 Work hardening

Work hardening is an increase in resistance to further plastic deformation caused by earlier deformation. A useful macroscopic test loads a metal beyond yield, unloads it and reloads in the same direction: further plastic flow then requires a larger stress. In a constitutive equation, this history is represented by evolving internal variables rather than by the current elastic strain alone.^[ref]

In a crystal, multiplication and interaction of dislocations can make later dislocation glide more difficult. Forest hardening and latent hardening describe particular aspects of that obstacle formation. Increased resistance to plastic flow is not the same as a large change in Young's modulus: the elastic unloading slope and the load required to restart permanent deformation measure different properties. Work hardening can delay necking by compensating for the shrinking loaded area.

Work hardening, also known as strain hardening, is a phenomenon that occurs in materials, particularly metals, where the material becomes stronger and harder as it is subjected to mechanical deformation. This process is a result of dislocation movements and interactions within the material's microstructure during deformation. When a metal is deformed (e.g., stretched, compressed, or bent), dislocations in its crystal structure move.