Unit cell stress analysis

antera,

Pro/MECHANICA is fundamentally no different from other analysis tool utilizing the Finite Element Method, so your statement on calculating strains from loads (by inverting the stiffness matrix) is correct. Stresses are indeed calculated from the calculated strains. I hope you are familiar with FEM theory, especially as you are in the nuclear industry.

I am confused about the symmetry constrain on 6 faces of the cube, however. This makes no sense to me. Why not analyze the actual geometry, taking care to properly represent the boundary conditions? It is good practice to only apply the constraints that eliminate rigid body motion (and those that provide symmetry constraints) and that the loads keep the structure in static equilibrium.

If you are still confused as to some of the basics of finite element modeling, I suggest making a post in the Finite Element Analysis engineering (forum727). Use this forum for questions specific to Pro/MECHANCIA.

Good luck!


Best regards,

Matthew Ian Loew
"I don't grow up. In me is the small child of my early days" -- M.C. Escher

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

Hey Matthew,

Thanks for answering!

The model is actually not a cube but a unit cell of a much larger model. The actual model is much too large to analyze in Pro/M, so I had to create that cell. The reason why I apply 6 symmetry boundaries was because the cell is symmetric in all 6 directions. My boss told me that by compressing any one face you would get a change in stress on that face of the cell, and use the change in stress to calculate an effective elastic modulus for the unit cell in that direction. But to do that I need to know how to find the stress on the face (possibly by integrateing the stresses over that face? I didn't find any function in Pro/M for that.)

The second thing I was trying to achieve is to find the actual stress state the unit cell would be in if the all the faces have an average stress equal to the ambient pressure the part will operate in. Which I can do if I could integrate the stress over the face.

I guess this problem is very confusing. I'll try out the FEM forum like you suggested. But if any one knows how to extract stress data from a plane in a model please let me know.

And thanks again for answering.