How to create voids PURPOSELY to test for NDT

[pkiskool]

Hey, I'm doing some NDT research here at my job and my boss has asked me to create artificial voids within the carbon panels using prepregs. I've tried two methods thus far which both didn't work:

1)I've tried curing small sections of a prepreg sheet by sandwiching it between two aluminum sheets with cut-out sections, and heating it in the radiation light source (so that the cut-out section will be cured, but the other parts won't since the UV will reflect off the aluminum sheets). I successfully cured the small sections of the prepreg sheet, then I laid this sheet up in the middle of a regular prepreg layup and cured the entire thing (with vacuum) in the oven hoping that would create a void somehow: but no, every layers sort of cured together, I couldn't even see the pre-cured layer.

2)This time I took 2 pieces of a small cured prepreg parts and stacked them together. I then sealed all four edges with a sealant tape and inserted this "pocket" of cured prepreg in between my layup of 14 prepreg plies, then cured the entire thing. I was so sure that this would create a void inside the panel, if not at least a piece of tape in there for my NDT device to pick up, but no, everything sort of melted together again and there is absolutely no void, no tape, na-da.

Anyone know a effective way of creating an artificial voids?
My NDT device is an infrared camera, FYI.
Panel must be made of prepregs as well.

Thank you all.

 

[pkiskool]

Breaking news; I cut a little beaver-tooth out of the panel, and it separated in two like the red sea.
Definitely created a dis-bond, just didn't notice until I cut out the piece.
So in a summary, a pre-cured prepreg sheet wrapped in a Teflon tape or blue Flash tape worked.

Too bad that our IR camera doesn't seem to pick up the disbond however...
Anybody worked with Infrared NDT?

 

[ESPcomposites]

Though processing is not my field of expertise, I have seen Teflon inserts used at at least two major companies to simulate delamination.

Again, I am out of my expertise, but when it comes to NDI, the methods are not perfect. If there is not a physical separation between the parts, I don't believe you can easily detect the delamination.

Now, here is the problem, just because there is a delamination, does not mean there is a separation. It is very possible to have "kissing" surfaces actually making contact with each other, though the have no ability to resist shear deformation.

Perhaps that will help to understand the situation.

Brian

http://www.espcomposites.com

 

[berkshire]

pkiskool

Have you tried ultrasound instead of IR. I think you may have a better chance of picking up the back face reflection of a dis bond that is close. Especially if you scan at a tangent.
B.E.

 

[Radagast]

pkiskool,

The defects were seen as voids/delaminations during scan. We have another set of test panels for FOD etc.

Mike