re:Re: RE:Re: Re: no thrust bearing - simple design ?

Hoyt McKagen wrote (in reply to my poorly explained post):

>At 10:17 AM 4/20/03 -0700, you wrote:
>>A long thin screw behave somewhat like a string on a musical instrument.

It

>>is made stiffer by tension.

>Actually, no. The material characteristics aren't affected at all by
>preload. IOW, deflection of a member under an increment of load is always
>the same throughout the elastic range, no matter what preload is applied.

Hoyt, load stiffening is a very common phenomena. I wasn't talked about
elastic stiffness of a differential unit of volume but rather the stiffnes
of a long screw or rod. A long rod can have a buckling force that is very
small compared with the force that can be generated by a screw. Putting
enough tension on the rod will prevent it from going into compression, thus
it will be stiffened.

Another common example is a partially full plastic soda bottle. With the
lid off the bottle can be squeezed and deflected easily. When the lid is
replaced the internal pressure will rise and the walls will become stiff,
lowest order resonance will increase & so on.

regards-
Elliot B.
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