Transversely Isotropic?

[Chantzypoo]

The question is, can I treat a Carbon/Epoxy pre-preg fabric as transversely isotropic? If not, how do you determine the shear modulus of the fabric, G12? MIL-HDBK-17 does not list G12 in the tables of properties for various pre-pregs, so I assume there must be an easy way to determine it, such as G12 = E21 / 4 ?

In terms of using micromechanical analysis, all the information I have been able to find is for unidirectional fabrics, and I don't feel the same theory is necessarily valid for woven fabrics. If anyone has any insight on this, it would be much appreciated.

The weave is a 5 Harness Satin is that helps.

Thanks.

 

[SWComposites]

I don't know what version of Mil-17 you have, but G12 values (0.514E6 msi at 70F) for AS4/3502 5HS fabric are given on page 4-151 of Volume 2, Rev F. You cannot calculate G12 from the axial modulus values. Typical G12 values for CF/epoxy tape and fabric are in the 0.5E6 - 0.7E6 msi range. If you have data for a similar tape material you can estimate the stiffness properties of a fabric by entering a [0/90]s laminate into a composite laminate code.

 

[Chantzypoo]

I am indeed using an old version of hdbk-17. I have decided to go the micromechanical route to get an individual ply characterization, and then approximating the weave as a 0/90 laminate. Thanks for the reply.

 

[RPstress]

Barbero's CADEC is quite good for micromechanics. The software is free with his book, which is worth having.

 

[tstanley]

Regarding Chantzypoo's question, are there any software programs out there that will actually calculate the properties of an individual ply made from a woven fabric? Something that would take into account the type of weave, fiber pitch, etc., etc. that you can then insert into the laminate analysis. Patran laminate modeler, Fibersim, Anaglyph kind of indicate they can, but don't say what the calculations are based on, at least in their sales literature. I have wondered if they just take the same approach as Chantzypoo decided to do and approximate the weave as a 0/90 laminate.

Tom Stanley