G modeling
==============


Characteristics of modeling
-----------------------------------

The aim of this modeling is to globally validate the entire propagation procedure *with cohesive elements*. The method GEOMETRIQUE is therefore used by PROPA_FISS, alternately with the operations DETEC_COHESIF and PROPA_COHESIF, to respectively update the tangent level-set (and therefore the propagation front) and the normal level-set (and therefore the "possible" cracking surface). The bifurcation angle is determined by CALC_G (in FEM, mesh crack), and the cohesive elements are introduced into the model by the DEFI_CONTACT command.


Characteristics of the mesh
----------------------------

An unstructured mesh is used, the initial crack being meshed. It has 16,632 elements of type TETRA4.


Tested sizes and results
------------------------------

Two propagation steps are carried out, then the position of the propagation front is extracted at the end of this operation. The validation consists of a non-regression test on the position of this front. In order to reduce the number of tests, the maximum and minimum coordinates :math:`Y` and :math:`Z` are tested along the front.


.. csv-table::

    ":math:`\mathit{Propag.}i` "," :math:`\mathit{Max}(Y)` "," :math:`\mathit{Min}(Y)` "," :math:`\mathit{Max}(Z)` "," :math:`\mathit{Min}(Z)`"
    "2", "3.14", "3.05", "3.05", "9.04", "9.03"


In figure, we represent a view of the deformation and of the stress field at the end of the second propagation step. The crack tends to straighten to propagate in a plane.


.. image:: images/100000000000029600000246E03283E3CE1A3A74.png
    :width: 4.4547in
    :height: 3.9165in


.. _RefImage_100000000000029600000246E03283E3CE1A3A74.png:

**Figure** 8.3-a **: deformed and stress field**