# How to model a viscoelastic material on ANSYS?

I am a mechanical engineer in Turkey in senior year. As a graduation project I have to model soft tissue cutting operation by using ANSYS. The main aim in the project is;

1.Choosing
the correct material properties (SOLID,SHELL etc.) and correct
method( Prony Series or Generalized Maxwell for
viscoelastic)

2.Creating a cylindirical model as an example
and than creating the orginial model as a representation of the soft
tissue(in this case the tissue must be some living organ ex:liver )

3.By
using the contact modeling (I learned that it requires to have some
detailed experience in writing subroutine) dividing the material into
two parts or just creating a deformation by the effect of cutting

The problem is my experience with
ANSYS is very very limited and with the aproaching deadline it is
becoming very overwhelming. Although I searched many resources from
many different sources, I couldnt find enough information to help me in
this project. I was wondering if you could help me in this project.
I am planing to chose 10 node SOLID 187 as a material type and create
an viscoelastic model. In the first step (on the cylindrical model
I just have to apply force and collect some data according to
deformation.).In the second step(after the completition of the model) I
have to write the contact subroutine for the cutting process.

I'll be very appreciated if you could guide me how to use the ANSYS properly in this project. Thanks for your all effort..

Regards

### Hi, Emre! 1. SOLID, SHELL

Hi, Emre!

1. SOLID, SHELL aren't material properties, these are element  type in ANSYS. Also Prony Series and Gen Maxvell are material models of viscous material. They can be used with several element types, this should be learned from docs.

2. It is simple to create cylindrical model in ANSYS, and also more complicated model.Though, sometimes, it is more convinient to create complicated geometry in any CAD, and thn import this in ANSYS.

3.  This point should be highlighted.

Best regards,

Ivan.

### Unconverged Maxwell material problem

Hello Ivan,

I am also working on Maxwell material using Ansys. I am facing different type of problem. In a simple type of problem I input only the value of C46 - C51 and C61 for maxwell material property. Rest constants remain zero. I used Visco88 element. The type of analysis is “Static”. But, for more number of substeps (like 10) I am getting incomplete results with error “For viscoelastic computation sum of TREF and TOFFST can not be equal to zero. Check your input”. If I remain the “Automatic time stepping” as Prog chosen it is converging. Kindly suggest me. How can I run the program with more than one substeps keeping "Automatic time stepping" off?

I look forward to some suggestions in this regard.

Best regards,

SK

### Try *Visco instead of *Static

ABAQUS has a different solution procedure for problems with a viscous response component.  To invoke that process, first try to use *VISCO instead of *STATIC.  Hopefully that will work.  If not, we'll probably need more information.

Matt Lewis
Los Alamos, New Mexico

### Needs Help

I am also working on the same kind of project. Can you help me out with that?