Same Stress values for different Materials????

Hello everyone,

I created an assembly with three different parts. I first ran an analysis by assigning al2014.mtl to all my parts and then by assinging fenodr.mtll . What I found out  that the vm stress values for both the analysis are same(almost) i.e 2.255e+02 and 2.264e+02. Howevere, there is big diference in other values like displacement, strain energy etc(which is OK as  the assigned materials are different in both the cases). How is this possible that stress values(von mises) are approximately same.I have added a snapshot showing the study status of both the analysis.Does it anything have to do with the warning mesage that is displayed at the bottom ??

Thank you,

Shashi.