anisotropic hyperelastic

Hello,

i wonder, how the inconsistencies in anisotropic hyperelastic material of Holzapfel-Gasser-Ogden form caused by Macauley-brackets and Heaviside step-function are beeing solved inside Abaqus (cf. Analysis User's Manual 22.5.3).

The Heaviside H(x) is beeing used to allow fiber reinforcement only on extension (in fiber direction). But analytical derivatives of the Macauley-bracket yield terms with H(x), and the Dirac-delta (infinite impulse at x_0).

Hello everybody,

in hyperelastic material models incompressibility is normally realised through Lagrange multipliers. But i can't find any instruction, whether i have to code that multiplier in a routine e.g. of type UHYPER, UANISOHYPER_INV or UANISOHYPER_STRAIN! The only instruction is on incompressibility (and hybrid element) flags, that have to be set, cf. Abaqus User Subroutines Reference Manual 1.1.20, 21 and 37.

Hello everybody,

i try to re-implement the anisotropic hyperelastic material of Holzapfel-Gasser-Ogden form already included in Abaqus (cf. Analysis User's Manual 22.5.3).

After successfully debugging the subroutine (Uanisohyper_Inv), i had some serious convergence problems, anyhow. My one-element test modelsdidn't even deform a bit.