**cfv_build

Description

This command is used to mesh a regular shape around a crack front (the command name stands for “Crack Front Volume build”). This volume can be used to perform accurate integrals for energy release rate computations with De Lorenzi or G-theta formulations. In order to be connected to a tetrahedral mesh, “c3d5” pyramid elements are located on every face which must be connected to the rest of the mesh.

The crack front be can specified by a liset (a Catmull-Rom spline interpolation is used), or volume must be completely described by a crack front method component (i.e. gtheta).

Warning

this method is only available for 3D meshes, and it generates linear meshes only.

Syntax

The command has the following syntax:

**cfv_build \(~\,\) [ *liset liset-name propagation-direction-vector ] \(~\,\) [ *ask_crack_to crack-method-name ] \(~\,\) *rc internal-square-length \(~\,\) *ri internal-radius \(~\,\) *re external-radius \(~\,\) *nbc number-of-square \(~\,\) *nbri number-internal-cuts \(~\,\) *nbre number-external-cuts \(~\,\) [ *delta square-deformation ] \(~\,\) [ *delta_p pyramid-height ] \(~\,\) [ *connect connection-radius ] \(~\,\) [ *opening opening-angle ]

Note that at least one of the command *liset or *ask_crack_to must be specified in order to select how to build the volume.

*liset

specifies whether one liset describes the crack front. A vector is required to define the orientation of the crack.

*ask_crack_to

specifies which crack-method describes the volume.

*rc

defines the semi-edge length of the interior square of the section.

*ri

defines the radius of the interior circle of the section.

*re

defines the radius of the exterior circle of the section.

*nbc

is used to define the number of sub-squares dividing interior square part of the section.

*nbri

defines the number of radial cuts between the square part and the interior circle.

*nbre

defines the number of radial cuts between the interior and the exterior circles.

*delta

is used to define the square deformation.

*delta_p

used to specify the height of pyramid elements.

*connect

used to specify the volume that should be connected to a hexahedral mesh: a layer of pyramidal elements is inserted.

*opening

used to create a volume with a meshed crack open in direction propagation-direction-vector. Initially this crack is filled by elset “ compl”.

Various elsets are created:

• “ int” contains the interior part of the volume with only hexahedral elements (on which integrations should be computed).

• “ pyr” contains the pyramidal elements used to connect the volume to tetrahedral meshes.

• “ ext” contains external pyramidal elements if the connect keyword is specified.

• “ compl” contains elements inserted inside the crack if the opening keyword is specified.

Various nsets are created:

• “ front” contains the nodes located at the crack front.

• “ skin” contains the nodes located on the skin made of pyramidal elements used to connect the volume to tetrahedral meshes.

Example

****mesher
 ***mesh volume.geof
  **open crack.geof
  **cfv_build
   *liset LISET_FRONT (-1. 0. -1.)
   *rc .3
   *ri .6
   *re 1.
   *nbc 2
   *nbri 1
   *nbre 2
   *opening .1
   *delta .07
   *delta_p .2
   *connect 2.
****return