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# Numerical singularity error

## Numerical singularity error

(OP)
I am trying to using the bolt load option in the load module.  It is a simple model with a bolt and nut connecting two plates.  Each plate is being pulled by a concentrate force.  When I run the model the program gives me warning messages that  there are numerical singularities on three nodes each on each plate.  Then it gives an error message saying there are too many attempts.  How do I fix the numerical singularity and what does it mean?  Thanks

### RE: Numerical singularity error

Numerical singularity would mean zero stiffness which in turn could be due to insufficient constraining of the material, buckling of a point in your system (geometry -caused such as a weakness pont (imperfection) or it could be due to the high distortion of the material point.

### RE: Numerical singularity error

(OP)
The nodes appear to be around the bolt hole.  Should I add constraints there or would making a finer mesh help?

thanks again

### RE: Numerical singularity error

dog2k5
I do not understand exactly what you are doing, but
if you define them as two seperate parts, you need to decide what kind of bonding should exist between them: full bonding (Tie) or with interface properties (allowing sliding at the interface)that you should reasonably estimate based on lab results or judgement say.
However if you define them under one part then the nodes are automatically constrained (full bonding).
Refining the mesh is helpful except in only few cases: for example when high distortion exists and one uses Nonlinear geometry then the small element areas will become zero/negative or close to  which results in stiffness being zero at the associated DOFs
Sometime the huge difference in the stiffnesses of the two adjacent materials will lead to this situation.
Also in order to get more info about the divergence problem you are experiencing you can go to the msg. file in the job directory

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