Out of plane properties for satin weave

[tom787]

I am analyzing a composite (carbon/epoxy) component.
For the Hashin-fabric failure criterion (see attachment), some out of plane properties are needed.
We do not have time for coupon testing.

Specific materials are:
- Standard Modulus Carbon fibre fabric 5H Satin 370 g/m²
- Liquid Epoxy Resin 180°C curing RTM6

Available properties/allowables from spec are (MPa):
E11=67000, E22=67000, G12=4700, NU12=0.2
Xt=730 --> actual warp allowable is 750 but weft allowable is used for both warp and weft.
Xc=630
Yt=730
Yc=630
S12=70

Guessed values are (MPa):
E33=4500, G12=1600, G23=1600, NU13=0.4, NU23=0.4
Zt=58 --> tensile strength UD-fabric in weft direction @RT
Zc=170 --> compressive strength UD-fabric in weft @RT
S13=UNKNOWN
S23=UNKNOWN

Are the guessed values realistic and how can I derive the missing properties/allowables?
Any help is appreciated.
Best Regards,
Tom

 

[RPstress]

Zc will be higher than 170 MPa, but it's not a bad lower bound. (UD in 2-direction compression fails as if by the "log rolling" sort of behaviour: imagine standing on a pile of logs all pointing the same way; they can roll over one another and collapse. Real multidirectional laminates, especially cloth, are much stronger through-thickness.)

Other numbers look fine and safe.

Through thickness laminate shear cannot be easily estimated. Five relatively quick short beam shear tests on 2 mm thick specimens would give a reasonable value. In the absence of real data, 20 MPa is a very safe lower bound. They may well make 40 MPa and 55 MPa is quite likely a safe lower bound for carbon fabric/RTM 6, according to a major aerospace prime's acceptance test value. The same source gives 65 MPa average test result with a standard deviation of 5 MPa, which probably explains the 55 MPa acceptance minimum.

RTM 6 doesn't appear in MIL-HDBK-17, but googling for it should get you something, as it's such a commonly used system with a longish history. NB: the Hexcel RTM 6 datasheet doesn't give any laminate properties, but it may be worth contacting Hexcel anyway.

 

[tom787]

RPstress, thanks for your advice.
We'll run a damage/strength(!) FE for this material with a virtual textile simulating software.
Regards, Tom.

 

[RPstress]

Hmm, so predicting strength theoretically...is that from micromechanics-type methods? Let us know how that goes. Even fancy methods like those in GENOA seem to need some link back to at least some practical strength result.

 

[CompoMan]

My only comment are the NU values - for fabrics, I believed they should be much lower. Check out the typical fabric values from MIL-HDBK-17

 

[RPstress]

Well spotted CompoMan. I missed that nu = 0.2 for the basic woven ply. It should probably be nearer 0.05 or 0.06.

To get MIL-HDBK-17 (material properties are in Vol 2, currently rev. F):

http://assist.daps.dla.mil/quicksearch/

(This is the link cited on

http://www.cmh17.org/resources.aspx

.)

Enter MIL-HDBK-17 in the 'Document ID' box.

On the next page click on the volume of interest.

On the next page scroll down to the bottom and click on the pdf symbol next to the revision of interest.

 

[tom787]

Thanks for your inputs!

The Material Specification SM_5H_satin_AIMS_05-04-009 defines the requirements for the Standard modulus carbon fibre fabric, 5H satin, 370 g/m² (with or without binder) and toghether with the RTM6 liquid epoxy resin (180°C cure), this material is qualified for aerospace applications.(Cured ply thickness is 0.370+/-0.025mm and FVF 57+/-5%).

Looking at the MIL-HDBK, I believe that AS4-6k/3502-6S (4.2.16) and AS4-6k/PRO500 (4.2.26) are similar specs. However no NU values are given.

Poisson's ratio's for a textile composite can be low indeed since there are stiff fibre running in the direction of the transverse contraction.

It has been decided that besides our check in meso-FE, we'll perform coupon tests in order to validate the theoretical data.
Best regards,
Tom