Polyurethane - Gaining Hyperelastic material constants
I have the experimental data from Uniaxial testing . I used these values for material evaluation in ABAQUS to gain material constants for MOONEY-RIVLIN model.
I have used least squares method in MATLAB to gain material constants for same data set. I am gaining the curve fit, but the material constants are different from ABAQUS.
I tried with Engineering stress and Engineering strain. Then I tried with 2nd-Piola kirchhoff stress and Green Lagrangian strain. Both provided me curve fits but not the same material constants as in ABAQUS. I have used the same procedure followed in ABAQUS manual for curve fitting.
Can anyone please guide me through the correct algorithm and correct stress-strain measures which should i implement, to gain the same material constants as in ABAQUS?