Will rubber damping increase with compressive force?

[GMarsh]

Hi,

I have a neoprene rubber sheet mounted on a structure. I am getting FRF using impact hammer testing and measuring damping through half power point method.

When I compress this rubber sheet with two different loads I am getting different damping values. Higher compressive load gives more damping.

I am finding it difficult to explain it with a scientific reason.

Thinking one way this looks contradicting - high compressive force reduces the internal molecular motion possible thereby should offer less damping. Is this right?

Any thoughts on this will be highly appreciated.

Kind regards
Geoff

 

[btrueblood]

Depends on how the load is applied - does deflection of the structure cause relative displacement between the load application device and the structure itself? If so, then varying shear loads are created within the rubber, and damping results. Google "constrained layer damping".

 

[GMarsh]

Thanks btrueblood. This answers the question! Yes, the structure is vibrating and loading is applied at an angle causing possible shear forces in the rubber.

Kind regards

 

[GregLocock]

From experience, yes increasing the preload on a rubber element will increase its damping. I don't have access to any graphs at the moment to confirm this, I'd be looking in "engineering properties of rubber" by the malaysian rubber institute if I knew where my copy is.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[boyze]

In general "rubber" damping will be dependent on steady load, temperature, frequency and amplitude of dynamic load and others. To add to the head scratching these dependencies will in turn be dependent on the type of "rubber" - i.e., neoprene, natural rubber, nitrile, silicone, etc. and furthermore, the damping will be further dependent on the filler type, % loading and curing system.

Keeping the rubber sheet the same obviously eliminates the last 2 groupings of dependencies.

Good Luck.

Jim