Modal Impact Testing

[@danielvieito6329]

Great application and excelent tutorial congratulations.....

[@abcdfhk-s8x]

Hi!! We're doing a modal test using 6061 aluminum shallow plate(15cm x 8cm) . We've attached 12 accelerometers on the plate, and fixed one edge of the plate to the vibration shaker. We're trying to find the 'response characteristics' of three different cases. 1. modal test using only impact hammer 2. random test using only vibration shaker 3. random test using only vibration shaker (condition : the fixed bolts of the vibration shaker is a little bit loosened) can you guess the reason why there are response characteristic differences? plus, do you think there's an algorithm to testify loosened bolts?

[@jjxie3291]

Great video. Shouldn't you set the impact range before impact setup?

[@SimcenterTesting]

Yes, it is recommended to range before measuring. The trigger detection step ranges the hammer channel, so only the accelerometers need ranging before the measurement.

[@jjxie3291]

@@SimcenterTesting Thank you for your reply. I like your video very much

[@karanmandothiya9711]

Informative video thankyou.

[@jjxie3291]

Hello, I would like to ask, how to determine which position is the first-order mode of the FRF curve obtained by the origin frequency response test according to the method in the video? In some test processes, such as the frequency response test of the muffler shell, there is no obvious phase change (such as 90°) in the position of the FRF curve. Is there a detailed introduction to how to determine the modal frequency according to the FRF curve? Thank you, looking forward to your reply

[@vaishanavikanse5382]

what accelerometers did you use??

[@jjxie3291]

Hello, I'd like to ask how much the bandwidth should be set better? For example, I'm testing the frequency response of the automobile air filter shell, and the mode I care about is about 250Hz. At this time, should bandwidth follow Nyquist's law and set the range to 2.56 times of 250?? Thank you and look forward to your reply

[@SimcenterTesting]

For a mode at 250 Hz, the minimum bandwidth would be 300 Hz. But a bandwidth of 500 Hz would put the mode of interest in the center, which is probably even better. Due to damping, a 250 Hz mode will be present in frequencies above and below this frequency.

[@jjxie3291]

@@SimcenterTesting OK, I think I see. Thank you

[@AlangTochoi]

Hi, some video taught that the proper way to do a impact test is we need to hanging the structure. Is it true?

[@SimcenterTesting]

That is not always true. If trying to correlate to a free-free simulation model of the test object then hanging from a soft suspension can approximate the same conditions as the free-free simulation model. If the modes of the test object as installed are of interest, then it would be mounted as it is used in a real life application. The simulation model can also reflect real life boundary conditions as well. Further discussion in the boundary conditions section of this article: community.sw.siemens.com/s/article/Modal-Testing-A-Guide

[@AlangTochoi]

@@SimcenterTesting thanks for your response😊

[@jjxie3291]

Hello, during the modal test, there are three kinds of data in the navigation bar: crosspowers, referenceautopowers and responseautopowers. What are the functions of these three?? Thank you and look forward to your reply

[@SimcenterTesting]

The reference autopower shows the force input level versus frequency. This should be as flat as possible over the frequency range of interest: community.sw.siemens.com/s/article/what-modal-impact-hammer-tip-should-i-use. The responseautopowers are the acceleration responses versus frequency. In general, these crosspowers and autopowers are used in the calculation of the FRF. By seeing the individual components, if there are any problems in the quality of the overalll FRF, it is useful to see where the issue might lie.

[@jjxie3291]

@@SimcenterTestinggreat ,thanks