Damping_measurement

[theampatz]

Hi guys!

I have started my MSc on composites one month ago, and now I am looking for a testing setup in order to measure damping on some specimens. I have designed a jig in order to simulate free free vibration and using an impact hammer and LMS to get the damping coefficient. Do you know if there is an existing solution out there, any testing equipment according to any of these standards: ISO 6721-3, SAE J1637, astm e756??

Thank you guys!
Have a nice week!!


Best regards,
Fanis.

 

[GregLocock]

"LMS" you mean LMS software?

I must admit, while I've seen a few proprietary rigs to measure this sort of thing, I wouldn't have thought there was much of a market. You could try contact vibration equipment manufacturers.






Cheers

Greg Locock


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[FeX32]

We do all of our damping measurements via custom computations of time data acquired.
I suggest you do similar. It will also allow you to use various models and see which fits your data best later.

 

[hacksaw]

what sort of damping are you investigating?

It comes in many forms: intrinsic (i.e. of the material itself), structural effects, effects that derive from the supports and how the specimen is supported, the affects of the ambient fluids or conditions, amplitude dependent damping (i.e. linear vs non-linear) and so on

There are no self-contained measurements of damping, basically tap tests are most commonly used

 

[theampatz]

What about this? ISO standard republished by ethiopian standards.

https://law.resource.org/pub/et/ibr/et.iso.16940.2008.pdf

 

[GregLocock]

Yes, that is pretty much what you'd need, although using an impedance head is very bad idea.

Cheers

Greg Locock


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[theampatz]

Why using an impedance head is very bad idea??

 

[theampatz]

I was thinking of getting a shaker and screwing the impedance head on the stinger of the shaker. Then, glue the sample on the impedance head.

 

[GregLocock]

Yes, that's how you use an impedance head. The driving point transfer function is not typical for what you'll see on the rest of the structure, in terms of mode count and damping. Therefore I'd rather use several accelerometer locations to establish damping, not just the impedance head.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[theampatz]

Ok, quite interesting stuff. I guess I just entered chaos...


Thank you for your info!!!!!!

 

[amanuensis]

Composites are specific structures. Actually, using experimental modal analysis techniques are not appropriated for composites. The main reason is that the (epoxy) matrix of the composite exhibits behavior depending upon the frequency and temperature.
So the best way for measuring the damping is the viscoalayser.
The main benefit of this method is that damping is obtained at every frequency instead of at just resonant frequencies.
Finaly, composite has a critical temperature where the damping increases strongly. There is a phase transition at this temperature.