= Work hardening
= Strain hardening
{synonym}
<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.<Applied Mechanics of Solids by A. F. Bower>[§3.7.5, reloading experiment and evolution of the yield surface]{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>.
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