equivalent strain

$$\tag{1} \begin{array}{rcl} \displaystyle \varepsilon_{\rm eqv} & = & \displaystyle \frac{1}{1 + \nu} \left[ \frac{1}{2} (\varepsilon _{xx} - \varepsilon _{yy})^2 + \frac{1}{2} (\varepsilon _{yy} - \varepsilon _{zz})^2 \right. \newline \newline & & \displaystyle \left.

• \frac{1}{2} (\varepsilon _{zz} - \varepsilon _{xx})^2 + 3(\varepsilon _{xy}^2 + \varepsilon _{yz}^2 + \varepsilon _{zx}^2) \right] ^{1/2} \end{array} $$