Z-mat Forge interface#

Description#

The Zforge interface enables the use of Z-mat material laws within Forge simulations. This section introduces the Zforge interface. Note that this interface bears a strong resemblence to the exisiting interface of Z-mat for ABAQUS, hence interested users can refer to the relevant documentation for an exhasutive overview.

Syntax#

% Zforge[ opts ]  *problem \(\hookleftarrow\) to launch the simulation called problem.ref
% Zforge-help problem \(\hookleftarrow\) to print the help for the command Zforge

Getting started#

Note

The interface is built for Forge versions \(>=\) 4.0

Ensure both the Z-set and Forge simulation software suites are installed. Setup the environment variables Z7PATH and FORGE_ROOT pointing to the respective installation directories. As a preliminary step to launch a Forge simulation using a Z-mat law, a user solver including the Z-mat/Forge library file must be registered as a new solver. The user subroutine file in the user solver must refer to: $Z7PATH/Zforge/tsv_mf2userroutines.so, or $Z7PATH/Zforge/tsv_mf3userroutines.so (*.dll for windows) for Forge 2D/3D cases respectively. Now a simulation using Z-mat/Forge interface can be launched in two ways:

  • using Zforge script (as shown above).

  • from the NxtGUI platform (Forge graphical interface)

Compatible Z-mat behaviors#

Forge’s FE solver uses the stabilized bubble finite element. This element is used to solve the Stock’s problem, where the unknowns are the velocity \(v\) and the pressure \(p\). When it comes to material integration using this type of element, the deviatoric stress and the hydrostatic stress are integrated independently. For this reason, only material behaviors for which the plastic deformation only depends the deviatoric stress tensor can be used in the Z-mat/Forge interface. For exemple, in the gen_evp assembly, the plasticity criterions that depend on the hydrostatic pressure (trace of the stress tensor) are not supported (e.g. unsym, cast_iron, tensile_mises, gurson, linear_drucker_prager, etc.). In addition, the integration of the hydrostatic stress assumes an isotropic elasticity, therefore only isotropic elasticity is supported in the Z-mat/Forge interface.

Input file changes#

Similar to other Z-mat interfaces, there are some lines in the user’s input deck (the .ref file or .tmf file) that must be modified to indicate that a user–material is being used, and to specify the number of state variables for storage. The syntax is dimension specific (2D/3D). For Forge 2D, the only change to be made is under the block .RHEOLOGIE, the Z-mat file must be indicated as: Thermoecroui:ZMAT:FILE=Z-mat file. Additional storage necessary for the associated state variables is allocated automatically. For Forge 3D, the Z-mat material file must be indicated under the block .RHEOLOGIE, as follows: LOIV RHEO Z-mat file. Also, all state variables necessary for the material integration must be added as shown in the following example.

For instance, for the following Z-mat material file:

***behavior gen_evp auto_step
 **elasticity isotropic
   young 1.105E+05
   poisson 0.3
 **potential gen_evp ep
  *flow norton
   K 75.0
   n 12.93
  *isotropic nonlinear
   R0 848.895020
   Q -3.20E+02
   b 120.0
  *kinematic nonlinear
   D 120.
   C 47280.
***return

the necessary changes to the .RHEOLOGIE block of the .tmf file are presented below:

LOIV RHEO Z-mat_file_name
ETA STRESSTENSOR(6)=0.D0,0.D0,0.D0,0.D0,0.D0,0.D0
ETA EQ_STRAIN=0.D0
ETA eel(6)=0.D0,0.D0,0.D0,0.D0,0.D0,0.D0
ETA epcum=0.D0
ETA al1(6)=0.D0,0.D0,0.D0,0.D0,0.D0,0.D0
ETA epi(6)=0.D0,0.D0,0.D0,0.D0,0.D0,0.D0
ETA temp0=0.D0
ETA eto(6)=0.D0,0.D0,0.D0,0.D0,0.D0,0.D0

This block of commands can be generated using Zpreload utility, as follows: % Zpreload Z-mat_file_name\(\hookleftarrow\)

Note, that for both Forge 2D and Forge 3D, the length of the Z-mat file name must not exceed 12 characters.

Zmaster interface#

The results of the Z-mat/Forge simulation are stored in files with extension .fg3 (for 3D simulations) and .fg2 (for 2D simulations). Let us consider an example provided with Z-set software distribution, in the following directory :

$Z7PATH/TESTS/Zforge_test/INP/Zforge_3D/

The resulting files produced in this simulation will be stored in :

$Z7PATH/TESTS/Zforge_test/INP/Analysis/ResultDataBase/Zforge_3D/results/
For each increment \(\%t\), there is \(\%n\) .fg3 file, where \(\%n\) is the number of processors used for computation. These .fg3 files can be visualized individually using GUI Zmaster, as follows:
% Zmaster problem_%nd%t.fg3\(\hookleftarrow\) It is also possible, using the Z-set result management functions for Forge (as described in the Z-set User Manual), to merge separate Forge results files (.fg3 or .fg2) in a unique Z-set database (i.e. for further visualization or post-processing purposes) :

  • A database in \(Z7\) format will be generated for simulations without remeshing ;

  • A database in \(Z8\) format will be generated for simulations with remeshing.