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-« Bloc Fissure » is a SMESH extension used to insert cracks in existing meshes. It has the advantage of meshing the crack front and the surrounding elements with a tore containing ruled elements. The rest of the crack contains a free mesh. The tore is made of prism elements (extruded triangles connected to the crack front) and hexahedrons elsewhere. The main interests of such type of mesh are:\r
+« Bloc Fissure » is an extension of SMESH used to insert cracks in an existing mesh. It has the advantage of meshing the front of the crack and the surrounding elements with a torus containing ruled elements. The rest of the crack contains a free mesh. The torus consists of prismatic elements (extruded triangles connected to the crack front) and hexahedrons elsewhere. The main interests of this type of mesh are as follows :\r
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- Having sets of Gauss points in plans perpendicular to the crack front in order to calculate stress field without any interpolation, which would be the case on free mesh. It avoids strong oscillations along the crack front on the energy release rate and stress intensity factors calculated by `extrapolation <http://code-aster.org/doc/default/fr/man_r/r7/r7.02.08.pdf>`_ or `G-theta method <http://code-aster.org/doc/default/fr/man_r/r7/r7.02.01.pdf>`_.\r
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-- Decrease the element number. In fracture mechanics, a fine mesh is necessary radially to the crack front and more rarely along the front axis. Yet hexahedrons and prisms elements can have geometrical aspect ratios up to 20 without major matrix conditioning problems. On the contrary, tetrahedrons of free meshes are generally limited to aspect ratios around 3. The use of very elongated elements is then no longer a limitation and number of elements can be significantly decreased.\r
+- Decrease in the number of elements. In fracture mechanics, a fine mesh is required radially at the fissure front and more rarely in the axis of the front. Hexhedral and prismatic elements can have geometric aspect ratios of up to 20 without major matrix conditioning problems. On the other hand, the tetrahedrons of free meshes are generally limited to aspect ratios of about 3. The use of very elongated elements is then no longer a limitation and the number of elements can be considerably reduced.\r
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-« Bloc Fissure » is not applicable every time. It is highly recommended to read the section on :ref:`general principles <general_principles>` to see how « Bloc Fissure » works. This section also gives the functional scope and the :ref:`limitations <recommendations>` of the tool. Finally, this part deals with cautions that the user must take using « Bloc Fissure ». The user can also refers himself to the :ref:`tutorial <tutorials>` to get some advice on how to make « Bloc Fissure » works.\r
+« Bloc Fissure » is not always usable. It is highly recommended to read the section on :ref:`general principles <general_principles>` to see how « Bloc Fissure » works. This section also gives the functional scope and the :ref:`limitations <recommendations>` of the tool. Finally, this part deals with cautions that the user must take using « Bloc Fissure ». The user can also refers himself to the :ref:`tutorial <tutorials>` to get some advice on how to make « Bloc Fissure » works.\r
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-If « Bloc Fissure » can’t be used on a case, the user may switch to the other FEM insertion tool Zcracks in SALOME (soon available). It’s more robust and has less limitations but the result is a cracked free mesh with tetrahedral elements. Another possibility is the `X-FEM method <http://www.code-aster.org/doc/v11/fr/man_u/u2/u2.05.02.pdf>`_ method in SALOME_MECA.\r
+If « Bloc Fissure » cannot be used on a case, the user can switch to the other Zcracks insertion tool in SALOME. It is more robust and has fewer limitations, but the result is a free mesh of the crack with tetrahedral elements. Another possibility is the `X-FEM method <http://www.code-aster.org/doc/v11/fr/man_u/u2/u2.05.02.pdf>`_ method in SALOME_MECA.\r
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General principles\r
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-« Bloc Fissure » is based on GEOM module geometrical Boolean operations. The initial structure being a mesh, a conversion from mesh to geometry becomes necessary. This operation is called extraction and reconstruction because it is only applied to a small part of the mesh, which is around the crack. The extracted mesh is called the « Box » and only external faces of this mesh are kept and converted into several geometrical surfaces. This operation implies some limitations on the input mesh. When all the Booleans operations are done, the geometry that contains the crack is meshed again with a ruled mesh in the tore and a free mesh elsewhere.\r
+« Bloc Fissure » is based on GEOM module geometrical Boolean operations. The initial structure being a mesh, a conversion from mesh to geometry becomes necessary. This operation is called extraction and reconstruction because it is only applied to a small part of the mesh, which is around the crack. The extracted mesh is called the « Box » and only external faces of this mesh are kept and converted into several geometrical surfaces. This operation implies some limitations on the input mesh. When all the Boolean operations are done, the geometry that contains the crack is meshed again with a ruled mesh in the torus and a free mesh elsewhere.\r
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In order to illustrate « Bloc Fissure » principle, the simple case of a crack insertion in a parallelepipedic specimen is detailed step by step:\r
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1. The first step consists in loading the structure mesh (a) as well as the crack surface geometry (b).\r
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-2. The crack is then meshed (c). A length criterion defines the size of the extracted « Box ». This length is called the length of influence. All elements having a node within this zone is included in the « Box ». A second operation adds elements in the Box in order to have continuous faces (d).\r
+2. The crack is then meshed (c). A length criterion defines the size of the extracted « Box ». This length is called the length of influence. Every element having a node within this zone is included in the « Box ». A second operation adds elements in the Box in order to have continuous faces (d).\r
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-3. A geometrical Box is reconstructed from the extracted Box mesh. The reconstruction is limited to faces which intersect the crack (e). A tore is created following the crack front (f).\r
+3. A geometrical Box is reconstructed from the extracted Box mesh. The reconstruction is limited to faces which intersect the crack (e). A torus is created following the crack front (f).\r
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-4. The geometrical Box is then cut by the tore and the crack (g). Several plans are created in order to partition the box and the tore into radiuses for the future mesh (h).\r
+4. The geometrical Box is then cut by the torus and the crack (g). Several plans are created in order to partition the box and the torus into radiuses for the future mesh (h).\r
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-5. The Box, the crack and the tore are meshed on their external surface (i) and then filled with volumetric elements (j). Crack nodes are doubled to « open » crack lips.\r
+5. The Box, the crack and the torus are meshed on their external surface (i) and then filled with volumetric elements (j). Crack nodes are doubled to « open » crack lips.\r
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6. Finally the cracked box mesh is reinserted in the initial mesh ensuring the connectivity (k).\r
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-All elements having a node at a smaller distance to the crack than the length of influence is selected. Then a filling algorithm fulfill the Box with elements to get a Box. The Box is not limited to rectangular shapes. See the section on :ref:`test cases <test_cases>` to see examples.\r
+Every element having a node at a smaller distance to the crack than the length of influence is selected. Then a filling algorithm fulfill the Box with elements to get a Box. The Box is not limited to rectangular shapes. See the section on :ref:`test cases <test_cases>` to see examples.\r
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.. _recommendations:\r
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4) **Crack front edges must exceed from the structure:**\r
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-For similar reasons, crack front edges must exceed from the structure mesh. The user shall be really careful when fusing crack front edges within the structure with edges outside of the structure because junction mustn’t be on the box external face. For example the following figure shows the bad and the good practice. In grew a 2D view of a structure to cut and in red the crack surface. Line 1 is the edge declared as the crack front. On the left case, Line 1 stops on the box boundary. Even if Line 1 is extended with Line 2 and 5, « Bloc Fissure» will fail. The good practice is to extend the Line 1 with the same shape. See how to extend the front edges in the :ref:`tutorials section <tutorials>`\r
+For similar reasons, crack front edges must exceed from the structure mesh. The user shall be really careful when fusing crack front edges within the structure with edges outside of the structure because junction mustn’t be on the box external face. For example the following figure shows the bad and the good practice. In grey a 2D view of a structure to cut and in red the crack surface. Line 1 is the edge declared as the crack front. On the left case, Line 1 stops on the box boundary. Even if Line 1 is extended with Line 2 and 5, « Bloc Fissure» will fail. The good practice is to extend the Line 1 with the same shape. See how to extend the front edges in the :ref:`tutorials section <tutorials>`\r
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.. image:: images/schema_lignes1.png\r
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