Hello everyone, is Nastran calculating a shear modulus from Young's modulus and Poisson's ratio when I leave the value open in the bdf-file (Material: isotropic, linear elastic), or is Nastran ignoring shear stress as a result?

Question

I have been supplied with a bdf-file to run normal modes analysis. The material section states the value of 80769.234 for the shear modulus. I cannot find significant changes in the result after deleting this value, but I am wondering why it has been set in the first place.

$ Description of Material :

MAT1* 11010302 210000. 80769.234 .3

* 7.8499998-9

Florian.Kaa · Accepted Answer

Hello Tizian,

Please see the remarks of the mat1 card in the Quick Reference Guide:

2. The following rules apply when E, G, or NU are blank:

• E and G may not both be blank.

• If NU and E, or NU and G, are both blank, then both are set to 0.0.

• If only one E, G, or NU is blank, then it will be computed from the equation:

E=2*(1 + NU)*G

If this is not desired, then the MAT2 entry is recommended. If E, G,

or NU are made temperature dependent by the MATT1 entry, then the equation is applied to the

initial values only. Caution: Inconsistent E and G can result in NU >.5 which for three

dimensional elasticity results in negative stress for positive strain. This can cause large max ratios.

Best Regards

Florian