Numerical simulation of die swell of polymer melts

Numerical simulation of die swell of polymer melts was undertaken with Galerkin's finite element method using three kinds of constitutive equations: the Giesekus type model, the Phan Thien-Tanner type model, and the Oldroyd-B model. The calculated swelling ratios for these models showed that the magnitude of the primary normal stress difference and the shear-thinning effect of viscosity are closely involved in the swelling phenomenon. From the calculated stress distributions it was also found that the swelling mechanism can be understood mainly from the viewpoint of stress. The calculated stress distributions for the Giesekus type and the Phan Thien- Tanner type models were compared with experimental data for a polypropylene melt measured by the flow birefringence technique and they were at least qualitatively in agreement. Ultimately the reliability of computer simulation and the constitutive equations was proved for polymer melt flow in lower shear rate region.