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Posts in Category: 'Rheology'


Workshop: Testing, Modeling and Validation for Plastics & Rubber Simulation in ANSYS

Plastics exhibit non-linear viscoelastic behavior followed by a combination of deviatoric and volumetric plastic deformation until failure. Capturing these phenomena correctly in simulation presents a challenge because of limitations in commonly used material models. We follow an approach where we outline the general behavioral phenomena, then prescribe material models for handling different phases of plastics deformation. Edge cases will then be covered to complete the picture. Topics to be addressed include: Using elasto-plasticity; When to use hyperelasticity; Brittle polymers – filled plastics; Failure modes to consider; Criteria for survival; Choosing materials; Spatial non-isotropy from injection molding; Importance of residual stress; Visco-elastic and creep effects; Strain-rate effects for drop test and crash simulations; Fitting material data to FEA material models; The use of mid-stage validation as a tool to confirm the quality of simulation before use in real-life applications.

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Density Rheology Thermal Mechanical Plastics Rubbers Hyperelastic Visco-elastic Plasticity Rate Dependency Yielding/Failure analysis Injection Molding Structural Analysis ANSYS Presentations Validation


Thermoplastic Material Testing for Use in SIGMASOFT and the Effect of Moisture on PA 6/6

Thermoplastic materials are one of the largest categories of materials to be injection molded. Moisture-sensitive materials can lead to issues in the molding process. Simulation of the injection molding process requires sophisticated and exact material properties to be measured. This presentation discusses the testing required to characterize a thermoplastic material for use in SIGMASOFT, as well as the effects of moisture on viscosity measurement of a moisture-sensitive material. Consequences of basing designs on wet or dry materials are covered. Implementation of material data into the software to produce a successful injection molding simulation simulation is described.

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Rheology Plastics CAE Vendor/Supplier Injection Molding Nonlinear Material Models SIGMASOFT Presentations


SPE Newsletter - Summer '15

Molding Views, brought to you by the Injection Molding Division of the Society of Plastics Engineers

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Rheology Mechanical Injection Molding Moldflow Moldex3D SIGMASOFT Multi-CAE Molding Simpoe-Mold Newsletters


Mold Tempering: Conformal Cooling - yes or no?

The tempering layout for injection molds is often designed departing from previous experiences. The manufacturing feasibility is the main driver when deciding where to place cooling lines. However, often the relevance of the tempering in the process profitability or in the part quality is underestimated, and due to the lack of better information sometimes the resulting tempering performs far from the optimum. As a consequence, the molding efficiency is reduced, the part quality is compromised and, once the mold is already built, sometimes expensive trial-and-error is required to bring the mold to an optimum configuration.

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Rheology Thermal Plastics Automotive Biomedical Injection Molding SIGMASOFT Newsletters


Ejection system design: Optimization with SIGMASOFT Virtual Molding

As the demand for functional integration and the need of design differentiation in manufactured products increase, the complexity of plastic parts increases as well; thus some previous knowledge on effective ejection systems becomes insufficient and the challenges in the design of ejection systems grow consistently.

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Rheology Plastics Rubbers Visco-elastic Automotive Biomedical Injection Molding SIGMASOFT Newsletters


Cold Runner Design - Getting the whole picture matters

The profitability of a molded rubber product depends to a large extent on the mold efficiency. To achieve the maximum productivity, besides the larges possible number of cavities it is desirable to minimize the rubber consumption and to produce parts without defects.

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Rheology Rubbers Automotive Biomedical Injection Molding SIGMASOFT Newsletters


Effect of Polymer Viscosity on Post-Die Extrudate Shape Change in Coextruded Profiles

Bi-layer flow in a profile coextrusion die was simulated. Prediction of post-die changes in extrudate profile was included in the simulation. Mesh partitioning technique was used to allow the coextrusion simulation without modifying the finite element mesh in the profile die. Effect of polymer viscosities on the change in profile shape after the polymers leave the die is analyzed. It is found that a difference in the viscosities of the coextruded polymers can lead to a highly non-uniform velocity distribution at die exit. Accordingly, post-die changes in extrudate shape were found to be widely different when the polymers in the two coextruded layers were changed.

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Rheology Plastics Extrusion PolyXtrue Research Papers


Effect of Wall Slip on the Flow in a Flat Die for Sheet Extrusion

Flow in a flat die with coat hanger type of manifold is simulated allowing slip on die walls. Flow in the same die was also simulated by enforcing the no-slip condition on the walls. With slip on the die walls, the pressure drop, shear rate, stress, as well as temperature increase in the die, all were smaller than the corresponding values with no-slip condition on the walls. For the case with slip on die walls, since the shear rate is smaller, the elongation rate in the die is found to be the dominant fraction of the total strain rate. Due to its high computational efficiency, the software employed in this work can be effectively used to design extrusion dies for fluids exhibiting slip on die walls.

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Rheology Plastics Extrusion PolyXtrue Research Papers


Numerical and Experimental Investigation of Elongational Viscosity effects in a Coat-Hanger Die

The flow in a coat-hanger die is simulated using the axisymmetric and planar elongational viscosities of a low-density polyethylene (LDPE) resin. Elongational viscosity is found to affect the velocity distribution at the die exit. Also, the predicted pressure drop in the die changed significantly when the effect of elongational viscosity was included in the simulation. However, elongational viscosity had only a minor effect on the temperature distribution in the die. Predicted pressure drop is compared with the corresponding experimental data.

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Rheology Plastics Extrusion PolyXtrue Research Papers


Elongational Viscosity of LDPEs and Polystyrenes using Entrance Loss Data

For two low-density polyethylenes and two polystyrenes, axisymmetric and planar elongational viscosities are estimated using entrance loss data from capillary and slit rheometers, respectively. The elongational viscosity is estimated by optimizing the values of various parameters in the Sarkar–Gupta elongational viscosity model such that the entrance loss predicted by a finite element simulation agrees with the corresponding experimental data. The predicted entrance loss is in good agreement with the experimental data at high flow rates. The difference in the experimental and predicted entrance loss at lower flow rates might have been caused by large error in the experimental data in this range.

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Rheology Plastics Extrusion PolyXtrue Research Papers


Estimation of Elongational Viscosity of Polymers From Entrance Loss data Using Individual parameter Optimization

The elongational viscosity model proposed by Sarkar and Gupta (Journal of Reinforced Plastics and Composites 2001, 20, 1473), along with the Carreau model for shear viscosity is used for a finite element simulation of the flow in a capillary rheometer. The entrance pressure loss predicted by the finite element flow simulation is matched with the corresponding experimental data to predict the parameters in the elongational viscosity model. To improve the computational efficiency, various elongational viscosity parameters are optimized individually. Estimated elongational viscosity for a Low Density Polyethylene (DOW 132i) is reported for two different temperatures.

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Rheology Plastics Extrusion PolyXtrue Research Papers


Estimation of Elongational Viscosity of Polymers for Accurate Prediction of Juncture Losses in Injection Molding

A new elongational viscosity model along with the Carreau-Yasuda model for shear viscosity is used for a finite element simulation of the flow in a capillary rheometer. The entrance pressure loss predicted by the finite element flow simulation is matched with the corresponding experimental data to predict the parameters in the new elongational viscosity model.

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Rheology Plastics Extrusion Injection Molding PolyXtrue Research Papers


Estimation of Elongational Viscosity Using Entrance Flow Simulation

A new elongational viscosity model along with the Carreau-Yasuda model for shear viscosity is used for a finite element simulation of the flow in a capillary rheometer die. The entrance pressure loss predicted by the finite element flow simulation is matched with the corresponding experimental data to predict the parameters in the new elongational viscosity model. For two different polymers, the predicted elongational viscosity is compared with the corresponding predictions from Cogswell’s analysis and K-BKZ model.

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Rheology Plastics Extrusion PolyXtrue Research Papers


Datapoint Newsletter: Fall '08, Volume 14.4

A Makeover for DatapointLabs.

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Rheology Thermal Mechanical Newsletters


Handbook of Plastics Analysis: Book Review

Assurance of quality in raw materials, control over production, and a basic understanding of criteria for performance all require a sure and complete knowledge of analytical methods for plastics. The present volume organizes the vast world of plastics analysis into a relatively compact form. A plastics engineer will find familiar territory in such subjects as rheometry, differential scanning calorimetry, and measurement of thermal properties. Polymer physicists and chemists will be at home with spectroscopic analyses, liquid chromatography, and nuclear magnetic resonance. All these topics and many more are covered in twelve chapters written by an impressive array of experts drawn from industry and academia.

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Rheology Thermal Plastics Structural Analysis Book Review


Polymer Melt Rheology: A guide for Industrial Practice: Book Review

Two approaches to polymer processing rheology are discernible; by theoreticians. who are concerned with a fundamental description of what would be happening if certain idealized criteria are met; and by practitioners, who are concerned with the results of what is actually happening.” In his newly revised book, Mr. Cogswell skillfully treads the middle ground between these camps, providing an interesting, informative guide to rheology for the design engineer.

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Rheology Industrial Goods Book Review