Viton sheet elongation % in X-Y plane......

[quizzical1]

Hi All,

Has anyone dealt with multi-plane elongation before?

I have a Viton sheet 1/32 thk that has an elongation % of 100. Thus I assume that a 1" long sample should be able to stretch to 2" long in the X direction before breaking.

I believe the std Elongation % test is only in one direction (X), but what happens when the sample is stretched in both the X and Y planes equally and simultaneously? It can't stretch to 2" x 2" right? Would it then be a function of the varying areas (e.g. Af/Ai = 2/1)?

All help greatly appreciated,

Quiz

 

[cloa]

You should search for Biaxial elongation.

 

[quizzical1]

Thanks cloa,

Will do....the more I think about it, something tells me it could be a funtion of area also. For the example I gave originally, if you stretch a 1 x 1 sheet in the X direction only 100% to a final length of 2 x 1 that is a 100% stretch and also a 100% increase in area. Does this make sense?

Quiz

 

[KllrWolf]

To get the increase in area, the thickness of the material will change. when one dimension is increased, it must be countered by a decrease in one, or both, of the other dimensions. If neither of the remaining dimensions are restrained, then both will decrease to make up for the increase in the elongated direction.

 

[quizzical1]

Thanks KllrWolf,

That's Poisson's Ratio you're referring to. Yes, I'm aware of that but was mainly concerned with the ultimate tear point at max biaxial elongation in relation to changing areas.

Quiz

 

[btrueblood]

Ideally you would test to determine the behavior in biaxial stress, especially if you want a predictive value of the rupture strength.

Rubber is a complicated material, and there is no easy way to predict its properties...see

http://www.axelproducts.com/downloads/WP_Nonlinear_FEA-Elastomers.pdf

http://people.mcgill.ca/files/pascal.hubert/2006_SAMPE_51_Wadham-Gagnon.pdf

A good friend and chemist/rubber expert once told me that molding rubber is like baking bread - you mix it, stick it in a mold and bake it, and hope it turns out like it did last time.

 

[MintJulep]

Rubber is made up of long chain molecules. In the relaxed state the chains are kinked or coiled. When you stretch the rubber the chains get straightened. When they are fully straight there is no more stretch - in any direction.

Think of a piece of string. If the two ends are pulled so the string is taught then the mid-point has a very limited range of possible movement. If the string is slack the mid-point is free to move over a much wider range.