Illustrated is a rectangular steel bar with simple supports at the ends and loaded by a force F at the middle; the bar is to act as a spring. The ratio of the width to the thickness is to be about
b = 16h, and the desired spring scale is 2400 lbf/in. (a) Find a set of cross-section dimensions, using preferred sizes.
(b) What deflection would cause a permanent set in the spring if this is estimated to occur at a normal stress of 90 kpsi?

4 h Secion A-A