Reply To: Large deflection convergence problem

[hdonner]

 

Your idea of activating Transient Structural is good. But if you activate quasi-static solution in static structural, this is the same since quasi-static means transient structural with high numerical damping. Check the doc especially 5.6.3:

5.6. Transient Dynamic Analysis Options (ansys.com)

Ok, so as I expected regarding the material. Note, the isotropic elastic material model is only stable for small strains. In case of modelling biological tissues, hyperelastic material models are state of the art and required. I would recommend to start with Neo Hooke hyperelasticity. This is still a rough approximation because artery walls are highly ansiotropic and this is usually modelled with anisotropic hyperelasticity: 

8.5. Modeling Material Nonlinearities (ansys.com)

I would recommend doing a literature survey on models for artery walls and especially parameter sets. 

But an initially much better approximation compared with isotropic elasticity will be hyperelasticity. You can convert the parameters as follows

 

1. Take the shear modulus from your existing isotropic elastic model (you can find it in the Engineering data) and use it directly as initial shear modulus.
2. Take the bulk modulus and convert it to the incompressibility parameter D1 or d = 2 / K. So if K equals 2000 MPa, than D1 or d = 0.001 MPa^-1.

 

If you do so, the small strain behavior of both models will be equal. Note, if the material behaves nearly incompressible (nu > 0.49) you need to activate u-p formulation. For Solid185 this is possible via an APDL snippet.

keyopt,matid,6,1

My settings would be (apply all simultaneously):

 

1. Neo Hooke instead of isotropic elasticity
2. u-p formulation in case of incompressibility
3. Quasi-static solution (assign a density!)
4. Unsymmetric stiffness matrix
5. Maximum substeps 1e9