Foam to reduce resonance

[locovibe]

I recently took a course in Random Vibration and Shock Testing with Wayne Tustin.

He presented several photos of engineers filling fixtures and head expanders with foam to reduce resonance.

Has anyone tried this?

Thanks!

 

[btrueblood]

I've heard of fixtures being filled with damping materials, e.g. semi-solid silicones, typically those from Lord company. But, as a senior structural dynamics whiz noted, it would be better to redesign those fixtures to eliminate any resonances within their intended duty (typ. 20-2000 Hz?).

 

[GregLocock]

I can see it helping to get rid of local panel modes, but struggle to believe that it would do much to the average text fixture, which usually seem to have been crafted (or hacked) from 10mm aluminium plate.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[GBor]

Depending on the method of "insertion" (sprayed foam that expands and fills the cavity, cut blocks "stuffed" in, etc.), I would think the results would depend dramatically on the adherence to the structure. Seems like it would also have much to do with the density of the foam.

If it isn't bonded to the structure, I would agree with Greg's local panel mode. If it is bonded, I would think it might turn the structure into a sandwich composite unless the cavity is particularly large...then I think you are back to the local panel mode.

 

[floattuber]

I replied in the other thread, but for future searches...

All of our head expanders are filled with some kind of expanding foam as delivered by the fixture company that specializes in vibration fixtures (Baughn Engineering). All head expanders that I've seen are made of magnesium. Our head expanders use ~2" thick mag plate for a horizontal surface with ~2" thick ribs to stiffen. The foam is injected between these ribs.