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The Influence of Permanent Volumetric Deformation on the Reduction of the Load Bearing Capability of Plastic Components

by Paul Du Bois5,463 views

"During the past years polymer materials have gained enormous importance in the automotive industry. Especially their application for interior parts to help in passenger safety load cases and their use for bumper fascias in pedestrian safety load cases have driven the demand for much more realistic finite element simulations. For such applications the material model 187 (i.e. MAT_SAMP-1) in LS-DYNA® has been developed. In the present paper the authors show how the parameters for the rather general model may be adjusted to allow for the simulation of crazing effects during plastic loading. Crazing is usually understood as inelastic deformation that exhibits permanent volumetric deformations. Hence a material model that is intended to be applied for polymer components that show crazing effects during the experimental study, should be capable to produce the correct volumetric strains during the respective finite element simulation. The paper discusses the real world effect of crazing, the ideas to capture these effect in a numerical model and exemplifies the theoretical ideas with a real world structural component finite element model."

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AutomotiveHigh Speed TestingLS-DYNAMechanicalPlasticsRate DependencyResearch Papers

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

by PolyXtrue5,496 views

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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ExtrusionPlasticsPolyXtrueResearch PapersRheology

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

by PolyXtrue5,509 views

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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ExtrusionPlasticsPolyXtrueResearch PapersRheology

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

by PolyXtrue5,391 views

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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ExtrusionPlasticsPolyXtrueResearch PapersRheology

Elongational Viscosity of LDPEs and Polystyrenes using Entrance Loss Data

by PolyXtrue5,524 views

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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ExtrusionPlasticsPolyXtrueResearch PapersRheology

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

by PolyXtrue5,362 views

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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ExtrusionPlasticsPolyXtrueResearch PapersRheology

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

by PolyXtrue5,245 views

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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ExtrusionInjection MoldingPlasticsPolyXtrueResearch PapersRheology

Estimation of Elongational Viscosity Using Entrance Flow Simulation

by PolyXtrue5,529 views

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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ExtrusionPlasticsPolyXtrueResearch PapersRheology