Maximum Energy stored in a wheel

Bob S

The stresses on a spinning flywheel are primarily radial and circumferential tension (not compression), and limit rotor speeds to much lower than relativistic velocities. Recall the stuxnet virus that infected the Iranian uranium enrichment P-1 centrifuges and were destroyed because they spun out of control. See http://itmakessenseblog.com/2011/01/...-bomb-program/

K^2

Note that if you combine these, the energy depends on mass and velocity of the outer edge. Furthermore, if you look at the equations for stress on the disk, you'll notice that disk will disintegrate pretty much at the same outer velocity regardless of radius. So the maximum energy stored in the disk would depend only on material used and mass of the disk.