Some follow-up questions:
Excelent post TET! I really like to see that power of using core. Beautiful!
Also, please notice the first two test. Fiberglass vs Carbon. Show that to customers that don’t understand why real carbon parts are more expensive and so much stronger.
problems with honeycomb are mostly in the realm of infusions. You can’t really use it in a VARTM/RTM part because the resin will just fill the holes. It’s mostly used in pre-preg, or the skin layers are bonded on the core with film adhesive.
Also, when bending it, say down a simple 45deg bend. The sides of the core that aren’t being bent down, will in fact bend UP. Foam cores if flexible enough, will just bend one way. There is a name to this effect, but I do not recall it.
Film adhesive, not plain expoxy? How does that work? For all types of honeycombs or just metals?
I didn’t really grasp the bending point.
film adhesive normally has a carrier layer (FB scrim, or even a woven layer), so it won’t flow like an epoxy. You can just lay the sheet of film adhesive over the core like a layer of fabric, and cure it.
as for the core… Let me try to explain this way. Visualize you are holding a 12" square honeycomb core. Grab 2 sides, and bend the core down. The 2 opposing sides will curve UPwards. Verses a sheet of paper, you bend the 2 sides down, and it has a nice simple curve.
So what you’re saying is if I bend paper it’ll look like a U but if I bend foam core itll look like W?
If possible could you show a picture? I’m extremely interested in this effect
I will see what I can find in the store room and take some pics…I did find this link.
http://www.cstsales.com/media/VacBag/Flexible_Honeycomb.jpg
you can look at the edges, and see that the bend core isn’t flat on the rounded side. Best I can find :-/
OHHHH I see what you’re saying.
If I have a square piece of core and I put my hands on the left and right sides, when if I bend those downward the side facing me will bend up.
Although I’m not an expert I think that has to because of the bending moment. The top surface is under tension and the bottom section is under compression. Therefore the top will pull and the bottom will push to maintain equilibrium? Definitely interesting though. Thanks for sharing that information
Suuuuure!!! something like that 
I think there are some honeycombs (as noted while look for pics) that are designed to bend smoothly. Shaped non-traditional, but gets the job done.
you don’t happen to have the force vs displacemnt graphs for these samples do you? I’d love to take a look at them to compare the stiffnesses. i’d also love to know the cross sectional dimensions.
I’m currently doing the same type of testing but with unidirectional, 2x2, and a mixture of both trying to find theb est resistance to bending without using a core. I’m also playing around with adding sleeving material in both carbon and kevlar materials.
I should start testing within the next week, and i’ll be happy to post up my results as well.
Please do, post up any photos or findings…
Yes, I have the graphs for each test. But that’s why I put the force and displacement values on the images.
As for max stiffness, unidirectional carbon in the orientation of the load will get you the best result.
yeah, we have several samples of unidirectional that we will be testing. the sleeving is there to try and deter delamination between layers and to resist any torsional forces our prototype piece (not the test samples) may incur.
will you be doing a 3 point bend test similar to TET or different?
yes, 3 point bend testing.
Is there a standard material sample length and width when doing 3 point tests for composite materials?
Awesome, is there a reason why you are not doing it with epoxy? I thought that was the strongest combination.
ASTM D 790 - 03
ASTM D 6272 - 02 for 4pt. bend
it mostly all depends on thickness, which changes the W and L sizes. Also, sometimes depends on fiber ori, but not always.
