Reply To: Large deflection convergence problem

[hdonner]

Have those modifications enabled the simulation of a higher load level?

From a mathematical point, unstable means that the stiffness matrix becomes singular and, in a purely static analysis, your displacement increments tend to infinity even for infinitesimal load changes. But usually, intertia effects, activated by quasistatic solution, will help overcoming this point since it regularizes the problem. Of course, if you have local instabilities this might not help. I also sounds like an instability to me. The question is now: is it realistic or artificial due to modelling defeciencies.

It is hard to judge this without reviewing the model. 

Can you answer the following questions:

• Can you tell us which material this is in reality? 21 kPa Young’s modulus is extremely soft (sounds like a biological tissue? ).
• Which strains appear in your model near the critical point? According to the change in radius, it sounds like ~100 % engineering strain?
• Which material model do you use (isotropic elasticity?) and is it maybe to simplified compared to the real material (hyperelasticity and maybe reinforced like artery wall)?
• Does this test has also been carried out in reality so that you know that it works at this pressure level?

Kind regards

Hendrik