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Non linear static capability (preload and contact) in SOL101 preoduces very large displacement!

[ Edited ]

To all,

 

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:

  1.  the rigid surface (down movement)
  2.  the bolt preload (bolts are modelled in with 3D elements)
  3. the bolts are held a the shaft "base" in all directions (and the head has a constraint in theta stop the head rotating) 

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?

 

Thanks

Regards

 

PS. Model cannot be posted

 

Production: NX9.0.3.4, NX10.0.2.6
Development: VB.NET (amateur level !)
6 REPLIES

Re: Non linear static capability (preload and contact) in SOL101 preoduces very large displacement!

Hello!,

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?.

 

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

Re: Non linear static capability (preload and contact) in SOL101 preoduces very large displacement!

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.

 

Thanks,

Bhumika

Re: Non linear static capability (preload and contact) in SOL101 preoduces very large displacement!

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

 

Production: NX9.0.3.4, NX10.0.2.6
Development: VB.NET (amateur level !)

Re: Non linear static capability (preload and contact) in SOL101 preoduces very large displacement!

Somehow, I am not able to select element type as rigid for my rigid body. How do I make sure I make it rigid?

 

Thanks

Re: Non linear static capability (preload and contact) in SOL101 preoduces very large displacement!

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

Production: NX9.0.3.4, NX10.0.2.6
Development: VB.NET (amateur level !)

Re: Non linear static capability (preload and contact) in SOL101 preoduces very large displacement!

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.