Yue Mu

Numerical Investigation of Viscoelastic Flow and Swell Behaviors of Polymer Melts in the Hollow Profile Extrusion Process

The viscoelastic flow and swell behaviors of polymer melts in the profile extrusion process can significantly influence the performance and dimension of the final products. In the study, the viscoelastic flow pattern of a commercial low density polyethylene (LDPE) extruded through out of the hollow profiled extrusion die is investigated by means of finite element simulation. The mathematical model of three-dimensional viscoelastic flow and swell of polymer melts is established with a differential Phan-Thien and Tanner (PTT) constitutive model. A penalty method is employed to solve the non-linear problem with a decoupled algorithm. The computation stability is improved by using the discrete elastic-viscous split stress (DEVSS) algorithm with the inconsistent streamline-upwind (SU) scheme. A streamface-streamline method is introduced to adjust the swelling free surface of the extrudate. The essential viscoelastic flow characteristics of LDPE flowing through out of the hollow profile extrusion die is investigated based on the proposed numerical scheme. Both the redistribution of flow velocity and the release of stress are found to be the reasons for the swell phenomenon.

Numerical Simulation of Driven and Pressure Flow in Compound Shaped Part of Co-Extrusion Process of Polymer with Metal Insert

The mathematic model for polymer extrusion has been established by using the penalty finite element method, and the analysis program has been coded. The driven and pressure flow of power-law fluid in compound shaped part of co-extrusion process of polymer with metal insert has been simulated. The velocity field and temperature field of polymer flow in die cavity are obtained though solving the momentum equation and energy equation, and the influence of various metal insert velocity on the polymer flow is studied. The potential defect is forecast, and the improved measure has been given further. It shows that the common rule of the compound shaped part of co-extrusion process of polymer with metal insert is given by the analysis of the example. The simulation results are very important for the process and die design of the polymer co-extrusion with metal insert.

Numerical investigation of the crystallization and orientation behavior in polymer processing with a two-phase model

Abstract The crystallization and orientation behavior of a polymeric material can significantly influence the performance of products in practical processing. In this study, the variations in morphology that occur during solidification in polymer processing are mathematically modeled using a two-phase model. The amorphous phase is approximated as a finite extensible nonlinear elastic dumbbell with a Peterlin closure approximation (FENE-P) fluid, and the semi-crystalline phase is modeled as rigid rods oriented within the flow field. The crystallization and orientation behavior are numerically investigated using the penalty finite element–finite difference method with a decoupled algorithm. The evolution of the crystallization process is described by Schneiders equation, which differentiates between the effects of thermal and flow states. The hybrid closure approximation is adopted for the calculation of the three-dimensional orientation tensor. The discrete elastic viscous split stress (DEVSS) algorithm, which incorporates the streamline upwind scheme, is introduced to improve calculation stability. The variations in morphology during polymer processing are successfully predicted using the proposed mathematical model and numerical method. The influence of processing conditions on the crystallization and orientation behavior is further discussed.

Finite Element and Experimental Analysis of Three-Dimensional Flow State of Plastic Melt in Slit Die Section

In this paper, penalty finite element method is applied to the simulation of three-dimensional incompressible viscous steady flow, and the program is coded for analysis of three-dimensional flow process of plastic melt in extrusion die. Slit die is typical in polymer extrusion process, and the relevant part is used widely. Because the flow law is different for various polymers with different rheological character even in the same die, the polymer flow in slit die is simulated for Newtonian fluid and power-law fluid by the program and ANSYS, respectively. Flow laws of two kinds of fluid are compared, and the result shows that the non-uniform velocity distribution in outlet is caused by the non-Newtonian effect of material. The penalty factor is important for the penalty finite element model, which decides the precision and efficiency to a great extent. The proper penalty value is decided by some factors, for example, the character of the whole equations and geometric model. Numerical solution with change of penalty value and viscosity is analyzed, and the result shows that the penalty value should be suited with viscosity in special range for penalty finite element model. The experiment has been developed, and the velocity distribution in outlet of slit die is measured. The result of finite element analysis is consistent with experimental result basically, and the reason of result divergence of the two ways is analyzed. The results show that the given model is suited for the polymer extrusion process, and the advice of the selection of penalty value is instructional for penalty element model.

Prediction for the mechanical property of short fiber-reinforced polymer composites through process modeling method

The fiber-reinforced polymer composites are important alternative for conventional structural materials because of their excellent comprehensive performance and weight reduction. The mechanical properties of such composite materials are mainly determined by the fiber orientation induced through practical manufacturing process. In the study, a through process modeling (TPM) method coupling the microstructure evolution and the mechanical properties of fiber-reinforced composites in practical processing is presented. The numerical methodology based on the finite volume method is performed to investigate three-dimensional forming process in the injection molding of fiber-reinforced composites. The evolution of fiber orientation distribution is successfully predicted by using a reduced strain closure model. The corresponding finite volume model for TPM is detailedly derived and the pressure implicit with splitting of operators (PISO) algorithm is employed to improve computational stability. The flow-induced multilayer structure is successfully predicted according to essential flow characteristics and the fiber orientation distribution. The mechanical properties of such anisotropy composites is further calculated based on the stiffness analysis and the Tandon–Weng model. The improvement of mechanical properties in each direction of the injection molded product are evaluated by using the established mathematical model and numerical algorithm. The influences of the geometric structure of injection mold cavity, the fiber volume fractions, and the fiber aspect ratios on the mechanical properties of composite products are further discussed. The mathematical model and numerical method proposed in the study can be successfully adopted to investigate the structural response of composites in practical manufacturing process that will be helpful for optimum processing design.

Numerical investigation of three-dimensional fiber suspension flow by using finite volume method

Fiber suspension flow is common in many industrial processes like papermaking and fiber-reinforcing polymer-based material forming. The investigation of the mechanism of fiber suspension flow is of significant importance, since the orientation distribution of fibers directly influences the mechanical and physical properties of the final products. A numerical methodology based on the finite volume method is presented in the study to simulate three-dimensional fiber suspension flow within complex flow field. The evolution of fiber orientation is described using different formulations including FT model and RSC model. The pressure implicit with splitting of operators algorithm is adopted to avoid oscillations in the calculation. A laminate structure of fiber orientation including the shell layer, the transition layer and the core layer along radial direction within a center-gated disk flow channel is predicted through a three-dimensional simulation, which agrees well with Mazahir’s experimental results. The evolution of fiber orientation during the filling process within the complex flow field is further discussed. The mathematical model and numerical method proposed in the study can be successfully adopted to predict fiber suspension flow patterns and hence to reveal the fiber orientation mechanism.

Finite element simulation of three-dimensional viscoelastic planar contraction flow with multi-mode FENE-P constitutive model

AbstractViscoelasticity is a characteristic of many complex fluids like polymer melts, petroleum, blood, etc. The investigation of viscoelastic flow mechanism has practical significance in both scientific and engineering field. Owing to strongly nonlinear, numerical method becomes a practical way to solve viscoelastic flow problem. In the study, the mathematical model of three-dimensional flow of viscoelastic fluids is established. The planar contraction flow as a benchmark problem for the numerical investigation of viscoelastic flow is solved by using the penalty finite element method with a decoupled algorithm. The multi-mode finitely extensible nonlinear elastic dumbbell with a Peterlin closure approximation (FENE-P) constitutive model is used to describe the viscoelastic rheological properties. The discrete elastic viscous split stress formulation in cooperating with the inconsistent streamline upwind scheme is employed to improve the computation stability. The numerical methods proposed in the study can be well used to predict complex flow patterns of viscoelastic fluids.

Numerical investigation of viscoelastic flow induced crystallization in polymer processing

The investigation of viscoelastic flow induced crystallization is of great engineering significance in polymer processing like extrusion, injection and blow molding. In the study, the behavior of viscoelastic flow induced crystallization of semi-crystalline polymers is investigated by using finite element-finite difference method. The Schneiders approach is introduced to describe the evolution of crystallization kinetic process. The numerical model of three-dimensional flow induced crystallization of polymer melts obeying Phan-Thien and Tanner constitutive model is established. A penalty method is introduced to solve the nonlinear governing equations with a decoupled algorithm. The effect of flow state on the crystallization behavior is investigated. The crystalline distribution within the flow channel is obtained based on the proposed mathematical model and numerical method.