Aluminum baseball bat

Highest-strength aluminum (~100 KSI yield) off the chart of Pellini's RAD. Bats engineered to last 100–150 hits and crack, not shatter — manufacturer-favorable degradation behavior at $300 per replacement. Used as closing example of how the strength/toughness trade-off plays out in consumer products. ## Figures referenced (recurring numeric anchors, not cases)

Design with structural materials is a balance between strength of fracture by force and strength of fracture by energy. You need both. It wasn't until the Liberty ships of World War II that we learned you had to have toughness as well as strength. You couldn't just go for high strength. We use baseball bats now made of highest strength aluminum, around 100 KSI strength, off the chart of the ratio analysis diagram that Pellini put together in the 1970s. Today we have aluminum alloys we can make super strong, and we make them into bats, which are very thin wall, and they typically will crack and won't work very well as a bat — they don't shatter in someone's hands, but they cost you another $300 to buy a new bat. The bat companies think that's fantastic. They could make these things that would last for one or two hits, but people would really get upset if it failed after one or two hits. So they make them so it only takes 100, 150 hits before you'll start developing cracks and have to buy a new bat, and they think that's fantastic.

Ash chosen for bats because it's the strongest wood on the Ashby plot; Kentucky ash availability is part of why Louisville is the bat-manufacturing center. Student question on maple goes unanswered.

Over here on the side, in terms of lightweight, some of the lightest weight to strength ratio materials are something called wood. Anyone heard of the Spruce Goose? What was the Spruce Goose? World's largest airplane. Howard Hughes decided to build the world's largest airplane. He built one of them. It was on display for years in Los Angeles, but it's in Oregon now — at that aviation museum in Oregon. I've been there but it wasn't there when I was there; it must have been moved there in the last 10 years. It's called the Spruce Goose because he built it out of spruce. If you look here, ash is the strongest wood. Where does ash grow? A lot of ash grows in Kentucky. And what do we build in Louisville, Kentucky? Baseball bats. Louisville Sluggers. What are they made out of? Ash. Why? Because it's the strongest wood.

Brief aside — the highest-strength aluminum alloys are in baseball bats, not aircraft. Used to land the precipitation-hardening point.

Twenty years ago someone published a paper in Science. They had gone to the Smithsonian, gotten the little sample from the Wright brothers' aluminum engine, put it in the transmission electron microscope, and measured the size of the precipitates which had been aging for eighty or ninety years at the time. They showed the size was consistent with an aging time of ninety years — the precipitates had been coarsening over ninety years. They compared that with a three-hour aging, a four-week aging, a one-year aging, plotted them on the same log plot and showed it was consistent with diffusion of copper in aluminum. So aluminum can be hardened. I could have brought my baseball bat — the highest strength aluminum alloys are actually baseball bats, they're not aircraft alloys. They're precipitation hardened.

Physical-object case. THT-100 scandium-bearing aluminum alloy, 100 ksi yield, ~28-thousandths wall, swaged from extruded tube. The world's largest single use for scandium (~2 tons/year global production). Sold through southern California aerospace-engineer-led firms. Used to land the "highest-strength aluminum is in consumer sports, not aerospace" homework answer.

[Tom produces an aluminum baseball bat.] So it's about the right time to tell you a story. I paid $130 on Amazon for this. Typically you might pay $300 for a bat. This has a THT-100 alloy, a scandium alloy. This is the world's largest use for scandium. We only make two tons of scandium a year. The Soviets discovered that scandium is a tremendous grain refiner. When they make these metal bats, they extrude them, and they have a relatively thin wall — this may have a 28-thousandths wall. It has 100 ksi strength, and when you hit it with the ball, it'll go farther than with a wooden bat. It's lighter than a wooden bat. It has to weigh a certain amount. This is a minus-10 bat — see the minus 10? That means it's 29 inches long and weighs 19 ounces. You take 19 ounces and subtract 29 inches, and you get minus 10. They were making minus-13 bats a few years ago, but they would almost crack the first time you hit a ball with them.

Cited as the highest-strength application of aluminum alloys (~100 ksi yield), achieved by ice-water quench for fine grain size. Used to make the "find the real technology in the market" point.

Student: Baseball bats.