Convergence issue in an indentation model with Drucker-Prager plasticity

[quentinflm]

Hi all,

I recently started to use Abaqus in order to simulate the spherical indentation of a porous layer.
Here is a quick description of my model (Download here the related files).
2D axisymmetric model with 2 parts:
- the indenter: discrete rigid body, real shape of the indenter defined by a spline curve (so it's not exactly an arc of circle)
- the sample with 2 sections:
=> the porous coating: elastic material with Drucker Prager Plasticity
=> the bulk: elastic material
Elements: CAX8 and CAX8-R.
Interaction: hard contact, no friction
Step 1: displacement control (loading and unloading)

I have the following convergence issues:
- If the coating is considered as elastic (no plasticity), I manage to get convergence. However I noticed 2 strange things that I dont't understand:
=> If I reduce the increment size from 0.1 to 0.01 I lose the convergence beyond a certain displacement
=> If I use a finer mesh under the contact, I lose the convergence beyond a certain displacement

- When I try to use the Drucker Prager plasticity, I cannot get convergence beyond a certain displacement

I’m a bit lost… I don’t know where the problem(s) come from. Is it contact related ? mesh related ? geometry related ?

I would be very grateful if you could suggest a methodology to solve this.

To finish one basic general question: how to know what caused the divergence in a simulation ? Sometimes I don’t have any warning before it stops and it is not clear either in the Message file.

Thank you very much for your help

 

[Mustaine3]

Have you tried the unsymmetric equation solver?


The reason for convergence issues can be found in the .msg file. See Getting Started 8.4 Example: nonlinear skew plate

 

[quentinflm]

Thanks for your reply. Yes I am using the unsymmetric equation solver. Thanks also for the reference, I will check it.

However in the message file, the last increment finishes with

THE CONTACT CONSTRAINTS HAVE CONVERGED.
[...]
THE FORCE EQUILIBRIUM EQUATIONS HAVE CONVERGED
[...]
THE MOMENT EQUILIBRIUM EQUATIONS HAVE CONVERGED"

I don't see any error here, that's why I was asking