What is the most incompressible elastomer?

• Twigg
Twigg
Gold Member
Hi all!

Usually, one would model a rubber as incompressible (##\nu \rightarrow \infty## or equivalently ##\kappa \rightarrow \infty##, where ##\nu## is Poisson ratio and ##\kappa## is bulk compressibility). However, I am trying to use rubber in an application where performance will improve the closer ##\nu## gets to 0.5. Are there any commercially available elastomers that are exceptionally incompressible (better than other elastomers)? (I know that relying on consistent material properties from something like rubber is generally a bad idea, but if this works it would be very convenient.)

For background, the reason I am doing this is to achieve a joint that is stiff axially and compliant tangentially. My thought was to use a thin disk-shaped pad of rubber. According to this reference (publisher link, open-access link), the axial stiffness of a thin cylindrical pad of rubber should scale like ##\frac{1}{1-2\nu}##, which will tend towards infinity as ##\nu \rightarrow 0.5##. In contrast, the transverse stiffness does not scale like this and does not explode as ##\nu \rightarrow \infty##. (See equations 3-3a (axial) and 3-3c (shear) in the linked reference for the exact formulae.) I've verified this trend with finite-element simulations (at least using a linear elastic material model, still working on a hyperelastic material model). But, this only works if the rubber's Poisson ratio is very close to 0.5 (the closer, the better). Hence my question above.

I realize that wires satisfy the same criteria above (stiff axially, compliant tangentially). But the rubber pads would be much simpler to implement in my application. Wires are my plan B if this rubber pad idea doesn't pan out.

Twigg said:
For background, the reason I am doing this is to achieve a joint that is stiff axially and compliant tangentially.
Hanging a mass from a support, using a flexible metal tape that is clamped at the ends, allows movement in one direction. One or two twisted tapes will give you two directions of freedom.

Twigg
Baluncore said:
Hanging a mass from a support, using a flexible metal tape that is clamped at the ends, allows movement in one direction. One or two twisted tapes will give you two directions of freedom.
I think this is similar to my plan B of using a wire to suspend the mass. I agree this is definitely a cleaner way of getting the desired constraint. However, the rubber pads (if they work) would significantly simplify the assembly because I wouldn't need to add features to anchor the the wires or tapes to. (If this is a silly endeavour and I should give up and settle on wires/tapes, just let me know. Thanks!)

What is the most incompressible elastomer?

The most incompressible elastomer is typically considered to be fluorosilicone rubber, due to its high density and low compressibility. It maintains its properties over a wide temperature range and is resistant to various chemicals.

Why is fluorosilicone rubber considered the most incompressible elastomer?

Fluorosilicone rubber is considered the most incompressible elastomer because of its unique molecular structure, which provides excellent resistance to compression set and deformation under pressure. It also retains its mechanical properties in extreme environments.

What applications benefit from using the most incompressible elastomer?

Applications that benefit from using the most incompressible elastomer include aerospace, automotive, and industrial sectors, where components are exposed to extreme temperatures, aggressive chemicals, and high pressure. Examples include fuel system seals, gaskets, and O-rings.

How does the temperature range affect the incompressibility of fluorosilicone rubber?

Fluorosilicone rubber maintains its incompressibility across a broad temperature range, from as low as -60°C to as high as 200°C. This stability ensures that it performs reliably in both very cold and very hot environments, making it ideal for demanding applications.

Are there any alternatives to fluorosilicone rubber for incompressibility?

While fluorosilicone rubber is highly regarded for its incompressibility, other elastomers like nitrile rubber (NBR) and hydrogenated nitrile butadiene rubber (HNBR) also offer good resistance to compression. However, they may not match the chemical and temperature resistance of fluorosilicone rubber.