# 7.4. Use of XFEM with Existing Capabilities

An `XFEM` command block may be used in conjunction with a number of other core code capabilities, as enumerated in the Sierra/SM User Manual. A brief list of compatible capabilities and usage guidelines are given below.

## 7.4.1. Contact

    BEGIN CONTACT DEFINITION <string>name
      ...
      CONTACT SURFACE <string>name CONTAINS
            <string_block_name>_CONTACT_SURFACE
      BEGIN INTERACTION DEFAULTS
        SELF CONTACT = ON
        GENERAL CONTACT = ON
      END
      ...
    END [CONTACT DEFINITION <string> name]

Contact may be enforced on a block that has been cut using XFEM, including the cut surface itself. Contact can be defined using the `GENERAL CONTACT = ON` command within the `INTERACTION DEFAULTS` section of the contact definition. A contact surface called `<string_block_name>_CONTACT_SURFACE` is created for each XFEM block; thus, a contact surface may be defined on an XFEM block by using the `CONTACT SURFACE <string>name CONTAINS <string_block_name>_CONTACT_SURFACE` command line. The XFEM contact surface is also output to the results file as a shell element block for visualization purposes.

## 7.4.2. CONWEP Blast Pressure

    BEGIN BLAST PRESSURE <string> name
      BLOCK = <string_block_name>_submesh
      ASSEMBLY = <string_assembly_name>_submesh
      ...
    END [BLAST PRESSURE <string> name]

XFEM can also be used in conjunction with a CONWEP blast pressure. The pressures that are applied to the cut faces are scaled by the area fraction of that cut face. The pressures are applied to the face throughout the duration of the blast. Assemblies may contain blocks, surfaces, or assemblies of these.

## 7.4.3. Implicit Dynamics

XFEM may be run in implicit dynamics. If an implicit simulation is run, it is highly recommended to include an adaptive time stepping block, as shown below. Adaptive time stepping helps to account for the increased complexity of the problem during crack growth. For additional guidance and command syntax, consult the Sierra/SM User Manual.

Warning

Convergence of XFEM simulations in implicit dynamics mode is currently tenuous; robustness issues may occur when using this analysis combination.