Drum Peel Test Coupon (sandwich) 1

[Cisnerjo]

Hello,

We are experiencing some low results on our mechanical drum peel test coupon, our drum peel test coupon is made using two plies of epoxy prepreg (7781 style fabric) on each side of the core which is .210" thick. We noticed production people uses several ways to build them, customer specification does not specify anything related with plies orientation or core thickness so it was noticed that some people build the test coupons placing all plies (warp face up)on the same direction always making sure the prepreg plies with predominant fibers (7hardness weave) run against the core run ribbon direction, while some others run the top and bottom plies with the fill face up and only the warp face against the core ribbon direction, checking the lab results both are pretty much the same but does any of you know any real or valid procedure to build a test coupon for drum peel purposes. I found on the internet an example which it mentions the skins against the core must run with predominant fibers against ribbon direction but don't know what about the top and bottom ones, should they run the same as the plies that are located against the core? or should be balance and be run with certain orientation in order to obtain better drum peel results? How can I improve our results? test coupons are Oven cured.

I'll Appreciate any advice or support on this matter.

 

[SWComposites]

First, standardize everything about the coupon layup. No exceptions, no layup tech creativity, etc. Period.

Now, do you have some previous configuration that produced good results? If so, standardize that configuration.

Are you using an adhesive? Or some magic self-adhesive prepreg?

I suspect that only the ply against the core is critical.

 

[Cisnerjo]

Hello SWComposites, in regards of standardize the procedure is something we are working at the moment. The configuration hasn't been changed except for the new requirements from out customer. Which increased the requirements. we don't use any adhesive at all there are placed two plies of prepreg on top and two at the bottom of the honeycomb core. We use epoxy prepreg 7781 style fabric.

In regards of your comment: I suspect that only the ply against the core is critical.

Do you consider that all four plies should run on the same direction? this is all plies with predominant fabric fibers run against the core ribbon direction? As mentioned before we tried to balance the sandwich that why we placed the top and bottom plies on the same direction as the ribbon while the plies that goes against the core the predominant fibers run against the ribbon direction.

 

[SWComposites]

Ah, so, the customer has changed the requirements. Hmm, I would a) demand they show you data justifying those requirements, b) define the specific layup to be used, which is consistent with the data.

Yes, in general I would lay all the plies up with warp fibers parallel to the core ribbon and loading direction. Though with 7781 glass I doubt it makes much difference.

 

[SWComposites]

Oh, and IMO the CDP test is a really crappy test for QC. It is not representative of any real loading, and has lots of test induced variation.