Volumetric strain
= Volumetric strain
{title2=$e=\nabla\cdot\mathbf u$}
The first-order relative change of volume for a small <displacement field>. It is the <trace> of the <infinitesimal strain tensor>. For a radial <displacement field> $u(r)\mathbf e_r$ in <spherical coordinates>, $e=u'+2u/r$.