I am getting very low value of loss factor like 0.0234 for a all side simply supported viscoelastic sandwich plate, where as as it should come approximately as 0.1734 or 0.1937. Also for CCCC boundary condition loss factor value is coming very low in the order of 10^-5 or e-5, but it should also come in the same range as SSSS i.e, 0.1734 or 0.1937. I am using Finite element code written in MATLAB.
Can anyone shed some light? Thank you.
Hi
The material loss factor for most materials is quite low. It tends to be determined by support and sound radiation damping, see here for some ramblings of mine on this topic. http://qringtech.com/2014/06/22/designed-damping-types-mechanisms-application-limitation/
0.02, i.e. 2% loss factor is a rather usual value and, actually, a bit on the high side and assumes some internal material friction.
It is not surprising that your get different results with changing boundary conditions as you change the way the structure is loaded. Try computing complex modes and you will find the modes to have different loss factors for the same reason.
If you are using viscoelastic materials, there will on top be a frequency (and temperature) variation. See here
http://web.itu.edu.tr/sanliturk/Publications/ESDA2010-24452.pdf
http://www.me.umn.edu/~gurkan/Inter%20Noise.pdf
http://www.sea-acustica.es/fileadmin/publicaciones/Sevilla02_mat01010.pdf
Hope this helps
Claes
Thank you Claes.
Actually its a constrained layer damping with viscoelastic core. What I m concerned about is benchmark problems have system loss factor in the order of 10^-1 for both SSSS and CCCC plates where as I m getting order of 10^-2 for SSSS and 10^-5 for CCCC.
Hi Deepak
For a Constrained Layer Damping (CLD) to work, one must allow shear sliding between the layers.
Could a problem be that your BCs somehow constrain such movement between the CLD layers?
You write that you are using a plate element so the cross section should be uniform in rotation, but one never knows. Just a thought. Take a look at the maths in the theory manual and see if it can shed some light and read out also ply motion from your analysis if this is possible.
As a side note. Sandwich plate elements have a tenedency to overestimate the damping effect as the cross section does not rotate uniformly for all CLD configurations.
/C
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