Interface files

The Z-mat interface file exists as a medium to configure the interface, translation, and provide extra convergence parameters for the local integration. This interface effectively duplicates the controls which exist in the Zebulon FEA input file.

All the different Z-mat platforms (target FEA systems) use the same basic controls described in this chapter. Some certain commands may however have functionality specific to one or some of the codes due to limitations or special features available in the user interfaces. These differences will be noted in the description section for each command.

Note that the interface file name itself is very dependent on the particular solver which is being interfaced to. For example, with materials are assigned character names, and that name will be the same ASCII filename to be opened by Z-mat. On other solvers such as only a material number is given as an identifier, and in that case a convention of naming the file as: 100+material number+“.txt” (for example 105.txt for material id 5). Please double-check in the different chapters specific to each solver for further information.

Syntax

The following commands are available in the Z-mat interface file. Reading of the commands will stop when a ***return command or the end of file is reached.

***automatic_time ***behavior ***debug ***external_storage ***material ***parameter ***save_energies ***skip_cycle ***state_var_engineering_shear ***state_var_no_change ***state_var_real_shear ***suppress_temperature ***symmetrize_tgmat ***verbose ***plane_stress_modifier ***zero_dt_for_first_dt

These commands and their options are the subject of the rest of this chapter. Some of the commands are simply switches and thus do not have any sub-commands. These simple commands will be discussed in the following.

***state_var_no_change

This command indicates that the user does not require changing the Z-mat internal format of shear variables to a real measure. Shear components output are multiplied by a factor \(\sqrt{2}\) from the actual tensor component (t12 in the output is \(\sqrt{2}t_{12}\)).

***state_var_engineering_shear

Transform shear variables to be output with an additional factor of \(\sqrt{2}\). (e.g. \(\gamma_{12} = 2\epsilon_{12}\)). This is now the default.

***state_var_real_shear

Divide the \(\sqrt{2}\) term out of the shear components so the output is the real component of the tensor.

***suppress_temperature

Eliminate the setup for temperature as a parameter. This optimizes slightly the computations so constant coefficients may be assumed.

***symmetrize_tgmat

Make an extra step to symmetrize the material tangent returned from the Z-set behavior.

***verbose

verbose message outputs.

***plane_stress_modifier

This command may be used to de-activate the automatic detection of the plane stress condition and allows the use of an explicitly defined plane_stress modifier of the behavior instead. Note that automatic plane stress treatment is not implemented for all behaviors, and that in the case of anisothermal loadings convergence may be very slow, In those two cases the plane_stress modifier method should be preferred.

***zero_dt_for_first_dt

use a zero \(\Delta t\) for the pre-step test (with zero strain increment). This pre-step is used by ABAQUS to get the initial tangent modulus. Time-dependent materials may be non-linear if the time step is \(>0\) even with zero strain increment, because of stress relaxation under fixed displacement.

The Z-mat material file

The Z-mat material file is the input which determines which constitutive model from the available models in Z-mat to use, and then specifies the particular coefficients accordingly. This file is the same as input for Zebulon, and for the Z-sim. The input format is the subject of chapters 4 and 5.

Note

By default, the input file name for the material file is the same as the Z-mat interface file, so the behavior definition can follow the Z-mat interface commands.

Example

The following small material file is a simple example of Z-mat use (taken from the interface tests which puts together some of these concepts. Many more examples will of course be given in the different code-specific chapters and around the discussion of each sub-command.

***suppress_doing_first
***state_var_no_change
***suppress_temperature
***material
  *integration theta_method_a 1.0 1.e-10 1500
  *initialize_variable
     epcum  0.43
     X11    7.529e-03
     X22   -1.065e-02
     X33    3.118e-03

***behavior gen_evp
**elasticity isotropic
  young 2.1e5
  poisson 0.3
 **potential gen_evp ep
  *flow plasticity
  *criterion mises
  *isotropic nonlinear
    R0 200.
    Q  2000.0
    b  0.26
  *kinematic nonlinear X
    C  25500.0
    D  81.
***return