Japan Steel Works 600-ton upset forging

Visual aid (photograph) showing barreling and oxide breakaway under the gripping tongs. Tom uses it to illustrate friction-induced inhomogeneous deformation and to anchor the practical scale: largest forgings today are about 750 tons.

This shape change would be a frictionless type of deformation, but you typically have something that causes this barrel shape. If you want to see the barrel shape in the real world — this is Japan Steel Works, doing upset forging of some big heavy piece. Here's upset forging of a big hot piece of steel and you can see it's starting to barrel.