Pin in oversize hole

[rlkillian]

Just as a learning exercise I modeld a pin in a hole using 2D elements. I was successful using nonlinear analysis both with and without material nonlinearity. With linear material I got a Hertzian contact stress within about 8% of theoretical so I either did it right or got very lucky. Is there a way to do this using linear analysis? The help file says there has to initially be no gap when solving a contact problem using linear analysis. I wasn't sure if it meant between the parts in general or between every pair of nodes involved. If it's the latter than it wouldn't work for a circle in a larger hole because you would only have one pair of nodes touching initially at the tangent point. All other pairs would have a gap.

Intuitively, it seemed to me like this should be OK, especially if you could get the pairs of nodes that you expect to touch to line up. If that is the case, how do you get the nodes to line up? I've attached a screenshot where you can see that the nodes don't line up. In other words, a node on the edge of the pin doesn't have a node immediately above it (same y coordinate) on the edge of the hole. Even if doing this wouldn't make the linear analysis work I'm still curious. If I lined them up I could put in gap elements just for fun.

[marwan_azzam · Accepted solution]

Hello,

In order for Linear Contact to work you would need the two parts to touch (zero gap) and the mesh to match (nodes line up).

If there is a gap between the parts, which is your case here, you need to use gap elements.  Gap elements cannot be zero in lengh as those automatically generated by the Linear Contact feature.  Gap elements have to have a certain (non-zero) length and should preferably be normal to the surfaces they connect.  For your model where the pin is smaller than the hole, you need to setup the mesh so that you have paired-up nodes between the parts.  You can do that by manipulating the mesh as shown in attached image.  I would also move the pin a slight amount to create a gap where the two parts touch so an gap element can also be created there.

[rlkillian]

Thanks for the response. Did you manually move the nodes so they line up or is there some automated way to do this?

[marwan_azzam]

The mesh is atomated but I helped it a bit by:

• Dividing each of the two circles into 4 arcs.  This way both parts will have a matching node at 90 degrees (top) and the rest of the mesh will align
• Using a specific mesh size rather than a mesh density.