Strain rates in channel flows

Flows in channels used in polymer processing, (a) and (b) are shear flows in a rectangular slot and a cylindrical die, respectively, (c) and (d) are combinations of shear and extensional flow in a spreading disc and a tapering cylinder. The non-zero velocity components are shown. 

Flows (c) and (d), although common in polymer processing, are not easy to instrument or analyse. Consequently, we concentrate on the simple shear flows (a) and (b). Even with these, tensile stresses can arise as a 

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