What is meant by "fatigue" in materials?

"Fatigue" in materials refers specifically to the weakening of a material that occurs due to the repeated application of loads over time. This phenomenon happens well below the ultimate tensile strength of the material, which means the material can endure many cycles of stress before it ultimately fails. Unlike a single large load that might cause immediate failure, fatigue is more insidious, as it results from many small cycles of stress that can lead to the development of micro-cracks within the material. These micro-cracks can propagate and ultimately result in catastrophic failure, even when the material may still be capable of withstanding a load under static conditions. Understanding fatigue is crucial in fields such as engineering and manufacturing, where mechanical components are often subject to fluctuating forces during their operational life.