PU Resin for Layer Damping?

[Tenson]

I'm not sure there is a clear relationship between modulus, even shear modulus and shear loss factor. So that's why I'm unsure the best resin or material to use.

Does high shear modulus translate to high shear loss? Probably not or a stiff solid would be best.

I know that butyl rubber is pretty good in this respect, it's what they use in car panel damping with a aluminium skin. I could wrap the inner tube in that, then fill the slight remaining gap with polyester resin (like car fibreglass) to constrain it.

But maybe PU though the whole gap is better? Mayne add hollow glass beads? Or fumed silliaca?

I've played with 'Green Glue' in the past but it always stays soft and would just slowly drop out I think. It needs to be captured between the constraining layer under some pressure.

Yes the gantry is moving, I considered concrete filling with a big dose of SBR but I guess it will weigh much more than a double skin alli tube with PU in the gap... maybe not?