Pellini explosion bulge test development

Second of the three post-WWII brittle-fracture research centers. Pellini at NRL, later came to MIT in retirement.

The other place that was important was the US Naval Research Lab. It was Pellini who did all the work down there, and we'll talk about Pellini at some point. After he finished at the Naval Research Lab, he came to a place called MIT in his retirement from the Navy, and he wrote up all the work he did at the Navy research labs. The third place where they did a lot of important work on brittle fracture was MIT. Morris Cohen and Ben Averbach had projects to look at brittle fracture of steel. So most of what we know about brittle fracture of steels came originally from those three places, as a result of going from riveted to welded ships.

This is called a ratio analysis diagram. It was developed by Pellini in the 1950s or '60s at the Naval Research Laboratory, and it's a complicated slide. I haven't given you this particular one. My paper, "The Future of Metals," has kind of a composite. This one is the fracture toughness versus strength of steels. I'm going to show it for titanium, for aluminum, and then I'm going to show you composites and ceramics and plastics. Your fracture energy for steels of low strength — these are your carbon steels down here; this is yield strength, so your bridge steels and stuff would be even lower, way back at the end of the slide — 10,000 foot-pounds, that's a lot of dynamic tear energy. This is the plastic region. As you get up to higher strengths like 180,000 pounds per square inch, you're approaching the strength of what we use for landing gear on aircraft. The toughness drops off, the energy of fracture drops off as you increase the strength, and it keeps on dropping off until you get up to things like piano wire, and the stuff really doesn't have much toughness.

Pellini at NRL develops fracture methods for Navy nuclear submarine steels; retires to MIT Ocean Engineering; his "ratio analysis diagram" referenced as the diagnostic plot to be discussed.

Then there was another place. A guy named Bill Pellini of the Naval Research Lab in Washington. Later, when Pellini retired from the Naval Research Lab, he came to a place called MIT in the Ocean Engineering Department, now known as Mechanical Engineering. Pellini wrote books, and I'll show you some of the things that he developed for the Navy to figure out how to build nuclear submarines without having them fall apart like the merchant ships did during the war.

Cited as the foundational toughness-testing work from the 1950s and 60s that supports HY80 confidence but does not yet exist for HSLA steels — hence submarine designers' conservatism.

You can see how HSLA steels can save tens of millions of dollars per ship. So the surface people use them, and some of the submarine people are conservative. Why are they conservative? They believe that there's not enough history on the toughness of the HSLA steels. They don't have all the work that was done in the 50s and 60s on the explosion bulge test. I showed you the explosion bulge test that Pellini did. They basically take it under water and they make a weld and they hit it with an explosive charge, and they get all those shock waves from the explosion, and they see if the thing will deform.

One of the three postwar research centers studying weld brittle fracture; Pellini later joined MIT Course 13 as a lecturer in the 1980s before retiring on Cape Cod.

The guy who was Mr. Steel before that was Morris Cohen. He was an assistant professor here after World War II, when they had all the welded ships cracked. There were three places that did the study based on this stay-dry report on Show HBU. One was MIT and Morris Cohen on brittle fracture of steels. Another was the Naval Research Laboratory, a guy named Pellini at the Naval Research Laboratory. We'll talk about Pellini — when he retired from NRL back in the 80s, he came and spent the last couple years as a lecturer here on course 13, which has ended now, and retired on Cape Cod. The third place was started in 1947 or so by a guy Richard Weck, who was a young engineer in England, pedaling through Cambridge. He was riding his bicycle into this little town called Abington — he decided this is where the British welding researchers should go. So the three places in the world that really studied the fracture of steel in the late 1940s, which is one of the things that caused all these ships [to fail], along with poor quality steel.

William S. Pellini at the Naval Research Laboratory developed the explosion bulge test to characterize ship-steel ductile-brittle behavior. Tom describes the 14-inch test specimen, the explosive-charge protocol, the ductile-brittle transition discovery (around room temperature), and the $50K–$100K per test cost today. Tests now run at remote sites (formerly White Oak).

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.

Pellini, at NRL, developed the ratio analysis diagram from his work on WWII Liberty ship brittle fracture. Tom built on Pellini's diagram thirty years ago.

Okay, so here's Ashby and fracture toughness versus strength — we've talked about this. But here's a plot I put together thirty years ago, which is called a ratio analysis diagram. Now, I didn't do the ratio analysis diagram. This guy Pellini, who worked at the Naval Research Lab on the Liberty ships that were breaking up due to brittle fracture, was the first person to put together a ratio analysis diagram, which is just fracture toughness versus yield strength on linear scales, not Ashby's logarithmic scales.