Re: Re: Re: Re: Vibration, damping, and weight


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Posted by Rick Denney on August 19, 2001 at 00:21:28:

In Reply to: Re: Re: Re: Vibration, damping, and weight posted by Laurence on August 18, 2001 at 10:27:20:

I'm quite confident when I say that it won't affect the stiffness. But I'm not at all confident that it won't affect the sound.

An example: Take a spring in the unloaded state. Hand a one-pound weight from it, and this spring will sag one inch, let's say. Now, hang a five-pound weight on it, and it will sag a bunch more. Here's the important bit: When you add an addition pound to bring the load up to six pounds, it will sag once inch more than it did with five pounds. The pound you added has the same effect whether the spring was unloaded or loaded, therefore the spring has the same stiffness despite the residual stress. This is true for all materials that are linearly elastic, which is most metals (including brass) below the yield point.

Now, to the sound. In that one, I have nothing useful to say. Releasing one preloaded joint or brace might indeed change the resonance, because perhaps some other material characteristic than stiffness is affecting by residual stress.

Does someone on the list know how to characterize damping in metals?

Rick "knowing there must be a materials scientist with much more understanding than I have on this list" Denney


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