I guess they may not work well with compression-only constraints. Just like regular contact (well-known issue in FEA).
I had the same problems with quadratic elements, the analysis can’t converge
Try reducing the default spring stiffness (it’s very high) and increasing the tensile force a bit for the compression-only constraints. It usually helps.
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Actually the bottom washer should be in contact with the sleeve, so the fillet would be more realistic in the top edge. Nonetheless, the sleeve would have a very small fillet, but since it’s a lathe machined part the edge is quite sharp; maybe adding a fillet of a fraction of a millimiter wouldn’t be so useful here…
I meant a small fillet to relieve artificial stress concentrations due to perfectly sharp edges (not possible IRL), but I’ve tried with this one for now:
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The max stress, in the 0.25mm size mesh with reduced integration elements, (it’s the same in the other case), happens near the end of the compression-only support. The 90° edges are not cause of stress concentrations:
Yeah, as long as there are compression-only constraints and/or BCs (top and bottom ones) ending abruptly at the partition edges, those will attract the stress concentrations.
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At the intersection of the horizontal support and the vertical of the sleeve, the material relieves stress. Therefore, the maximum stress is above the edge of the rigid support. Further on, in the hole, the stretched material suddenly falls into the hole. The support must be flexible, and the reactions will spread over a larger surface area. The area of the material under tension will increase. This is what FEAnalyst wrote about.
There is a very good article about stress concentrations and singularities here: Stress singularity - an honest discussion - Enterfea
If you don’t want to add a small fillet, you can also try with plasticity. This would allow for some stress redistribution.
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