Considère reconsidered: Necking of polymeric liquids

We review the Considère construction and discuss its applicability to the prediction of the inception of necking in extensional flow. The behaviour of simple fluid models is used to illustrate the importance of fully specifying the flow conditions. Even for a Newtonian liquid there is a marked difference in the prediction of necking under the application of a constant force and the imposition of a constant rate of strain.