What is the definition of plastic deformation in materials science?

Plastic deformation in materials science refers to the permanent change in shape or size of a material that occurs when it is subjected to a stress level beyond its elastic limit. When a material is in the elastic range, any deformation it undergoes is recoverable; that is, when the load is removed, it returns to its original shape. However, once the stress exceeds the elastic limit, the material enters the plastic range where the deformation becomes permanent. This means that even after the removal of the applied load, the material does not return to its original dimensions but instead maintains the new shape.

This phenomenon is particularly important in engineering and manufacturing processes, as understanding how materials respond to different stresses helps in the design of components that can withstand specific loads without failing. It is fundamental in processes such as metal forming and machining, where controlled plastic deformation allows for shaping materials into useful parts.

The other options do not accurately capture the essence of plastic deformation. Temporary elongation within elastic limits refers to reversible deformation, while permanent shortening of the material does not encompass the broader concept of deformation—it's specific and does not describe the elongation aspect. Elongation at high temperatures might relate to material behavior under thermal conditions, but it is not a defining characteristic of plastic deformation itself.