Stress' in rotating discs. HELP!! I am working on an independent project where I am analyzing the maximum possible angular velocity of a solid disc of a given diameter and material. The Diameter is 6.75" Material is 440c E= 29,000 Ksi Density of .275lb/in^3 Ultimate tensile strength: 294,426 Psi (294Ksi) How fast can this rotate? Part2: How do I quantify the stress concentration of RADIAL holes in this disc? I have found numerous papers on eccentric holes but not radial on the periphery. Holes are blind and tapped. Maximum speed should be around 40K-60K RPM. I have been using these formulas: https://www.physicsforums.com/latex_images/14/1425557-0.png [Broken] https://www.physicsforums.com/latex_images/14/1425557-1.png [Broken] I have taken R to be zero for radial stress (the center) and 3.375 for tangential stress. I originally used the ultimate stress and solved for omega, but those results were 10x lower than realistic. So i used E, and the results seem reasonable. Although I am not sure WHY I had to use E or if this was the right thing to do. Can I get some assistance? Thanks.