In a fatigue test, stress is plotted against which variable?

In a fatigue test, the relationship between stress and the number of cycles is of great significance. Fatigue testing typically involves applying varying loads or stresses to a material over a specified number of cycles to determine how it behaves and ultimately fails under repeated loading conditions.

Plotting stress against the number of cycles allows engineers to identify key fatigue characteristics, such as the fatigue strength and the endurance limit of materials. The resulting S-N curve (stress-number of cycles curve) illustrates how much stress a material can withstand for a given number of cycles before failure occurs.

This approach provides critical data that inform material selection and design processes, particularly in applications where materials are subjected to cyclic loads, such as in bridges, vehicles, and machinery. Understanding the relationship between stress and the number of cycles helps engineers anticipate serviceability limits and longevity of structures, which is fundamental in civil engineering and structural design.