I am trying to model contact between spherical surfaces, one concave and one convex (ball on cup contact). The difference in diameters of the two surfaces is very small, approximately 0.1 mm difference out of 30mm nominal diameter.

The two surfaces are constrained to be coincident and tangent at a point, and force is applied in line with that point to the ball while the cup is fixed. I get an artifact in the contact pressure surrounding the point of initial contact that seems like it may be due to interferences of the spherical meshed surfaces. Besides that artifact, the solution seems reasonable. Has anyone else encountered this problem or have any ideas to fix it?