I'm doing a Shock analysis on this assembly. I chose to use the bonded (welded) connection for the rod and the plates. I varied the thickness of the hollow rod and the top and baseplates together using three different thicknesses (T=0.3", 0.5", and 0.7"). For some odd reason, as I increased the thickness, the Von Mises stress and deflection also increased. This was the opposite of what I was expecting. I assumed that if you make the rod thicker (less hollow), it should deflect less. Any thoughts on what could have gone wrong?
p.s. I used a shock profile from MIL-STD 810G (Hazard Shock)