Damping Measurement: Shaker Table vs Ping Test 3

[flash3780]

I'm interested in performing a vibration test on a piece of hardware; we're quite interested in damping, specifically.

I'm looking for a comparison of the accuracy of damping measurements with a shaker test vs a hammer test. Shaker tests seem as though they would be more accurate, as you control the forcing amplitude, rather than interpolate the damping from the response. But, this is mere conjuncture on my part. Comments?

 

[GregLocock]

Yup, I'd go shaker table. Then I'd explore how the damping changes with steady state sine frequency and amplitude, vs random noise excitation, vs chirp or impact. You might need to keep an eye on temperature as well.



Cheers

Greg Locock


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[Ezlifer]

Actually we have done the NF and Transmissibility measurement on isolation system consists of 4 air spring isolators by both ping test and shaker experiment. Shaker got more consistent result.

 

[Rob45]

This is an interesting subject.
Recently I have been doing quite a lot of damping material tests, to screen candidate materials for a new application. Not having a shaker, I have done this using my trusty hammer. I devised a panel test using the same substrate material & thickness as the intended application, and I sized the panel to achieve approximately the same first mode frequency as the problem frequency in our structure. Using LMS TestLab software, which calculates the damping ratio directly, I have gotten very consistent results, with good repeatability. And I have run several manual calculations of the half-power bandwidth of the FRFs to assure that the software IS calculating correctly.
The issue I have run into, however, is that my principal supplier uses the B&K modal package to calculate damping ratio, and they occasionally get very different results.
But repeatable ones. No conversion factor is possible, though, because they also sometimes get identical results to what I get.
I guess we're stuck without access to a shaker. I may ask them to see what sort of results they'd get using their shaker.
Best regards,
- R

 

[Vibac]

Rob45, just a comment: Modal analysis covers a wide range of different algorithms. Some are more appropriate for certain conditions than others. As an example, frequency domain based algorithms/methods may tend to exaggerate the damping ratio estimate for low frequencies (and or low damping rates). Here, time domain algorithms might prove better suited. My point is: If you and your supplier get different results you should not think of "LMS vs. B&K", but rather discuss the methods applied. Check up on the manuals and other literature to find the most reliable method for your specific case.