Bolt modeling for large gap with MPC

[amaranth22]

Hi? ALL

I have sandwich panel with solid fitting, the assey is fastening panel and fitting through the hole with bolt.

Fitting constructed with SOLID Elms and SHELL(Laminate) Elms for panel side with core.
Panel base line is OML(tool side), the solid fitting above 1.5in from panel elements as below;

fstr
===.======= <-- Solid Ftg. . <- RBE2(123)with solid node
| 1.5in Core | <- RBE2(12345)
-----.------- <-- Laminate . <- panel node

Solid fitting have fastener hole, the RBE2(123) have center and around nodes at the fastener hole but no hole in laminate panal.
RBE2(12345) have panel and hole center node in fastener hole. Loads applied to panel and B.C at Ftg. end.

I want to more good FE model in this case (large gap) and get the resonable fastener loads.

Please feel free for any comments and advices.

Thank you.

 

[SWComposites]

Using a RBE to connect the fitting and panel is way too stiff and will not give correct results. You need to replace the RBE with spring type elements, using spring constants calculated using fastener flexibiity formula (search the aircraft engineering forum for references) The RBE connecting the solid hole edge to a center node is generally ok if all you want is fastener loads, but the stresses in the solid near the fastener holes will not be correct.

 

[amaranth22]

Thanks SWComposites.

I can't find RBE with spring type elements in NASTRAN R-Type elements. Could you recommand any R-Type element if you have?

And fastener flexibiity formula is avilable to composite panel with core also?

 

[SWComposites]

All "RBE"s are RIGID elements - e.g. infinite stiffness. You need to use CELAS or CBUSH type spring elements.

I doubt you will find fastener flexibility data for a sandwich panel in a joint; you will have to use basic solid strap formulas and engineering judgement; you should probably run the model with a range of flexibilities and use the worst case loads at each fastener to be conservative.

 

[amaranth22]

OK! Good suggestion. thank you. I will try.