Parameter

Values

Description

SHPBCKOR

<1, 2>

Default = 1

PARAM, SHPBCKOR defines the type and order of approximation used in plate bending geometric stiffness for linear shell elements (CQUAD4 and CTRIA3).

1: First order approximation, expressed using displacement degrees-of-freedom in the geometric stiffness matrix. It is more numerically stable and includes both bending and transverse shear contributions. Being first order, this option may over-estimate buckling loads, especially when the mesh is coarse relative to the buckling wavelength (only a few elements per wave length).

2: Second order approximation, expressed using rotational degrees-of-freedom in the geometric stiffness matrix. This option ignores contributions of transverse shear to buckling.

Note:

Second order approximation is appropriate and provides better accuracy for buckling of thin shells, which is dominated by bending.

For thick shells or for composites with soft cores (where transverse shear contributions are significant), it is advisable to use PARAM, SHPBCKOR,1, which captures both bending and transverse shear effects. Since PARAM, SHPBCKOR,1 is more numerically stable, it can also help if there are difficulties in the eigensolver.