What does the term "fatigue" refer to in material science?

In material science, "fatigue" refers specifically to the weakening of materials caused by the process of repeatedly applied loads over time. This phenomenon occurs when a material undergoes fluctuating stress that doesn't exceed its tensile strength but is significant enough to cause microstructural changes. Over repeated stress cycles, microscopic cracks can develop and grow, eventually leading to failures well below the material's ultimate tensile strength.

Understanding fatigue is crucial in engineering because it informs how materials behave under real-world conditions, where they are often subjected to variable loads. This insight allows engineers to design structures and components that can withstand such stresses over extended periods, thereby preventing catastrophic failures.