MSE_F2016_06

Yes okay. Yes I mentioned shape charges and I said bring my shape charge piece in. [Tom produces a shaped-charge copper piece.] This is a shaped charge piece of copper, and it basically is just a saucer-shaped piece, and it's got little places where you would put a little bit of explosive in each one of those. And when you set it off, the saucer will invert, okay. You'll have a downward force on the outside rim of this thing and the thing will invert, and all the copper will be squeezed into the center underneath. And as it does that, you'll have adiabatic heating and the copper will melt, and you'll shoot out a jet of liquid copper out of there. And that jet of liquid copper will penetrate a piece of steel to about whatever the length of the piece of copper is, and it will do it in microseconds, okay. So this is another shaped charge design.

So this is your terrorism lesson for today. If you just took a piece of copper, a round copper bar, and you milled a 90-degree slot in it, okay — I guess I could do a little better job of — so you're just gonna mill a 90-degree slot in it, and then you put your stick of dynamite on here. Then when the dynamite explodes, this unfolds back on itself and you will get a shaped charge. And in fact that is exactly what they use when they want to tear down buildings, demolish buildings. They'll take a little bar of copper, they'll put it right up against the I-beam, and they'll put a little tape, stick of dynamite to it. And when they set that off, the molten cotta— the dynamite will go off, the stick of dynamite here will go off, the copper will fold back on itself, adiabatic heating from all the energy, molten copper will just slice right through the beam, okay. So that's how they demolish buildings.

Okay so I know a little about some of this stuff, mostly because I used to be on the Army's advisory board for their ballistics folks, but also because of my World Trade Center paper. The conspiracy theorists say that was the thermite reaction that brought down the World Trade Center. And I said that's ridiculous, no one would use a thermite reaction to bring down the World Trade Center, it wouldn't work. And it turns out National Geographic ran a special and spent three hundred sixty thousand dollars, and most of it went to actually testing the theory of whether a thermite reaction — which is a reaction between iron oxide and aluminum powder which will melt steel, that's the way we weld railroad rails together, is with thermite reactions, we've been doing it for a hundred years — but they actually set it up at the Explosions Research Center in Socorro [Soccoro?] New Mexico, which is part of the University of New Mexico Institute of Technology I guess. They have a big mountain there and they have an explosives research center, and they'll still blow up anything for a fee. And they actually ran the test for National Geographic. Had an I-beam column, packed it around with thermite reaction, set off the thermite, and all it did was make a bunch of heat. Didn't cut the beam in two, just like I said, okay.

But anyway, there's a National Geographic special on the World Trade Center collapse that actually shows me holding that little piece of copper as I was explaining to him, this is how you would set it off. And then they went to a dormitory in Louisiana where some demolition guys were blowing up this dormitory, because it is an old dormitory. And they actually had these types of shaped charges, and they duct-taped them to the building beams and stuff. And anyway, when they told the demolition experts the conspiracy theorists' hypotheses about how the World Trade Center came down, those guys just laughed on the screen. They said that's — okay, I said it was ridiculous. Though anyway.

So we were talking yesterday about these quotes, and I was thinking a little bit more. One of you said that you didn't believe the quotes, and this is for new materials, it's not for older materials that are more mature, that have gotten into the reduction of cost processing stage. This is some new material with fantastic properties, and it's always not quite as good as the developer thinks. But I think the criticism yesterday was correct, and we'll actually, when we get to steel, show that steel technology is now in the reduction in cost — reader cost — reduction through processing stage, and it's not a new material, okay. And so Sprague's law doesn't apply to an old mature product. Yeah.

But the people who are selling it are not really being honest about the science. They usually improve one property, and when you're actually designing a system you need a suite of properties. You need strength, you might need corrosion resistance, okay. Originally steel was a wonderful material, had plenty of strength and ductility, but it still today has lousy corrosion resistance, okay. That's one of the Achilles' heels of steel, is corrosion resistance, even today. Well someone came along with stainless steel and everybody thought that was wonderful, and we'll talk about the fact that stainless steel is not as wonderful as everybody thinks. It's stainless, not stain-free, okay.

So usually if you start thinking about the various properties — sort of like my example of the electrically conductive polymers, they said oh well, they've got a specific electrical conductivity. Yeah, but that's not the figure of merit for the design, okay. And so people will talk about composites and fancy composites. I remember Professor Gutowski in mechanical engineering — I guess it's over twenty-five years ago now, when the LFM programs first started — he had a group of students go to Boeing working on advanced composites. This was supposed to be for the 777, was supposed to be 80% composites. Well they canned that after a couple of years and they made it mostly aluminum, just like the previous aircraft. The 787 finally, twenty years later, did make it to a fair amount of composites, but there's lots of problems. But I remember Professor Gutowski came back — he works in the environmental things now, but he was working in advanced composites — and he came back and says, I've been working on the wrong thing, okay. He says I've been trying to make better composites. What we need are cheaper composites, okay. Which is sort of Jim Williams's corollary — people have fantastic composites with tremendous strength, but you can't afford them, okay.

So whether it's cost or whether it's properties, these things often have an Achilles heel, and you kind of need to go to someone who's gonna be an honest broker, who's gonna say — who knows the area, okay. I knew superconductivity and I knew that we weren't gonna — and it wasn't just me, I said there were five people in the department who had worked in superconductivity, and the only one who joined the bandwagon, aside from all the other people who knew nothing about superconductivity, was the untenured one. The four tenured professors would not touch this material because we knew what the problems were, okay. Other people who didn't know what the problems were, oh they were cheerleading, they were saying oh, you know, we're gonna be riding on magnetically levitated trains. Well that was twenty-five years ago, okay, and we're still not riding on magnetically levitated trains.

That's not to say that the high-temperature superconductors haven't found a niche. Anybody know what their niche is? The generators for wind turbines. Turns out you really need lightweight up there, and those generator shafts are steel shafts that can be twenty inches in diameter in one of these really big wind turbines. And you need lightweight. Well it turns out you want something that has better electrical conductivity than just straight copper. Copper is pretty heavy, silver is pretty heavy too. And these superconductors are actually silver wires, but if you cool them to liquid nitrogen temperatures you will get some superconductivity in this silver matrix.

And I remember twenty years ago at a National Materials Advisory Board meeting, and they were talking about, well we should have some talks about certain things, new materials. And this wasn't too long after — you know, five or six years after — the high-temperature superconductors came along. And someone says, oh we should have a talk from somebody about high-temperature superconductors. I said, you mean cold silver? And there was only one person in the room who understood what I meant. If you cool copper to liquid nitrogen temperatures, it will have about five times lower resistivity because it's cold. If you go down to liquid helium temperatures it'll have about twenty times lower resistivity. It's not a superconductor, okay. And silver is even better than copper, we said, as an electrical conductor. Well at the break, Van Roos [Van Reuth?] who works at the Naval Research Lab and has worked there on superconductivity all his career, comes up to me, he says Tom, it's not just cold silver. He didn't say it wasn't cold silver, okay, he says it's 20% better than cold silver, okay. Oh wow. I mean, we spent billions of dollars studying high-temperature superconductors and we've got something that's 20% better than cold silver, okay.

But it has found a niche, and its niche — it has actually two niches. They've tried to put a transmission line in the center of New York City, for a DC transmission line. Has to be DC because superconductors don't work well with AC, that's another story. But they built a DC transmission line. There's not a lot of room underground in New York City, it's all kinds of wires and pipes and everything else, and things are very crowded in Manhattan. And so they actually put in half a mile or something as a trial, and that was a number of years ago. But I don't know if they've ever done anything beyond that trial. But all the technology that had to go with that was horrendous. And there are applications for looking for submarines from space, okay — superconducting quantum interference devices. But most of the great promises of high-temperature superconductors have not held up.

And it's because of some of the critical parameters. There's high temperature — there's three parameters actually, the first figure in my doctoral thesis. There's high temperature, there's high magnetic field, and there's high critical current density, okay. If you go to high current density, it loses its superconductivity. And I have this little phase space with three axes with each of these three things and saying this is where you have superconductivity, in this little octant of space. And the thing is, they had improved one property, temperature, and they actually had, along with that, got in a high magnetic field, but they hadn't improved critical current density, and they still haven't today, twenty-five years later, okay. And people were reporting all kinds of wonderful critical current densities parallel with the magnetic field. And all of us — I mean, I did my thesis over at the Magnet Lab — anybody who tried to publish a paper measuring the critical current for a magnet with the conductor parallel with the magnetic field, you wouldn't have gotten your paper accepted, okay. Because anybody knows you got J cross B forces which will destroy the critical current. If you have your conductor perpendicular, and that's how you design a magnet — you don't design, you can't design a magnet with the current parallel. I mean J cross B, the vectors, the vector products — the current has to be perpendicular to make the self-magnetic field. That's physics, okay. That's what's-his-name, Maxwell, Maxwell's equations, okay. We're going back to Maxwell's equations.

But I'm sitting there reading Science magazine, and people have got wonderful critical currents. I had the highest critical current in the world for my thesis, okay. And people were publishing things that were two orders of magnitude above what I had, except they were parallel with the magnetic field, which means that was garbage, okay. But if you didn't know anything about superconductivity, and the people who were publishing this, the people who were reviewing the papers, they didn't know what they were talking about, okay. They might as well have gotten a high school student to do this, okay. And so, one of the problems when there's lots of money, you bring out all the people who don't know what they're doing, okay. Because everybody else takes the money, right. Does that answer the question? I have strong opinions about some of these things, and I'll tell them to you later, okay.

So, people oversell new materials, and actually — oh, new materials are actually very useful, but they're not quite as wonderful as people say, and it takes time to develop them, okay. We're talking about cost still, and now we're going to talk about speed versus cost. And it turns out lightweight is more valuable the faster an object moves. And so the value, I said that for an automobile is two dollars a pound, but, or for an aircraft it's $200 a pound of weight saved. But if you're talking a disk on the engine, it might be not $200 a pound, it might be two thousand dollars a pound, depending on where you say that. So part of your criticism yesterday was, when you make a blanket statement, the blanket statement doesn't always apply, right, it's too general. Well this is one of the places where the blanket statement of two dollars a pound for automobiles and two hundred for aircraft doesn't apply. You can actually spend more for the material if it's in a critical application.

And one of these is called a bladed disk, or a BLISK. And you'd love to be able to take the turbine disk, which right now has this complex geometry to join the turbine blade to the disk, and you have this heavy structure right in here. If you could weld these things together or cast them together, you could reduce a lot of weight in this thing. And it turns out that's exactly what has been done in some cases. I'll tell you the commercial case, and secondly here I got circling the areas where we've saved weight on this BLISK. The only commercial BLISK that I know of actually happens to be on the Detroit Diesel Allison, now Rolls Royce, M250 engine, which they've made something like 10,000 of these engines. They go in helicopters and other things. And they actually cast the blades to the alloy, to the superalloy, it's all cast as one unit. I said they've made 10,000 of these things, and it's a small turbine engine for helicopters and small planes, but not for great big commercial planes. People can't cast with the quality they need in the big disk. But that is one application. People are trying welding. The Air Force has spent tens, if not hundreds, of millions of dollars trying to figure out how to weld blades to disk, because there's tremendous value.

In fact, if you go to a typical aircraft, the weight savings multiplied — if I can save twenty pounds on a disk, and I got multiple disks in the aircraft, I got multiple engines in many of the aircraft, saving twenty pounds on a disk will mean two hundred pounds on the engines, and two thousand pounds on the airframe. Yeah, that's not a big deal for a commercial aircraft, but for the Air Force, two thousand pounds either means two thousand pounds more fuel and extended range, or two thousand pounds more ordnance and more bang for the buck, so to speak, okay. It is literally bang for the buck, okay.

Sprung weight is more important in automobiles. Here we have a disk brake and a drum brake, just nice color pictures off the internet. At one time, back in the mid-80s, some people had developed a technique to cast aluminum silicon carbide metal matrix composites. Reagan had started Star Wars, and people thought, oh this is inexpensive, we've lowered the cost of this composite material. And one of the things they wanted to do — and several of the automotive companies tried it — they made the caliper housing, caliper assembly, with — has the little hydraulic pistons in here that squeezed against the disk pad. Here you have the little pistons — actually have the piston right here which pushes the drums up against the outer housing. Anyway, they wanted to make this out of aluminum silicon carbide metal matrix composite. It's cast-iron right now. It's heavy, it's on the axle which is bouncing up and down. If you can reduce the weight on the axle, you'll get better maneuverability and handling and whatnot. Anybody know what the automotive companies call the whole general area of handling and noise and stuff like that? NVH. Noise, vibration, and harshness, okay. And so the sprung part, what's on the axle, is a large contributor to noise, vibration, and harshness. And so if you're going to buy a Cadillac that's nice and quiet running and stuff, you want to have less mass on the axles.

Anyway, they did, and everything was fine, except if you put the brakes on hard two or three times, this would start to overheat. Aluminum is a low-temperature metal, it will creep at elevated temperatures, and all of a sudden the dimensions of this thing change, and when you apply the brakes you have no force, okay, because the thing just sprung open, okay. So that didn't work. That was twenty-five years ago, but I've heard — I haven't looked at it, but I've heard — that they have solved the problem, probably with design and cooling and stuff of these things, so you don't get brake fade, okay. So you'll pay more — the point is you'll pay more than $2 a pound if you're on the sprung weight, okay. So this $2 a pound is the general rule, it's not specific to everything.

Another example from the aerospace industry is the X-33 space plane. This thing I've handed around, I won't hand it around again unless you really want it. [Tom holds up a piece from the X-33 hydrogen tank.] But this came off one of the two liquid hydrogen tanks. The X-33 space plane was a project in the early 90s, $1.3 billion dollar project to build a prototype to replace the space shuttle. NASA had — the space shuttles, they had five of them, they weren't going to last forever, and they weren't economical like they were supposed to be. That was their purpose in the early 70s. And most people think the space shuttle was a civilian project. No, okay. Let's not — I have a fantasy here. It turns out it was sold to the public, this big program to build a space shuttle, as, we'll be able to, you know, we'll be able to colonize the moon and we'll reduce the cost of a pound in space from $20,000 to $1,000. That was their goal, was the thousand dollars a pound. If you go back and look at the 1970s type of data, it really — but it wouldn't have gotten through Congress if they didn't have the support of the Defense Department, okay. It turns out the space shuttle main cargo bay just happens to be the same size as a space laser weapon, okay. Just a coincidence, okay. And if it weren't for the fact that the Defense Department was cheering on NASA and the committees in Congress, they wouldn't have gotten it approved, because you couldn't justify it on just purely commercial reasons.

Anyway, the fuel for this reusable space plane was supposed to be H2O — H2 hydrogen tanks and one oxygen tank, H2O, okay. And they were going to save further weight because they — you're gonna integrate, the tanks were gonna be part of the structural strength of the whole system. So this was just the skin on the outside that was gonna deflect the hot gases and things like that. This was an aluminum tank, these were supposed to be composites for hydrogen. And this was gonna go all the way from Edwards — ever see it was gonna go from Edwards to Dugway Proving Grounds in Utah. That was its flight, I can't remember where it started and where it ended, was more either vice versa, one or the other. It was supposed to get up 200 miles in space and land, and essentially had wheels on it, okay. It was supposed to land. Well they built it. In fact they built it, and I was there, I got to go there, in the same hangar — well, where they built the Stealth fighter at Edwards Air Base, Edwards Air Force Base, okay. So this was a super-secret hangar at Edwards.

And the problem was, when they were building this thing — well, they had it after the first Gulf War, the Defense Department decided they should go for rapid prototyping. That was a big thing twenty-five years ago. Because — you won't remember, but we held off the war for six months while we mobilized, okay, in Saudi Arabia. And remember Hussein had taken over Kuwait, and we — so we announced we were going to invade Iraq and take back Kuwait and stuff, and the Saudis were in favor of all of this. And so we took six months to move everything over there by ship and everything else. The Second Gulf War didn't take that long, we basically announced we were gonna go to war and we were at war within a week. And you know, the first Gulf War lasted like three days, okay, because we took six months to prepare for it. You don't always get to prepare for a war like that.

But in any case, the Defense Department decided they needed to rapidly prototype things, because they were not ready in 1994 for a desert war, okay. For example, the helicopters in the desert with all the sand — the helicopters would last, the engines would last thirty minutes. All that sand would go through the engines and would abrade away your engines, okay. Engines only lasted thirty minutes. They had to solve problems like that. So they decided to make this a rapid prototyping project. It was thirty months, thirty-three months maybe, I don't remember, from let of contract to first flight, okay. Design it, build it. They tried to design it out of rib-stiffened, three-dimensional woven composites. And that was what they bid on. And then they actually got the contract — this is Lockheed Martin Skunk Works in Edwards Air Force Base. And then they went out to price this, and they found out, oh, composites are expensive, okay. In fact they were gonna blow their whole budget on these 3D woven composites, plus it was going to take a while. You know how you make 3D woven composites? You have someone with a needle and thread, okay. Literally, okay, running the carbon fibers in a third dimension. You know, the labor was expensive.

Anyway, so they decided they only had two months left of their six-month budget for the design phase. So they came up with — yes, which was the Nomex honeycomb core which you could buy off-the-shelf — not at Home Depot, but you could buy it from the companies that made it, was an off-the-shelf product. And the graphite fiber laminate tape, you know, cloth you could buy, and you could buy the resin. And they just happened to have a big autoclave at the Morton Thiokol plant in northern Utah near Logan, Utah. And they looked on the website and 3M was selling this adhesive that they could glue the whole thing together in the autoclave. And they looked at the data sheet for the 3M adhesive, which you had to keep in a refrigerator. It said that it had a shelf life of ten days outside of the refrigerator, and they decided they could lay everything up and get it into the autoclave within ten days. What they didn't say was the strength was only 10% of the original adhesive strength after ten days, okay. They were figuring it would have 80, 90% of its strength, not 10% of its strength.

So they put it into the autoclave, and they made — they needed for each four little lobes of each one. They put them in the autoclave, and they were gonna join each of those four lobes together to make two tanks. They made ten just in case, they knew they might have some problems. They came out, and some of them had delaminated in the autoclave. One of the problems with the composites, there's no way to repair it, okay. If you don't get it right the first time, it's junk. Well they had about seven of them that were pretty good. So the eighth they decided, well it might be okay, and they had a design safety factor of two. Only with the delaminations it wasn't quite two anymore. So they sharpened their pencil, and they really sharpened their pencils, and they had a design safety of 1.05, okay. Wow, 1.05 is greater than one, so therefore it's good, right, good to go. After all, we got a $1.3 billion dollar contract here, and we don't want to go and tell them that, you know, we have a thirty-three-month deadline and blah. So let's put it in test.

So where do you put it in test where you can get five thousand gallons of liquid hydrogen? Well, used to go down to your, you know, your local — no, you can't. You have to go to Huntsville, Alabama, and NASA has — where are you from, okay? And what do they have in Huntsville? A big facility. Well NASA and the Army both have a facility, but this was actually at the NASA facility, but the two are sort of joined at the hip, you know, Redstone Arsenal and — anyway. So, and I got to go there, okay, and see this tank of liquid hydrogen. And then one of these tanks got to go there, and it got to be filled up with liquid hydrogen. And they were sort of sweating their 1.05 safety factor. They fill it up with liquid hydrogen, the whole thing doesn't spring a leak, and they're given— they're starting to cool it, or warm it up, and they're giving each other high-fives. And they're on the video camera, because you don't let anyone right in the place with the 5000 gallons of liquid hydrogen that might leak and go boom. So they're giving each other high-fives, and on the video camera they see this burst, and they have a leak, okay. And it turns out hydrogen got inside the pores — as it, a liquid, hydrogen got inside the pores, as it warmed up I'll decide and built up pressure and it blew up. And they cancelled the $1.3 billion program, okay.

So we didn't — we did not for a while have a replacement for the Space Shuttle. In fact now we have SpaceX and other things, but that program got cancelled. But this was $12,000 a pound fabricated, okay. It was the size — each one of these tanks was about the size of a two-story house and stuff. But it was all part of structural frame design. They had Inconel little struts holding things together. That's what these things are, these little triangular frame things are Inconel struts holding everything together and everything else. Just the skin on the outside for aerodynamics.

Another material from aerospace, I said this before — the first large-scale production of carbon fiber aircraft was the V-22 Osprey, which is a tiltrotor helicopter. Bell had invented tiltrotors back in the 1960s, they built a couple of prototypes for NASA. And basically the advantage of a tiltrotor was — anybody know the advantage of the tiltrotor versus a fixed wing or a helicopter? It's actually a hybrid of both. And the hole in the nacelle, that nacelle is large enough for a person walking. I walked into the nacelle of ship four, okay. I could stand up, okay. Carbon fiber. Has to be lightweight, because these are big powerful engines. But when you're in helicopter mode you need a big powerful engine. When you're in regular airplane flight mode, you don't have to have such a powerful engine. But in case when you're going to go into helicopter mode, you need a lot of power. And the engines were tied together with carbon fiber composite tubes, torque tubes.

And anyway, they had — ship one was just a prototype mock-up so you could walk in it, never flew, it wasn't designed to fly, I'm not sure it ever had engines in it. It was just to see if things would fit together, okay. Ship two was at Philadelphia Boeing Vertol plant in Philadelphia, and they'd taken it up about ten or twelve feet off the ground. And they have this all on video, sort of an interesting video, I'm sure you can probably find it on YouTube now. But anyway, so it's hovering there in helicopter mode, and then all of a sudden you see it start to oscillate a little bit, and then it goes — flips on its back and destroyed itself. What happened was, they had a test pilot, and they all walked away. But someone had miswired the controls, okay, two wires, so that if the pilot put in the input to go right or left — it was supposed to go right or left, well when they flipped the wires it would go left when you said right and vice versa. And so what happened is, he was trying to stabilize the thing, he just made the oscillations bigger until he flipped it over like a turtle. And that was sort of an embarrassment.

And then ship four was the one that I worked on. It had crashed at Patuxent [Pawtuxet?] Maryland, and a number of people died. And it was a problem, they had a fire, and then this — okay. And the question, did the fire start in the engine in the bottom or the gearbox in the top? The Navy determined that it was a fire in the engine in the bottom. They had 4,400 findings of facts. I disputed it, and after — went to trial and I testified, and afterwards the Judge Advocate General Corps of the Navy went back and looked at the Navy's 4,400 findings of facts and reversed it to what I said happened. It was, they had a hydraulic leak up here, okay, and they had a big fire when the hydraulics let go. That's a longer story. Anyway, it does fly, supposed to cost like six million dollars, ended up costing forty to sixty million dollars. But it flies.

And it was a V-22 Osprey that was the first aircraft in when they captured Osama bin Laden. Why? Because they're quiet. Helicopters are noisy. Airplane mode is nice and quiet, okay. And they can go three hundred miles range and stuff on these things. Anybody know why helicopters can't go — why they're so noisy and why they can't go faster? I mean this thing can go three hundred miles an hour and a three hundred mile range or something, whereas helicopters can't go more than about two hundred miles an hour. Anybody know why? [Tom gestures with rotor blades.] Turns out if you're going in that direction, the rotor blades are going around like this. There's no problem for the rotor blade that's retarding, but the one that's going forward is sweeping around, and when it reaches sonic velocity, all of a sudden you get vibrations and noise and everything else. And so you can't exceed the speed of sound on a helicopter blade without having tremendous energy. NASA did it, and if you go to Langley you'll see a test helicopter where they actually did go faster with the tip speeds above the speed of sound, but only for a few seconds, okay.

So there's carbon fiber, you couldn't have built this aircraft without it. We actually have gotten carbon fiber — anybody know anything about the BMW i3? So how could you afford carbon fiber composites that might cost you $50 a pound fabricated, when you can only put $2 a pound into the vehicle? Well first of all, it's not a $20,000 vehicle, it's a $60,000 vehicle if you start pricing it out. Second of all, they basically decided to build it in the state of Washington next to hydroelectric plants, because one of the big costs of the carbon fiber is the energy to take this stuff and turn it into carbon fiber. You have to heat it up to 2,000 degrees centigrade and stuff to make the carbon fiber composites. And they basically built it where energy was cheap, okay. They moved to the price of cheap energy. And the other thing — I don't, I haven't looked at one, there were a number of things they did that were very innovative on the part of BMW to get the price down.

One of my former students bought a BMW i7 [i8?], which is the big hundred thousand dollar sports car, $140,000 list, but Chris tells me they deep-discount them, he got his for a hundred. And he did his thesis on polymers, and his comment was the carbon fiber composites are junk, okay. Maybe they're not made well. They're fine for just a shell on the outside of the vehicle, okay, and it's lightweight, but the quality of the resin transfer molding would never pass the aerospace industry, okay. So low quality, high cost material. But they've innovated, and they've made a couple of vehicles, first ones in the world. And twenty years ago no one ever thought they could do it, but it's been done, okay.

Some things like ships need very little energy to move. All you got to do is slide them through the water, and so there's — that's how you get down to low enough the material cost. Some things you don't care about density. Like this is a big pressure vessel, and they're actually just transporting one half of it, the rest of it. It's a great big reactor for a refinery, and this is just the front of it when they're transporting it, and see all the wheels and stuff here. Large vessels don't usually move, so we don't care if we make them out of something heavy like steel, okay. So speed versus cost, there's lots of different price points depending on what you're doing.

So now we're gonna change topics. Anybody have any questions or any examples of your own on price points of speed versus cost? And this $2 a pound for an automobile can have a wide range depending on where your actual application is.

If we get back to the science of material properties, we're finished up on — we did externalities and we did cost and availability, and now we want to talk about material properties. There are limits to the properties of materials, and some people will design systems that are way beyond whatever we can really do. Did I tell you about the Air Force propulsion program, and they wanted to — this is a committee I was on down in Washington about twelve years ago. And the Air Force had a couple of requirements. One is, they wanted to have an engine that could go Mach 17. Well Mach 17 is, you know, basically the speed of the satellites going around the earth, right, 15,000 miles an hour or something like that. And I said, in air? And they said yes. I said, this is human-powered, you know, man-rated? And they said no, it's not. And I said, why do you need something that will go Mach 17 in air? Because if you look at the frictional heating of the skin, you get to temperatures of seven thousand, six or seven thousand Kelvin. And now we're only talking about three or four materials in the world — carbon, hafnium carbide — I mean there's only three or four materials that don't melt or vaporize at 6,000 Kelvin, okay. And so you have a very limited choice of materials.

Now they said well, we can use things like active cooling. That was what they had proposed for the National Aerospace Plane back in the mid-80s. Well the National Aerospace Plane was going to be hydrogen fueled, and they were going to make the skin out of copper, because it had great thermal conductivity. And they were going to pump the liquid hydrogen through the skin, and the copper was going to be one or two millimeters thick. And so you'd have, on one side you'd have four or five thousand degrees Kelvin, and on the other side you'd have liquid hydrogen at 20 degrees Kelvin. And as long as you didn't have a leak, everything was fine. But if you ever had a leak, you have a big bomb. So it wasn't a great design. But that's what the Air Force wanted to do.

And I said, why do you need Mach 17 in air? And they said — this is like 2003, 2004, 2005 timeframe — I said, well, once we knew where Osama bin Laden was, we had to get ordnance on site within fifteen minutes, and we didn't have anything fast enough to get there, okay. We couldn't fly helicopters in there in fifteen minutes, we couldn't get a cruise missile in from an aircraft carrier in the Gulf within that time frame. And we couldn't get him, okay. But they knew where he was. But he was gonna be gone in fifteen minutes. Well, he got away that time. So they wanted something that'll go Mach 17, and they would have been able to launch it off an aircraft carrier in the Gulf, and they could have gotten the word that's in there and blown them up, okay.

Well that was one thing they wanted to do. The other thing they wanted to do is, they wanted to have an aircraft that would fly 25,000 miles without refueling. And I said, excuse me, the earth is only 25,000 miles in circumference, and so you should only need something you can get to any place in the world with a 12,000-mile flight, okay. In fact, I last summer, not this summer but the summer before last, I took the longest flight in the world, seventeen hours Dallas to Sydney. Seventeen hours on one airplane, the Airbus A380. It's a long flight, but you can get there, and that's about 12,000 miles, and there's never gonna be a longer flight than that, because you go a great circle. Well they said, we figure that in the future we will not have any air bases except in the continental United States, we can't expect to have air bases. They didn't say it, but the Filipinos are gonna kick us out, and you know the Japanese are gonna kick us out of Okinawa, you name it. We won't be able to use Diego Garcia or whatever. And so they wanted to have an aircraft with a — okay. Well the requirements to have these types of things for lightweight materials are horrendous, okay. But that's what people will design when they have no constraints. They'll say that's what they'd like to have.

But we do have constraints, and it's the strength of a chemical bond. So this is what's called — originally was called the Lennard-Jones potential, in the 1920s, came out of quantum mechanics and Bohr atom and stuff. And basically this is the energy of a bond versus spacing between the atoms. So if I got one atom here and I got another atom, and I bring it closer and closer, there'll be a minimum of energy of separation. X is the intermolecular, intramolecular separation between the atoms in the crystal. As you heat things up, at lower temperatures you'll have a certain vibrational energy, and at higher temperatures, with more thermal energy, you'll have greater vibration. And that leads to thermal expansion, okay. Higher thermal expansion at higher temperatures and higher vibrations.

And if we look at thermal expansion, we find that some of the polymers have very large thermal expansion. This is a log scale, folks. Then you've got some metals, then you've got some ceramics. Diamond has the lowest coefficient of thermal expansion, of ten to the minus six per degree Kelvin, okay. If you look at Young's modulus, it goes the opposite direction. Diamond has the highest Young's modulus. Metals are down here, an order magnitude lower. And sort of the polymers are another order of magnitude down. So we're limited by the strength of the chemical bonds.

And if we look at the strength of chemical bonds, we've got different bond lengths. So we got primary bonds — covalent, metallic, ionic. Should have learned this in freshman chemistry if you were an MIT student. And they have these bond lengths. You can also talk about the bond energy in kilojoules per mole. I learned it in electron volts. The main primary bonds are typically one to three electron volts. Metallic bonds have a larger range, they go over several atomic distances — I mean that's five angstroms, that's more than one atomic distance — I'm not — yeah, five angstroms. The secondary bonding, van der Waals and hydrogen bonds, are an order of magnitude or two lower as far as that goes. And so that determines the properties of things.

Polymers are low temperature materials, because they have — they are not held together in a three-dimensional structure with covalent bond, or primary bonds. They're held together with van der Waals bonds. Along the length, where the primary bonds, are tremendous strength. That's Kevlar and stuff. The fibers can be very strong because you got primary bonds along the front of the fiber, but you got secondary bonds between the fibers, and therefore polymers are low-temperature materials. The strongest material in the world is diamond, because it's a three-dimensional structure of covalent bonds.

So everything relates back to the bonds. We can look at this — there's in thermodynamics, there's Richard's rule and Trouton's [Troutman's] rule. Basically if you look at the enthalpy of melting or boiling and you find the transition temperature, Richard's rule and Trouton's rule is basically just the energy necessary to break all the bonds — break 10% of the bonds for melting and break all the bonds, 100% of the bonds, for boiling. And there's a very good relationship between the strength of the bond, the temperature melting point, and all those things.

If we look at the properties that are limited by bonding — yes, it's true that diamond is a thousand gigapascals. But most materials, like molybdenum, carbon fibers, are about 60,000 ksi, 400 gigapascals. Steel is half of this, which is actually very high and good, but it's nowhere near the few materials like molybdenum, tungsten, and carbon fibers that are double steel. Melting temperature — tungsten, it's got the highest melting temperature, just like it has the highest, one of the highest, moduli, because it's the strength of that chemical bond.

Toughness — what is toughness? Toughness is the ability to absorb energy. Something that is, in the science of fracture mechanics, something that is brittle will be very sensitive to flaws and defects. I can take a piece of paper — see me doing this on the History Channel — and you can pull on it with several pounds of force. If you put a notch in it, a flaw, instead of pounds it takes ounces. You can lose 80 to 90% of your strength because of the flaws in the material. One of Bob Sprague's comments was, physicists think that structure controls properties of materials. Metallurgists know that defects control the properties of materials. It's the defects in the material, and we'll talk about that later as well as that goes.

If you have a tough material, rubber is a tough material. Put a great big notch in this and I can pull on it, and all it does is blunt, and I no longer have a sharp notch. So rubber is a tough material. Paper is a brittle material. You can tell a brittle material — if you break it and you try to put it back together, it matches. You take a ductile material and you break it — and Brian will bring in some samples tomorrow, it'll show a ductile material — you can't put it back together in the same shape because everything's stretched and deformed. The highest toughness in the world is some of the superalloy metals, around 300 megapascal square root of meter, unusual units, we'll get to that. The cost can go from gravel stone to unlimited people — tremendous prices for some materials. Ductility — a good material would be 30%, a brittle material can be essentially one-tenth of a percent, up to a thousand percent for some super-plastic materials. Generally these things vary over about a factor of a hundred thousand, not just on the chemical bonds but on other things as well, and we'll talk about those.

So Brian will lecture tomorrow, Simone will be here on Thursday, Friday's off, and I'll be here all of next week, and Dr. Belmar will be back after that.