Is "performing Impact Hammer test" an ART?
Is "performing Impact Hammer test" an ART?
(OP)
I've been doing Impact Hammer test on a motor end cap (just the end cap alone, i.e. the end cap is not attached to the motor frame) for several days. However, I'm still not able to get consistent results, let alone to determine the natural frequency of the end cap. Is performing Impact Hammer test an ART which requires 'skill'?
I followed the procedure stated in "Section 11: Modal Testing Using a Hammer and Accelerometer" in the Supplemental Operator's Guide for the Agilent 35670A Dynamic Signal Analyzer (http ://www.hom e.agilent. com/upload /cmc_uploa d/All/EPSG 090090.pdf). I recorded the frequency response function (FRF) plot as well as the coherence plot (an indicator of measurement quality) of the hammer testing. I repeated the hammer testing many many times. I found out the coherence results were not consistent, and most of the coherence results showed that "my measurement" were not "good". How can I improve my measurement? How can I obtain consistent measurement? Please kindly share your experience on performing Impact Hammer test.
Thank you very much
I followed the procedure stated in "Section 11: Modal Testing Using a Hammer and Accelerometer" in the Supplemental Operator's Guide for the Agilent 35670A Dynamic Signal Analyzer (http
Thank you very much






RE: Is "performing Impact Hammer test" an ART?
Your remarks indicate that you are not able to make consistent results idicate that your system might not be linear. Is the time data and autospectrum of your excitation okay? any multiple hits? how about your time response? Look whether you have any sort of signal clippings, gain,etc.
This should depend on your structure, excitation force, contact stiffness, contact time, mass of the hammer,mass loading of the sensor, windows, etc & many more.
Atleast you should be able to see first few modes repeatedly to look anything further on the data.
Regards
Jeyaselvan
RE: Is "performing Impact Hammer test" an ART?
The end cap was placed on a sponge. An accelerometer is glued to the end cap by using wax. Hammer test was done at a point near to the accelerometer.
The time data of the excitation is OK. There is no multiple hits. The autospectrum of the excitation is OK too, e.g. the gain is rather flat over the frequency of interest. The level input signals are within the input range settings of the DSA. "Force Exponential" window is used and the setting is done according to the experimental procedure stated in Agilent application note.
I find out that the "shape" of Frequency Response Function (FRF) results for different hammer tests are quite similar. But the difference in coherence results are not consistent. I really wish to know how to perform Impact Hammer test to obtain consistent coherence test results.
Thank you very much
RE: Is "performing Impact Hammer test" an ART?
What I would suggest is that you get your hands on this book:
http:
beginning on page 290 (of my version) there is a very good section on hammer shock.
It includes many practical sample problems along with very clear analysis.
RE: Is "performing Impact Hammer test" an ART?
Thanks for your suggestion. I will get the book for reference.
Thank you very much
RE: Is "performing Impact Hammer test" an ART?
I do have another paper, which might be of interest to you title " My coherence is better in some measurements than others when impact testing. Am I doing something wrong?"
Good luck
Jeyaselvan
RE: Is "performing Impact Hammer test" an ART?
Jeyaselvan, the article is great. One of my problem might be the one explained in the article.
Thank you very much
RE: Is "performing Impact Hammer test" an ART?
Obviously you'll have a coherence of 1 after the first hit, then it will be awful, and then after a few more hits it'll settle down. If your technique is good it'll slowly improve.
On some structures one good clean hit is more useful than several hits with varying forces, angles and locations (ie poor technique). So often I will take 3 independent FRFs at the same location, overlay them, and then actually use the one that looks like the best.
On the other hand if I just want to know if a panel is causing a particular peak, I'll deliberately get the average response by hitting all over the panel.
The article is good, but I'd often accept even the worst of his examples as being good enough!
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: Is "performing Impact Hammer test" an ART?
Thanks for your reply. I have some experimental results here:
http://www
I will be glad if you could comment and provide some advices to improve my coherence plots.
Thank you very much
RE: Is "performing Impact Hammer test" an ART?
If you are desperate to improve the coherence round the antiresonances then you need a more sensitive accelerometer and to get rid of noise in that channel.
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: Is "performing Impact Hammer test" an ART?
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: Is "performing Impact Hammer test" an ART?
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: Is "performing Impact Hammer test" an ART?
Thanks for your replies and suggestions, which are practical knowledge and very useful.
RE: Is "performing Impact Hammer test" an ART?
1 - When a V8 crankshaft is placed in the block with 5 main bearings, the lateral response changes immensely.
2 - Press a guitar string against a fret, and the note changes many octaves.
RE: Is "performing Impact Hammer test" an ART?
Oh, another practical point, take the hammer extension off and fit a softer tip, I think the hammer may be too heavy.
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: Is "performing Impact Hammer test" an ART?
As Greg says, it is primarily for validating FE model for a known boundary condition and then utilize the modal model for predicting whatsoever boundary conditions, loads, etc.
Jeyaselvan