Time-dependent deformation occurring under sustained stress is a phenomenon observed in numerous materials, particularly at elevated temperatures. This deformation, which continues to increase over time, even under constant load, is a significant consideration in structural design. An illustrative example is the gradual sag of a lead roof over many years due to its own weight.
Understanding this gradual deformation is crucial for ensuring the long-term structural integrity of components and systems. It affects the performance and lifespan of structures operating under constant stress, such as power generation equipment, bridges, and aircraft components. Historically, the study of this phenomenon has been essential for developing materials and design strategies that mitigate its detrimental effects.