Ply Orientation

General Composites Discussions Composites Talk
#1

Hey guys we are wrapping up our research work for our Carbon fiber monocque. I have one last question.

We have two types of dry Carbon Fiber to use.
6k 45degree orientation 2x2 twill
5harness 3k “plain weave”

What I need to know is? Should we mix and match the weave patterns?

What orientation should we use for the plain weave?
What orientations would you do if you mixed the carbon?

We did some destrcutive testing with one ply plain weave and one ply of the 2x2 twill.

And this was stronger than the 2 plies of 2x2 twill at 0 and 45 orientation.

I was initally think of using all plain weave. with 3 plies per side of our honeycomb. Orientation being 0 45 0 this would be a total of 9k of fabric per side of the honeycomb.

Help please. How does the ply orientation affect strength

#2

Without even understanding ply orientation, you could be in big trouble! In all honesty, it really doesn’t sound like the “team” is ready for a monocoque.

These are questions that are impossible to answer without seeing the model, how it’s built, and what parts are attached.

A great suggestion would be to make a tube frame and use carbon bodywork. Get some composites experience and do something more advanced next year.

#3

GOT FEA?
You’d save a lot of time material and money - by designing the monocoque/tub (in a good CAD program) then doing FEA of it for stresses etc to sort out your loads and ultimaty the fabric orientation!

If you don’t know what FEA is - then you’d be better off delaying the monocoque for this season! I second TET’s recommendation.

Cheers - Jim

#4

Edited: There are no worthless replies. All opinions and help is welcome.

We use FEA. The brand is MSC Nastran but we have also run the NEI Pastran to verify all analysis.
Then we did destructive testing to verify the software’s analysis on the same size sample panels.
THE TEAM has been building a monocoque for 4 years now.

Ill post an image of the 3d model that has been developed.

Now, back to the question at hand. How can we determine the ply orientation?

I ask because we are possibly straying off the “typically” path that has been done. We have 250yards of 3k Plain weave that we would like to try and use. But, in the past we have used 2x2 twill 6k prepreg.

Our destructive testing showed us that the a ply of 3k 2x2 twill with a 6k 2x2 twill at 45degrees is stronger than a 6k 2x2 twill prepreg with a 6k 2x2 twill 45degree layer of prepreg material.
This likely occured because the prepreg we have is not the best stuff.
But it is important to say that the method of failure was different. The panel with the one layer of 3k, split where the two prepreg layers permanently deformed.

#5

Gosh - I was in bed - (currently in Japan) so I must have missed something. :rolleyes: Maybe I can get the drift – given the editor’s comments in line 1.

BIGMANSM: If I sparked a flame reply - I’m sorry – and apologize , was not intended - simply the amount of details provided seemed to indicate to me that FEA either was not used - or not available. That you have it - and have done some testing shows due diligence. Had that been shared in earlier postings, I would not have asked.

So, I am still wondering why the fiber orientation remains a question - From your destructive testing - I’d guess that your prepreg might not be what you want to use. Given that it fails with 2 lamina of 6K and the 3K doesn’t = something is not right with the prepreg. I’ll defer to prepreg experts. (Poor cure temp? - bad lot - maybe thats why its free?)

Look forward to seeing the CAD/FEA output if you can share. The testing results would be nice too - do you have a website up you could share? Maybe that would be easier than dragging it all here?

Cheers - Jim

#6

I am waiting on the chassis designer to send me some JPEGS
I am slo waiting on the guy in charge of the FEA and destructive testing to give me the webaddress he is using the host the pictures of the destructive testing.

From what it seems. The prepreg panel had a core failure and it was NOT the carbon. As to where our infusion panel had the carbon fail.

We are going to do some shear testing, insert tearout testing with different plies.

I know the plies help with the shear strength. They also help with the deflection of the panels. I was just hoping that someone would be able to chime in and help us determine what orientation we should go with for the plain weave panels and if it would be advisable to mix the plain weave with the twill carbon.

I have received authorization to post all our data now that we have finished our CDR (critical Design Review).
I will also take pictures of our infusing testing we have been doing. its very interesting stuff

#7

are you using film adhesive for your core? and if so what s the GSM of it?