Stresses in a clamped circular plate
Sjoerdtje: I think the place to start on your problem is an FEA model with 1x the load and do an elastic analysis. From this, multiply the worst stresses and deflections by 5 to see if, and where, things will be plastic. I certainly would not just leap into a plastic analysis from the start.
I think FEA is your best bet because of the odd aspect ratio of the part you are considering. As mentioned in my previous post, plate formulas simply do not apply to anything this thick. -- Sam