What type of loading is most commonly associated with fatigue in metal structures?

Cyclic loading is the type of loading most commonly associated with fatigue in metal structures. This type of loading involves the repeated application of stress or load over time, which can lead to the gradual formation and propagation of cracks in the material. Unlike static loading, where the load is applied and held constant, or impact loading, which involves sudden forces, cyclic loading continuously varies in magnitude and direction, resulting in repeated cycles of stress. This repetitive nature is particularly detrimental as it can weaken the material at a microstructural level, leading to eventual failure even if the peak loads are below the material's yield strength. Environmental loading, while important for other effects like corrosion, does not directly cause fatigue in the same manner as cyclic loading. Thus, understanding cyclic loading is crucial for predicting fatigue life and ensuring the structural integrity of metal components in aviation and other engineering fields.