# Example: polyx_mfront¶

The example described below demonstrates on a large polycrystalline simulation:

• The ability of AMITEX_FFTP to take advantage of massive parallelism (simulation performed on 1024 cores)
• The ability of AMITEX_FFTP to take into account a behavior law elaborated with the code generator MFront developed at CEA (http://tfel.sourceforge.net/documentations.html)

The algorithm converged with a total number of 102 iterations and the computation time, on 1024 cores (64 nodes, bi-processors Sandy Bridge E5-2670), was approximatively 4 hours.

The microstructure (A), the average behavior (B) and the local stress (C) and strain (D) fields are presented below.

 Microstructure (A) Average behavior (B)

 Local stress (C) Local Strain (D)

## Geometry¶

The unit-cell consists of 42875 grains (Voronoï tessellation).

The unit-cell is discretized with a 1024x1024x1024 grid (almost 30x30x30 voxels per grain).

## Behavior law¶

The behavior law accounts for crystalline plasticity for Cubic Face Centered crystals in a small perturbation framework (description in the Code_Aster documentation R5.03.11). The implementation is provided with the code generator MFront (http://tfel.sourceforge.net/documentations.html) using the so-called “UMAT” interface, also compatible with the finite element code CAST3M (http://www-cast3m.cea.fr/). The material parameters are those furnished with the MFront code with 42875 crystalline orientations (one per grain) randomly distributed with an isotropic crystallographic texture.

## Specificities¶

The number of internal variables (required at each voxel) is 54.

The numerical integration of such behaviors is quite “heavy”.

The applied loading is a tensile test loading (axial strain component and zero-stress on the five other components are imposed), at a strain rate of $$10^{-4}s^{-1}$$ until 1%.
The criterion (stress divergence and applied load) is $$10^{-4}$$.