Assumed a disk loaded with external pressure Po, internal Pressure Pi and rotating at the speed ω. I'm sure that average tangential stress for uniform thickness rotating disk can be calculated using equation below : σ avg = (PiRi/Ro-Ri) - (PoRo/Ro-Ri) + (ρω^2) / 3(Ro^2+RoRi+Ri^2) Ro = outer radius Ri = inner radius ρ= density now if the disk have nonuniform thickness (e.g. L1,L2,...,Ln) and Rn as the radius for each interface of two segment (thickness variable). How do we calculate the average tangential stress for this case? I would really appreciate any kind of help, i will gladly describe further information if necessary. and sorry for my bad grammar, English is not my native language. thank you very much.