08-23-2017 12:50 PM
Hi Everyone,
I'm very new to FEMAP/Nastran. I built a test model in FEMAP that consists of a simple cantilever beam with a pointload at the end. The visualizations yield the correct stresses, but the .f06 output shows stresses in the out of plane direction, which is inaccurate. I'm sure I've messed up the model somewhere, any ideas? I've attached the incriminating model and .f06 file along with a screenshot of the beam diagram (EndA pt1 comb stress). I'm using Femap v11.3.2 and NASTRAN v 10.2
Thank you in advance.
.f06 file:
Visualization:
08-23-2017 12:52 PM
08-23-2017 01:59 PM
hoc,
What are you seeing in the .f06 file that is making you think the stresses are out of plane?
I took a look at the .f06 and see the stresses for the 4 different stress recovery points along with the max and min.
08-23-2017 02:33 PM
Hi T_Giampietro,
Honestly the clearest result came from loading the associated .op2 file into Matlab with the IMAT toolbox, and taking a look at the stresses line by line. I may be misreading the .f06, but it looked consistent with the .op2 readout (I've attached the IMAT output below). I was expecting a stress tensor like this:
S = | s11 s12 0 |
| s21 s22 0 |
|0 0 0 |
but the output shows that s11 = 0 (which isn't true for XY planar beam bending), and that S13 and S23 are non-zero which shouldn't happen in planar loading either.
I'm equating the following .f06 values to matlab values: SXC = s12, SXD = S22, SXE = s13, SXF = s23.
08-23-2017 03:01 PM
From the NASTRAN Element Reference -
• The SXC, SXD, SXE, and SXF columns list the superposed stress resulting from both bending
and axial loading at locations C, D, E, and F of the cross section, respectively.
These are stress values at the stress recovery points on the beam, they are the simple combination of Bending Stress (Mc/I) an Axial Stress (P/A). They are not a stress tensor.
This is useful data, but does not represent the full stress state in a beam cross section. It is the reason we added Beam Cross Section stress calculator to FEMAP (View - Advanced Post - Beam Cross Section) functionality to FEMAP. This tool uses the forces recovered from NASTRAN - Axial, Bending, Shear and Torsion to do a full analysis of any cross section.
Mark.