STRESS RESULTS FOR CQUAD4 ELEMENT IN MSC/NASTRAN

Hi,
you are right about this standard stress output of CQUAD4, but i think this is because CQUAD4 shell element models the membrane or plate problems. Hence the shear stress in teh z-direction (Tau XZ and Tau YZ) is negligible. I'm afraid, you should modify the CQUAD4 element using DMAP, to enable you getting the Tau XZ and Tau YZ, any comments?

regards

belondo,

Have you looked in the theoretical manual to see if the element formulation you are using provides transverse shear stiffness? If it does not, then you'll have to find an element in the standard element library that does, or modify your idealization.

Belondo,
What do you use for mesher? Patran, Hypermesh, FEMAP, or your defined ? I am using Femap and i am always getting all stress out (iam reading the stress via FEMAP too). I'ts probably because your model 2D (solid mechanics). FEM S2 Student: ABQ,NAS,COS,ANS,MAR,SAP,
STaaD,ETABS,GTSTRUDL, Civil Eng.
LOOKING FOR A JOB ....

belondo,

I just took a quick look in the NASTRAN Quick Reference Guide for PSHELL card entries. The 7th entry on the PSHELL card (MID3) determines whether or not transverse shear is included.

If you are using a preprocessor, look at the bulk data file it generates to see if the PSHELL card contains the material ID for tranverse shear.

For example, there should be a line in the bulk data file that looks like:

PSHELL PID MID1 T MID2 I21/T3 MID3 TS/T

Where,

PID = property ID
MID1 = Material ID 1 for membrane stiffness
T = thickness
MID2 = Material ID 2 for bending
12I/T3 = bending moment inertia ratio (default is 1.0 when this entry is blank)
MID3 = Material ID for transverse shear
TS/T = transverse shear thickness ratio (default is 0.8333 if this entry is blank).

Actual line might look like

PSHELL 5 1 .050 1 1

or

PSHELL,5,1,.050,1,,1,

Here the property ID is 5, the material ID for membrane, bending and transverse shear is 1, the thickness is 0.050 and defaults are used for 12I/T3 and TS/T. Note that the material properties are specified by the MAT1 card (for linear isotropic materials).

Bottom line, I think you're going to want to check the reference guide for the PSHELL and MAT entries required to get transverse shear, and also check the theoretical manual to make sure you are getting an element that behaves the way you want it to behave. Lastly, make sure the case control section of the BDF is requesting all available stress output.

Good luck