I'm trying to understand how 2D solid elements work. I want to study the local buckling of a simple aluminium pipe with thin walls. From what I understood, I can use 2D solid elements and model just a section of this pipe .

I've drawn a surface on the XZ plane (Z axis of simmetry). This surface is just a long but very thin rectangle that rapresents the pipe's wall. The pipe is open so no caps etc. I applied the property 2d solid axisimmetric, my costrains and my loads. I then created my mesh with quadx elements. In analysis, I selected SOL105 for bucking analysis.

When I run Nastran, I get some errors, the first one being:


Indeed, checking the bdf file, there's no property to be found, nor the material definition!

I tried to group elements with no properties in Patran, but it found none.

What am I doing wrong?

Thank you for helping me out.


1 Answer 1


You almost certainly selected the wrong element type, and then didn't set up the special material data it needs. To quote from this online Nastran manual

The CTRIAX and CQUADX elements ... are fully nonlinear elements supported in solution types SOL 106 and 601 but only support hyper-elastic material defined on the MATHP bulk data entry.

(My emphasis). Aluminium is not a hyperelastic material. For a linear buckling analysis, the element type you probably wanted was the CQUADX4.

  • $\begingroup$ in the nastran referece guide there's no CQUADX4, only CQUADX. When I create the mesh I do select quad4 elements for my axisimmetric elements and I get CQUADX. I'm using MSC Nastran 2018 $\endgroup$
    – gbos
    May 18, 2019 at 12:20
  • $\begingroup$ Your error message said "QUADX", and the manual I referenced describes the difference between a QUADX and a QUADX4. Sorry, but I'm not a mind reader. $\endgroup$
    – alephzero
    May 18, 2019 at 13:47
  • $\begingroup$ Yes but the manual you linked is for NX Nastran. Shouldn’t it be different from MSC Nastran? $\endgroup$
    – gbos
    May 18, 2019 at 13:48

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