A steel alloy (Su = 150 ksi, Sy = 100 ksi, Sn = 70 ksi) is used to make a five-leaf (each leaf is 0.1 in. * 1.8 in.) semielliptic leaf spring. Kf (which is due to stress con- centration at the clips and the center hole) is 1.2. Use the simplified "triangular plate" model.
(a) What total spring length is needed to give a spring rate of 80 lb/in. (i.e., 80 lb applied at the center causes a 1-in. deflection at the center)?
(b) In service, the spring will carry a static load (applied to the center) of P, plus a superimposed dynamic load that varies from +P to -P. What is the highest value of P that will give infinite life, with a safety factor of 1.5?