high deformation problem with simple shear tests

[christian]

Hallo,
I want to do a simple shear test with PUR foamelastomeres of an apparant density of about 500 kg/m³.
The problem we have with all elstomeres are high deformations.
Under linear elastic conditions thrust can be bsorbed only by tangential forces at the lateral faces of an rhomboid.
With high deformations there also exist normal stresses, which must be take into account (Poynting effect).
How can I messure pure shear forces? Does anybody have exerpiences? Must I be content with smal deformations?

[Jorgen]

Hello Christian,

I am not sure I understand your question. Are you interested in simple shear or pure shear? It should not be difficult to do a simple shear test to large strains, I have those tests in the past. You are right in that you will get normal forces (Poynting effect), but I don't see that as a problem. I do not think that you should simply limit your experiments to small strain.

[Christian1]

Hallo Jorgen,
thank you for your attention. I think, that the normal forces result in normal stresses, but that this stresses just remain in the inner material, without reaction at the plates. So I reseice stresses in all Parameters of the cauchystress tensor, although I just want the tau12/21/23/32.
I think I must read more about material laws, to continue the dialogue, but I fear, that there are problems to take into acount?!?!

I am just from a university of applied siences, so I must repead some theory, sorry!

[Jorgen]

If you apply simple shear to any material, at finite deformations, then you will get not only the shear stresses that you mentioned but also normal stresses. The normal stresses are typically smaller than the shear stresses but can be important in certain applications.