NASTRAN 2-D Solid Elements


Brief description of the DOFs supported for 2-D solid elements types and how these property types relate to the MSC/NASTRAN property entries.


Plane Strain – The 2D solid element in PATRAN writes out either a plane strain QUAD/PSHELL or an axisymmetric CTRIAX6 depending on the option selected in the properties menu. For the rest of this discussion, comments pertain only to the plane strain option.


You can look up the definition of plane strain in an elasticity text book, but basically, plane strain dictates that the strain in the z direction (normal to the element face) is zero all the way through the thickness. This type of analysis is useful for thick solids loaded on edge.


For example, consider the “dam” below loaded on edge. We are looking at the cross-section and assume is very long (thick) such that Z strain is essentially zero.. Therefore we make the plane strain assumption and mesh with 2D solids. Patran does not prompt for a thickness, and will insert a thickness of 1.0 on the PSHELL by default so that all edges loads are input in units of force per unit depth. Note that all loads for the 2D solid should be in-plane edge loads.


The PSHELL/QUAD for the 2D solid looks like this:


$ Elements and Element Properties for region : 2d-solid

The -1 in the MID2 field is the flag that tells MSC NASTRAN to use a plane strain formulation.


If the 2D solid is in the XY plane as shown above, it will have stiffness in the X and Y directions only.  There will be RZ stiffness if K6ROT >0.0.


Examination of the grid point singularity output below shows that DOF 3456 are constrained to avoid singularities.