Stretching energy
= Stretching energy
{title2=$\mathcal E_s=\frac12\int C(\alpha-1)^2\,dS$}
The part of <elastic energy> associated with a change of material length. A simple quadratic <constitutive equation> assigns energy density $C(\alpha-1)^2/2$ per reference <arc length>, where $C>0$ is stretching stiffness and $\alpha$ is the <stretch ratio>. Such a small-<strain> model need not remain realistic as $\alpha\to0$.