I have been reading post on this subject and something is bothering me.  Is there a rule of thumb for when you use a shell over a solid mesh?  Looking at the Solidworks Simulation, the definition of a thin shell is a thickness to span ratio less than 0.05.  The normal definition of a solid or plate element is mid-surface is flat and a shell has curvature. Do you always use a shell element in Simulation if the thickness to span ratio is less then 0.05?