Lyndon you are blowing my mind. We totally need to talk more. I had a blast at the SCCA Divisional championships.
For a guy who works with computers, your a natural mechanical engineer!
Your assumption is correct. The formula I was given is called exactly the thread title: “Tangential Stresses in rotating ring”. I was assured by the Dynamics professor they were totally applicable for discs when Ri is 0.
You will note several terms fall right out of the equations for this unique condition. I left all terms in my excel formulas, only eliminating terms that divided by zero.
Its a shame I don’t drink. 