# OVERVIEW¶

## Contributors¶

• GELEBART Lionel, Engineer - Researcher, CEA Saclay/DEN/DMN/SRMA : lionel.gelebart at cea.fr

Development and organization

• DEROUILLAT Julien, Engineer - Researcher, Maison de la Simulation : julien.derouillat at cea.fr

HPC support

• DOUCET Nicolas Internship (12 months) at CEA Saclay/DEN/DMN/SRMA :

The first version of the code!

• OUAKI Franck, Post-doctoral (19 months) at CEA Saclay/DEN/DMN/SRMA :

Extension to Finite Strains

• MARANO Aldo, PhD (36 months) at CEA Saclay/DEN/DMN/SRMA and Mines-ParisTech :

Introduction of composite voxels

Definition of a general framework for couplings (application to strain gradient plasticity)

• DUVERGE Jérémy, Internship (6months) at CEA Saclay/DEN/DMN/SRMA :

Additional work on composite voxels (focus on I/O)

### Collaborations¶

• CHEN Yang, as a post-doc at IMT Lille-Douai (France), then at Oxford University (UK)

Implementation of the phase field model for damage (from Miehe’s work)

• BOIOLI Francesca, as a post-doc at LEM-ONERA (France)

Coupling between AMITEX and the DD code microMegas http://zig.onera.fr/mm_home_page/

• BOISSE Julien, reseracher at Université de Lorraine (France)

Preliminar implementation of various metallurgical phase field models (proofs of concept)

## General description¶

AMITEX_FFTP is a distributed solver based on FFTs for non-linear mechanical simulations on heterogeneous unit-cells (described by regular 3D images). AMITEX_FFTP can be run either on individual PC, local clusters or on large High Performance Computing platforms to perform large scale simulations such as the example given in the figure below.

Since recent developments, the usage of AMITEX_FFTP can now be divided into two parts :

• The Standard usage is based on a user interface described in USER. It doesn’t require any code development.
• The Extended usage is mainly devoted to the implementation of various “couplings” (different physics, different codes). It requires code development. If interested, feel free to contact us.

The purpose of the further developments are now to :

• stabilize and add new functionalities for the AMITEX_FFTP-Standard usage
• facilitate and promote the developments of new “couplings” through the AMITEX_FFTP-Extended usage

## Code informations¶

AMITEX_FFTP is written in modern FORTRAN and relies on the 2DECOMP&FFT library (http://www.2decomp.org) that provides:

• a user-friendly programming interface to work with a 2D pencil decomposition for data distribution on distributed-memory platforms,
• an interface with most popular external FFT libraries,
• parallel I/O.

For the user interface, the reading of XML files in AMITEX_FFTP relies on FoX (http://www1.gly.bris.ac.uk/~walker/FoX/) a Fortran library for XML.

FoX and 2DECOMP&FFT have been added to the source files of AMITEX_FFTP, external libraries are required:

• MPI library : openMPI and intelMPI implementations are regularly used
• FFT library : fftw3 is the only library used during developments

## Features¶

The user interface of AMITEX_FFTP allows to:

• “read” the heterogeneous microstructure from VTK files (legacy file format),
• “assign” and “distribute” material behaviors and their corresponding properties over the 2D pencil decomposition proposed by 2decomp.

The mechanical FFT-based solver within AMITEX_FFTP allows to:

• Solve non-linear mechanical problems on unit-cells with prescribed average stress or strain components,
• Solve the problems with the classical fixed-point algorithm (see Moulinec 1994) combined with an acceleration convergence algorithm,
• Choose between a small perturbation or a finite strain framework (mechanics),
• Choose between classical or finite difference based discrete Green operators (better than the classical),
• Use composite voxels for voxels crossed by an interface

The mechanical behavior law is evaluated within a standard UMAT procedure which ensures compatibility with both:

Of course, the UMAT procedure coming from ABAQUS, a good compatibility is also expected with this FE code.

Finally, if the code mainly focuses on mechanics, stationary diffusion problems can be solved on unit-cells with prescribed average flux or gradient.

## Distribution¶

For a Standard usage, AMITEX_FFTP is freely available for research and education purposes here.