The TBFT command in ANSYS allows one to perform curve-fitting for hyperelasticity, viscoelasticity, and creep material models.

For hyperelasticity, uniaxial data is straightforward, where positive values are tensile, negative values compressive. All values should be engineering strain and stress. Biaxial and shear data are similar.

For volumetric test data, the first column should be volume ratio, not volumetric strain, which is often a point of confusion. The second column is hydrostatic pressure, which is a positive quantity (think of it being the negative value of NL,HPRES).