Im trying to learn how to program UHYPER. To achieve this, I gave myself an exercise where I program a default ABAQUS material model and then compare the results with tensile tests on unit cube. For this I chose hyperelastic material Yeoh model. I programmed it and my results are comparable with inbuilt ABAQUS material. But, for a certain choice of material constants the material could be unstable and ABAQUS gives drucker stability for certain preprint settings in .dat file. It looks like this for the following constants.
HYPERELASTICITY - POLYNOMIAL STRAIN ENERGY FUNCTION WITH N = 3
D1 C10 C01
D2 C20 C11 C02
D3 C30 C21 C12 C03
10.0000000 0.190000000 0.00000000
10.0000000 -8.057500000E-04 0.00000000 0.00000000
10.0000000 -1.490000000E-04 0.00000000 0.00000000 0.00000000
STABILITY LIMIT INFORMATION
***WARNING: UNSTABLE HYPERELASTIC MATERIAL
UNIAXIAL TENSION: UNSTABLE AT A NOMINAL STRAIN LARGER THAN 2.5500
UNIAXIAL COMPRESSION: UNSTABLE AT A NOMINAL STRAIN LESS THAN -0.8438
BIAXIAL TENSION: UNSTABLE AT A NOMINAL STRAIN LARGER THAN 1.5300
BIAXIAL COMPRESSION: UNSTABLE AT A NOMINAL STRAIN LESS THAN -0.4693
PLANAR TENSION: UNSTABLE AT A NOMINAL STRAIN LARGER THAN 2.4500
PLANAR COMPRESSION: UNSTABLE AT A NOMINAL STRAIN LESS THAN -0.7101
VOLUMETRIC TENSION: STABLE FOR ALL VOLUME RATIOS
VOLUMETRIC COMPRESSION: STABLE FOR ALL VOLUME RATIOS
And I want to exactly program this for my UHYPER, and this is should be printed in .dat file. Could somebody explain me how to program it ?