Defining a superelasticity model

The superelastic model and the plasticity model for superelastic materials are based on the uniaxial stress-strain response of phase transforming materials. Such materials (e.g., Nitinol) are in the austenite phase under no loading conditions. Austenite is assumed to follow isotropic linear elasticity. On loading the material, the austenite phase starts transforming into martensite beyond a certain stress.

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Superelasticity
Plasticity Model for Superelastic Materials

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In the superelastic model martensite is also assumed to follow isotropic linear elasticity. During the phase transformation, elastic properties are calculated from the elastic constants of austenite and martensite.

In the plasticity model for superelastic materials martensite is assumed to follow an elastoplastic response, with elasticity characterized by the linear elastic model and the plastic behavior represented by the Drucker-Prager model. Martensite exhibits plastic behavior after full transformation.

  1. From the menu bar in the Edit Material dialog box, select MechanicalSuperelasticity.

    (For information on displaying the Edit Material dialog box, see Creating or editing a material.)

  2. Toggle on Nonassociated to specify the volumetric transformation strain, εVL. Otherwise, Abaqus assumes the volumetric transformation strain is equal to the uniaxial transformation strain, εL.
  3. Enter the following data in the Data table:

    Young's Modulus (Martensite)

    Young's modulus of martensite, EM.

    Poisson's Ratio (Martensite)

    Poisson's ratio of martensite, νM.

    Transformation Strain

    Uniaxial transformation strain, εL.

    Start of Transformation (Loading)

    Stress at which the transformation begins during loading in tension, σtLS.

    End of Transformation (Loading)

    Stress at which the transformation ends during loading in tension, σtLE.

    Start of Transformation (Unloading)

    Stress at which the reverse transformation begins during unloading in tension, σtUS.

    End of Transformation (Unloading)

    Stress at which the reverse transformation ends during unloading in tension, σtUE.

    Start of Transformation in Compression (Loading)

    Stress at which the transformation begins during loading in compression, as a positive value, σcLS.

    Reference Temperature

    Reference temperature, T0.

    Loading

    Slope of the stress versus temperature curve for loading, (δσδT)L.

    Unloading

    Slope of the stress versus temperature curve for unloading, (δσδT)U.

    You may need to expand the dialog box to see all the columns in the Data table. For detailed information on how to enter data, see Entering tabular data.

  4. Select Superelastic Hardening from the Suboptions menu to define piecewise linear hardening of martensite. See Defining superelastic hardening for details.
  5. Select Superelastic Hardening Modifications from the Suboptions menu to specify the variation of the transformation stress levels of a superelastic material as a function of the plastic strain. See Defining superelastic hardening modifications for details.
  6. Click OK to create the material and to close the Edit Material dialog box. Alternatively, you can select another material behavior to define from the menus in the Edit Material dialog box (see Browsing and modifying material behaviors, for more information).