MixedQuad#

This command is used to construct a four-node quadrilateral element, which uses a bilinear isoparametric interpolation, derived against a three field variational principle in \(\boldsymbol{u}-p-\vartheta\).

model.element("MixedQuad", tag, nodes, section)#
Parameters:

  • tag – integer tag identifying the element

  • nodes – tuple of integer tags identifying the nodes that form the element

  • section –

    tuple or int. If int, it is the tag of a previously defined PlaneSection. If tuple, it is a tuple of the form (thick, type, material) where

    thick float

    element thickness

    type |str|

    string representing material behavior. The type parameter can be either 'PlaneStrain' or 'PlaneStress'

    material integer

    tag of an General Materials

Note

This element is PlainStrain only.

../../../../../_images/Q9.svg

Fig. 29 MixedQuad element node numbering#

The valid eleResponse queries to this element are

  • 'forces',

  • 'stresses' and

  • 'material $matNum matArg1 matArg2 ...' Where $matNum refers to the material object at the integration point corresponding to the node numbers in the isoparametric domain.

Theory#

With four nodes, the element is equivalent to the Q1/P0 formulation. This formulation is suitable for nearly-incompressible response, but is not suitable for bending dominated problems.

Code Developed by: Edward Love, Sandia National Laboratories