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Two-Dimensional Elements

Two-dimensional elements, commonly referred to as pl

ate and shell elements, are

used to represent areas

in your model where one of the dimensions is small in comparison to the other two.In the finite element field, the membrane stiffness of the two-dimensional elements can be

calculated using one of two theories: “plane stress” or “plane strain.” In the plane strain

theory, the assumption is made that the strain across the thickness t is constant. Note that a

two-dimensional element can be in either plane stress or plane strain, but not both. y

default, the commonly used linear two-dimensional elements in !"# Nastran are plane stress

elements.

The two-dimensional elements that are discussed in this chapter are

$

#"%&'( - ' shear panel element, i.e., the element can transmit inplane shear forces only.

$

#)*'+, #T(I' - eneral-purpose plate elements capable of carrying inplane force,

 bending forces, and trans/erse shear force. This family of elements are the most commonly

used 0-+ elements in the !"# Nastran element library.

$

#)*'+1, #T(I'2 - %igher order elements that are useful for modeling cur/ed surfaces with

less elements than are re3uired if you used the #)*'+ and #T(I' elements. In general,

the #)*'+ and #T(I' elements are preferred o/er the #)*'+1 and #T(I'2 elements.

$

#)*'+( and #T(I'( - This family of 0-+ elements are complementary to the #)*'+

and #T(I' elements.

$

#('#0+ - ' element used to model surfaces with a discontinuity due to a crack.

In general, 3uadrilateral elements 4#)*'+ and #)*'+15 are preferred o/er the triangular

elements 4#T(I' and #T(I'25. The #T(I' element is a constant strain element. It ise6cessi/ely stiff, and when used alone, it is generally less accurate than the #)*'+

element, particularly for membrane strain. 7hene/er feasible, the #)*'+ element should

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 be used instead of the #T(I' element. #T(I' should only be used when necessary for

geometric or topological reasons, for e6ample, mesh transition between regions of

3uadrilateral elements with different meshes or near the polar a6is of a spherical shell.