Reference problem
=====================


Geometry
---------

We consider a parallelepiped of size :math:`30\mathrm{\times }30\mathrm{\times }10\mathit{mm}` which has three holes and a crack on one of its sides (figure).


.. image:: images/100000000000040A000002F79AF1B444991D5FBE.png
    :width: 5.3264in
    :height: 3.6354in


.. _RefImage_100000000000040A000002F79AF1B444991D5FBE.png:

**Figure** 1.1-a **: geometry of the structure under consideration**


Material properties
----------------------

No material is defined because we cannot solve the finite element model in a step.


Boundary conditions and loads
-------------------------------------

No boundary conditions are defined because we do not solve the finite element model: we will calculate two propagations in mode I of the existing crack with imposed and constant displacement along the bottom. The crack remains flat during propagation.

At each propagation step, an advance equal to :math:`\Delta a\mathrm{=}12\mathit{mm}` is imposed. The bottom of the crack spreads while always staying straight.


Initial conditions
--------------------

The initial crack is a half-plane. Its length is equal to :math:`{a}_{0}\mathrm{=}4\mathit{mm}`. The bottom of the crack is straight.