Normal strain
= Normal strain
{title2=$e_{nn}=\Delta\ell/\ell$}
The fractional change in the <length> of a <material line> in a specified direction. For infinitesimal deformation with unit direction $\mathbf n$, it is $\mathbf n\cdot\boldsymbol\varepsilon\mathbf n$, where $\boldsymbol\varepsilon$ is the small <strain> tensor.