Difference of modeling jointed bolts using CFAST vs CBEAM(CBAR)+RBE2 in NX / MSC Nastran?
Difference of modeling jointed bolts using CFAST vs CBEAM(CBAR)+RBE2 in NX / MSC Nastran?
(OP)
Hello,
We are modeling a FEM model for an aerospace company. This structural system is built of several components, attached via jointed bolts (screws).
What would be the difference of using these techniques for FEM modeling the jointed bolts in NX / MSC Nastran?
1- CFAST elements
2- CBEAM(CBAR)+RBE2 elements
Can both formulations support bolt-preload? I found these bulk cards in the docs (maybe for Technique # 2-). Is this also supported for Technique #1-?
a- BOLTFOR or BOLTFRC (NX Nastran)
b- BOLT (MSC Nastran)
Thank you in advance.
Regards,
Francesco
We are modeling a FEM model for an aerospace company. This structural system is built of several components, attached via jointed bolts (screws).
What would be the difference of using these techniques for FEM modeling the jointed bolts in NX / MSC Nastran?
1- CFAST elements
2- CBEAM(CBAR)+RBE2 elements
Can both formulations support bolt-preload? I found these bulk cards in the docs (maybe for Technique # 2-). Is this also supported for Technique #1-?
a- BOLTFOR or BOLTFRC (NX Nastran)
b- BOLT (MSC Nastran)
Thank you in advance.
Regards,
Francesco
RE: Difference of modeling jointed bolts using CFAST vs CBEAM(CBAR)+RBE2 in NX / MSC Nastran?
another day in paradise, or is paradise one day closer ?
RE: Difference of modeling jointed bolts using CFAST vs CBEAM(CBAR)+RBE2 in NX / MSC Nastran?
RE: Difference of modeling jointed bolts using CFAST vs CBEAM(CBAR)+RBE2 in NX / MSC Nastran?
RE: Difference of modeling jointed bolts using CFAST vs CBEAM(CBAR)+RBE2 in NX / MSC Nastran?
If you want to investigate preload effects you will need to use a very detailed 3D FEM, and even that is likely to be only an approximation of little practical value.
What exactly are to trying to analyze?
RE: Difference of modeling jointed bolts using CFAST vs CBEAM(CBAR)+RBE2 in NX / MSC Nastran?
1) assume all fasteners nominal preload,
2) assume all fasteners minimum preload, or
3) assume all fasteners maximum preload ...
but these are so coarse that the assumption will swamp any significant effect (which is IMHO insignificant).
From a hundred years of designing preloaded bolts, I think we understand how to design safely. And how "sharpening the pencil" will usually equate to maintenance costs (inspection or replacement). Preload is generally only significant in tension joints under fatigue loads.
Now, of course, you could be in a field where money spent on analysis is not viewed as a cost, and extracting the last "psi" (stress optimised) or the last "gram" (weight optimised) from the structure is more important. In that case "fill your boots" ... pick any appraoch and analyze away. Remember you'll need a full ground test program to validate this analysis.
another day in paradise, or is paradise one day closer ?