Sketch of a cylindrical tension test specimen: 
<ul><li><i>l</i><sub>0</sub>: standard length (≈ 5×diameter for steel);</li>
<li>S<sub>&lt;0</sub>: section.</li></ul>
<a href="//commons.wikimedia.org/wiki/User:Cdang" title="User:Cdang">Cdang</a>
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<span class="int-own-work" lang="en">Own work</span>