Liberty ships and SS Schenectady

Cited as an example of WWII engineering achievement (two-week keel-to-launch) that competed with the physicists' Manhattan Project for postwar prestige.

The scientists got the credit, but there are other things, like the production of Liberty ships. From keel to floating the ship off — in some cases they got down to two weeks to build a ship. That's a pretty significant engineering achievement. Aircraft too. People were recognizing it wasn't just scientists, it was engineers. In 1960, right after he stepped out as president, Eisenhower was presented the Hoover Medal. The Hoover Medal is given by an assemblage of four engineering societies: American Society of Civil Engineers; AIME, which is mining, metallurgical, petroleum, and twentieth-century materials engineers; American Society of Mechanical Engineers; and the Institute of Electrical Engineers. The four big engineering societies basically give out the Hoover Medal. They decided to give it to Eisenhower. In the past it had gone to people like Vannevar Bush — Vannevar Bush had been Dean of Engineering at MIT, and he was down in Washington during World War Two helping direct the science programs. Charles Kettering — anyone know who Charles Kettering was? He basically invented leaded gasoline. He went to General Motors. If you look him up on Google, he invented all kinds of things that had nothing to do with anything. He could just invent in any field. He was just very creative. A great engineer.

The case that motivated fracture mechanics. ~5,000 ships built; ~40 with major cracks; several total fractures. Used to teach the distinction between strength (force of fracture) and toughness (energy of fracture).

Student: The Liberty ships?

Tom reads from the 1946 Maritime Commission report: 4,694 welded merchant vessels investigated, 970 with fracture casualties, 24 complete strength-deck fractures, 8 vessels lost (4 broke in two, 4 abandoned), 26 lives lost. Schenectady famous photo (split at dock); SS Manhattan more dramatic (mid–North Atlantic). Three postwar investigation centers: NRL (Pellini), British Welding Institute, MIT metallurgy (Cohen, Averbach). Outcome includes the Pellini explosion bulge test.

[Tom holds up the 1946 Maritime Commission report.] There are lots of other studies on how codes change. Next Monday we'll have class, which may be the last. One of my students got this out of the MIT Library when they were selling old books that no one had checked out in years: the 1946 report on design and methods of construction of welded steel merchant vessels. Report of Investigation, 15 July 1946. This is the Liberty ships. It has great photos in here, some of which you have not seen before.

Submerged arc welding (originally Union Melt, Union Carbide) is invoked as the engineering solution to plasma-jet instability at high currents: the flux blanket constrains the molten metal so currents of 600–700 A become workable. Roosevelt's letter to Churchill describing the new process for Liberty Ship welding is cited.

Plasma jets do influence things. I end up solving the plasma jet problem because I put flux around it — you can go to 600, 700 amps in submerged arc welding because you cover the outside with this sandy flux, which melts and creates a molten glass tent that collects those drops of metal, and they fall by gravity back into the weld pool where you want them. That was the submerged arc welding process, originally called Union Melt after Union Carbide.

The Titanic had brittle steel, but the problem was the iceberg cut through six compartments and all six of them flooded, and it became heavy on one end. It wasn't until the early 1930s that we started building critical structures of all-welded construction. The first one was the Big Inch pipeline from Louisiana up to New Jersey. It's a 30-inch diameter gas pipeline, and it was all-welded construction — first really critical thing that had been built. As far as I know it was successful; it probably was taken out of service for corrosion, or it just wasn't big enough — we have much bigger pipelines and higher strength pipelines now that can take more gas pressure. But it was World War II when we started to go into all-welded steel construction that allowed the Liberty ships, if you get a crack start it could run all the way around the ship and split the ship in two, because there was nothing to stop the crack.

Origin story for fracture mechanics. 4,694 welded merchant vessels built in WWII; 970 (~20%) suffered fracture casualties; 24 had complete strength-deck fractures, 8 lost, 26 lives lost. USS Schenectady fractured at the dock; SS Esso Manhattan fractured mid-Atlantic.

This turns out — we knew about Galileo and the force of fracture 400 years ago, and by the 1880s engineers were designing bridges and buildings and calculating beam theory and saying what the force was on a building. But it really wasn't until World War Two that we learned we should also be worried about the energy of fracture. In World War Two we had to mobilize and build lots of things, and so we built almost 5,000 Liberty ships. This is the report at the end of the war of what happened to some of those Liberty ships. This is an island off the coast of Washington state where Henry Kaiser — you can see all these Liberty ships lined up — basically took Henry Ford's ideas of an assembly line and produced lots of ships for World War Two, and they were called Liberty ships.

The historical motivation for fracture mechanics as a discipline. George Irwin at NRL extends Griffith's brittle-material formula to ductile materials in response to WWII Liberty-ship failures.

If you go to titanium — and the reason we only have three ratio analysis diagrams is because this is what the U.S. Navy is interested in, building submarines out of, back in the 1950s and 60s. George Irwin, the father of fracture mechanics, was head of mechanical engineering at Naval Research Laboratory. He's considered the father of fracture mechanics because he took this idea Griffith had, that you could study the fracture of a brittle material like glass, and came up with the fundamental equation: the fracture toughness equals this times the square root of pi c. That came out from Griffith in 1925. Everyone thought it only applied to brittle materials. Irwin showed it can also be applied to ductile materials, so it's much more general than just brittle materials.

Referenced as the 1946 baseline — Liberty ships that fractured had less than 10 ft-lb toughness. Used as the historical anchor for the 1950s 15 ft-lb minimum spec, walked up to 20 in the 70s, 30 in the Alaska pipeline era, with proposals to push to 80.

It turns out it's not that big a deal, because what's happened over the years is we put safety factors on top of safety factors. That report I showed you from 1946 showed that the problem for the Liberty ships were Liberty ships that had less than 10 foot-pounds of toughness. So when they came out in the 1950s with requirements they said, we'll add another 5 foot-pounds — you have to have 15 foot-pounds minimum. That was through the 50s and 60s. Then starting in the 70s the Coast Guard decided, well, some people are playing games, we'll go to 20 as the minimum. And then when they started building pipelines in Alaska and places they said, let's go to 30. At one point they were talking about going to 80 foot-pounds minimum, which is just way beyond anything anyone would ever need. Hey, but if you're not paying for it and you're just regulating someone, you just tell them what to do. You don't care — it's their nickel, not yours.

Brief invocation of the ductile-brittle transition lesson learned from Liberty ship fractures. Pellini (Naval Research Lab) and Morris Cohen (MIT) credited for the design framework, developed through the 1950s.

Let's go to ferritic stainless steels. Some of the medical instruments are actually ferritic stainless, like a 430 — they don't turn to martensite, because of the ratio of carbon and nickel and chrome. The problem with the ferritic stainless steels is the same thing we had with the Liberty ships, which were not stainless steels obviously, but carbon steels. Ferritic steels have something called a ductile-brittle transition temperature. So it's impact energy versus temperature. Remember I told you with the Liberty ships, we learned it's not just the force of fracture, it's the energy of fracture. This is what Pellini at Naval Research Lab and Morris Cohen at MIT and other people had known about for years, but they didn't really learn how to design with it until the 1950s.

Frames the origin of probabilistic fracture mechanics: classified Air Force work at Lockheed in Georgia, early 1950s, by a Norwegian expert (father of Tom's childhood friend) brought to the U.S. around 1950. Deterministic fracture mechanics (Griffith, 1925) extended probabilistically for fleet-scale aircraft reliability assessment. ## Cases mentioned in passing

It is uncertainty. He was giving you some stuff — I saw his overheads before he did, from a book on safety factors in design or something like that. It goes through a big probabilistic thing. Remember he had that three-dimensional Gaussian picture. People are now trying to apply statistics to safety factors. Right after World War II, in the Liberty ships, we knew about fracture mechanics. But the big thing in the early '50s was probabilistic fracture mechanics. You took your deterministic — you can calculate the fracture mechanics, the fracture toughness has to be greater than the stress times the square root of pi times crack length. We've known that since 1925, and that's a deterministic formula. You can plug the numbers in and you get, is this greater than that.

The 1946 Navy report on Liberty Ship brittle fractures, finding that the fractured hulls all had less than 10 foot-pounds Charpy toughness. This is the foundational data behind the Navy's 1950s 15 foot-pound and the Coast Guard's 1960 20 foot-pound specs.

Low heat-affected zone toughness due to grain growth. Here's my HY80 weld from 30 years ago. You can see the heat-affected zone — this little black region next to the fusion line. Let's go back to that Navy report from 1946 about the Liberty ships. They found that the ships that sustained the big cracks in the hull structure had less than 10 foot-pounds of Charpy toughness.