What does 'plastic deformation' refer to in materials science?

Plastic deformation refers to a permanent change in the shape or size of a material when it is subjected to stress that exceeds its elastic limit. When stress is applied to a material, it initially deforms elastically, meaning it can return to its original shape once the stress is removed. However, when the stress surpasses a certain threshold known as the elastic limit, the material undergoes plastic deformation, leading to irreversible changes in its structure.

This concept is crucial in materials science because it helps in understanding how materials behave under different types of loads and the limits of their adaptability or resilience. Understanding plastic deformation is essential for applications in manufacturing and engineering, as it dictates how materials can be shaped, formed, or manipulated during processes such as forging, molding, and machining. It also aids in predicting the failure modes of materials when they are subjected to operational stresses.

The other options describe aspects of material behavior but do not accurately represent plastic deformation. For instance, a temporary change in shape under stress refers to elastic deformation, while a reversible change in size or shape also pertains to elastic responses. A transition point in temperature behavior typically relates to phase changes rather than deformation processes.