Which term best explains the process of physical alteration of a material under stress?

The process of physical alteration of a material under stress is best described by the term "deformation." Deformation refers specifically to the changes in shape or size that a material experiences when subjected to external forces or stress. This can include bending, stretching, compressing, or twisting, and is a fundamental concept in fields such as materials science and engineering.

When materials are stressed, they may not instantly return to their original shape; instead, they may undergo elastic or plastic deformation depending on the magnitude of the stress and the properties of the material. Elastic deformation is reversible, while plastic deformation is permanent.

The other terms, while related to material conditions, do not specifically capture the idea of physical alteration. Deterioration typically refers to the decline in condition due to age or environmental factors rather than stress-based changes in shape. Relaxation relates to the gradual decrease in stress within a material over time, often due to internal structural changes, but it does not denote the immediate alteration in shape or form. Deflation is associated with a reduction in volume, particularly in gas-filled structures, and is not applicable to the context of material alteration under stress.