How is "fatigue" defined in relation to aircraft materials?

Fatigue in relation to aircraft materials refers to the process where a material weakens over time due to repeated loading and unloading cycles. This phenomenon occurs because materials experience internal changes that accumulate over time with each cycle of stress, even if the applied loads are below the material’s ultimate tensile strength. These changes can lead to the formation of microscopic cracks, which may ultimately result in structural failure.

Understanding fatigue is crucial in aerospace engineering, where components are subject to varying loads during flight, such as turbulence and other dynamic forces. This aspect of material science emphasizes the importance of assessing and predicting the lifespan of aircraft components to ensure safety and reliability throughout their operational life.