Numerical Simulations of Capillary Extrusion of Low Density Polyethylene Melt

doi:10.19491/j.issn.1001-9278.2021.05.013

Abstract

Abstract:

With the help of two differential viscoelasticity constitutive models， i.e. DCPP model and S?MDCPP model， the complex rheological behavior of branched polymer melts was described， and the problems of convection dominance and the lack of elliptic operators in the process of viscoelastic flow were solved by means of the discrete viscoelastic stress splitting method and upwind streamline method. A pressure-stabilized iterative fractional step scheme based on the finite incremental calculus method was used to solve the mass and momentum conservation equations. The flow behaviors of PE-LD melt in the capillary and extrusion swell were simulated， and the simulation and experimental results were compared. The results indicated the extrusion-swelling ratio and wall shear stress predicted by the model at low shear rate were close to the experimental results. The velocity， stress and backbone stretch predicted by the two models were also in good agreement with the experimental results. This indicates that the two models can well predict the complex rheological behavior of PE-LD melt in capillary and the algorithm is reliable to be used to resolve the S-MDCPP model.

Key words: low-density polyethylene melt, numerical simulation, finite incremental calculus, constitutive model

CLC Number:

TQ320.66⁺3

LU Jing, WANG Wei. Numerical Simulations of Capillary Extrusion of Low Density Polyethylene Melt[J]. China Plastics, 2021, 35(5): 79-85.

Figures/Tables 13

Fig.1. Schematic diagram of geometric model

Fig.2. Computational mesh

Maxwell参数		非线性参数
G/Pa	λ_b/s	q=2/ν	r	ξ
10 377	0.4	10	1.2	0.02

Tab.1. Constitutive parameters of DCPP model and S?MDCPP model（T=170 ℃）

Fig.3. Comparison of the extrusion swelling ratio predicted by S?MDCPP model with the experimental results at different shear rates

Fig.4. Variation of wall shear stress and maximum backbone stretch degree with shear rate

Fig.5. Velocity distribution predicted by DCPP and S?MDCPP models

Fig.6. Variation of velocity predicted by S?MDCPP and DCPP models

Fig.7. Distribution of stress predicted by DCPP and S?MDCPP models

Fig.8. Variation of stress along the line Y=0.001m and free surface predicted by DCPP and S?MDCPP models

Fig.9. Variation of stress on the center axis predicted by DCPP and S?MDCPP models

Fig.10. Variation of shear stress τxy along the free surface with time predicted by S?MDCPP model

Fig.11. Backbone stretch contour predicted by DCPP and S?MDCPP models

Fig.12. Variation of backbone stretch predicted by DCPP and S?MDCPP models

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