracking]. But frankly, eighty percent of this book is about problems we have known in the past that we don't experience anymore, because the aluminum companies don't make alloys, and they don't advertise it as well, unless they've already [solved it], so they don't run into this.

You either come over here with the processes if you [are doing aluminum?]. Someone find a vision, use this box. Oh man, [I'll be kind of] call them — of course, the banker bonus, okay. So well, I'm wondering now that I see that, as if the basis is, you know, the wax is a little bit less. But wax is melted [at] different temperatures, right? So you put one box on, it's supposed to melt, and you did a different floor wax. You use light over the area that you're preheating, and it doesn't melt, [you know] that your temperature's [in] range, right? It's not a range — that vertical [shock striking?] you're gone. There are you trying to minimize out the slurry. On the other side, so different problem.

Different different problem. The seals [steels] generally don't have — I don't know, BCC has heat affected zone equation, because iron based alloys just don't have this. I have seen the weld solidification cracking when you're trying to weld over a high phosphorus paint, okay. The problem they're talking about, it [reproduce] — is hydrogen-induced surface crack, and we're gonna go over that [as a] base because this I see half a dozen times here, even though Stout wrote this book about how to avoid a hydrogen-induced cracking, but now seventy, eighty years later, we still see the [Sea Wolf?] submarine that I talked about, just [had] hydrogen [induced] cracking, okay.

We're gonna go over that, because it's still a problem. People still don't follow the welding procedures, and they still fall off the cliff with hydrogen-induced cracking. My point is, most of what's in this book on welding metallurgy is a compendium of what John [the pole?] has worked on for the last forty years. But that doesn't mean it's the practical things that you really need to know. This is the science of all the different ways a weld can go wrong, but I'm not going to spend all that time on some of these things that we — they're here and we know about them, but we've learned to fix some of these. It's the ones we still trip on every day.

Student: Okay, so we find that most of the [problems] we have is based on the process, not like the material selection [itself]. And [if we] figured out what materials [weld well] with [other] materials, and what regions would be to have transition material, [it's] the actual welding process that is messed up that [causes the issues] mostly, yes?

It's the processing. I went back to my little plot before, talked about properties. We don't have an engineer the properties of the material — we spent billions of dollars doing that. The processing, which is out there in the shop, [still has shortcuts]. Okay, if you don't take the shortcuts [from view], okay. If you start taking shortcuts — but in fact, I can't teach you all the things that are in this book, what's all those books. And so [it's enough] for you to know that what I teach is sort of what I've seen from thousands of failure analyses over forty years of my career. And then emphasize what I consider to be the most practical, as opposed to the most scientific. These things great science offer, okay. It's not that we don't have some decent [science] on hydrogen cracking, but okay.

So now, having thought — friend of mine, John, [wrote] this book. There's a great book, I go — I refer to it, okay. And I can talk about lamellar tearing, okay, which was a problem in the 1970s when I worked about [Bethlehem] Steel. And I've got to go to Australia this summer, and there's a guy there — there's [also this] mill, this crushing machine that is four stories tall in the Philippines that was [for] mining for gold. It was all [cracked] because of the steel had — was [lamellar tearing?] — when we're carrying, [where] something occurs to the base plate. You ever have baklava? Three kilos those three layers, and so you know, however they put the nuts that this falls apart, okay. Well, that's why [Layer A Karen?], okay, that occurs in the base. But it does [not] encourage well [welding behavior]. No, the problem is these cracks occurred in the [base plate?] — had nothing to do with the base level. This guy wrote a report, 237 paragraphs, I read it.

In a hundred and eight paragraphs he works with — mentioned the word laminations. Five sets of inspectors inspected the steel, no one found any laminations, but he writes a reply report and he's still talking about laminations, okay. That's sort of what's going on in a lot of these networking books. They're still talking about problems that have been solved in the past, okay.

Now, this [is] right — you're not going to come out of this being an expert in all these different things, and I don't want to confuse you telling you about all these problems we used to have that we really have solved. You solve the problem [of] laminations in steel by producing good quality steel with low sulfur content and low inclusion content, and we make better steel today than we did in 1940 or 1950. So unless you get some sort of third-world steel where they're still making it like they made [in] the 1930s, you won't run into laminations. I've never — I've never seen — I'm not sure I've ever seen real [laminations].

Okay, I do want to talk a little bit about steel, so we [were] talking about brittle fracture. And here's a little graph that I put together to explain brittle fracture. Ductile metals — this is just a stress raiser in green, and this is stress versus strain. We're [going] here, mechanical force versus stretch. And to test some percent offset, you'll have the yield point of the material. Of this, I have pictures of steel fractures here. This is intergranular fracture, very little fracture, no ductility. There are some steels that, if you don't process them properly, will fail in intergranular [mode]. About a — matter, little matter — are we looking at this? Big — so the fracture surface, we're looking at — a skin of the fracture surface at high magnifications, they're probably 500x. These are all quite 500x. And I've got better pictures of some of these.

But in the red area, basically, it's like stretching a rubber band. If you release the force, it comes right back to its original [shape]. Once you get [above] the yield point, that's where you stretch it and takes a permanent set — it doesn't come back to its original shape. It turns out brittle fracture occurs in the elastic range. We talked about elastic fracture — supposed to be elastic-plastic and brittle-elastic. The elastic fractures are [exemplified] by glass. And steel can be that way. There's certain types of steel that we [call] high-strength steel — to be a [cleavage] fracture, that's three to five percent strain. That's enough stretch to avoid most catastrophic failures, but you're still getting deformation of a steel before you break here. In a little range — you can get [some] range before you ever get to the yield strength of the steel on sort of [brittle] fractures. Unpredictable in terms of strength levels, the actual fracture — you have to get the fracture mechanics to explain.

Anyway, ductile is over a little bit, okay. And here's better pictures next [in the] book. We have ductile failure, which is like a happy [cup], okay. [Tom gestures.] But the [middle that the middle?] of the [bond] forms. You see the edges and the [four] people, happy cup cones fractures. Cleavage fracture looks like this. There's a little bit of strain, and actually it's not completely brittle. It is some [low] courtroom, the buckle. And then there's completely brittle, intergranular, where you have less than one percent strain. And so that's the difference in the fracture behavior.

I didn't want to say something also about how much we use particular materials. I have this [chart] — [Tom finds a chart.] We use about half a billion tons of steel in the world. [Major countries], the United States uses about 100 million of that — a hundred million tons. But the world makes one and a half billion tons. Actually, [more] now, okay. Aluminum is only 45 [million?] tons. That's — you go down here, you look at some of these other elements. Well, a hundred bucks a pound — of course, you're up by [those] many tons, okay.

But nonmetals — these ceramic-type materials are actually the larger volume materials. We use about six billion tons of stone each — you just pick rock and crush it, okay. Cement is aggregate, use it to fill up holes, you put it as railroad bedding, okay, for the railroad tracks. We use lots of stone, okay. So [cement] is currently at 2.2 billion tons, okay.

I told you one of the advantages of steel is that it's recyclable. At one and a half billion tons, we recycle over a billion tons of steel here. And one time someone says, well, hell, we're gonna run out of steel. And actually some guys bet on that about fifty years ago, and they built what they call mini-mills, and they made a fortune by using 100 percent recycled steel. Because for a hundred years [we were putting] about fifty million tons a year of steel — into the 500 million pounds of steel a year into the environment — and that stuff eventually comes back as scrap.

It turns out today — when I started working, when I worked at Bethlehem Steel, seventy percent of [the] steel came from virgin iron ore, thirty percent was from scrap. Today over 50 percent [is recycled]. Aluminum is not quite that far along in its recycling, but the more aluminum we use, the more it's gonna go into the environment, and the more it's going to come back. There's a tremendous volume of scrap. If we ever had a steel shortage, it will come back [in] twenty dollars for the [scrap?] soon, yeah. We [re]cycle — we make big stones out of smaller stuff.

One of the problems with cement: how do you recycle cement? Worth it to break it apart into stone? Takes a lot of energy. The more the [problem is stone], cement. If you take my material selection course, I talk about these things. That's where this [plot] came from, okay. And it talks about the cost of the materials and the usage. And it turns out the less the [care of cost], the more gets used. Well, duh, okay. But you know, most materials scientists don't [think about that].