Damping Test of Concrete & Steel Tube

[Tenson]

I did try a measurement with one end of the beam clamped to my drill press and the other end free. I saw the same modes but they were all more suppressed, I assume damped by the clamping interface. This is probably why they use quite thin samples in the industry standard procedure.

When the beams are longer and part of a structure, the resonances will also be lower. The lossy damping will be less effective at lower frequencies. There is less internal friction generated in the structure at lower speeds of vibration. That's why friction welding uses high speed vibration.

One way to improve damping at the lower frequencies is to use constrained damping layers. Outer skin - Damping layer - inner core. However that becomes more difficult than simply pouring a filler in the structure. I also wonder how that would effect over-all stiffness compared to a directly coupled core.

I believe you can calculate loss factor as a ratio of the upper and lower -3dB points on the main resonance before and after damping. However I don't think it will provide any data that can be compared with other info found on the web. My test set up is not industry standard. Also as this test demonstrates a simple loss factor figure only looks at damping of the initial amplitude, ignoring energy storage. EDIT: Although if you calculate energy loss over a number of cycles like you suggest maybe it is more representative than the method I mentioned. I can provide the impulse response if you want to have a crack at it? Maths is not my strong suit.

[redfedoradog]

I can provide the impulse response if you want to have a crack at it?

Yeah sure, send it over. Not sure if we can compare between different test setups, but it can't hurt.

Maybe the best test for hobbyists is to assemble the whole machine, place it where it's going to be used and start whacking it with a mallet? It'll be affected by the floor material, friction, etc but in the same way as when it's running.


This test was done very similarly to yours and I've been using it as a reference.

[Tenson]

Yeah sure, send it over.

I uploaded the files to a google drive folder. There is an install file for the (free) software to view and analyse the files. The only limitation of the free version is that you can't save.

Once you open the file it will directly display the impulse response. You can zoom vertical and horizontal axis and scroll with the buttons at the side.



EDIT: Helps if I link the folder! https://drive.google.com/drive/folde...j9?usp=sharing