Hi Ming,
An important feature of real parts is that they are not geometrically perfect. The sides are not perfectly flat, the edges are not perfectly straight, the parts are not perfectly aligned.
The CAD geometry you meshed is geometrically perfect. This can cause much larger forces to be found in simulation compared with what was measured on real parts in the lab.
The corrective action is to introduce geometric imperfection into the geometry prior to running the simulation. You can do that manually in CAD. You can do that by performing an Eigenvalue Buckling analysis and adding a small percentage of the buckled shape to the perfect geometry to make it imperfect.
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