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anisotropic hyperelastic

Inconsistencies in Abaqus material


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).

Incompressibility in hyperelastic ABAQUS-Subroutine

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.


Convergence of Anisotropic Hyperelastic Abaqus-Subroutine

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.

Sutured tendon repair; a multi-scale finite element model.

We've recently published an open access journal paper that looks at the mechanics of sutures used to repair severed tendons. A homogenization strategy is used to derive effective elastic properties for tendon fibrils and intracellular matrix. We have found that regions of high stress correlate with the regions of cell death (necrosis) that are sometimes observed in patients.

If this is of interest, please feel free to view the paper here.



Tissue strain-rate independence

Choose a channel featured in the header of iMechanica: 

I have two basic questions for the experts in the soft tissue biomechanics community. 

a) I am interested in the biomechanics of a specific tendon in a specific high-speed deformation. How plausible is it for me to assume strain-rate independence, and therefore, the existence of a strain energy function? In other words, how accurate is the assumption of pseudoelasticity for tendons under high strain-rate? I feel comfortable with the assumption (evidence would help a lot, however) for tissues such as mesentery, skin and, I guess, even muscle. 

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