Large Deformation Convergence Issue

[ABallisat]

Hello all,

I am trying to get a model of compression moulding up and running which will involve large plastic deformation. I am using the Tensor Mechanics module (eventually I will couple in thermal as well for temperature varying material properties) and set up a simple example. I have attached the input file (side not: GitHub won't allow .i files to be uploaded so I had to change extension to .txt).

The model will not converge, no matter the time step, after about 5.7 seconds. I cannot work out why, I have spent the last couple of days reading around the mailing list for ideas and trying many things but it just will not solve. Up until that point it solves in only a couple of non linear iterations per time step, then just explodes. I have tried letting the solver iteratively reduce the time step but even when it is down below e-10 it still breaks.

Am I missing something obvious here? Any help would be greatly appreciated!

Thanks,

Alex

LargeDeformation.txt

[jiangwen84]

Could you draw a picture and let us know what are you trying to model?

I quickly checked your BC names in Paraview, and there are some inconsistencies of the name definition. In addition, you do not need to set 'use_displaced_mesh' for mechanics related materials as they should be correctly set by the TensorMechanics Action.

[ABallisat]

See attached. The basic idea is that the charge is heated (red boundary condition) and compressed into a mould (modelled with Dirichlet displacement BCs) so expands outwards to the right. The other block is effectively the side of the mould so will prevent the charge (if it is large enough) spreading out the side. It is a simplified representation of a block of thermoplastic being compression moulded in a heated mould.

The side set issue is caused by using the CombinerGeneration - this does not seem to maintain the side sets so after the merge I have to re-define the side sets. I suspect this is a bug, the redefinition is to get around this.

I've made some progress with understanding the issue. If I just use Tensor Mechanics, so no temperature coupling, then the model will converge. When I couple in a temperature variation, and thus the extra eigenstrain that introduces, the model does not converge. I suspect it is due to the thermal expansion causing the top right corner of the charge, for lack of a better description, to start sagging over the edge. I have attached an image of it, below. I have come across this problem before but never managed to solve it.

I am going to try different solver types tomorrow to see if anything works but any suggestions are greatly appreciated!

[jiangwen84]

I ran your previous input file and did not get it converged. The previous input doesn't have temperature variable. Could you let me know how did you make it work?

[ABallisat]

Apologies, attached is my most current input file which has temperature coupling. I effectively disabled the temperature by setting the temperature function BC to be a constant of 0. This model will converge if I do that, otherwise even a temperature increase of 2 degrees per second causes it to not converge.

Thanks for all your help!

ThermalPlasticDeformation.txt

[ABallisat]

If it ever helps anyone, I eventually used use_displaced_mesh=true in Kernels, UserObjects, BCs and Materials as appropriate and increased the exponent in the plastic hardening to 0.6 (or greater) and it will converge.