Visualization Of Rheological Behavior Of Viscoelastic Polymer Melts In Polymer Processing Flow Fields

In recent years,scientists have proposed lots of viscoelastic constitutive models and numerical calculation methods which are in good agreement with the rheological behavior of viscoelastic fluids.People have begun to use numerical methods to simulate the complex rheological behavior of polymer fluids in various flow channels.In this paper,two differential viscoelastic constitutive models,DCPP and S-MDCPP model,were used to simulate the flow of two polyethylene melts in capillary rheometer and the complex rheological behavior of branched polyethylene melts in cross-slot with cylinder channel and two T-shaped channels.The DCPP model adopted in the commercial software Polyflow,which calculated by the numerical computation method of DEVSS/SU,and the quadratic velocity interpolation,linear pressure interpolation and linear stress interpolation are applied.Moreover,the S-MDCPP model are calculated by our in-house code,which adopts the pressure-stabilized iterative fractional step scheme based on the finite incremental calculus method and the low-order linear interpolations for velocity,pressure and stress are adopted.Firstly,the flow behavior in capillary rheometer and extrusion swell of two polyethylene melts are simulated by using the DCPP model and S-MDCPP model.The predicted results show the variation regularity of the shear stress relaxation and tensile behavior of macromolecules near die exit and extrusion process,which is of positive significance to reveal the complex rheological behavior of polymer melts in the extrusion process.Comparing the simulation results with the experimental results under different shear rates,it was concluded that when the shear rate is relatively low,the simulation results of the DCPP model are in good agreement with the experimental results and when the shear rate exceeds a certain value,the predicted results of the DCPP model begin to deviate from the experimental results.Both cross-slot flow and viscoelastic flow around a cylinder are classical flow channels in non-Newtonian fluid mechanics.In this paper,we combined the cross-slot channel with a cylinder to study the complex rheological behavior of branched polyethylene melt.By verifying the convergence of mesh and comparing the prediction results of two models,we verfied the stability and reliability equal low-order interpolation elements and pressure stabilized iterative fractional step algorithm adopted for the S-MDCPP model,and discussed the influences of cylindrical radius,inflow velocity and constitutive parameters of the S-MDCPP model on the complex rheological behavior of the branched polyethylene melt in the cross-slot with a cylinder channel.Finally,we adopted the DCPP and S-MDCPP model to simulate the complex rheological behavior of branched polyethylene melt in T-channel without square cavity and T-channel with a square cavity,and we compared the contour of the shear stress,first normal stress difference and backbone stretch of the branched polyethylene melt in the two T-channel predicted by the two models,and analyzed the influence of the existence of square cavity on the flow state of polyethylene melt.And we discussed the influence of inflow velocity on the position of the free stagnation point in T-channel with a square cavity,and the influences of the ratio r of the backbone orientation and stretch relaxation and the amount of arms at the end of a backbone q on the flow of branched polyethylene melt in two T-channel.