What phenomenon continues to deform a material under a sustained load until a sudden fracture occurs?

Creep is the phenomenon that describes the gradual deformation of a material under a constant load over time. This process occurs at elevated temperatures or near the material's yield strength, leading to a slow and continuous strain that ultimately results in fracture if the load persists long enough.

In contrast, fatigue refers to the failure of a material resulting from repeated loading cycles, typically involving a lower load than what would cause static fracture. Elastic strain involves temporary deformation that is reversible once the load is removed, meaning the material returns to its original shape. Plastic deformation, on the other hand, is a permanent change in shape that occurs when a material is subjected to a load beyond its yield point, but it does not necessarily imply continued deformation over time under a sustained load until fracture occurs.

Creep specifically focuses on that sustained application of stress leading to potential failure, making it the most relevant choice for the question posed.