A Simple Model of Melt Fracture

The PI produced an excellent explanation of the unpleasant shark- skinning observed in certain polymer extrusion processes. This work has been brought to the attention of researchers at Corning and Hoechst Celanese and Greenberg and Demay will work this summer with members of the Materials Sciences Center at the Ecole Nationale Superieure des Mines de Paris led by J.F. Agassant. One goal of this work is to see if the same oscillatory phenomena is present when one replaces the slip boundary condition by a no slip one and looks instead at materials whose shear stress - strain rate constitutive equation has a spinodal type nonlinearity. A difficult question also worth pursuing is whether now understanding the nature of the flow instability - a switch from a slip to a no slip boundary condition at the wall of the capillary tube - if it is possible to control the inlet flow to the capillary in the unstable regime in such a way as to reduce the oscillations and shark skinning of the final product.