Trains made of aluminum foam, a material that’s stronger, lighter, and better in a crash than fiberglass or regular old metal. Engineers in Chemitz, Germany unveiled a prototype high-speed train cab made with the stuff earlier this year. The composite material is built like a sandwich. Between two pieces of aluminum, each just two millimeters thick, is a 25-millimeter-thick layer of the “foam,” actually a low-density, sponge-like composite of magnesium, silicon, copper and aluminum. And like a good sandwich, there’s no glue. The layers are held together by metallic bonding, the electrostatic attraction of negatively charged electrons and positively charged ions.
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