Modeling bolted/riveted joints 2

[eix]

I wanted to post a question in thread2-419088 but it has been closed.

In the thread Burner2k asked about 2 methods of joints modeling:

Currently, we use two methods to model joints.

1. We represent the fastener holes in the DFEM/Local FEM structure. The rivet or fastener is still represented by 1D CBUSH element but it is attached to the hole nodes using RBE2/RBE3 rigid elements.

2. No holes are modelled in the GFEM or even DFEM. The rivet or fastener is represented by 1D CBUSH element.


aerostress82 explained the 2nd method. I was wondering if you could comment on the 1st one in which holes are included in FEM. How do you assess plate strength in the hole vicinity then? Rigid elements distort the stress field but I've heard about following methods:

a) discarding stresses in the 2 rings of elements closest to the hole (

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150006844.pdf

page 13)
b) discarding stresses in the clamping region or 1 ring of elements (

http://pages.mscsoftware.com/rs/msc...+Form+Calculation+Method+and+FEA+Results.pdf)

c) discarding elements in 2.5D region from centre

Any references on the topic?

 

[rb1957]

We do it both ways. I prefer burn2k's approach ... simple mesh, model rivet as CBUSH (if you really have to), and do a hand calc with the CBUSH load (fastener shear, skin bearing). Or you can mesh with a nominal 1 pitch size so that each node represents a rivet and GPFB shows you the load transferred.

another day in paradise, or is paradise one day closer ?

 

[SWComposites]

Dont use method 1. Period. Just overly complicates postprocessing for no benefit. If RBE2s are used likely rubbish results will be produced.

 

[eix]

What about using RBE3s with 6DOF connected?

 

[SWComposites]

Just don’t.