Unwanted jumps of the strain-rate

[Martin Lesueur]

Hi,

I am running an extended version of the 1D spherical hollow sphere test of MOOSE where I add a constant loading rate and a J2 plasticity.

But my strain-rate has jumps that are not supposed to appear.

The jumps start at the end of elasticity (but before plasticity) and exist only at small timestep size.

I tried to debug it without success. I thought it was a problem of tolerances but I reduced all of those and nothing changed.

I also have noticed that it does not happen if I remove the plasticity material.

Anyone can help me with that ?

Cheers,

Martin

[Cody Permann]

Pinging the list for help here? Can anyone familiar with the tensor mechanics and/or J2 plasticity modeling assist?

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[Jason D. Hales]

Specifically, the input file uses ComputeMultiPlasticityStress.

On Wed, Jun 14, 2017 at 8:46 AM, Cody Permann <codyp...@gmail.com> wrote:

Pinging the list for help here? Can anyone familiar with the tensor mechanics and/or J2 plasticity modeling assist?

On Mon, Jun 12, 2017 at 10:11 PM Martin Lesueur <martin....@ecl2015.ec-lyon.fr> wrote:

Hi,

I am running an extended version of the 1D spherical hollow sphere test of MOOSE where I add a constant loading rate and a J2 plasticity.

But my strain-rate has jumps that are not supposed to appear.

The jumps start at the end of elasticity (but before plasticity) and exist only at small timestep size.

I tried to debug it without success. I thought it was a problem of tolerances but I reduced all of those and nothing changed.

I also have noticed that it does not happen if I remove the plasticity material.

Anyone can help me with that ?

Cheers,

Martin

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Jason D. Hales, PhD

Department Manager

Fuels Modeling & Simulation

Idaho National Laboratory

(208) 526-2293

[Andrew....@csiro.au]

​I think i'd output all the plastic related Material properties from ComputeMultiPlasticityStress: plastic_strain; plastic_internal_parameter; plastic_yield_function; plastic_NR_iterations. Then you can more easily inspect where and why you're getting plastic failure (assuming you are). It may be, for instance, that you get failure at just a single quadpoint because of the non-infinite resolution of the finite-element mesh, and that gives you the "jumps".

Does this make sense? If not i can be more specific.

a

From: moose...@googlegroups.com <moose...@googlegroups.com> on behalf of Jason D. Hales <jason...@inl.gov>
Sent: Thursday, 15 June 2017 1:07 AM
To: moose...@googlegroups.com
Subject: Re: Unwanted jumps of the strain-rate
 

Specifically, the input file uses ComputeMultiPlasticityStress.

On Wed, Jun 14, 2017 at 8:46 AM, Cody Permann <codyp...@gmail.com> wrote:

Pinging the list for help here? Can anyone familiar with the tensor mechanics and/or J2 plasticity modeling assist?

On Mon, Jun 12, 2017 at 10:11 PM Martin Lesueur <martin....@ecl2015.ec-lyon.fr> wrote:

Hi,
I am running an extended version of the 1D spherical hollow sphere test of MOOSE where I add a constant loading rate and a J2 plasticity.
But my strain-rate has jumps that are not supposed to appear.

The jumps start at the end of elasticity (but before plasticity) and exist only at small timestep size.
I tried to debug it without success. I thought it was a problem of tolerances but I reduced all of those and nothing changed.
I also have noticed that it does not happen if I remove the plasticity material.
Anyone can help me with that ?
Cheers,

Martin
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Jason D. Hales, PhD

Department Manager
Fuels Modeling & Simulation
Idaho National Laboratory
(208) 526-2293

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[Martin Lesueur]

Thanks for the advice Andy, I did output those variables, but nothing seemed abnormal.

The problem might come from the fact that I do not impose any BC on the hole.

In comparison, MOOSE problem of the hollow sphere has no displacement on the inside.

Do you think this might cause these fluctuations? I remember that in NS, MOOSE had a necessary BC for a sideset withtout BC, NoBCBC.

Cheers,

Martin

[Andrew....@csiro.au]

Well that is rather strange. I think if there is zero plasticity at every quadpoint then ComputeMultiPlasticityStress does exactly what ComputeFiniteStrainElasticStress does. Did you try to compare with that? Did you check every quadpoint?

a

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[Martin Lesueur]

To answer on your previous post, the jumps come from the node of the inside hole.

After refinement of this boundary, I get unchanged jumps of specific pattern, see file attached in the first post.

This is why I don't think there is a problem with "non-infinite resolution of the finite-element mesh" because I obtain mesh convergence.

Also I don't get these jumps using ComputeFiniteStrainElasticStress.

[Andrew....@csiro.au]

Blast, this is looking like a bug in ComputeMultiPlasticityStress. Probably something quite simple, but that is a beast of a piece of code so it'll take a while to track down. Are you able to send me your input file + mesh?

My only other suggestion is to try plastic_models='' in your input file, which you've probably already tried. That way you're using the entire machinery of ComputeMultiPlasticityStress, but you're guaranteed to have no plastic yield at any quadpoint. If you still get a "jump" then it's a bug, if you don't get a "jump" then probably there is some plasticity somewhere but you failed to see it.

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[Martin Lesueur]

Hi Andy,

The jumps do not appear using as you say plastic_models=''. To rectify my first post, I am pretty convinced that the error comes from a plasticity computation. Some help to understand the problem would really be appreciated Andy. I am currently also comparing with Redback which seems to be giving different results.

The file exposing the jumps is linked to my first post and it is using a generated mesh.

Cheers,

Martin

[Andrew....@csiro.au]

​
OK, thanks for doing lots of diagnostic work, Martin. The evidence suggests to me that the machinery of ComputeMultiPlasticityStress is fine, but there is some craziness going on with the individual plasticity model you are using, which makes my work of identifying the error much easier. I'm on holiday at the moment, but will try to get to this ASAP as lots of people are using plasticity and we don't want it to be buggy! Give me about a week,

a

Martin

a

a

Martin

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[Andrew....@csiro.au]

Hey Martin, do you think you could attach (a link to) your input file and the quad mesh (not tri) that you used, at:

https://github.com/idaholab/moose/issues/9391

Please also include a description (can be inside your input file) of which times you see the unwanted jumps of strain rate, as i might accidentally try to debug the wrong thing!

a

________________________________________
From: Wilkins, Andy (Energy, Pullenvale)
Sent: Tuesday, 27 June 2017 5:52 PM