Recoverable Shear Strain and the Barus Effect in Polymer Extrusion

Following essentially the analysis of Nakajima and Shida but using a one‐constant stored energy function a simplified relationship is given between recoverable shear strain imposed on a flowing melt during capillary flow and the magnitude of the extrudate swelling on emerging from the capillary. Where experiments on capillaries of several different (L/R) values cannot be carried out there are some advantages to studies using a zero‐length (orifice) die rather than a long capillary.