Evaluating hyperelastic, hyperfoam and viscoelastic material
behavior
Abaqus/CAE provides a convenient Evaluate option that allows you to view the
behavior predicted by a hyperelastic, hyperfoam, or viscoelastic material and that allows you
to choose a suitable material formulation.
You can evaluate any hyperelastic or hyperfoam material, but a viscoelastic material can be
evaluated and viewed only if it is defined in the time domain and includes hyperelastic,
hyperfoam, and/or elastic material data. If your material definition includes viscoelastic
data defined in the frequency domain, you cannot evaluate its viscoelastic material behavior
in Abaqus/CAE, but its material evaluation data are written to the data (.dat) file.
The Evaluate option prompts Abaqus/CAE to perform one or more standard tests using an existing material. (For information on
standard tests for hyperelastic, hyperfoam, and viscoelastic materials, see Hyperelasticity, Hyperelastic Behavior in Elastomeric Foams, and
Linear Viscoelasticity, respectively.) Once the standard tests
are completed, Abaqus/CAE enters the Visualization module and displays the test results in new viewports as X–Y plots.
(For more information on X–Y plots, see X–Y plotting.) Abaqus/CAE also displays an informational dialog box containing the stability limits and coefficients
for each hyperelastic strain energy potential and the viscoelastic material parameters for the
viscoelastic response. The information from the evaluation is saved in the
material_name_i.dat file, where
i starts at 1 and is incremented
for subsequent evaluations of the same material. You can review the evaluation results and
adjust the material definition as necessary.
To initiate the evaluation procedure, select MaterialEvaluatematerial name from the main menu bar. Alternatively, you can select the material of interest
in the Material Manager and then click Evaluate.
The Evaluate Material dialog box appears in which you can specify how you
want Abaqus/CAE to perform the standard tests.
The material evaluation procedure generates jobs with the same names as
the materials; therefore, these material names must adhere to the same rules as
job names (see
Using basic dialog box components,
for more information on naming objects).
The Evaluate option is particularly useful in the
following scenarios:
Comparing test data with the
behavior predicted by a particular strain energy potential
When you define a hyperelastic or hyperfoam material using experimental
data, you also specify the strain energy potential that you want to apply to
the data.
Abaqus
uses the experimental data to calculate the coefficients necessary for the
specified strain energy potential. However, it is important to verify that an
acceptable correlation exists between the behavior predicted by the material
definition and the experimental data.
You can use the Evaluate option to calculate the
material response based on the experimental data using the strain energy
potential that you have specified in the material definition. When the tests
are complete,
Abaqus/CAE
enters
the Visualization module
and displays X–Y plots of the test results. Each
plot includes the experimental data and a curve for each evaluated strain
energy potential.
Abaqus/CAE
also opens a dialog box containing the stability limits and coefficients for
each strain energy potential.
For example, the X–Y plot in
Figure 1
shows the results of a planar test using the Ogden
N=3 strain energy potential.
Figure 1. Results of a planar test.
In addition, the following information is reported to the data
(.dat) file:
The coefficients calculated for the strain energy potential.
Any material instabilities that were detected during the tests.
The path to the data (.dat) file appears in the message
area of the
Abaqus/CAE
main window once the analysis has completed successfully.
Evaluating
multiple strain energy potentials
If you are defining a hyperelastic material using experimental data and you
are unsure which strain energy potential to specify, you can select
Unknown from the Strain energy
potential list in the material editor. You can then use the
Evaluate option to perform standard tests with the
experimental data using multiple strain energy potentials.
When the tests are complete,
Abaqus/CAE
enters
the Visualization module
and displays an X–Y plot for each test and a dialog
box containing the stability limits and coefficients for each strain energy
potential. Each plot includes the experimental data and a curve for each
evaluated strain energy potential. You can visually compare the strain energy
potential curves and the experimental data curve and select the strain energy
potential that provides the best fit.
Once you have determined which strain energy potential provides the best fit
with the experimental data, you must return to the material editor in the
Property module
and change the Strain energy potential selection from
Unknown to the strain energy potential that you have
chosen.
Viewing behavior
predicted by coefficients
If you have acquired coefficients for a particular strain energy potential
(either by evaluating one or more hyperelastic strain energy potentials, as
described above, or from another source), you may want to verify that the
behavior predicted by the strain energy potential acceptably matches your
experimental data or meets other criteria.
You can use the Evaluate option to plot a curve of the
strain energy potential using the coefficients you provided in the material
definition. If the material definition also includes experimental data, a curve
for that data also appears in the plot.
Viewing response
curves for viscoelastic materials
If you have shear or volumetric test results, you may want to verify that
the creep and relaxation behavior predicted by
Abaqus
acceptably matches your experimental data or meets other criteria. Likewise, if
you have frequency data, you may want to verify that the predicted storage and
loss components of the shear and bulk moduli match your data.
You can use the Evaluate option to plot curves using
the coefficients you provided in the material definition. If the material
definition includes experimental data, curves for those data also appear in the
plots. The types of curves produced depend on the material definition. For
viscoelastic materials defined using a Prony series, creep test data, or
relaxation test data for time, you can produce creep and relaxation plots
versus time. For viscoelastic materials defined using frequency data for time,
you can produce plots of the storage and loss components of the shear and bulk
moduli versus a logarithmic scale of frequencies.
Adjusting
material data
If you are unsatisfied with the fit between the test data and the behavior predicted by the
material, you can return to the Property module and adjust the test data and then evaluate the material again. You can repeat this
process until you are satisfied with the material behavior. In some cases it may be
possible to use this approach to optimize the coefficient values included in a
hyperelastic material definition. For more information, see “Improving the accuracy and stability of the test
data fit,” in Hyperelastic Behavior of Rubberlike Materials and Hyperelastic Behavior in Elastomeric Foams for hyperelastic and hyperfoam
materials, respectively.
For detailed instructions on evaluating materials, see the following sections:
