IV$.$ The axial stress$-$strain $()$ relation for uniaxial tension test is given as

$=\{\begin{array}{cc}E,& <msub><mrow><mi></mi></mrow><mrow><mi>s</mi></mrow></msub>\\ [E{}_s+E_1(-{}_s)],& {}_s\end{array}$

where ${}_s=\frac{{}_s}{E},{}_s$ and $E,E_1$ are known parameters. Please write out the shear stress$-$sh

strain $()$ relation for pure shear $($simple shear$)$ test based on the "single$-$curve" postulate

the shear parameters $G=\frac{E}{3},G_1=\frac{E_1}{3}$ and ${}_s=\sqrt[\phantom{2}]{3}{}_s$ can be assumed$).$