damping determination at 20kHz
damping determination at 20kHz
(OP)
Hello All,
I am doing one experiment to find the damping of component made of polycarbonate material at 20 kHz frequency (the first natural frequency of the part is in the range 80 Hz). I want to use this damping in the FEA to simulate the response of the component.
Source that I am having can produce vibrations at fixed 20 kHz. Instrumentation I have are accelerometers and CRO.
Is there anyway to find the damping.
Regards
I am doing one experiment to find the damping of component made of polycarbonate material at 20 kHz frequency (the first natural frequency of the part is in the range 80 Hz). I want to use this damping in the FEA to simulate the response of the component.
Source that I am having can produce vibrations at fixed 20 kHz. Instrumentation I have are accelerometers and CRO.
Is there anyway to find the damping.
Regards





RE: damping determination at 20kHz
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: damping determination at 20kHz
RE: damping determination at 20kHz
https://www.youtube.com/watch?v=PnsFFhKqXXo
Jim
Jim Kinney
Kennedy Space Center, FL
RE: damping determination at 20kHz
The stated 80 Hz natural frequency suggests that the part is rather large and yet you want the damping at 20 KHz.
As far as modeling goes, you assume a damping parameter.
RE: damping determination at 20kHz
You state that you need the damping at 20kHz, however the decay method will yield a damping coefficient at its resonance frequency only.
Many materials (likely polycarbonate too) have damping that is dependent on deflection amplitude, frequency, heat, ect.
RE: damping determination at 20kHz
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: damping determination at 20kHz
Do you have an analytical reference for this?
RE: damping determination at 20kHz
I will find the damping by decay method as you suggested.
The lower frequency measurement issue will occur in hammer test, but if I am operating at 20 kHz, then decay method should also work.
Regards
RE: damping determination at 20kHz
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: damping determination at 20kHz
RE: damping determination at 20kHz
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: damping determination at 20kHz
Walt
RE: damping determination at 20kHz
In fact if he flicks the part with his fingernail or a small screwdriver he'll generate a spike, so long as his accelerometers work that'd do. It's the decay characteristic that matters.
Good point though.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: damping determination at 20kHz
Damping measurement in complex systems is always an interesting topic.
Unrelated to the attachment;
Seems first try is: 1) Setup experiment and locate (ideally a few) sensors onto the structure. Keep in mind the locations in relation to the theoretical mode shapes.
2) Use hammer test method to excite as many modes as possible. A harder hit will likely excite more of the high frequency modes.
3) Collect data of several trials.
4) Break data up into frequency components with FFT. Then packet it into the frequency you are interested in.
5) IFFT and perform 1dof decay method calculations.
Any comments?
Cheers,
RE: damping determination at 20kHz
That's a testable hypothesis. Of course if the system is linear it'll make no odds.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: damping determination at 20kHz
RE: damping determination at 20kHz
RE: damping determination at 20kHz
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?