But
===

The aim of operator PROPA_FISS is to cause a crack to propagate, this crack being defined with the X- FEM method. Three types of methods are available:


*a method based on a*fast marching* algorithm (METHODE_PROPA =' SIMPLEXE ',' UPWIND '): this method is available in 2D and 3D for all types of finite elements. The initial crack can be defined on the model mesh or on an auxiliary mesh.


* a purely geometric method by calculating distances to the crack front (METHODE_PROPA =' GEOMETRIQUE ')


* a method using an intermediate surface mesh of the crack lip (METHODE_PROPA =' MAILLAGE '): this method is available in 2D and 3D for all types of finite elements. The initial crack must also be defined using a mesh.

The operator PROPA_FISS thus calculates the crack resulting from fatigue propagation according to a local Paris law, from the previous crack, and from the table of stress intensity factors from CALC_G or POST_K1_K2_K3.

For half-straight cracks (in 2D) or plane cracks with a rectilinear background (in 3D), the surface mesh of the initial crack can be created by the operator PROPA_FISS (METHODE_PROPA = 'INITIALISATION').

The operator produces:


* or a fiss_xfem concept defining the propagated crack (case METHODE_PROPA =' SIMPLEXE ',' UPWIND 'or' GEOMETRIQUE ');


* or the mesh of the initial crack (case METHODE_PROPA =' INITIALISATION ');


* or the mesh of the propagated crack (case METHODE_PROPA =' MAILLAGE ').


* The theoretical aspect of the propagation of level-sets for the X- FEM method is discussed in [:ref:`R7.02.12 <R7.02.12>`].