quad4, quadb, mitc4

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quad4, quadb, mitc4

Purpose

4 and 8 node quadrilateral plate/shell elements.

Description

In a model description matrix, element property rows for quad4, quadb and mitc4 elements follow the standard format

 [n1 ... ni MatID ProID EltID Theta Zoff T1 ... Ti]

giving the node identification numbers ni (1 to 4 or 8), material MatID, property ProID. Other optional information is EltID the element identifier, Theta the angle between material x axis and element x axis, Zoff the off-set along the element z axis from the surface of the nodes to the reference plane (use feutil Orient command to check z-axis orientation), Ti the thickness at nodes (used instead of il entry, currently the mean of the Ti is used).

If n3 and n4 are equal, the tria3 element is automatically used in place of the quad4.

Isotropic materials are currently the only supported (this may change soon). Their declaration follows the format described in m_elastic. Element property declarations follow the format described p_shell.

quad4

Supported formulations (f value stored in il(3) p_shell entries for isotropic materials and element default for composites) are

0 element/property dependent default. This is always used for composites (p_shell subtype 2).
5 Q4CS is a second implementation MITC4 elements that supports classical laminated plate theory (composites) as well as the definition of piezo-electric extension actuators. This is the default for SDT. Non flat shell geometries are supported with interpolation of normal fields.
1 4 tria3 thin plate elements with condensation of central node. Bad formulation implemented in quad4.
2 Q4WT for membrane and Q4gamma for bending (implemented in quad4). This is only applicable if the four nodes are in a single plane. When not, formulation 1 is called.
4 MITC4 calls the MITC4 element below. This implementation has not been tested extensively, so that the element may not be used in all configurations. It uses 5 DOFs per node with the two rotations being around orthogonal in-plane directions. This is not consistent for mixed element types assembly. Non smooth surfaces are not handled properly because this is not implemented in the feutil GetNormal command which is called for each group of mitc4 elements.

The definition of local coordinate systems for composite fiber orientation still needs better documentation. Currently, q4cs the only element that supports composites, uses the local coordinate system resulting from the BuildNDN 23 rule. A temporary solution for uniform orientation is provided with model=feutilb('shellmap -orient dx dy dz',model).

quadb

Supported formulations (p_shellil(3) for isotropic materials and element default for composites) are

1 8 tria3 thin plate elements with condensation of central node.
2 isoparametric thick plate with reduced integration. For non-flat elements, formulation 1 is used.