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Unintended Interference

If you're not careful, you'll end up like me with unintended interference. The problem can be illustrated with a pin and hole-part assembly. Three identical geometry assemblies are created. From left to right, firstly a Tet mesh, then two others of different Hex mesh controls (Figure 1). Though the pin has the same diameter as the hole diameter, there may be interference in the model due to geometry discretization.

Figure 1: Identical Geometry but Different Mesh

The difference in results are clear from the contact pressure shown in Figure 2:
Figure 2: Contact Pressure at Frictionless Contacts

The coarse Tet mesh does not 'curve' well (Figure 3) thus bumping into each other. The interference in the second assembly with hex mesh is less acute but still present (Figure 4). The third assembly with hex mesh with nodes of both the pin and hole aligned has no interference (Figure 5) hence almost no pressure.

Figure 3: End View Tet Mesh Shows Interference at Hole

Figure 4: End View of Hex Mesh (Not Aligned) Has Interference

Figure 5: End View of Aligned Hex Mesh

In summary, a good mesh size and controlled hexahedral meshing does make a difference. The v18.1 archived WB file can be downloaded here.

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