I'd like to know if other users have seen similar behaviour when doing/using Non linear static capability (preload and contact) in SOL101. here's the problem
Consider a part bolted down to a rigid surface and one wants to apply a external load. For the sack of this discussion let's assume it's gravity. In effect the only constraints (preventing the part "flying away") are:
There are not other constraints. One therefore rely entirely on the bolt preload (and friction) to stop the part "flying away".
I did a test with set up described and the analysis ran . I did 2 load cases (in 1 analysis)
LC1 - (bolt) preload only with all the contacts - SOL101
LC2 - (bolt) preload + gravity with all the contacts - SOL101
while nastran solved the problem (I have numbers!) the displacements for LC2 are very large (in my test ~ 60mm) when one would expect very small. Essentially all the numbers are very large (stress/contact presure are in 1e6MPa!)
Result for LC1 appears to be OK
Any thoughts or suggestions on such problem?
PS. Model cannot be posted
To understand better your problem I suggest to post here a simply FE model, a pilot study that demonstrate the error you are having, or at least a simply picture showing the model setup (remember, one picture is better than 1000 words!!).
Remember, solids don't have rotations DOF, then if you prescribe in the bolt head nodes a theta rotation constrain is useless.
Also, SOL101 is a linear static solution, not nonlinear, then you are running a linear static analysis with bolt preload + linear contact, OK?.
Hey Selex_ct ,
Would you be able to guide me through how you did this particular analysis starting from how you made the rigid body and then applied preload. I am having a hard time doing this. just on the basis of diameter of the hole, i cant come up with the preload. Also, i only have G-loads as external forces on the structure.
Old problem so can't remenber every details but here we go...
1.rigid body - coarse mesh with quad4 elements a surface slightly larger than needed. When defiing teh surface region select rigid. in NX9/10 there is no way to define an analytical "rigid" surface like in MSC.Patran &Nastran. I think you need to give the elements some material properties . I used alu in my test if I recall
2. Preload. I modelled the bolt as with chexa (cynlider shape, nothing fancy) and use the preload option. The cut plane was ~ halfway way along the shank.
3. in 101, you may need to apply all your forces in teh same subcase. There may well be a way of "restarting", like in a normal NL analysis, but I have not looked into that
Somehow, I am not able to select element type as rigid for my rigid body. How do I make sure I make it rigid?
it's not the element type you make rigid it's the (contact) surface (in the .sim)
If the Region definition, see the "type" at the bottom of the GUI - 2 options: FLEX or RIGID
Note that TYPE=RIGID (and the associated Master Grid Point) is only supported in Advanced Nonlinear (SOLs 601 & 701). Contact regions in SOL 101 are always flexible.