Von mises and Tresca Yield criterion - theory of plasticity

progiangbk

1. The problem statement, all variables and given/known data
Please help me with this homework, I have not understood much even I've tried to read many books about the 2 criterion. The reason maybe my teacher write english on blackboard but he explains in korean so i cant understand what is the condition of the tube in this homework :P


2. Relevant equations
In my opinion, this one is about 2 above criterion, I have to complete the part 2, please see the attached picture!
The second condition must be pure shear stress or something.
I have uploaded the picture and word file of this homwork, please see for more detail

http://imageshack.us/photo/my-images...lasticity.png/
http://www.mediafire.com/?pxr4b7ea8zbqycx

3. The attempt at a solution
Best regards,