Johnson-Segalman extensional response (${\eta }_E=3{\mu }_0+\frac{3{\alpha }^2{G}_0\tau }{(1-2\alpha \tau \dot{ϵ})(1+\alpha \tau \dot{ϵ})}$)

In uniaxial extensional flow, the conformation equations give $A_{xx}=1/(1-2\alpha \tau \dot{ϵ})$ and $A_{yy}=A_{zz}=1/(1+\alpha \tau \dot{ϵ})$. Their stress difference gives the displayed extensional viscosity. A stable positive steady conformation requires both denominators positive; a first pole marks loss of a bounded steady response. At zero extension rate the Trouton ratio is three relative to the zero-shear viscosity.