What process occurs when a metal is subjected to repeated cycles of stress or strain?

When a metal is subjected to repeated cycles of stress or strain, the process that occurs is known as fatigue. This phenomenon involves the gradual and progressive deterioration of the material's mechanical properties, often leading to the formation of small cracks which can eventually propagate, resulting in failure. Fatigue failure typically occurs at stress levels significantly lower than the material's ultimate tensile strength, making it particularly insidious in engineering applications.

The fatigue process takes place when materials experience fluctuating loads over time, leading to cyclic loading that can cause microscopic changes in the material structure. Repeated stress will cause these microscopic cracks to grow under certain conditions until they reach a critical size, at which point the material will fracture under continued loading. Understanding fatigue is crucial for engineers to design more reliable structures and components that can withstand the expected loading conditions throughout their service life.