Output/Calculating the plastic strain components for crystal plasticity models

[wnoh3]

Hello,

I have the objective of trying to calculate the plastic strain components of my crystal plasticity models, whether elemental or nodal based.

After reading through chapter 2, 3, and appendices, I am not quite sure if there is a pre-made output/postprocessing way to do this. I wanted to double check in case I have overlooked something which is quite possible?

Are there any recommended approaches?

Thank you for your time.

[reverendbedford]

We do not output the plastic strain tensor for these models.

We do output:

1. Equivalent plastic strain
2. The integrated slip along each slip system ($\gamma_i$)

A small strain type approximation to the plastic strain tensor is

$$ \varepsilon_{p,approx} = \sum_{i=1}^{n_{slip}} \gamma_i \mathrm{sym} d_i \otimes n_i $$

With $d_i$ the slip directions and $n_i$ the slip normals, rotated into the intermediate configuration (i.e. through the crystal orientations.

If all you're doing is trying to infer strain from the grain boundary deformation this might be an okay thing to look at. (I'm not psychic; I spoke with Huy today 😄).

You can calculate the actual plastic strain tensor in large deformations with the information from the output as well if you want to do that. But it will involve numerical integration. Let me know if you want to do that.

[ttruster]

The longer listing of options for history output are listed in the file https://github.com/rhdodds/warp3d/blob/master/src/mm10_f.f. You can search for "output" and find some of those lists near the bottom of the file.
The elastic lattice strain tensor is in there, so you could subtract that from the total strain as a crude approximation. Also, there are plastic strain rate tensors.
Section "3.12.9 Model Output: State Variables – Flat Files" mentions the place in the input file to select the output option (0 to 7)