What is meant by "fatigue" in the context of materials used in aircraft?

In the context of materials used in aircraft, "fatigue" refers to progressive and localized structural damage that occurs due to cyclic loading. This phenomenon is critical to understand in aviation, as aircraft materials are subject to repeated stress over time, such as during takeoff, flight, and landing. These cyclical stresses can lead to microscopic cracks that grow progressively larger with each loading cycle, ultimately resulting in failure if not identified and mitigated.

Fatigue is particularly relevant because it does not usually result from a single overload event but rather from the cumulative effect of repeated stress cycles. As the material experiences these cycles, it becomes increasingly vulnerable, highlighting the importance of regular inspections and maintenance to detect early signs of fatigue damage before it can lead to catastrophic failure.

The other options, while related to material performance in a broader sense, do not accurately capture the specific definition of fatigue in materials. Rapid wear due to environmental exposure refers to degradation from factors like weather or chemical exposure but does not specifically involve cyclic loading. Sudden failure of a material relates to an immediate catastrophic event rather than the gradual process of fatigue. Lastly, corrosion caused by moisture involves chemical reactions leading to deterioration, which is distinct from the mechanical processes at play in fatigue.