FEA of hyper-elastic arteries

[ChellBells]

Hi all,

I am attempting to model an artery under internal pressure in ANSYS APDL.. This is my current attempt..

1. select solid 8 node 183 element type (and specify thickness)
2. select 5 parameter Mooney-Rivlin (for which I have constants)
3. create quarter area model dimensions
4. map mesh with quad area elements
5. Apply symmetry Boundary Conditions to artery inner cut lines
6. Apply pressure load on internal area line
7. Activate large deformation (NLGEOM,ON)
8. Solve using static analysis

This approach works fine for linear-elastic materials, but I cannot understand why it yields no results in this situation????

ANY ADVICE??
Thanks in advance

 

[rstupplebeen]

I am most familiar with Abaqus routinely using hyperelastic materials such as Mooney-Rivlin but hopefully I can help with your question. Are there any error messages?

In Abaqus there is a function to evaluate a material model. It is basically an automated routine that creates 1 element models placed in: Uniaxial, Biaxial, Planar (Pure shear), Simple shear and Volumetric. It's important to load each mode up or even slightly beyond what you expect for the actual model. From here make sure that the stress/strain plots are stable and reasonable.

I hope this helps.

Rob Stupplebeen

http://www.optimaldevice.com

https://sites.google.com/site/robertkstupplebeen/

 

[ChellBells]

Thanks for the reply Rob,
Unfortunately the errors given within ANSYS APDL can be very unclear to a novice like myself,and lack description. Solving the problem gives no results (or signal of completion) at all. It does however indicate that there are 1-2 'warning' pertaining to the loads before it attempts to solve. The constants I am using were evaluated from a single biaxial stress/strain graph. Are you suggesting that the loads/ constraints I am applying to not 'match up' to the material behaviour I have set? Sorry for the confusion, I am very new to FEA.

 

[rstupplebeen]

I was thinking that if the strains in the model exceeded where your material model was stable that the solve could fail. But it sounds like no solution steps solve.

You could try modeling with a simple dummy material model such as a Young's modulus E=1MPa and Poisson's ratio of nu=0.45. If that solves you know that the material model is the culprit. In problematic simulations try taking it 1 step at a time.

You have the 2 symmetry planes constrained which should handle 4 DOFs. Do you constrain the remaining 2?

I hope this helps.

Rob Stupplebeen

http://www.optimaldevice.com

https://sites.google.com/site/robertkstupplebeen/

 

[IceBreakerSours]

Like Rob, I too am (almost entirely) familiar with Abaqus.

Abaqus generates a status file as soon as the solver begins solving the system of equations. ANSYS must generate a similar sort of output in your runtime folder. Check such a file and see if the model managed to converge a few increments before crashing or not (i.e., ANSYS kept on iterating in the very first increment).

ANSYS must generate more warning/error messages in one or more output files. Gaining a good understanding of those messages is extremely important - if you wish to do sound FEA. Perhaps you should post those messages in the forum (but please google or search the archives before you post).

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083