Select Mesh
Edit from the main menu bar to convert a closed three-dimensional shell of triangular elements into a solid mesh of tetrahedral elements. The original shell part must be meshed with triangular elements that fully enclose a volume with no gaps.
To convert a shell mesh to a solid mesh:
Enter the Mesh module.
From the Object field in the context bar, select Part and select a part from the list. This tool is available only for working on orphan mesh elements.
From the main menu bar, select MeshEdit.
Abaqus/CAE displays the Edit Mesh dialog box.
Tip:
You can also display the Edit Mesh dialog box using the 
tool, located at the bottom of the Mesh module toolbox.
From the Category field, choose Mesh.
From the Method list, select Convert tri to tet.
From the buttons that appear in the prompt area, click Yes.
Abaqus/CAE converts the triangular mesh to a tetrahedral mesh.
Tip: You can recover the triangular mesh in its state just before the conversion by clicking Undo in the Edit Mesh dialog box.
After editing an orphan mesh, you should always verify node-, element-, and surface-based features such as section assignments, loads, and interactions to ensure that they are correctly applied to the modified mesh.
