Composite Carbon Fiber Foam Core Hole Tests
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- čas přidán 24. 08. 2024
- The combination of carbon fiber fabric types and foam core hole and score line patterns can effect vacuum resin infusion. In this video we explore several carbon fiber fabrics with several foam core hole patterns and optional scoring of the foam core to see how the mold surface fill an finish is effected.
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I used to do vaccum infusion molds for boats, planes and some work with NASA. 19 years old it was the best job of my life.
Your videos aren't getting many views, but the content is excellent. Most builders don't appreciate the science you are demonstrating. Keep up the good work.
A lot of folks are just looking for entertainment. As you can tell that is not really what these videos are for. Thanks for watching.
Just seen the video. I use 3mm scored and perforated H80 divinycell, Biaxial 3oz +/-45 and 2x2 twill on both sides. Infused on glass, come out with a great finish. I do run a little stronger vacuum then yourself. Its approximately 5mm thick, very light, almost zero flex and takes a good impact for CF.
You have to pre wet out the bottom layer before vacuum bagging it, unless you use a more porous sandwich layer, like a honeycomb nomex. Also make sure you are using an epoxy meant for this. It will be a bit thinner.
Thank you for making this video series; much appreciated!
I think this may be too late. however for learning purposes, i used to do infusion with foam core some time ago. normally, i would have flow media and peel ply on both sides . this would ensure full wetness of the composite.
Well done and good scientific approach.
This is a great approach if you don't need a glass smooth surface on the mold side. You can still get a smooth surface after you pull the part but it takes more work filling/Painting and sanding. Another issue on the mold side is if the surface is very curvy. You have to take some effort to void wrinkles in the peel ply, but it can be done with only small ridges where peel ply overlaps and again filling/painting and sanding to hid the ridges from the peel ply. But if you don't need that smooth surface (like for bulk heads, ribs, etc) then putting flow media and peel ply on both sides is fantastic. Thanks for the comment!
Great Video and great edeting! I usually swich of my Pump and a little later clamp my resin
I have not tried shutting off the pump and total clamping. That might be another good experiment.
As you have intent to paint, instead, in your glass smooth mould, paint two layers of gelcoat in your desired color, then a 90gsm cloth, then two 200gsm, then a core with built in flow channels, then two layers of 200gsm.
Great example of the inquisitive mind of homebuilt aircraft guys...Now take it a little further, incorporate
more of your main structure in your outer covering thereby reducing the inner support structure, that
will reduce the total overall weight and allow an increased skin thickness for a better draw through infusion process... Light weight means putting strength only where needed, takes a more detailed
analysis but can give better results.. That is the main advantage of composite construction...
Interesting video. If you intend to replace aluminum sheet metal you may have sufficient thickness of sandwich to eliminate some of the bulkheads including rivets. This gives you some reserve if you simply compare the sheets.
Great subject and great tests 👍
Use rohacell. For a good finish start with a 80g-100g glass fiber layer. Making holes in the foam core is a mistake (sucks epoxy for no mechanical benefit). Infusion isn't suitable if you wish to wet both inner and outer layers simultaneously. Finally you consider that paint coating weights 10g/sqft. I use less than half. All together your 1sqft finished sandwich (2x200 carbon + 1x100 glass + 3mm rohacell + paint) should weight less than 65g without optimization, and around 55g after fine tuning the process.
Mr. Workshop
You love to "Think outside the Box" as I do.
You are very on track with something big in the way small aircraft are built.
I do think your going in the wrong direction....think "Flow Mechanics" in your testing.
I believe your holes in your cores are hindering the flow of resin.
As I am sure you know, anything that flows, water, gasoline, river, resin, will flow
to its least resistant path. The resin that is flowing while under vacuum is moving
in the direction of the pull of your vacuum. When the resin gets to a hole, that resin can not move forward
until THAT hole fills up, thus, stalling until. This happens at every hole the resin meets.
Scoring is more of a direction, from my experience.
Get a .062 (1/16") ball end mill. Setup this up in your router(table). With a fence setup, you can make straight, very accurate channels in the core.
.005 -.0010 deep. the full length of your core. The vacuum should be pulled PARALLEL to the channels. NO holes!
Now you have great Flow Mechanics.
Hope this helps!
Interesting idea. Thanks!
You dont want channels as that will mess with the final product finished surface and add weight to the resin.
Also the main stream packet sells foam with 1/8 holes on a one inch grid pattern.
The idea behind this is not to get flow but to get full and equal saturation of the part with the least amount of resin possible.
You can buy pree cut foam with groves not need for the extra effort but that is not the purpose of the scores its there for flexibility and i get your point but i dont agree.
And the rest of the yacht industry has been doing it with foam with small holes for a long time.
What about just using prepregs so that you can specify the exact percentage of fiber and epoxy? You will get the lightest, strongest structure possible in the final product as the epoxy is controlled from the get go.
If you are considering an electric powered part 103 ultralight you may consider a glider like design with high aspect ratio wings, a very bullet shaped cockpit and a narrow boom out to a T tail. High aspect ratio wings are long and narrow and produce the most amount of lift. Using carbon fiber is perfect for an ultralight as you only have 254 lbs of weight to work with and the hardest part to comply with is the very low stall speed of 24 knots (27.6 mph). Carbon fiber give you ultimate strength and stiffness at the least weight possible. You may consider the Burt Rutan Quickie (Q1) as the front canard/wing houses the landing gear at the wingtips decreasing drag significantly and the empty weight is 245 lbs so it is already an ultralight. The Quickie cannot spin or stall, the front wing/canard stalls before a full stall of the aircraft develops, the nose drops, and it regains flying speed. The Quickie has two sets of narrow high aspect ratio wings for great lift. The other great aspect of many of Burt Rutan's designs is that no tools/molds are needed as the aircraft is built with hot wired foam to form the shape. Burt Rutan is an aeronautical engineering genius who has dozens of amazing aircraft to his credit. Your issue with an electric ultralight is the weight of batteries, while the FAA allows for 5 gallons of gas you will have to have much more weight in batteries to have the same range as 5 gallons of chemical energy. If your end goal is an environmentally friendly design you may consider a small single/twin cyl diesel engine, but instead of running the engine on diesel you can use B100 biodiesel or waste vegetable oil instead of using batteries. I hope this helps
Thank you I appreciate your tests.
Perhaps I missed it. How heavy is the viscosity of the resin?
When I'm doing core composite I often find it easier to do it in two steps. I do my first layer, then do the foam with another layer or two. Complete wet-out it's much easier. And it comes out with less weight since you're not filling more surfaces of the foam with holes and scores. Also hot knives and hot wires or punches work much better and cleaner. You take your piece of plywood drill your holes and take your wire plunger and poke through them. It's a much cleaner consistent hole with a extremely smooth surface, which is the idea. The less resin the stronger and lighter the part. That's the whole idea behind the low crimp fabric also.
Now with Zylon and textream your part could be just a stiff without the foam and even stronger. The money you save on foam could go towards the extra money spent on the fabric.
Thanks for the suggestions. I do appreciate it. I've been accumulating suggestions and hope to make some more videos experimenting with the suggestions.
The resin I used (if I remember correctly) was Proset inf-114. The hardener was Proset inf-211. The mixed viscocity is 296 cp. at 72*F.
Nice idea clarify the infusion process for divinicel sandwich. But the question is in tension text what's the max load for panels and in flex or buckling string load. It's possible to define easyly?
Love your work mate.
aaand subscribed. Great Video! I really like your scientific approach.
Thanks. I'm frequently tempted to just try something to see if it works instead of trying to unders it first. But my engineering mindset will not let me. :)
You should have been the one to test the submarine materials so they wouldn’t have imploded it.
I could have missed it, but it seems you never mentioned what kind of resin you're using. Is that a proper low viscosity infusion resin? It is another important knob you can turn in you experiments.
I probably did forget to mention it. I've been using the infusion resin Pro-set with the 114 resin and 211 hardener. Your timing is also pretty good. I've recently purchased a new infusion epoxy that is a house brand of Composite Envision's. I had purchased it to have a thin and inexpensive epoxy for creating my plugs but I will also experiment with it on my composite samples.
Loved the vided, but one production suggestion, turn down your mic gain - you are overloading your preamp and distorting the audio a lot. Hard to listen to it.
You are such a cool guy. You've made me subscribe to your channel. Thanks for the help man
Thank you very much for the subscription. It is greatly appreciated.
Findings
maybe 4 to 8 layers of carbon fabric adds a lot of stiffness and may not be eligible for boat building compare than to the 2 layers of carbon fabric and yet with minor vacumm psi pressures may be directly supervised as before to decide it yet onto the qualified flexible structures for boat building
me;
Not a boatbuilder nor an Aerospace Engineers but I study from these as a non-academic learner as yet I better to decide with S Glass grade Fiber Reinforced Polymer for its desirable qualities as yet the ballistic stoppage capabilities may not found any of the highest grade on the Carbon Fibre composites, but the S Glass research may have strong eligibilities from it
I could have guessed the surface would not fill any better after that mold sanding as it is not going to affect the viscosity of the epoxy which is really the cause. Probably an ultra low viscosity epoxy would make a difference. The sanding most certainly made it hard to release from the mold. There are a number of things epoxy doesn't really stick to unless you sand them- at which point it absolutely sticks.
I had heard that one way to ensure that the weave is filled with epoxy at the mold surface is to reduce the surface tension of the mold and one way to reduce the surface tension is to lightly sand the mold surface. But what grit to use was not mentioned or anything else about surface prep was not mentioned so I took a guess and gave it a try.
I also saw an interesting high viscosity epoxy intended for infusion that worked really well (I saw this at Oshkosh in 2019). I think they must have some additive to help it flow and I wonder if was something to reduce the surface tension?
@@Designer103 Here is an example of ultra low viscosity epoxy available in up to 3 gallon sizes. Its viscosity is 195 cps (centipoides) atcepoxy.com/wp-content/uploads/CRACKBOND-SLV-302-TDS.pdf Whereas the typical low viscosity epoxy has a viscosity of 600 cps. (See MAS epoxy) West System with fast hardener is 975 at 72 degrees. With their slow hardener its 725 cps, and their extra slow is 760 cps. You can see the big difference. Water of course is 1 cps. So much for those who think their epoxy is as this as water,
Which configuration has the best impact damping properties (sound deadening)?
That is a great question. But I don't have an answer for you. I have not done any testing along those lines. I'll have to think about that.
How about testing eGlass and sGlass, just for fun. The results might surprise you. After all the Rutan designs used it. I'd also like to see a comparison between Divinycell and 40, 60 and 100 PSI Dow type foam.
I think that I will test with some glass. After thinking about it I'm beginning to wonder if fiberglass might be a cost effective alternative for the inside side of the skin. Yep, I think some testing is in order. I will be getting some Dow foam when I start making my plugs. I'll do some testing with that at least for a possible foam core alternative.
@@Designer103 Don't forget that when you mix two different composites together, it's like a chain. It is only as strong as the weakest link. Once/if the fiberglass breaks, your carbon fiber layer will have all the stress to deal with by itself.
Does 2 ply mean 2 lots of 2 twill on top of each other and 4 ply 4 lots of 2 twill on top of each other and so on?
That sounds correct.
Ultralight Airplane Workshop ayes looked at another one of your vids and could see that was the case, thanks for the reply 👍🏻
I've been doing this stuff for a long time and I'm learning lots from you. Great viedos! At what point are you measuring the vacuum? Thanks
I'm measuring the vacuum at the resin trap. I also have a gauge on the vacuum pump. Thanks for watching. I'm learning all the time. I think that is the way it should be.
Why not apply the epoxy to the fiber by hand prior to sandwiching?
By using vacuum infusion you should be able to have the correct fiber to resin ration every time where adding the resin by hand has significant variability. By having consistent and predictable resin/fiber ration you can reduce the structure safety factor and thus make the structure. But with hand application of resin you should use a large safety factor which makes the structure heavier.
@@Designer103 I think what Davis is suggesting is to wet the fabric by hand first, layup the sandwich, THEN assemble the vacuum materials. What I have done is use 2 layers of clear construction plastic. Lay the plastic sheet down, put the fabric on it, wet out the fabric and work with a roller/squeegee, put another layer of plastic and then squeegee out all the excess resin. Peel off one layer of plastic and then apply the fabric side to the mold, peel off the other layer of plastic, put on the core and then another layer of fabric using the same technique. Put together your vacuum materials and a couple hours later you have a FANTASTIC laminate! Basically you're making a wet version of a prepreg.
I have also been working on light sandwich infusion for sailing boats. My core is 80 or 100kg pvc foam with 2mm holes at 20mm centres and no grooves or scoring. The foam preparation includes screeding the foam cell surface quite hard with epoxy filler first which is done 1 side at a time and then blow the filler back out of the 2mm holes while still wet. Then sand the cured foam surface clean and check all the holes are still clear. Set up the whole laminate and then infuse. I believe this saved about 290g per sq metre compared to just infusing resin only into all the surface cells. On our 9 sqm hull the saving was about 2.7kg.
Thank you for the videos and the information you're sharing. Have you thought about testing 3D Core for your core cell? It has a hexagonal shape, supposed to help a lot with infusion.
Thanks for bringing this product to my attention. I had not seen it before. If I can find a sample I'll give it a try.
@@Designer103 Easycomposites.uk has some. shop.Hp-Textiles has lots of different core and 3D Core selection. They are both in the EU though.
@@Designer103 3D Core is an excellent infusion core, but for this application, it might be overkill (and expensive overkill, at that!). I would suggest that you definitely need an infusion core material, but something like Lantor Soric SF might be better, and at less than half the cost of 3DCore. Alternatively, you could look at a Two Hit Infusion process, starting with the mold side.
Great video. Question: What do you precoat large cell blue syrofoam before lay up with carbon fiber? Also. would you use the the same technique to epoxy two pieces of large cell syrofoam together?
My only experience with large cell blue Styrofoam was back in the 1990's. Since I was doing a hand layup I did fill the pores of the foam first. I tried a micro balloon slurry and an epoxy filler from Aeropoxy. My testing verified that they saved weight over just doing nothing (since the epoxy alone filled the pores during the hand layup). But they were a pain to deal with since they added significant time to wait for the filler to cure and then sand, and in the case of the epoxy filler, added money. I ended up using the Aeropoxy filler since it was easier to sand. I've heard that there are better fillers on the market now but I have not looked at them so I can not really help with that. For adhering two pieces together, I used a micro balloon slurry. The adhering part worked great. But you have to be very careful that you do not get slurry all the way out to where you will be sanding the surface. The slurry, when cured, will create a hard ridge at the surface that will not sand easily but the foam does sand easily. When sanding you will create divots on each side of the ridge. What ever you use for adhering two pieces of foam you have to be sure that the shear strength of the bonding compound is greater than the shear strength of the foam. It would also be nice if the elastic modulus was similar to the foam but that may be hard to find. I did not really give you a direct answer but hope I've helped with giving you some things to consider. If you like to experiment you could try Aeropoxy Light Filler. It was one of the recommendations I heard about while attending Air Venture 2019.
@@Designer103 thank you. This helps.
Do you have to worry about the foam having a different rate of thermal expansion/contraction than the carbon fiber?
That is a great question that I've wondered about myself. And I've never heard it addressed. Let me give you my opinion. And it is only and opinion. Not backed up by direct knowledge. I think that the foam has enough flexibility to handle a certain number of thermal cycles before the difference in thermal expansion becomes a problem. At least on parts the size of our ultralight airplanes. What that number of thermal cycles would be, I don't know. But based on the number of airplanes our size that have been built and flown for years I'm guessing (only a guess) that at least a decade for "normal" fight activity. I know that this does not really answer your question but until I find some information the issue this is the best I can do.
use a piece of glass to lay up on you see resin penetration
I've done a couple of videos using acrylic with a view of the under side. It is always interesting.
What infusion resin are you using?
Whats its viscosity?
For some reason my replys keep disappearing. For most of these samples I used Pro-Set 211 hardener and Pro-Set 114 resin. This Epoxy in designed for the infusion process. You'll be able to find the viscosity numbers in the data sheets for these products.
You are designing/building an ultralight and you worry about speed?
Why not just web the bottom layer with right amount of epoxy before infusion. I am sure it will use less matrix than going the holes/channel route.
Wetting out the bottom layer before infusion is been suggested several times. I have not tried it yet but I will. Thanks.
As for worrying about speed of an ultralight, from the perspective of most pilots that fly faster airplanes I can certainly understand thinking that the difference between 45kts cruise and 55kt cruise is only 10 kts and is not worth thinking about. But going going from 45 to 55kts is a 22% reduction in flight time to get to a destination. That is significant. If I can use composites and some good design to keep the drag down at 55kts that is a big win (assuming I dont count the material cost for going with composites).
Thanks for your comment!
Hi, I have learnt s lot. Can I import carbon fibre cloth from you to Africa?
Hi James, I don't sell CF but I'm sure some distributors can send it to you in Africa. Give these folks a try: compositeenvisions.com/
By making the holes you're just making it resin Rich it's not making it stronger
You should try impregnating the foam with epoxy. It would make it extremely heavy though.. so maybe don’t do that
I've been wondering about skimming the foam with an epoxy tooling filler that would be light weight and then doing the infusion. It is possible that trapped air under the filler would expand and cause problems so have not tried it (yet).
62g/ft2. the easies way to piss of the metics & the imperialists at the same time lol
I had not thought of it that way but you are correct. lol