• Jorgen

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    Most FE software has the capability to calibrate simple material models, such as hyperelasticity and linear viscoelasticity. But the calibration functions do not give you much flexibility about what experimental data to use and how the calibrations should be performed. MCalibration is an application that is much more powerful and faster. It contains functions for cleaning up experimental data, it contains a library of already calibrated material models, and it can calibrate all material models Abaqus, ANSYS, and the PolyUMod library. Many of the commonly used viscoplastic material models in Abaqus and ANSYS are directly built into MCalibration. That means you can calibrate those models very fast without even using a FE solver. MCalibration is awesomely great. Contact me if you would like a trial license.
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    Through my research and industrial consulting I have noticed that there is a huge need for more advanced material models than what is provided by Abaqus, ANSYS, LS-DYNA, and other FE software. To overcome this limitation I developed the PolyUMod library of advanced material models that are significantly more accurate and provide the ability to capture the mechanical response of virtually all polymers, including everything from simple non-linear elasticity to large strain anisotropic viscoplasticity at different temperatures. The PolyUMod library also contains a large number of failure models that can be used to predict when a material fail during monotonic or cyclic loading.

    If you ever need to accurately predict the non-linear behavior of an elastic, thermoplastic, or other polymer, then you should check out the PolyUMod library and PolyUMod.com!
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    This website is an independent forum for discussing finite element simulations of all types of polymers. To perform an accurate FE simulation requires 3 types of inputs:
    • Geometries
    • Material models
    • Applied loads and boundary conditions

    The specification of the material models is typically the most challenging, and is therefore the focus of this site. I have been working in this field for close to 20 years, and this site now has more than 10,000 posts and 16,000 members. My goal of running this website is to provide expert advice on how to perform proper computer simulations of polymers, and to discuss some of the tools that I have developed (PolyUMod and MCalibration). Researchers and users are encouraged to submit results and to request information.
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    Experimental testing can be performed for different reasons. Sometimes the purpose is simple to make sure that a material satisfies a given set of requires property values. Other times the purpose is to obtain sufficient experimental data to calibrate a suitable material model. When the goal of the testing is to calibrate a material model then the testing can be performed using "smart experiments" in order to obtain as much information as possible using as few tests. The required number of tests will depend on the material behavior and the material model that will be used. If a material is isotropic then it is frequently sufficient to perform only uniaxial tests with multiple load-relax-unload cycles.

    When possible, I also typically recommend that validation tests be performed. Validation tests are specific tests that are typically multiaxial and are specifically designed to probe the material in a way that is similar to the intended application. The calibrated material model will then be used in Finite Element (FE) simulations of the validation experiments. If the calibrated material model match the validation results then the material model likely provides a reasonable representation of the true material response. Validation experiments are often performed using Small Punch testing, V-notch shear testing, or Indentation testing.

    Contact me if you are interested in obtaining a quotation for experimental characterization of validation testing.
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    The PolyUMod library contains a number of material models that are significantly more advanced than any of the buit-in material models in ANSYS. Using the PolyUMod library it is possible to model, for example, the large-strain anisotropic thermomechanical response of strain softening polymers. The PolyUMod library can also be used to predict damage, fatigue, and failure of anisotropic materials.

    See PolyUMod.com For more information about the PolyUMod library.
    by Published on 2014-12-27 21:29

    The PolyUMod library contains a number of material models that are significantly more advanced than any of the buit-in material models in Abaqus. Using the PolyUMod library it is possible to model, for example, the large-strain anisotropic thermomechanical response of strain softening polymers. The PolyUMod library can also be used to predict damage, fatigue, and failure of anisotropic materials.

    See PolyUMod.com For more information about the PolyUMod library.
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    Different polymer classes require different experimental tests for proper characterization, and also need different material models for proper FE predictions. Further complications arise due to the strong temperature-dependence of my polymers, and the sensitivity of failure behaviors on environmental conditions.

    This section discusses some basic guidelines for common classes of polymers.
    by Published on 2014-12-27 10:50

    ANSYS has built-in support for multiple material models that can be used to represent the behavior of polymers. This includes:


    The theory behind these models, when and how they should be used, and equally important when they should not be used are discussed in detail in my different training classes.
    by Published on 2014-12-27 10:39

    Abaqus has built-in support for multiple material models that can be used to represent the behavior of polymers. This includes:


    The theory behind these models, when and how they should be used, and equally important when they should not be used are discussed in detail in my different training classes.



    Date 8:30 AM - 4:30 PM (EST*)
    Wed, Nov 4, 2015 Veryst Engineering Office
    Thu, Nov 5, 2015 Veryst Engineering Office
    *EST = Eastern Standard Time (Boston time)
    Location: Veryst Engineering, 47A Kearney Road, Needham, MA 02494, USA

    See the following brochure for more information about the class.


    INTRODUCTION
    • Predicting both the high and low strain rate response of different polymers can be difficult due to material non-linearities and sensitivity to the load environment.
    • This class will demonstrate different experimental techniques for determining the true material response, and exercise suitable material models for capturing the material response in both slow rate and impact conditions.


    PREREQUISITES
    The training class is intended for people with some experience running finite element programs. The examples presented in class will use the commercial finite element program Abaqus. The material models presented in class are available for both Abaqus and ANSYS, and the course is applicable to all finite element codes.

    COURSE OUTLINE
    • Review of polymer mechanics
    • Modern mechanical testing techniques for polymers
    • Finite element analysis as an engineering tool
    • Differences between polymers and metals
    • Continuum mechanics review: stress, strain, deformation gradients, invariants, balance laws
    • Elasticity / hyperelasticity: review of hyperelastic models
    • Review of viscoelasticity theory: strengths and limitations of linear viscoelasticity
    • Review of metal plasticity theory: strengths and limitations of metal plasticity models
    • User-material models in Abaqus and ANSYS, including advanced viscoplastic constitutive models incorporating rate- and temperature-dependence
    • State variable models
    • Advanced finite element simulations of different classes of polymers
    • Material parameter extraction techniques using MCalibration and the PolyUMod library of user material models



    LEARNING OBJECTIVES
    By the end of this class you will be able to:
    • Design a relevant high strain rate experimental test program for a new polymer material. Know what experimental tests are necessary and sufficient for material model calibration.
    • Know the strengths and weaknesses of various material models with respect to predicting both the slow and high strain rate response.
    • Use experimental data to calibrate the selected material model, and perform impact simulations using an FE code.



    ABOUT THE INSTRUCTOR
    Dr. Bergstrom is a Principal Engineer at Veryst Engineering, LLC, and consults primarily in the modeling, testing, and failure analysis of polymeric materials. Dr Bergstrom received his Ph.D. from M.I.T. in the area of computational polymer mechanics, and has lectured in the department of Mechanical Engineering at M.I.T.
    by Published on 2013-12-06 20:51

    I am actively looking to hire someone with experience in experimental characterization and finite element modeling of different polymers. This is for a full time position of in our Veryst Engineering office outside Boston. Please send me a private message if you are interested in applying to this interesting opportunity in a growing consulting company.
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    A new version of MCalibration and PolyUMod was just released (v.2.6.0). The new version contains a large number of interesting and useful new features, for example:
    • Restructured the material models by FE solver.
    • Selecting one or more load cases now highlights the corresponding graph curves.
    • Improved the convergence of anisotropic viscoplastic material models.
    • Various bug fixes.


    Check out the following page for more info, you can also read the detailed change log here.
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    You can now follow me (and PolyUMod + MCalibration) on Twitter: @PolymerFEM
    Info about updates, new features, etc, will be provided.
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    We have created a new website specifically for the PolyUMod library of material model. The new website, PolyUMod.com, contains lots of information about how to accurately perform Test-Calibrate-Simulate workflows using the PolyUMod library of advanced user-material models for Abaqus, ANSYS and other non-linear FE solvers.

    We encourage everyone who is interested in accurate FE simulations of polymers and rubbers to checkout PolyUMod.com!
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