= Weissenberg number
{c}
{title2=$\mathrm{Wi}=\tau\dot\gamma$}
{wiki}
The Weissenberg number measures deformation accumulated over a <viscoelastic relaxation time>, often as the product of that time and a <shear rate> or an extension rate. Its precise rate convention should be stated. Unlike a <Deborah number> based on externally imposed temporal variation, it can remain nonzero in a steady flow. A weak-flow constitutive expansion generally requires both slow temporal change and small deformation over the memory time.
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