Composites Failure Question

[mathlete7]

Hello,
I have a question about interlaminar shear failure of composites, specifically pertaining to finding an appropriate interlaminar shear stress using Nastran.
I'm analyzing a carbon fiber overwrapped pressure vessel (COPV). In the region I'm looking at I have modeled two plies; one 17 deg ply and one -17 deg ply.
The nastran output gives stresses/strains in the fiber and matrix directions however gives interlaminar shear in the defined elemental material direction (0 deg in this case).
My question then is would it be appropriate to RSS the shear stress in the XZ and YZ directions to establish a maximum interlaminar shear stress? Is there some transformation that should be applied to yield the max interlaminar shear stress?
Any advice would be greatly appreciated...
Thanks much

 

[plasgears]

In the end, you need to test this thoroughly. Analysis is fine, but it doesn't acct for all the nuances of the details.

 

[RPstress]

I think, yes, you can root sum square *interlaminar* shear stresses this way.

Nastran allows use of an allowable interlaminar shear stress. It might pay to check out how this is handled. Does Nastran do an RSS to compare with the allowable?

A pressure vessel shouldn't have that much ILSS knocking about. Are the values significant?