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Authors: Flyboy Wakesurf
We’ve completed the first cell of the test honeycomb (HC) and we wanted to share with y’all a couple of decisions that we made along the way. Now as an introduction, the BBBs (basic building block) that we molded using a single layer of 6 oz carbon fiber. Most likely you’re heard that carbon fiber is crazy stiff and if you’ve never worked with it, you might get this impression that it’s like titanium in these super thin layers. It probably is, but a thin layer of titanium can still be bent with your bare hands. Same is true with this carbon fiber structure. It’s really stiff, but it doesn’t take on the “stiffer than steel” characteristics until you build it up to about 3 mm or so. You know what it’s like? Aluminum. Aluminum cans or aluminum foil aren’t that stiff, because the material is thin. BUT pour the molten aluminum 3 inches thick like the shape of a brick and it’s crazy stiff! THAT’s what’s going on with a single layer of carbon fiber in a resin matrix.
Ok, so that said, who cares?! You do obviously! Remember that we started this project wanting to see if we could sort of test the concepts that would be made available to us with 3D printing. Well one of those things will be to actually print a HC internal structure for a wakesurf board. We wanted to attempt to create that structure using currently available construction techniques. Pop-outs (oh no!) and the creation of a honeycomb structure.
What would be different between a honeycomb we can make TODAY and something that was created using 3D printing? Well, for one, we can’t really effectively create a single HC structure from a homogenous material. With 3D printing, that’s easy. Design it. choose the material and then all of it would be the same material. But for our test, after we make the pop-out BBB section, we have to glue those all together to form a structure. That glue, will be slightly different than the carbon fiber and epoxy matrix.
So lets show you a picture of the final glued up test section.
We have glued the various crests together to form a single structure. You can see that we are holding it by the section at the top and the bottom is stuck to that!
Now you might think that the glued sections would be the LEAST STIFF areas because they won’t have the carbon fiber in that glue, it would just be epoxy or whatever we used, but that’s not the case! The crests of the two BBBs are like rail channels or the rails of our boards, those sections of complex curves make that area crazy stiff! The same will be true with a homogenous material structure, the complex bends will resist forces in specific directions very well.
So we sat with that for a bit and decided we would use 5 min epoxy to glue the sections of the BBB together. Here is the logic we used. Now we aren’t saying, at this time, that we know best! It’s strictly an educated guess at this point, and we’ll share that logic now.
Epoxy is a medium-soft plastic. Sadly you’ve probably read where folks compare a fiberglass wakesurf board with an epoxy wakesurf board and those folks are ignorant! They’ve mislead folks with their egocentricity. Epoxy is just a resin, fiberglass is used as the reinforcement in virtually all wakesurf boards, regardless of the resin used. Also epoxy is less stiff than polyester resin when cured. We’ve demonstrated that before in prior posts. The 5 min epoxy that you’ve seen at your neighborhood hardware store is almost junk! It’s flexible and adheres sort of OK, but it’s really bad as a glue. What it does well is glue together just about anything. Dissimilar material isn’t a problem. So that aside, we thought the flexibility of the 5 min epoxy and it’s ability to stick to anything, would be perfect for this test panel. In the final product there simply won’t be much flex in the core of the board. Well, at least we HOPE there won’t be!
We’ll need the joints to be able to withstand a bunch of flex cycles without separating, hence that somewhat flexible glue, plus the ability to adhere to whatever we created! Also a more rigid glue would NOT be able to withstand that flex, that is to say it has a lower flexural strength and we believe would tend to separate under load quicker than the 5 min epoxy we chose.
So here is a short unedited clip of our very rudimentary test of the cell to see if it would withstand all manner of forces in as many directions as we could come up with!
For our mobile enabled friends here is a link to that honeycomb flexural test.
Obviously the final product shouldn’t experience deflections anywhere near the level we subjected the test panel too. Maybe at most a few thousands of an inch, but not the level we demonstrated above, so we are thinking that so far we’ve made the right choice. Time will tell!
Did you notice something about the cell in that video? It displayed some of the characteristics of a hunk of EPS foam, didn’t it? Flexes all over and returns to the original shape. Now that cell is all open, but if it were sealed it would actually have more buoyancy than a section of EPS foam, because it’s so much air! We’ll talk more about that in an upcoming post.
So thanks so much for following along as we experiment with this honeycomb build. Oh! And also, thanks for keeping an open mind as we discuss the facts of pop-outs, carbon fiber and epoxy.
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