help on damping constant
help on damping constant
(OP)
Hi there:
I am working on the structure analysis of the electronic circuit board assembly. Can anybody tell me what the damping constant should I use for the FR4 board, the ceramic components, and the stiffener (aluminium).
Thanks
I am working on the structure analysis of the electronic circuit board assembly. Can anybody tell me what the damping constant should I use for the FR4 board, the ceramic components, and the stiffener (aluminium).
Thanks





RE: help on damping constant
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RE: help on damping constant
RE: help on damping constant
If it thuds use 0.3, if it rings 0.02
Or measure it properly.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: help on damping constant
xbmath - just to clarify, if it is unitless it's (usually) called the damping ratio; the damping coefficient is units of Force*time*length/radian (usually). Like greg says, you probably need to measure it experimentally (give it a whack and measure the response!), unless there are some figures floating around on the web.
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See FAQ569-1083 for details on how to make best use of Eng-Tips.com
RE: help on damping constant
The damping coefficent (for linear motion) must have units of force/velocity. This is analogous to a spring rate which has units of force/distance. A damping coefficient will have units such as lb/(in/sec), sometimes written as lb-sec/in, and always spoken as "pounds per inch per second."
The damping ratio is the actual damping coefficient divided by the critical damping coefficient, and is therefore unitless.
OK this is funny. I just read Drej's last post and realized he already covered most of this. Oh well, I'll post anyway!
RE: help on damping constant
RE: help on damping constant
I don't remember this source, since in the company I work in, for "bulk" steel parts we use a Raleygh damping approach, and the values we input for alpha and beta are statistically fixed (probably not extremely precise in absolute, but they work for the parts we handle).
If you think it can be useful, I can post these values.
Bye!
RE: help on damping constant
You can perform a forced response or base excitation analysis as a modal analysis. In this case, you would specify the damping ratio for each mode instead of the damping coefficients. This is the method that I prefer.
As an alternative, the amplification factor Q can be specified.
Q = 1/(2*damping ratio)
Steinberg gives an empirical formula for the circuit board Q in his book "Vibration Analysis for Electronic Equipment."
The best approach is make your measurements, however, as has been previously suggested.
Tom Irvine
www.vibrationdata.com