July 22, 2015 | by Paul Du Bois | views 3715
"Simulation of rubber-like materials is usually based on hyperelasticity. If strain-rate dependency has to be
considered viscous dampers are added to the rheological model. A disadvantage of such a description is timeconsuming
parameter identification associated with the damping constants. In this paper, a tabulated formulation is
presented which allows fast generation of input data based on uniaxial static and dynamic tensile tests at different
strain rates. Unloading, i.e. forming of a hysteresis, can also be modeled easily based on a damage formulation. We
show the theoretical background and algorithmic setup of our model which has been implemented in the explicit
solver LS-DYNA [1]-[3]. Apart from purely numerical examples, the validation of a soft and a hard rubber under
loading and subsequent unloading at different strain rates is shown."
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Mechanical
Rubbers
Hyperelastic
Rate Dependency
Yielding/Failure analysis
Automotive
High Speed Testing
LS-DYNA
Research Papers
July 22, 2015 | by Paul Du Bois | views 3551
"Reliable prediction of the behaviour of structures made from polymers is a topic
under considerable investigation in engineering practice. Especially, if the
structure is subjected to dynamic loading, constitutive models considering the
mechanical behaviour properly are still not available in commercial finite element
codes.
First, we give an overview of material laws for thermoplastics and show how the
behaviour can be characterized and approximated by using visco-elasticity and
metal plasticity, respectively. Experimental work is presented to point out
important phenomena like necking, strain rate dependency, unloading behaviour
and damage. A constitutive model including the experimental findings is derived.
In particular, different yield surfaces in compression and tension and strain rate
dependent failure, the latter with damage induced erosion, need to be taken into
account. With the present formulation, standard verification tests can be
simulated successfully. Also, an elastic damage model is used to approximate
the unloading behaviour of thermoplastics adequately."
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Mechanical
Rate Dependency
Yielding/Failure analysis
Automotive
High Speed Testing
LS-DYNA
Research Papers
July 22, 2015 | by Paul Du Bois | views 3304
"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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Mechanical
Plastics
Rate Dependency
Automotive
High Speed Testing
LS-DYNA
Research Papers
June 11, 2015 | by DatapointLabs | views 4441
With the growing interest in 3D printing, there is a desire to accurately simulate the behavior of components made by this process. The layer by layer print process appears to create a morphology that is different from that from conventional manufacturing processes. This can have dramatic impact on the material properties, which in turn, can affect how the material is modeled in simulation. In the first stage of our work, we seek to test an additively manufactured material for mechanical properties and validate its use in ANSYS simulation using the Cornell Bike Crank model.
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Mechanical
ANSYS
Research Papers
Validation
3D Printing
June 09, 2015 | by PolyXtrue | views 3352
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.
...read full post
Rheology
Plastics
Extrusion
PolyXtrue
Research Papers
June 09, 2015 | by PolyXtrue | views 3325
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.
...read full post
Rheology
Plastics
Extrusion
PolyXtrue
Research Papers
June 09, 2015 | by PolyXtrue | views 3251
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
June 09, 2015 | by PolyXtrue | views 3431
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
June 09, 2015 | by PolyXtrue | views 3211
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
June 09, 2015 | by PolyXtrue | views 3196
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.
...read full post
Rheology
Plastics
Extrusion
Injection Molding
PolyXtrue
Research Papers
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