Learning Forum

[ansysuser]

Hello,

 

I understand the latest versions of ANSYS no longer allow the user to create a custom material model by modifying the USERMAT.f template. What options are there for doing this as alternatives?  I know that Engineering Data has many material models, but the model I need to implement is not listed there.  Can it be done through USERELEM.f or is there a preferred method to this?

[Sandeep Medikonda]

As far as I am aware (and according to the 2019R2 documentation) you should still be able to do this:

Help Link 1

Help Link 2

[ansysuser]

 Thanks SandeepMedikonda!  That is great news. 

 

I am a bit confused on where to put the code for my own simulation. I am modeling an active stress such as found in a muscle contraction. In this formulation the total stress is broken into components like this:  TotalStress = PassiveStress + ActiveStress. The passive stress is due to the material model alone and the active stress is a function of time. 

Would I program this into the USERMAT or would it be better to put it into USERELEM?  Or do I need to do both, with the USERMAT only accounting for the passive stress component?  I want to know the recommended way to accomplish this, since it seems simpler to implement USERMAT and add the active component as long as I have access to the time variable i.e., the current simulation time.

 

Thanks again

[Sandeep Medikonda]

Please refer to Section 2.4: Subroutines for Customizing Material Behavior of the Programmers Reference

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v194/ans_prog/Z7K4r1e5lcd.html%23UPFusermatjwf032800403

There is also an example in Appendix C of the same guide:

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v194/ans_prog/Hlp_P_UPFC.html

I am not sure how you are dividing the total stress into active and passive components, I haven't come across anyone trying to do this...Either way any operations on the material response should come from the constitutive response....

[ansysuser]

 Thank you for the example, SandeepMedikonda.

The division of stress into active and passive components is a common practice in the biophysics modeling field.  For just a few examples are posted below: Many researchers have used Abaqus for this, but I am interested in doing the same thing with ANSYS.  So it sounds like you are saying it is better to put this into USERMAT than to try to add to a custom element via USERELEM?  PLEASE confirm.  Thanks

Johansson, T., Meier, P. and Blickhan, R., 2000. A finite-element model for the mechanical analysis of skeletal muscles. Journal of theoretical biology, 206(1), pp.131-149.

Baillargeon, B., Rebelo, N., Fox, D.D., Taylor, R.L. and Kuhl, E., 2014. The living heart project: a robust and integrative simulator for human heart function. European Journal of Mechanics-A/Solids, 48, pp.38-47.

Muehlhausen, M., Janoske, U., & Oertel, H. (2015). Implicit Partitioned Cardiovascular Fluid–Structure Interaction of the Heart Cycle Using Non-newtonian Fluid Properties and Orthotropic Material Behavior. Cardiovascular Engineering And Technology, 6(1), 8-18.

Shavik, S.M., Jiang, Z., Baek, S. and Lee, L.C., 2018. High spatial resolution multi-organ finite element modeling of ventricular-arterial coupling. Frontiers in physiology, 9, p.119.

[Sandeep Medikonda]

I briefly skimmed through the first paper:

https://www.sciencedirect.com/science/article/pii/S002251930092109X

It looks like they're implementing this without using the usermat. That paper describes the procedure, it's not a standard procedure so we don't support it for commercial customers too. You would have to follow the paper and implement it and ask us specific questions.