Pineapple juice composite can (steel/aluminum)

Materials-competition case demonstrating that composite metal cans solve a corrosion-resistance/cost optimization. Pull-tab needs aluminum's low toughness; sidewalls and bottom benefit from steel's lower cost given pineapple's mild acidity is tolerable on aluminum only intermittently.

[Tom holds up a pineapple juice can.] This is a pineapple juice can, except the top is made out of aluminum. Why? You need low toughness so you can do the pull-tab. The aluminum, you can put a little seal around. Here at the bottom it's made out of steel. But you also notice something else when I compare these two metal cans — what's the difference? It's a more slender shape. Why? Because someone used calculus of variations. This was one of the problems they gave me as an undergraduate in one of my math classes: figure out what has the maximum volume to hold the beverage and the minimum surface area for the material that I'm paying for. It turns out you take a Campbell Soup can, and it's just about perfect, where you vary the diameter and the height under certain constraints.