The importance of extensional viscosity on an peculiar ear-flow front for injection molding simulations of fiber-reinforced composites

Abstract

An ear-flow front is discovered in the industrial practice of injection molding, especially for fiber-reinforced composites; the advance of the flow front in the center of the cavity is obviously slower than at the edges. To date, such a peculiar flow has not yet been predicted theoretically or computationally and is beyond the predictive capabilities of existing commercial computer aid design (CAE) packages for the injection molding process. Recently, the GNF-X (Generalized Newtonian Fluid eXtended) model of weighted shear/extensional viscosity has been incorporated availably in state-of-the-art predictive engineering software of the 3D-CFD (three-dimensional computational fluid dynamics) framework to show the extension-induced vortex growth in contraction flows of polymer melts. Through 3D-CFD coupled with GNF-X in injection molding simulations, it is significant to demonstrate the importance of extensional viscosity on the ear-flow formation in relation to the weighted viscosity and extension fraction for long-branched and fiber-filled polymer materials. In addition, one can point out that the ear-flow front probably occurs in fast filling conditions for anisotropic fluids.