DIYbanter - View Single Post - Bursting speed of flywheels (and overspun ball bearings)

In article ,
Ned Simmons wrote:

In article ,
says...
In article ,
"Ken Davey" wrote:

wrote:
Joseph Gwinn wrote:
Machinery Handbook has long had a section of flywheels. In the 20th
edition, on page 346, states that all that matters is surface speed
at the periphery, and the tensile strength of the steel, and gives a
formula: V=Sqrt[10*s], where V is surface speed in feet per second,
and s is tensile strength in pounds per square inch.

- IF - The surface speed is what really matters, not the diameter,
what would be the force with a surface speed of 1047 MPH or 1535 feet
per second?

An intersting number that is... It is very roughly (check my math) the
surface speed at the equator. How much reduction in weight do we
expect with that much surface speed?
Aparently, 1535 feet per second is not enough speed at that
diameter(?)

Thus the diameter -And- the surface speed are important,
or:
Something strange needs to be explained.

Someone please educate us all.
Pete

From Machinery handbook - 22nd edition. (page 226)
"The bending stresses in the rim of a flywheel may exceed the centrifugal
(hoop tension) stress predicted by the simple formula s = V(squared)
divided by 10 by a considerable amount.
See relevant section for further edification.

That's if you try to change the axis of rotation while the flywheel is
madly rotating.

No, that's if you're talking about a real flywheel with a thick rim and
spokes. The formulas we've been bandying about are only strictly
applicable to thin cylinders.

Hmm. On second thought, I think you're right.

With balls rolling on the outer ring at very high speed, we should see
some metal fatigue effects from the cyclic bending seen as the balls
pass by.

Wonder if we are running through the fatigue life of the steel, which
then cracks, precipitating the burst? One problem with this theory is
that one would not expect this mechanism to lead to the essentially
symmetrical explosions that have been universally reported.

Joe Gwinn