= Steady uniaxial extension of the differential pom-pom model
{title2=$\eta_E=\frac{G\tau_1(1-s\tau_1)}{(1-s\tau_1-s^2\tau_1\tau_2)^2}$}
For extension rate $s>0$ and $x=s\tau_1<1/2$, the steady <conformation tensor> is $\operatorname{diag}((1-2x)^{-1},(1+x)^{-1},(1+x)^{-1})$. Its normalized orientation has axial component $(1+x)/[3(1-x)]$ and transverse components $(1-2x)/[3(1-x)]$. Stretch is finite only if $s^2\tau_1\tau_2<1-x$, when $\lambda_\infty=(1-x)/(1-x-s^2\tau_1\tau_2)$ and the displayed <extensional viscosity> follows. Above $x=1/2$, the unnormalized axial tensor grows exponentially but $B\to\operatorname{diag}(1,0,0)$; then stretch remains bounded only if $s\tau_2<1$. Orientation normalization and stretch relaxation therefore impose different thresholds.
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