.. _R5.03.19:

**r5.03.19** Hyperelastic and visco-hyper-elastic laws of behavior: almost incompressible material
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**Summary:**

Two laws of hyper-elastic and visco-hyper-elastic behavior adopted for elastomers are described here. The parameters characterizing the two materials are defined in [:ref:`DEFI_MATERIAU <U4.43.01>`] with the keywords ELAS_HYPER and ELAS_HYPER_VISC.

The hyper-elastic part is the same for both models, of the Signorin type, which is a generalized version of the Mooney-Rivlin laws. It is implemented "natively" for ELAS_HYPER and under MFront for ELAS_HYPER_VISC. The viscous part of the latter is modelled by a generalized Maxwell type viscoelastic branch, placed in parallel.

These models are chosen in the [:ref:`STAT_NON_LINE <U4.51.03>`] or [:ref:`DYNA_NON_LINE <U4.53.01>`] command using the keywords RELATION =' ELAS_HYPER 'and RELATION =' ELAS_HYPER_VISC 'and under the keyword [:ref:`COMPORTEMENT <U4.51.11>`]. This relationship extends to large transformations; this feature is chosen using the keyword DEFORMATION =' GREEN_LAGRANGE '. It is available for 3D, 3D_SI, C_ PLAN, and D_ PLAN elements.


.. toctree::
    :hidden:

    self

.. toctree::
    :maxdepth: 2
    :numbered:

    Formulation_de_la_partie_hyperelastique
    Formulation_de_la_partie_visqueuse
    Expressions_analytiques
    References_bibliographiques