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Ansys Mechanical: Anisotropic Hyperelasticity Material Model

I am currently researching the
fluid-structure interaction (FSI) of fistula and av-grafts in the region
of the brachial artery in dialysis patients. I will be using ANSYS
Mechanical and FLUENT as the coupling offered is strong/implicit which
is necessary for my model. I'm having some trouble implementing the
anisotropic hyperelastic material model for the artery. This material is
in the 'Special Hyperelastic Materials' section and thus needs to be
inputed through command snippets. I get a solution, but it is not behaving as it should because my command snippet material is being ignored..

My issues are the following:

  • It seems that I need to choose a
    material in engineering data in workbench to run the simulation. I then
    either delete that material or make the new one active. The engineering
    data material that I am forced to initialize is the material used in
    solving. The AHYPER material added in the command snippet is ignored. I
    cannot find how to delete or unassign the initial material.
  • I want to make the fiber directions of
    the material be based on a local coordinate system which is an arbitrary
    curvilinear one (ie. based on location). This does not seem possible
    based on the documentation. Only cartesian, cylindrical, spherical and
    toroidal coordinates seem possible. I want to apply a coordinate system
    that moves and rotates with respect to an arbitrary artery surface.

Below is my command snippet:

--------- Command Snippet Start------------------

! make local coordinate (12) active

csys,12

! defining material constants for anisotroic hyperelastic material with
exponential-function-based strain energy potential function

tb,ahyper,2,1,10,expo

! a1,a2,a3

tbdata,1,3820,0,0

! b1,b2,b3

tbdata,4,0,0,0

! c1,c2

tbdata,7,996600,524600

! e1,e2

tbdata,9,996600,524600

!compressibility parameter d

tb,ahyper,2,1,1,pvol

tbdata,1,0

!orientation vector A=A(x,y,z)

tb,ahyper,2,1,3,avec

tbdata,1,0.75448,0.65632,0

!orientation vector B=B(x,y,z)

tb,ahyper,2,1,3,bvec

tbdata,1,0.75448,-0.65632,0

! make material (2) active

*set,matid,2

! make global coordinate active again

csys,0

! change keyopts (not necessary)

keyopt,1,2,0

keyopt,1,6,1

--------- Command Snippet End------------------ 

I would greatly appreciate any help
and advice on these issues, and what might be missing from my command
snippet. Also if 'special' local coordinate systems are possible, how I
might add them would help me immensely

Hi,

I have the same problem in ansys. I need to use a hyperelastic orthotropic material in soft tissue modeling and it is not in ANSYS engineering data library. I should implement my own material model, but I have never used subroutines in ANSYS. Is there any useful source I could use in order to fix my problem?

Thanks to the time you dedicate

Arash

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