Export NASTRAN File: Properties

Description

Beam Properties

Straus7 posts standard isotropic beam properties as PBEAM entries. Bars, cutoff bars, springs, cables and point-contact elements are all posted as PROD entries. User-defined beams are not exported. All properties are posted with property and material ID numbers, in large field format.

PBEAM entries define cross section area A, moments of area I11 and I22, and torsion constant J. PROD entries define cross section area A.

Beam properties always post a MAT1 structural material entry, and a MAT4 thermal material.

Plate Properties

Straus7 posts shear panels as PSHEAR entries, laminates as PCOMP and all other plate property types as PSHELL entries. All properties are posted with property and material ID numbers, in large-field format. Straus7 includes the option to also post thermal material data as indicated below.

PSHEAR entries define the thickness T, using the membrane thickness. If this value is non-zero, the non-structural mass per unit area (NSM) is defined as the material density divided by thickness.

PSHELL entries define the thickness T, using the membrane thickness.

For 2D plane strain plates, material MID2 is set to –1, and material MID3 is left blank; otherwise, MID2 and MID3 are set to MID1.
For user-defined plates, the PSHELL references three separate MAT2 cards via the MID1, MID2 and MID4 entries, where MID1 is the membrane matrix, MID2 is the bending matrix and MID4 is the coupling matrix. MID3 card is left blank.

Plate properties post a MAT1 structural material entry, except that:

Anisotropic plate properties post a MAT2 structural material entry.
Plate/shell, ply and orthotropic plates post a MAT8 structural material entry.
User-defined plates reference three separate MAT2 cards via the MID1, MID2 and MID4 entries.

Anisotropic plate properties post a MAT5 thermal material; other plate property types post a MAT4 thermal material.

Brick Properties

Straus7 posts all brick properties as PSOLID entries. All properties are posted with property and material ID numbers, in large-field format. No property data is posted for PSOLID entries.

Brick properties always post a MAT1 structural material entry. Anisotropic brick properties post a MAT5 thermal material; other brick property types post a MAT4 thermal material.

Exporting Materials

One or two material definitions are posted to a NASTRAN file immediately after each property is posted, based on whether the user has elected to export thermal material data. One material is a structural MAT entry; the other is a thermal MAT entry. Both are given the same material ID (arbitrarily chosen to be the same as the parent property ID). NASTRAN solutions will use either the structural or thermal material definitions, depending on which solver type is being used.

Property Numbering

NASTRAN property numbers must be globally unique, whereas Straus7 property numbers need only be unique within that entity type.

Thus, property numbers are not conserved when exporting to NASTRAN format.

For example, a Straus7 model can have both a beam property 12 and plate property 12. In contrast, a NASTRAN file cannot have both a PBEAM 12 and PSHELL 12.

The Straus7 approach to exporting NASTRAN property numbers is as follows:

When exporting beams, export each beam property number directly
When exporting plates, add a multiple of 100 to each plate property number. This offset is used to ensure plate property numbers don't conflict with any beam property numbers. If there are no beam properties, this offset will be zero.
When exporting bricks, add a multiple of 100 to each brick property number. This offset is used to ensure brick property numbers don't conflict with any beam or plate property numbers. If there are no beam or plate properties, this offset will be zero.

This approach ensures unique property numbers, but still leads to recognisable property numbers. For example, suppose a model contains beam properties 1-63 and plate properties 1-12. These will appear in the NASTRAN file as PBEAMS 1-63 and PSHELLS 101-112. This is more useful than simply assigning the PSHELLS 64-75.

If the beam properties were in the range 1-112, the PSHELLS would then be 201-212.