Rigid Body Connector not Included in Analysis

[jonathan.p.kelly]

Hello all,

I am working with Inventor Nastran 2020.

It appears that Nastran is not defining the rigid body connectors (RBE2s) in the .nas file, even though it shows them as having been defined in the Inventor Nastran user interface within Inventor (i.e. it shows the glyphs and the items in the model tree, but it doesn't show them in the .nas file).

I have two plates that are to be connected by several bolts.  I am not concerned with local stresses on the top plate - I just need it to transfer forces into the bottom plate appropriately and to have reasonable deflections.  To model the connection between the plates, I did the following:

1.  Put the bolt holes in the bottom plate and points on the bottom surface of the top plate that lie on the axes of the bolt holes.  I connected these with rigid body connectors (RBE2s), each bolt hole to the corresponding point on the top plate.

2.  I assigned a separation contact surface between the top plate and the bottom plate (in order to get the points on the top plate to which I could connect the RBE2s, I had to split the bottom surface of the top plate into several surfaces, so there are several surface contacts between the top plate and the bottom plate).  As far as I can tell, they are all correctly identified as being separation contacts.

When I run the analysis, I don't get any errors or warnings, except the multitude of warnings that state the positions of slave elements in the contact surface definitions have been modified.

When I look at the results, I see that stresses are transferring primarily through only one of the RBE2s and that the displacements look like the top plate is moving relative to the bottom plate, irrespective of the RBE2s that are defined.  In troubleshooting this problem, I looked into the .nas file and found that the RBE2s are not all being defined.  The file has placeholders for all of the RBE2s (the comment lines that introduce the elements) but they don't declare some of the elements or define which nodes are to be attached to them (see attached photo).  Indeed, it only defined 12 of the 24 RBE2s that it was supposed to define.

I greatly appreciate any help that anyone can offer on this matter.

Thanks,

Jonathan

[John_Holtz]

Hi Jonathan,

If you are using shell elements, this might be the problem: Rigid connector applied to edge of shell is missing some nodes in Nastran.

One possible solution that is not mentioned in that article would be to split the shell so that the rigid connector can be connected to a face instead of an edge. (The "Point" end of the rigid connector should not be a problem, so you do not need to make any changes there.)

[jonathan.p.kelly]

Hi John,

Thank you for your prompt response.  Unfortunately, I don't think this will help, since I am using only solid elements and am not using continuous meshing.  I will keep that in mind for future projects that use shell elements.

Thanks,

Jonathan