Starting from equation (3) show that
where s {\displaystyle \mathbf {s} } is the deviatoric part of σ {\displaystyle {\boldsymbol {\sigma }}} and e {\displaystyle \mathbf {e} } is the deviatoric part of ε {\displaystyle {\boldsymbol {\varepsilon }}} .
From equation (3) we have
The deviatoric parts of the stress and strain are
Therefore,
Now,
Hence
This shows that