Laminate Sample #44: Prepreg Carbon with Rohacell Cored Stiffeners

This sample is a thin carbon panel with stiffeners formed over Rohacell (PMI Foam) core. The idea here is to show how panels can be stiffened with stringers or omega-style cored beams that are interleaved into the layup. The Rohacell 71 IG-F used here is very stable and will not deform at the temperatures required to cure the prepregs.
The base laminate is [0/90,90,+/-45,90,0/90] and the stiffeners have unidirectional reinforcements in the [0] direction.
For more information on Evonik Rohacell cores:
performance-foams.evonik.com/en
For more information of Gurit prepregs:
www.gurit.com/en/our-business...

[@allisonpower2594]

Thanks for the great detailed info. Clear and concise. I appreciate your efforts.

[@AboutComposites]

excellent work

[@fullsendmarinedarwin7244]

This is awesome. Be so cool to see a hull made this way but man it would be some work!!

[@ExploreComposites]

Some ocean racing boats replace core with solid laminate and stringers in the forward hull - to help reduce damage from slamming into waves. Often the stringers are molded off the boat and bonded in but there are probably some quite similar to this in construction. And yes - a ton of work!

[@fullsendmarinedarwin7244]

@@ExploreComposites I used coosaboard core in my boat build for the stringers etc, good stuff but it's so itchy it makes sanding fiberglass feel like candy floss :) Hand layup epoxy and biaxial. heavy way to do it. next time I'll try to use vacuum techniques

[@GrantOakes]

Cool

[@angstromperformance]

I'm wondering why you are using the peel ply and stack that sucks epoxy from the prepreg? Are not prepregs at the perfect resin to fabric ratio? Normally I see most prepreg stacks just have a non perforated release film and then vacuum bag. So was wondering why the different stack makes sense here? Thanks for the answer!

[@ExploreComposites]

That is a good question! The bleed is done here to make sure the air can escape from the curing laminate. My rule of thumb is that in an autoclave with several atmospheres of pressure, you don't need to bleed off resin to get air to not be a problem. But without an autoclave - especially with core and thicker parts - you should allow some resin to bleed off and that this helps. (This is a very common approach in most of the factories I have worked in or visited.). For thin (less than 1mm) parts that are well debulked, it is fine to not bleed resin off - sometimes this helps with cosmetics - this is probably what you see most. Check out my Laminate Sample #12 for some "semipermeable" Dahltex membrane to let air out but no resin. kzbin.info/www/bejne/rYbMg3uYZb6FeZI The resin content of the biaxial here is quite high and the weight of the resin bled off is probably less than 15g total for this small sample. The woven bleeder is very thin and doesn't take up much resin. If average resin content is 40% this sample probably bleeds off about 10% of that resin, so the overall ratio ends up around 35%, which is fine. It is common to measure and then calculate how much resin you bleed off using a certain combination of perforated film and weight of breather. Used consumables can be weighed and the uptake of resin calculated. In very general terms, keeping resin content above 32-35% for mostly unidirectional carbon is a good place to be. It is totally possible to bleed too much!

[@angstromperformance]

@@ExploreComposites thank you so much for the answer. I knew I had to ask. Thanks for all of these videos, I’ve learned so, so much from you! Keep making these awesome gems ❤️🤘

[@botoepfer8588]

very nice,, ! what leak detector do you like ?

[@ExploreComposites]

I have a few of the Amprobe ones which I like but the headphone jacks are delicate. I just get used ones but have used nice expensive units but the real big thing that helps are good padded over the ear headphones to block outside noise - which you can plug into most detectors that come with cheap headphones.

[@Anton-zb9dc]

Hey, what do you think, how would this foam feel in direct contact with a skin. Does it fill similar to polystyrene foam? If you could find something more similar I'd love to know

[@ExploreComposites]

This foam is very hard and almost sharp. It does have a similar brittle sharp feel to the blue Dow Styrofoam that comes in big billets - but more so. Not something I'd want to spend lots of time in direct contact with...

[@Anton-zb9dc]

@@ExploreComposites, I am new to foams and foam cores. It would be interesting to know how does it compare to some rigid pour pu foams

[@charliegates1088]

What is that device you used to check the pressure was holding?

[@ExploreComposites]

Its an absolute vacuum gauge - digital. Very handy tool. This one is a Greisinger GDH 200 - its pretty old. They make a newer smaller one now.

[@Kicker700]

Where do I find that adhesive sheet? Can you do a video on the types of fittings you like to use?

[@ExploreComposites]

The sheet is “film adhesive” and it is just prepreg resin of a certain weight. This came from Gurit by way of Composites One.

[@ExploreComposites]

Fittings: explorecomposites.com/articles/tools-and-equipment/vacuum-stuff-hoses-fittings-and-accessories/

[@charliegates1088]

where can i find that caclulator you used at the start of the video?

[@ExploreComposites]

The spreadsheet? Its just a template I use for these samples...

[@russellmiller2564]

Do a primer video on NDT techniques of composites!

[@ExploreComposites]

It’s something I’d love to do! The little Flir camera works surprisingly well for seeing voids and core details. And you can learn quite a but just tapping but its not exciting to watch. Need to borrow some better gear to show things that actually work. I bought one of those very cheap ultrasonic thickness gauges and it seems to work fine on metal but is absolutely useless on composites!

[@russellmiller2564]

@@ExploreComposites I think what’s likely happening is the frequency of the signal is way too high. I recall reading that ultrasound typically used for metals is on the order of a 20 kHz signal, whereas composites need a 5 kHz signal. (Or are these in MHz? I don’t know) it’s got to do with the acoustic properties of the materials, and the size flaws you are trying to pick up Thanks for trying the cheap(ER) instrument, I’d always wondered if that would work. Now you saved me learning the same lesson! Really enjoy what you do with your channel

[@ExploreComposites]

@@russellmiller2564 The one I have is 5mhz and the model is TM8812. Works great for metal, and sometimes works in expected ways on dense composite, but just when I think there's a pattern and that its just not calibrated for the right velocity - it shows unexplainable results and I give up. Needs more testing, but I'd love to get something that shows the waveform - just so much more intuitive and interesting.

[@patrickstroupe4769]

What is the tan layer you put down first on top of the metal base. I've seen you use this before in other vids and nothing seems to stick to it.

[@ExploreComposites]

It’s adhesive PTFE release film. explorecomposites.com/articles/tooling/adhesive-teflon-its-awesome/

[@ExploreComposites]

Good stuff! No need for chemical release agents.

[@patrickstroupe4769]

Thank You! I saw the list of suppliers at the bottom of the article. Who did you get your material from?

[@ExploreComposites]

Probably Taconic. Composite Envisions and RockWest in the US sell it by the yard I think.

[@patrickstroupe4769]

Thanks!

[@Anton-zb9dc]

Hey, but what about pressing hard with the thumb on rohacell foam, will there be a visible dent left or not. What about pressing with fingernail?

[@ExploreComposites]

It comes in varying densities - and the light stuff will dent with a finger. This will easily dent with fingernail pressure but quite stiff and brittle over larger areas.

[@MonstroLab]

3d printer bed heater is a great idea I think ill try shine a hot lightbulb at the bottom of my mold made from a 1” glass coffee table

[@ExploreComposites]

Heat lamps are great, just be careful of the whole fire issue! I've had some scares with hot bulbs. Is there any risk of breaking the glass by heating unevenly? I guess table tops are probably tempered glass...

[@MonstroLab]

@@ExploreComposites great questions I didn't consider. Testing soon. Hopefully 3' long by 2' wide 1" Glass mold doesn't distort much when lightbulb heated.

[@bitsurfer0101]

Can you buy just the PMI foam offcuts?

[@ExploreComposites]

It is a hassle to buy a small amount of Rohacell - and $$$! These were from a job I worked on long ago where we used quite a bit of it.

[@CCROSS5882]

I don't like it! LOL great work Chris

[@ExploreComposites]

Me neither Jerry, me neither! Thanks!

[@laptopasus4788]

apa nama plastik warna biru yang anda gunakan di vakum

[@Jimmy_Moon]

I thought I was listening to theradbrad for a moment.

[@TariqKhan-77]

I saw a few of his videos and for sure thought it was the guy from BoatworksToday.

[@noe616]

This is a complicated and long process that is only applicable to aerospace work. The waste is considerable and certainly can't be considered a green process.

[@ExploreComposites]

Oh for sure! So much composites work is very wasteful especially as things move up the performance/weight curve. It is a fundamental problem that needs lots of attention and effort!