Section VIII Failure Theory Basis 1

[cougaggie]

In preevious versions of the Code the allowable stress intensity values were based on Tresca (Max Shear Stress) Failure theory. I see the latest version of Div 2 has been converted to Von Mises (max strain energy) failure theory.

Is Div 1 still based on Tresca, or have the allowable values for Div 1 also been "converted" to Von Mises?

Thanks!

 

[TERIO]

I think the answer is c. none of the above. Quoting from the old Criteria document:

"Section I and Division 1 of Section VIII use the maximum stress theory, by implication, but Section III and Division 2 use the maximum shear theory."

Obviously, Div. 2 has changed to Mises (Section III has not). As far as I know only Sec. VIII, Div. 2 got a major overhaul.

 

[cougaggie]

You are absolutely correct. The Div 1 allowables are based on maximum principal stress theory. I finally found a good reference explaining this. Pressure Vessels Design and Practice, by Somnath Chattopadhyay, 2005, CRC Press. Obviously this edition does not reflect the lastest change for Div 2, but that change is very explicit that the methods in Part 5 are all based on Von Mises failure theory. The Mandatory Appendices of Section II Part D are not abundantly clear on this point.

At any rate, thanks for the correction, I am now back on track.