Analysis Of Rheological Response Of Viscoelastic Polymer Melts In Molding Processing Fields

With the full development of computer hardware and the finite element method, the computer aided design combined with the finite element method provides a convenient approach to simulate the complex rheological behavior of viscoelastic fluids in the molding processing channels. The rheological property of polymer material is a key factor that affects the quality and performance of final product. Hence, there is an important theoretical and practical significance of studying the rheological behavior of viscoelastic fluid in the molding processing. Nowadays, in the field of polymer rheology, it still has some challenges to attain the experimental condition. However, numerical simulation can achieve the results that the experiment cannot perform, and it provides an effective way to make further study of the rheological property. Hence, numerical simulation is adopted to study the complex rheological behavior of the molding processing in the present paper.The complex rheological behaviors of polyethylene melts described by the DCPP and S-MDCPP models in different channels, such as planar flow past a square cylinder, planar contraction-expansion flow, and the extrusion die swell, are simulated. The results predicted by the DCPP model are obtained with the Polyflow software, and those predicted by the S-MDCPP model are calculated with our in-house code. The discrete elastic viscous stress splitting/streamline upwind(DEVSS/SU) method is applied to solve the convection-dominated problem. Meanwhile, the modified finite increment calculus(FIC) is adopted to enhance the computational stability, and hence the equal low-order elements can be applied to solve the velocity, pressure and stress.Square cylinder in a channel and contraction-expansion channel, as well as the extrusion die swell are common in the molding processing of polymer. The velocity, pressure, stress and backbone stretch predicted by the DCPP and S-MDCPP models are compared, and the rheological responses in different molding processing channels are analyzed. At the same time, the calculated results are compared with the experimental results. Moreover, the effects of Weissenberg numbers(Wi) and constitutive parameter of S-MDCPP model(q、r and ?) on the rheological behaviors of viscoelastic fluids are discussed. Based on the simulation results of polymer melts extrusion, the decay law of stress and backbone stretch in the extrusion free surface is obtained. The results predicted by the S-MDCPP agree very well with those of the DCPP models, and have a good consistency with the experimental results. Both of the constitutive models can describe the complex rheological behaviors of viscoelastic fluids very well. But compared with the DCPP model, the S-MDCPP model is simple, and the variables are less. Consequently, when the S-MDCPP model is solved, the computational time can save. Moreover, the spurious oscillations of pressure and stress fields do not occur, which indicate the equal low-order interpolation elements adopted in this investigation are stable.