Which option correctly defines fatigue stress range?

• A. Min to Max stress of a detail, may be partially compressive
• B. Average stress over life
• C. Maximum stress only
• D. Minimum stress only

Answer: (C)

Fatigue damage comes from how much the stress swings during a load cycle, not just how high the peak is. The fatigue stress range is the difference between the cycle’s maximum and minimum stresses—the full swing from the lowest to the highest value. This range (sigma_max minus sigma_min) captures the fluctuating demand the detail sees, which drives crack growth and fatigue life. Describing only the maximum stress misses the lower part of the cycle and doesn’t represent the cyclic loading the material endures. Likewise, averages or single-end values don’t convey the stress variation that dictates fatigue behavior.