Question

2, A flywheel with a radius R = 200 mm is designed to spin up to 8000 rpm. It is proposed to make it out of cast iron, but the casting shop can only guarantee that it will have no crack-like flaws greater than 2a 2 mm in length. Use the expression for the maximum stress in a spinning disk in the textbook (Appendix B), and that for the stress intensity at a small enclosed crack (ovra). Take Poisson's ratio v: 0.33. Use 7150 kg/m3 and Kse 38 MPa.m12 for cast iron. (a) What is the maximum rpm that you can achieve without causing the crack to propagate. (b) You want to maximize the stored energy per mass. What is the best material ignoring the cost. Derive the material index, show the chart you used and draw guideline(s) to explain your selection.

Answer 1