When Abaqus/CAE generates a free mesh on a solid with tetrahedral elements, it first generates a boundary mesh of triangles on the exterior faces of the solid regions, as described in “What is a tetrahedral boundary mesh?,” Section 17.10.4.

When you are creating a free tetrahedral mesh, Abaqus/CAE can create either a free mesh or a mapped mesh on the boundary faces; two mechanisms control the mesh pattern for this triangular surface mesh:

Global mesh control associated with the three-dimensional region: Global controls always exist. They are set when you assign the free tetrahedral meshing technique to the region. You can use them to create a mapped mesh in areas where Abaqus/CAE determines that mapped meshing is appropriate or to create a free mesh on all bounding faces.

Local mesh controls specified on selected faces of the region: To assign local controls, you select one or more faces of the region and specify whether Abaqus/CAE should create a free mesh or a mapped or structured mesh on the selection. If you define local controls, they override the global controls.

If you assign the structured technique to faces of solid regions that will be tetrahedral meshed, these faces are colored green to show the technique assignment for the surface mesh. (For detailed instructions on assigning mesh controls, see “Assigning mesh controls,” Section 17.18.1.)

In addition, Abaqus/CAE highlights any faces on the boundary that failed to mesh. These failures are usually due to mesh seeding that is too coarse or to tiny edges or faces. You can save the highlighted faces in a set, and you can apply finer seeds to only the faces in the set. For more information about seeding faces in a set, see “Can I seed a face or a cell?,” Section 17.4.2. You can use display groups to display only the faces in the set. For more information, see “Plotting display groups,” Section 78.2.4.

You can query a boundary mesh using the Query toolset. In addition, you can check the quality of a boundary mesh using the mesh verify tool. The mesh verify tool allows you to check the quality of all boundary triangles, or you can use the selection filters to check the quality of the boundary triangles of only selected faces.

If tiny edges or faces prevent Abaqus/CAE from generating an acceptable tetrahedral mesh, you can try the following:

• Use the geometry diagnostics tool to find small entities such as short edges, small faces, and faces with small face corner angles that can affect the mesh quality. You can create a set containing these small entities. For more information, see “Using the geometry diagnostic tools,” Section 71.2.4.

• Use the Geometry Edit toolset to remove redundant edges and vertices. You can also remove a face and stitch over the resulting gap. For more information, see “An overview of editing techniques,” Section 69.2.

• Use the Virtual Topology toolset to ignore tiny edges or faces. For more information, see “What can I do with the Virtual Topology toolset?,” Section 75.2.

• Add partitions to reduce the aspect ratio of long, narrow faces or cells. For more information, see Chapter 70, “The Partition toolset.”

• Use the Edit Mesh toolset to modify the preview mesh. You can do the following in the Mesh module:

  • Edit nodes

  • Collapse element edges

  • Swap the diagonal of a pair of adjacent triangular elements

  • Split element edges

  For more information, see “What can I do with the Edit Mesh toolset?,” Section 64.1.

In some cases you will not be able to mesh an imported solid part with tetrahedral elements because of very thin triangular elements in the surface mesh or because some sliver faces cannot be meshed with triangles. “Using a combination of tools to mesh an imported solid part with tetrahedral elements,” Section 64.3.6, describes how you can use the Edit Mesh toolset and other tools in the Mesh module to mesh the part successfully.