= Johnson-Segalman extensional response
{c}
{title2=$\eta_E=3\mu_0+\frac{3\alpha^2G_0\tau}{(1-2\alpha\tau\dot\epsilon)(1+\alpha\tau\dot\epsilon)}$}
In <uniaxial extensional flow>, the conformation equations give $A_{xx}=1/(1-2\alpha\tau\dot\epsilon)$ and $A_{yy}=A_{zz}=1/(1+\alpha\tau\dot\epsilon)$. 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.
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