`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.