Measuring coupling dynamic torsional stiffness
Measuring coupling dynamic torsional stiffness
(OP)
Hi All
I am looking for a test equipment, which could measure the dynamic torsional stiffness of couplings. If you have come across the same, kindly let me know.
Regards
Jeyaselvan
I am looking for a test equipment, which could measure the dynamic torsional stiffness of couplings. If you have come across the same, kindly let me know.
Regards
Jeyaselvan





RE: Measuring coupling dynamic torsional stiffness
RE: Measuring coupling dynamic torsional stiffness
RE: Measuring coupling dynamic torsional stiffness
I am doing quite a good amount of torsional analysis calculations. I am concerend that my results are only as good as my inertias and stiffness used in the drive train, particularly that of the coupling. Most of the times, the recommendations and failure reasons are attributed to this. Hence I feel it is high time to sample test the dynamic torsional stiffness at operating torques (static + dynamic).
I am interested to know that anything like that of a sweep test in vibration shaker is available for this sort of measurements.
Thanks in advance
RE: Measuring coupling dynamic torsional stiffness
ht
One tip - if you try a bump test, bump tangentially in vertical direction and measure tangentially in horizontal direction - tends to limit the radial response. But no matter what bumping for torsional resonance would be tricky.
The other possibility is shaker, but of course where are you going to find a torsional shaker without so much mass. If it's motor driven there may be ways to use the motor for variable torsional excitation.
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RE: Measuring coupling dynamic torsional stiffness
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RE: Measuring coupling dynamic torsional stiffness
RE: Measuring coupling dynamic torsional stiffness
If you do a hammer test then use enough accelerometers that you can identify the mode shapes properly, then you can back-calculate the torsional properties. For instance, if you have 3 tangential accelerometers then you can calculate the pure torsional response in one plane.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Measuring coupling dynamic torsional stiffness
I use elastomeric elements, which ivymike rightly forewarned that the stiffness varies with amplitude.True.
Also I have seen coupling manufacturers providing static and dynamic torsional stiffness (some provide this at 10Hz) in their catalogs. We use the latter for all our design calcuations. Their ratio varies from 1.5 to 10 or higher.
Is there a way to deduce analytically or experimentally the dynamic torsional stiffness? I suppose, this depends on the torsional ampltiudes as well as on the frequency(?). For your comments
RE: Measuring coupling dynamic torsional stiffness
Note that manufacturers often state that a margin of 30!% may exist on catalogue stiffness values. They also give guidelines for frequency factors and temperature influences in their catalogue. Note that these factors depend strongly on rubber hardness. a trend it the harder the rubberm the larger the dynamic factor
.
Bottomline: if you calculate using polymer components, use a safe margin, and don't try to calculate up to the 0.1 Hz
RE: Measuring coupling dynamic torsional stiffness
Unless...
there is non-linearity (in which case you might try varying the amplitude)
or there is stiffening under torque load...
or there are speed-dependent effects ...
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RE: Measuring coupling dynamic torsional stiffness
RE: Measuring coupling dynamic torsional stiffness
Fe
RE: Measuring coupling dynamic torsional stiffness
see this article for more
http
RE: Measuring coupling dynamic torsional stiffness
thread335-102034: Rubber spring rate
I suppose one could argue that the dynamic stiffness effect is actually due to damping.
RE: Measuring coupling dynamic torsional stiffness
The 30% modifier that is being bandied about is actually the Holy Grail for complex bushings, I see figures of 80% routinely.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Measuring coupling dynamic torsional stiffness
BobM3 : Thanks for the reference to thread on rubber spring rate.Interesting.
I am little confused with the use of "dynamic stiffness" terminology being used in this scenario. I am aware of using (K-mw^2+iwC)as dynamic stiffness for a conventional academic SDOF model. Does this hold good in the context of coupling dynamic torsional stiffness as well? The manfr often gives this value and depedency on frequency factors and temperature influences as rightly said by Rob 768.
Or is this a two step approach? Meaning,we get the dynamic torsional stiffness assuming coupling as a individual system (which is normally calculated and provided by manfr). Then we use this dynamic stiffness in the drive train torsional analysis.
electricpete: That is exactly my doubt.
In linear dynamic systems, in the (K-mw^2+iwC), when w-->0, the stiffness what we arrive is the static stiffness.
Say from 10 - 50Hz at low frequencies where the system's coupling torsional mode normally lies (where the coupling manfr usually gives the dynamic torsional stiffness data), is it good to assume that the dynamic stiffness is K+iwC (Greg, is that your argument?).
My problem is from the measured torsional stiffness, say from static test or by bump test, can I estimate the dynamic torsional stiffness at my excitation frequency of interest?
Can I say we can approach this in two ways?
1)Measure static torsional stiffness (measuring torque/deflection) using rotor1-coupling-rotor-2 setup. Then estimate the dynamic torsional stiffness as (K+iwC) at excitation frequency w and use that for torsional analysis calculation
2)with Bump test, get the dynamic stiffness directly at the excitation frequency from the frequency response function and use the same for torsional calculations
Only thing in both cases is that I can't see the amplitude and frequency effect of torsional stiffness?
Your suggestions and opinions, please
Jeyaselvan
RE: Measuring coupling dynamic torsional stiffness
To the OP: I would do a full dynamic test if possible modeling 'C' as a nonlinear function. (I assume you have 'C' highly nonlinear which is why you are in this direction)
Just my opinion,
Fe
RE: Measuring coupling dynamic torsional stiffness
Is there anything else he needs to consider apart from the static design, contact angle, etccc? Say, whether a torsional analysis is required to see whether he is operating in some out of phase modes? Could this also be point of concern? Any other check points.
Thanks in advance
Jeyaselvan
RE: Measuring coupling dynamic torsional stiffness
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RE: Measuring coupling dynamic torsional stiffness
Thanks. That was a mistake and I have already listed this in the new thread
http://www
Only after posting, I realised that I made the mistake. Sorry about that.
Regards
Jeyaselvan