COSMOS running of shelled surface model

[CalculatorDave]

Hi all,

I am modeling a sheet metal assembly for linear stress/strain analysis in COSMOS/Works. I have been approaching this by constructing the entire assembly from surfaces, as opposed to solids. By doing this, I can make the entire assembly as a single part. Also, because each sheet metal piece has just a single surface, it makes it much easier for me to "select surfaces" for shell meshing.

The resulting models mesh readily and quickly, although the meshes of adjacent components do not match. The problem is: sometimes the linear stress/strain analysis will run, and sometimes it won't. The error message I get usually says "not sufficient constraints". Is this because I did not create split lines necessary for the adjacent components to have matching meshes? I hate to think of having to make a lot of split lines to get this thing to run.

David

 

[JNR]

This is really a FEA question. I think you need to address this to an more appropriate forum.

John Richards Sr. Mech. Engr.
Rockwell Collins Flight Dynamics

A hobbit's lifestyle sounds rather pleasant...... it's the hairy feet that turn me off.

 

[jamesh8448]

Shell part models make the most sense for sheet metal analysis. Create a surface model with minimal detail (eliminate bend radii and unimportant holes) for the first pass. The elements can be quite large compared to the thickness. The meshes must match for joined surfaces. This can be accomplished somtimes by increasing the mesh tolerance but be sure it is less than half the element size or you will get some ugly results. Mesh the part but do not run the analysis until you have thoroughly examined the resulting mesh to see that all surfaces are meshed together. If you can't get the results you want by increasing the tolerance, then you will have to use split lines at the joints.

When you have the first results you may find that you need to add back some of the detail in high stress areas. Instead of a bend radius, use a chamfer. To eliminate false stress concentration at bolt hole constraints, create split lines to define the washer contact areas. Try a smaller element size and compare results. Shell models mesh and run very fast, so you can run several iterations in a short period of time.