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Cohesive material models

In LS_DYNA V971, solid formulations ELFORM 19/20 and material models *MAT_138, *MAT_184, *MAT_185, *MAT_186 (*MAT_COHESIVE_MIXED_MODE, *MAT_COHESIVE_ELASTIC, *MAT_COHESIVE_TH, *MAT_COHESIVE_GENERAL) correspond to cohesive elements, whereby *MAT_138 is not available until LS-DYNA V971 R3.

The force per unit area components in solid formulations ELFORM 19/20 are in the local coordinate system, where the local-z is normal to the midsurface of the solid. They are stored in the D3PLOT files at the s_xx, s_yy, and s_zz locations. Nothing else is written.

Remarks on *MAT_184

In *MAT_184, failure is based on the tensile_force/element_area in the element normal direction only, not the forces tangential to the element midsurface. Midsurface is reliant on the element connectivity. Normal compression does not factor into the failure criterion.

Units for EN, ET, FN_FAIL:

  • EN or ET is unit_stiffness/unit_area or unit_force/(unit_displacement*unit_area)
  • FN_FAIL is the tensile_force/element_area at failure in normal direction.

User written cohesive material model

See Appendix R in the LS_DYNA V971 Users Manual for information on a "User_Written Cohesive Model". (Subroutines umat41c and umat42c in dyn21b.f are like *MAT_184 and *MAT_185, respectively.) See the Remarks under *MAT_USER_DEFINED_MATERIAL_MODELS in the V971 User's Manual for information specific to cohesive user-defined materials.

 

See also: Cohesive element formulation