Lsdyna simulated crack in several ways (reproduced)
1.
CONSTRAINED_TIED_NODES_FAILURE must take common node between the nodes of discrete units can be used ls-prepost or femp implementation. Then by matlab write small programs, or other languages, for in the same position to establish node node set, add * CONSTRAINED_TIED_NODES_FAILURE keywords. Use this method to achieve crack simulate drawback is that preprocessing too much trouble. Application examples refer Baijin
Ze " lsdyna3d basic theory and case analysis. "
2.
mat_add_eroson about in this keyword Excerpts a lot of discussion, can search. It should be noted that, in lsdyna 971R4 previous versions, this material model brought the failure modes are only applicable to a single point of integration of two-dimensional and three-dimensional solid elements. But in the R4 version later, this keyword has been greatly improved:
 in addition to limiting single-point integration, and also supports 3 -dimensional shell and thick shell elements of type1 and type2 .
 you can define the initial damage value, an increase of several injury model, specific reference lsdyna 971R5 edition keywords.
3.
with the failure of the material model itself on the failure of some material models, you can define the units with failure to simulate expand cracks. As * MAT_PLASTIC_KINEMATIC like. If some material models without failure mode, you can use method 2 , or by custom material constitutive achieved crack simulation.
4.
with contact failure model or a spring element to simulate crack
this method personally feel a little far-fetched, but is also seen in some literature. Cracks may appear region must be known before the definition of crack, through face to face contact with the binding with the failure mode CONTACT_TIED_SURFACE_TO_SURFACE_FAILURE or spring unit to simulate crack surface.
5.
using a special material models ( some material models such as
* MAT_120 ( * MAT_GURSON ), * MAT_120_JC ( * MAT_GURSON_JC ), * MAT_120_RCDC ( *
MAT_GURSON_RCDC ), also Some damage models, such as * MAT_96 ( * MAT_BRITTLE_DAMAGE ), etc., with damage value instead of the cracks, damaged by observing cloud to determine crack propagation.
6.
EFG and XFEM Cohesive
these two methods is lsdyna key development for simulation crack propagation method which EFG method is suitable for 4 points of the solid element nodes, XFEM only applies to two -dimensional plane strain and shell elements. These two methods use specific reference LS 971 R4 EFG User'sManual and
XFEM User's Manual
7.
personal summary
The following is a summary of the individual, not necessarily for reference purposes only.


1, with a unit failure or node failure to simulate the crack, which uses the methods herein 1-3, the result largely dependent on the division of cells. Grid must draw a very fine, in order to get crack senses.
 using the contact with failure models or when spring unit to simulate crack, crack surface area produced must be known, so this method is only applicable to a some special occasion.
 when using a special material model to simulate crack, no method of claim unit 1-3 so high. The disadvantage is that parameter setting is more complex, difficult to find in the current literature about this model The material parameters. Document "Identi Fi cation of Gurson-Tvergaard
Material Model parameters viaKalman Fi lteringtechnique. I. Theory "this model to study the influence of various parameters on the results, while setting parameters for reference
 recommended EFG and XFEM Cohesive, these two methods should represent the development direction of the crack of the simulation. Currently these two methods has been greatly improved, but still not perfect, and the support of the unit is limited.

LSDYNA crack extensions are not crack front of the stress intensity factor, with Franc3d do think crack is much more convenient.