YOKOTA AIR BASE, Japan — Tech. Sgt. Tylar Cravens believes he has an idea that could change the way the Air Force trains aircraft maintainers, and he’ll soon pitch it to top leaders at the Pentagon.

3D printing is a powerful tool for creating all kinds of stuff, but it has its limits. Hobbyist-focused machines that dispense melted plastic through a nozzle can only make parts that are so strong.

If we asked you to design a circuit to blink a flashing turn signal, you would probably reach for a cheap micro or a 555. But old cars used bimetallic strips in a thermomechanical design. Why? Because ...