= Plastic deformation
<Plastic deformation> is the part of a body's <deformation> that remains after the applied <stress> has been removed. Bend a metal wire gently and it springs back through <elastic deformation>; bend it far enough and its unloaded shape changes. In small-<strain> <plasticity in continuum mechanics>, the total <strain> is separated as $\boldsymbol\varepsilon=\boldsymbol\varepsilon^e+\boldsymbol\varepsilon^p$, where the superscripts denote elastic and plastic parts.
In a <crystal>, <dislocation glide> can produce <plastic deformation> without all the <chemical bonds> across a plane breaking simultaneously. Repeated <plastic deformation> can increase the required <yield stress> through <work hardening>. A loading-and-unloading <tensile testing> experiment distinguishes the recoverable extension from the residual extension; the area of a closed <stress> versus <strain> curve measures net supplied mechanical <work> per unit initial <volume> in the small-<strain> description. It equals dissipation when the material's internal state also returns to its starting value. This distinction is essential when shaping a component permanently while keeping its service loads within the elastic range.
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