For those who are better versed in FEA I would like to know if this workaround will work. I have a sheet metal pan (7 ga) that in cross section looks like a "U" with additional flanges at the top of the legs (picture the letter U with serifs). I need to add some cross ribs across the base that connect to the side flanges. Since Simulation Express won't do assemblies, my plan is to make the pan into a part and then model ribs or gussets and run the analysis that way. Does that seem like a valid method?
One question about FEA and sheet metal - why is a mid surface required? At what point does a sheet metal model not become a sheet metal model? When running these calculations by hand, the section properties are the same whether the part is sheet metal or not. How does a mid surface represent the section properties of a sheet metal part?
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That sounds like a valid workflow. At least in Femap it is. I don't use Simulation Express but so long as you can generate some proper mid-surfaces and the geometry is not too complex, it should be able to handle it. You just need to make sure all the surfaces are connected. Don't use a 3D solid mesh as the program will throw its' hands up in horror.
Mid surfaces are required in order to provide some geometry to put a shell-type mesh on. A sheet metal model stops being one if the geometry is "chunky". In other words a "sheet metal-like" model is one where the geometry contains lots of "thin walls" such that the wall thickness is small in relation to the overall dimensions of the model. These become very problematic if you try to mesh them with a 3D solid mesh. In order to capture the stresses you would need probably a minimum of five layers of elements through the wall thickness. This translates to far too many elements if you tried to mesh a sheetmetal or thin-walled structure with a 3D solid mesh. The model would be so huge that you would have to wait for the Second Coming before the model would solve -- assuming that you had a supercomputer to run it. So instead, you use 2D shell-type elements for thin-walled structures. Those elements take wall thickness into account and the model is a lot smaller. Good luck with Simulation Express!