`Liberty ships and SS Schenectady`

The Schenectady at dry dock as the photograph in every fracture-mechanics textbook. Subsidiary to the broader WWII vessel case.

We had a number of problems, and this is the 1946 US Navy report on design and methods of construction of welded steel merchant vessels. It's an investigation the US Navy ran right after World War II, because during the war they built Liberty ships, and they were building some of them from laying the keel to sailing away in 2 weeks at the height of the war. They really learned how to pump them out. They built 4,700 Liberty ships, of which a thousand suffered casualties involving fractures. 24 vessels sustained a complete fracture of the strength deck — the top deck would give strength in bending. One vessel sustained a complete fracture of the bottom, eight vessels were lost. Of these, four broke in two, 26 lives lost. The famous picture of the USS Schenectady sitting at dry dock, never having been out to sea — it just decided to break in two one day, sitting at dry dock. If you go to a fracture book, this is the classic book they usually show. What they don't show is one of the plates from this book of the USS Esso Manhattan, where the same thing happened out in the middle of the ocean, which was a lot worse than doing it at dry dock. They lost a few ships.

The Liberty ship hull fractures of WWII as the historical pivot that elevated energy of fracture (Charpy toughness) from a Griffith abstraction to a Navy specification. The 1946 Navy inquiry found problem plates averaging five foot-pounds; the Navy mandated ten, then fifteen (safety factor), then twenty (Coast Guard, 1960), then sixty-to-seventy for line pipe (Alaskan pipeline era).

So we've been talking about fracture toughness and strength of materials. There's the force of fracture, which is tensile strength and yield strength — or in composites and polymers it may be just the ultimate tensile strength, because they don't really have a yield point. But we also have energy of fracture. Griffith pointed it out in 1925. It didn't become important until World War Two and the Liberty ships kind of emphasized it. Even today we are still running into problems. The Northridge earthquake in the early '90s in California — all the codes and standards had designed to force of fracture, and they had no real criteria for energy of fracture. You come along and have these static structures that get vibrated in an earthquake, and it caused five billion dollars worth of damage. Since then we've rewritten the codes and standards, and those structures now in California have to be able to absorb a little bit of energy, a little vibration that comes around every now and then. But there's still other industries where we haven't really gotten around to helping people figure out what the energy of fracture should be.

Brief reference: "we didn't know we needed good toughness until after all the Liberty ship failures" — frames why plate-application alloy steels developed post-WWII.

We did make alloy steels for Henry Ford and Alfred Sloan at General Motors in the 1920s and 1930s, but we didn't have big plate applications until after World War II. One of the reasons is, we didn't know we needed good toughness until after all the Liberty ship failures.

Student: Does martensite form in any kind of metal?

In steel, in some titanium, in some copper alloys, but in general 99.9% of the martensite you'll ever be interested in is steel. Other crystal structures don't have this ability. There are other martensites in other things. A martensite is now defined as just an example of a shear transformation of the metal. The atoms slide past each other due to shear stress, internal shear.

Single-sentence reference to low-temperature brittle fracture in Liberty ships. Foreshadows later discussion not in this segment.

We just talked about a redeeming social value for undermatching before class — these brackets on the Coast Guard cutters. They had plenty of weld area. They were welding a high-strength steel because they needed a deflection of the beam. But they had plenty of weld area holding it together, so you can go to lower strength. They wanted better corrosion resistance in the weld than any other material. They also wanted toughness, which we'll talk about — we haven't talked a lot about lower-temperature brittle materials. That's one of the problems with the Liberty ships. And it is generally a problem.

After the Liberty Ship failures in World War Two, the Navy learned that it's not just the strength of the material, it's the energy of fracture, and you have to understand both if you're really going to understand fracture of materials. A guy at the Naval Research Lab, George Irwin, was head of the mechanical engineering department, and he took on this problem in 1946. He is now known as the father of fracture mechanics, even though Griffith had worked on it 25 years before, because he showed the same equations could be applied to metals as well as glass. So your question was about whether it can be applied to glass. Well, it was first applied to glass and then applied to metals. Dr. Belmar is an expert on fracture mechanics; I teach it some, and we can talk about that later. That's an aside.

Anchoring case for the entire brittle-fracture arc. Tom produces the 1946 Maritime Commission report; cites the 4,694-vessel / 970-casualty / 26-fatality figures; shows the famous Schenectady-at-dock and SS Manhattan-at-sea photographs; attributes the failures to brittle steel plus weld-defect notches plus wartime workmanship shortcuts (electrode stubs welded into grooves).

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.