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Crystal Plasticity Finite Element Method
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CPFEM is based on a crystal plasticity constitutive model incorporated in the UMAT user subroutine of the commercial finite element software ABAQUS 6.9. The single crystal or polycrystal of face-centered cubic (FCC), body-centered cubic (BCC) and hexagonal closed (HCP) structures will respond to an applied stress by dislocation slip which is simulated using CPFEM. Orientations of grains will rotate during deformation. At the same time, the threshold stress of each slip systems will increase because of the self-hardening and latent hardening of the deformation modes. As such, the mechanical response (stress-strain curve) and the orientation of the crystals (texture) will be captured by the CPFEM. By comparing predicted results with experiments, one can get useful information about deformation mode activation, stress-strain data and crystal re-orientations, aspects that lead to a fundamentally understanding of the nature of metal deformation at the grain scale.
- Introduction to Crystal Plasticity Finite Element Method (PDF file).
Abaqus Documentation
- (CAVS users only): sources of the examples given in the introduction.
Introduction to CPFEM
The present document is an introduction manual on how to use the crystal plasticity finite element method (CPFEM) for materials deformation simulation. CPFEM is based on a crystal plasticity constitutive model incorporated in the UMAT user subroutine of the commercial finite element software ABAQUS 6.9. The single crystal or polycrystal of face-centered cubic (FCC), body-centered cubic (BCC) and hexagonal closed (HCP) structures will respond to an applied stress by dislocation slip which is simulated using CPFEM. Orientations of grains will rotate during deformation. At the same time, the threshold stress of each slip systems will increase because of the self-hardening and latent hardening of the deformation modes. As such, the mechanical response (stress-strain curve) and the orientation of the crystals (texture) will be captured by the CPFEM. By comparing predicted results with experiments, one can get useful information about deformation mode activation, stress-strain data and crystal re-orientations, aspects that lead to a fundamentally understanding of the nature of metal deformation at the grain scale.
The general workflow for running Crystal Plasticity simulations using ABAQUS is illustrated in the figure below:
Crystal Plasticity FEM Models
A crystal plasticity model in the ABAQUS subroutine UMAT.
Input files using CPFEM for an aluminum simulation
The ABAQUS input decks and a step-by-step Tutorial on how to use them to run CPFEM simulations can be downloaded from the cpfem decks repository (CAVS users only) , or can be viewed online by clicking on the name of each of the files below.
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- umat_xtal.f- constitutive model - polycrystal average model
- texture.txti - initial orientation distribution
- fcc.sx- single crystal parameters
- test.xtali- control for the time step and deformation
- params_xtal.inc - number of slip systems
- numbers.inc - numerical constants
Input files using CPFEM for a magnesium simulation
The ABAQUS input decks and a step-by-step Tutorial on how to use them to run CPFEM simulations can be downloaded (CAVS users only) here, or can be viewed online by clicking on the name of each of the files below.
- umat_xtal.f- constitutive model - polycrystal average model
- texture.txti - initial orientation distribution
- hcp.sx- single crystal parameters
- test.xtali- control for the time step and deformation
- params_xtal.inc - number of slip systems
- numbers.inc - numerical constants
- vert_hcp_121.01- vertices parameters in Mg
- vert_hcp_121.03 - vertices parameters in Mg
- vert_hcp_121.05 - vertices parameters in Mg
Running CPFEM with a One Element Geometry
Step 1
Have access to ABAQUS finite element software. The crystal plasticity files were composed for ABAQUS and will not work with alternative FEA codes.
Step 2
Create a new directory in a location in which you have permission to do so. Then download copies of all the input files and store them within the newly created directory.
Abaqus Cae
Step 3
Open the file called: 'umat_xtal.f', and locate the following lines:The test located between the single quotes needs to be replaced with the path to the new directory.
Step 4
Open ABAQUS CAE and load the one element model called 'oneelement.cae'. Then set/verify the boundary conditions and generate a new input file. Alternatively there is a default input file: 'oneelement.inp' that can be used.
Output files
Output files of CPFEM include the texture.txto, test.xtal.trss, test.xtal.strs, test.xtal.strn, test.xtal.efss and test.agg.efss. some output files will change according to the model development. The texture.txto contains the deformed texture at various strain levels. One can use this file to plot any pole figures and calculate orientation distribution functions (ODFs) using the texture software MTEX (a MATLAB tool box), or this custom MATLAB function. The output file test.agg.effss includes the effective stress-strain data. At present, one can use the ABAQUS CAE to output any stress- strain data as shown in the Manual.
Users Manual
CPFEM Simulation Aluminum Results
Nastran
Example of polycrystal tension of an aluminum simulation
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