An erosion operation is done on all solid materials of the structure by the number of voxels (or the thickness) entered in Erode by.... The erosion process occurs when the empty voxels (in the example in white) invade the solid voxels (in the example in red).

The erosion can be applied also periodically in any of the three directions or in all of them.

An example of erosion with and without periodicity is shown using the following (very simple) structure.

Each of the eight solid objects in the structure is made of 16 red voxels. Each group of solid voxels forming an object alternates with empty space (pore space) made of 16 white voxels.

Without the Periodicity checkboxes selected, the solid objects (red) are eroded by 1 voxel anywhere an empty voxel (white) touches a solid voxel (red). However, at the boundaries of the domain, where no white voxels are present and no periodicity has been assigned, the red voxels are not eroded.

After setting the periodicity in X-Direction and in Y-Direction and choosing again to erode by 1 voxel, the objects are eroded also from the boundaries of the domain. This occurs because by setting this periodicity in X- and Y-Direction, it is assumed that beyond the domain boundaries there is a periodic copy of the complete structure.

In our example structure, this periodic copy places empty voxels (white) immediately adjacent to the solid voxels (red) of the example structure. These white voxels erode the red voxels at the domain boundary.

Finally, observe that by setting the periodicity only in X-Direction, or only in Y-Direction and choosing to erode by 1 voxel, the objects are eroded from the boundaries only in X-Direction or only in Y-Direction.