deformation induced grain nucleation for dynamic recrystallization

[jbair34]

Hi All,
I am having trouble figuring out how to make new grains nucleate in a dynamic recrystallization model with deformation induced nucleation. I am trying to follow the https://mooseframework.inl.gov/modules/phase_field/Nucleation/DiscreteNucleation.html instructions below:

"Direct order parameter modification
...
Nucleation of new grains in a polycrystalline model with GrainTracker requires the use of reserved (or staging) order parameters (order parameters which the grain tracker detects new grains in, but never uses as a target for remapping) in which new grain nuclei can be inserted and successively get picked up and remapped onto the evolving order parameters.

Apply both a DiscreteNucleationForce and a Reaction kernel to a reserved order parameter and set the hold_time in the inserter to 0. This will cause the modification of the reserved OP during only a single timestep, which will be enough for the GrainTracker to pick up and remap the new nucleus."

From that I have made a discrete nucleation inserter which has a rate dependent on the stress as a function of dislocation density and it does make the nuclei as the domain deforms. However, the nuclei just disappear without forming new grains. Is there something missing in this description where I can set a new random euler angle in the nucleus or make sure the relevant non conserved OP goes to 0 or something so a new grain will form?

I have combined moose/modules/combined/examples/phase_field-mechanics/hex_grain_growth_2D_eldrforce.i with the nucleation inputs in moose/modules/phase_field/examples/nucleation/refine.i which I modified as a test to have a probability linked to the vonmises stress. The probability seems to work fine putting nuclei in reasonable locations they just don't seem to stick...
Thanks,
Jake

[laagesen]

Hi Jake- when you say the particles are appearing and disappearing, are you saying that based on what's happening in the reserved order parameter? Or are you looking an AuxVariable generated by DiscreteNucleationAux? I'm trying to figure out if the problem is with the reserved OP not getting modified, or with the GrainTracker not picking it up and remapping it.

[ykvishal]

I don't know any solution to your problem, but I am curious about bnds and gr plots. Are you using some modified version of BndsCalcAux as the max value is more than 1. Similar trend is present for gr plot. For normal grain growth problem, both plots will have 1 as a max value. That is why I am curious.

[jbair34]

Hi Sudipta,
I am sorry I was misreading one of the console outputs that indicates the number of grains on each OP. They are showing up as new grains I am just dumb and was looking at the wrong spot on my console output. I am still concerned about the euler angles all going to 0 instead of random values though in new grains. Once we have enough grains I think that will just make them all merge right? So we do have remapping grains in the hexagonal starting point with the total number of grains increasing and I think with some fine tuning we will be able to get that one going but the EBSD one still will not increase the total number of grains without errors. Thanks again for your help and sorry I misread my own output yesterday!

Hi Vishal,
We are using the normal bnds and gr parameters. The overly large values seems to be from my settings in nucleus value for the DiscreteNucleationForce kernel. I was trying to make sure they remapped to new grains and overdid it a little bit so I will be playing with that value a bit to optimize. But it seems like the nucleus_value needs to be at least about 13 or so for our case for any remapping to occur. In the images I posted I had it set to 17 which was giving bnds max at around 1.9 and gr max around 1.1. It seems to be a finicky parameter, I'm not getting consistent max OP values in my nuclei between runs.

[FHilty]

I decided to move my question to its own discussion, it seems divergent to Jakes question.
#20198

[SudiptaBiswas]

I am glad the issue is somewhat sorted. Regarding the EulerAngles, you will have to have an additional object that assigns random EulerAngles to the new grains, or for the EBSD case, it can be read from the file (might necessitate some addition to GrainTracher, I don't think it's done by default). For my simulations, I did not assign Euler angles to grains (it was more like an isotropic model), but I was still able to capture recrystallization.

[YXY101676]

Hi, I was wondering what your file does for GR7 as a variable in the Reaction kernel？

[YXY101676]

Hi, I want to know how you implemented nucleation in polycrystalline structure. I tried to combine the two files you mentioned, but there was an error that the variable could not be found.Can you teach me how to solve this problem?Thanks

[GiudGiud]

hello

please create your own post and include the input files and the error
you can reference this post for context of course

Guillaume