7. (a) A thick-walled closed cylinder has an outside-to-inside diameter ratio of K. Derive expressions for the pressure P to initiate yield in the bore of the cylinder according to the Tresca and von Mises yield criteria. (b) Determine the pressure P for closed cylinder with an internal diameter of 30 mm, an external diameter of 50 mm and the material of the cylinder has a yield stress 250 MPa. = of Y Tresca: von Mises: 61 - 63 = (01-02) + (02 - 03) + (01 - 03) = 202 For a closed cylinder: Pr? Pr Oh = 1+ r = 1 = r = r r = r Pr r = r