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 \(\boldsymbol{u}-p-\vartheta\).

PythonTcl

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

Note

This element is PlainStrain only.

MixedQuad element node numbering

Alternative element names that map to this element include "bbarQuad" and "constantPressureVolumeQuad".

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 (Simo, Taylor, Pister 1984), also referred to as the mean dilation formulation of Nagtegaal, Parks and Rice (1974).

This formulation is suitable for nearly-incompressible response, but is not suitable for bending dominated problems.

See also FEAP elmt11

Code Developed by: Edward Love, Sandia National Laboratories