C modeling: validating DETECT_COHESIF
=============================================


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

In this modeling, the initial crack is meshed. It is extended in its plane by a cohesive cracking zone, represented by level sets and whose discontinuity is described by method XFEM. Law CZM_LIN_MIX is introduced into model XFEM by command DEFI_CONTACT.

A *monotone* tensile load is applied: the cohesive zone opens, thus propagating the crack. At the end of the calculation, a detection of the new propagation front is carried out, which determines the upstream limit of the cohesive zone. It is performed by the operator PROPA_FISS, with the GEOMETRIQUE method, by specifying the operation DETECT_COHESIF (OPERATION = 'DETECT_COHESIF').


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

The mesh is fairly coarse, but refined at the initial crack point. To make the detected front more regular, it is a mesh radiating around the tip.

Number of knots: 18167

Number of meshes and type: 15120 HEXA8 and 2440 PENTA6


.. image:: images/1000000000000239000002372B7FF1C7AB02DE76.png
    :width: 3.2846in
    :height: 3.2728in


.. _RefImage_1000000000000239000002372B7FF1C7AB02DE76.png:

Figure 5.2-1: sectional view of the cracked surface and radiating mesh

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

Validation is carried out on the progress of the detected front after this first propagation step. In the absence of experimental data for a monotonic loading, this is a non-regression test. We have represented in figure the initial crack font and the front detected after the first propagation step. Although we do not have a quantitative reference, we note that the qualitative appearance of the forehead is similar to that of fatigue experiences.


.. image:: images/Object_41.png
    :width: 6.2772in
    :height: 2.8882in


.. _RefSchema_Object_41.png:

Figure 5.3-1: initial edge and edge detected after the first propagation step

The position of the deepest crack bottom point is tested. This is equivalent to testing the maximum coordinate along the :math:`Y` axis of the points at the bottom of the crack after a propagation step.


.. csv-table::

    "**Identification**", "**Reference Type**", "**Reference Value**", "**% Tolerance**"
    ":math:`\mathit{max}(Y)` ", "'NON_REGRESSION'", "1.61048 10-4", "0.1%"