It is not clear from the documentation whether you can use the hyperelastic curve-fitting routines
with compressive test data. If so, how should the data be entered? Would you reverse the signs
of compressive uniaxial test data and enter them as positive equi-biaxial tensile data?
For the uniaxial test, just start with the most negative strain and keep increasing to zero strain
and then continue on in the positive range (see attached ANSYS 10.0 example). Technically, the
order that the data is input does not matter, as it will do a fit, but the curve might look a little
screwy if you do not do it in the order noted above.
However, uniaxial compression data is generally not too good. The specimen tends to stick due to
friction, so the results are not that accurate. Axel Products (www.AxelProducts.com) recommends
using equi-biaxial tension tests instead of uniaxial compression tests for increased accuracy. The
two tests are the same, but the equi-biaxial tension lacks the friction issue.