Figure P12.57D shows a fish-shaped ponytail hair clip that utilizes a helical torsion spring to help clamp and hold a ponytail of diameter less than 30 mm. Assume that the force exerted at the tip of the clip when closed is approximately 0.25 N. The spring has D = 4 mm, d = 0.4 mm, and five turns. The clip should open at least 70°. Select a material for the spring and calculate the safety factor for a torsion spring design providing infinite fatigue life.
