= Stress-strain curve
A <stress-strain curve> plots a material's <stress response> against a specified <strain> measure during a loading <experiment>. Its initial slope gives an <elastic modulus> in a linear regime; yielding, hardening and fracture can produce later changes.
The curve depends on <temperature>, loading rate, sample history and the definitions of <stress> and <strain>. <Engineering stress> divides <force> by original <cross-sectional area>, whereas true <stress> uses current <area>. After necking these can differ greatly. Unloading can distinguish recoverable <elastic strain> from permanent deformation, so one loading curve alone does not specify every constitutive property.
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