What does the term "fatigue" refer to in the context of aircraft materials?

In the context of aircraft materials, "fatigue" specifically refers to progressive structural failure that occurs under cyclic loading. This means that repeated stress or strain, often from normal operations such as takeoffs, landings, and turbulence, can lead to the eventual failure of a material.

Fatigue is a critical factor in aircraft design and maintenance because it can result in cracks that develop over time due to these repeated loads. Unlike the immediate failure that might occur due to a single overload, fatigue can lead to a gradual deterioration that may not be easily detected until significant damage has occurred. The phenomenon is particularly concerning because it can take years for fatigue to manifest, emphasizing the importance of regular inspections and maintenance to ensure the integrity of aircraft structures.

The other choices illustrate different material behaviors or issues but do not accurately define fatigue. Deformation under heat relates to thermal properties rather than cyclic loading, corrosion pertains to chemical deterioration of materials over time, and loss of material elasticity is a different mechanical property, rather than the failure mechanism characterized by fatigue.