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Author: deajohn5556
Time: 08/28/07 08:12 PST
This is a reply to message no. 19072 by tracylam
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Current Topic:
Resonance

Tracy

See my last post on structural damping.  If there are ways to compute this,I am unaware; I have often done it experimentally. For a clamped or any beam frequencies define the mode shape but not amplitude, as you indicate, since amplitude is a function of output to input, or Q.   Metals have a Q of about 50 (about 1% damping) while some brittle materials have a Q of 100 or more.   Rubber has a Q of  3-10 or so.

Once you introduce joints, Q drops significantly, so for structures with a lot of joints this can drop to from the 50-100 values to 10-25 values, but you have to determine this experimentally. Also, as you increase the load input (energy) damping also increases (lowers the Q).

 John

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