Viscoelastic elastomers. 1

[Highspeed]

Hi all,
When dealing with rubbers, silicons and others, it's rather easy to find data's around shore and all the "elastic" properties of a given material.
The viscoelasticity of those materials is something I am interrested in to evaluate efficiency of vibration dampers and I did not find a lot of data's on that subject.
We builded in house a machine to evaluate this property on a given sample but, so far, silicon manufacturers we contacted , when they understand what you are talking about ,don't have much informations.
Any tips, books, or ideas on that subject will be welcomed.
Thanks,
HS

 

[berti]

Hi highspeed,


maybe I am misunderstanding your question?

Visco(sity) and elasticity are imho two sides of the same coin.

Any dynamic tests like torsion pendulum or forced vibrations give on the end a modulus of elasticity and a loss modulus and a loss angle (tan delta) describing their correlation.

Berti

 

[Highspeed]

Yes, re-reading me.. wasn't that clear!
I am a newbie in this area.
What I'd like to understand is in fact what is the rational approach when designing vibrations dampers using elastomers given constraints such as thickness Shore, expected absorbtion coefficient....
The Visco part as far as I understood is transforming vibs in heat

In our "home made" setup we've tested miscellaneous silicons & rubbers in various conditions

For our application
We want to get rid of vibrations in the range 150 --- 600 Hz
basically having a unit weighting 60 grammes
A 10dB attenuation would be fine and the max dimension of a layer is 3 mm x 50 x 50
we would like to optimize this; currently the best performer is a Nusil silicon that wasn't specially designed for that application but that we could test.

The manufacturer just provided samples of miscellaneous silicons, some of them worked others not.
This test approach will work but I was just wondering if a more rational approach could be found.
Cheers,
HS

 

[ParaDoc]

...well, if you need to have a rational procedure to optimise your "vibration-damping" device you first need to know the so called visco-elastic properties of the anticipated rubbery material in a sufficiently broad frequency range. This can be done easily by DMA measurements (Dynamical Mechanical Analysis). At the end you get the so called relaxation spectra of the rubber in question from which you can derive all the properties for your "device".

If you need further help you may contact:

http://www.ViscoData.de

or read the relevant section of the book: "How to Design with rubbers" edited by A. Gent; Carl Hanser Publisher
Good Luck !

 

[Rogerio1]

Hello Highspeed,

when designing polymers for dampening of noise and vibrations there is another factor which must be taken into account besides the viscoelastic properties: the density of the polymer. More mass absorbs more energy. This is usually accomplished in elastomers by adding heavy fillers.
Check out the density of the products you've tested as well.

Good Luck!
Roger

 

[ElastomerXpert]

You've gotten some good advice on getting Gent's book, the best reference work there is on this topic. You can get the U of Akron library to do literature searches for you as well, or go to the Rubber Div, American Chemical Society, website, check out their books on rubber. They have some basic ones (Introduction to Rubber Technology, Fundamentals of Rubber Technology) that are easy to read and can be quite helpful to the person new to this field.

But you should know that really appropriate measurements of rubber's dynamic properties requires first-class knowledge of the methods and equipment.