A helical compression spring was subjected to a load fluctuating between 100 and 250 N. Fatigue properties of the spring wire corresponded to the curve for shotpeened wire given in Figure 12.16. The spring failed in service after about 10^5 cycles. A replacement spring was found that was identical in all respects except that its free length was slightly shorter. To correct for this, a technician stretched the spring slightly to increase its free length to exactly that of the original spring. Show, by means of a tmax?tmin plot, whether you would expect the life of the replacement spring to be the same as, less than, or greater than that of the original.

FIGURE 12.16 Infinite-life fatigue dia- gram. Pretempered carbon or alloy steel high-duty spring wire, d 5 mm (0.2 in.). 12.8 Design of Helical Compression Springs for Fatigue Loading *max(MPa) 1000 800 600 400 200 0 689 510 200 800 (965, 965) (862, 862) Infinite life without shot peening (Static load line) - (Load line, slope 600/300 for Sample Problem 12.2) Infinite life with shot peening 400 600 800 1000 (MPa) min