compressible incompressible

Dear All,

I got confused on the hyperelastic experiment that the uniaxial, equibiaxial, and planar test are based on the material is incompressible. What if the material is compressible, are the experiment the same as incompressible material? Except for the volumetric mode, what is the different between incompressible and compressible material experiment? Thanks!

Regards,

Bob