FRP Composite panels ( US Source)

[sprocket3]

In my view, avoid screws at all costs. They cause local stress concentrations when they resist differential expansion forces.
The secrets to adhesive use are: 1) Surface prep, 2) Appropriate primers, 3) Maximise surface area. 4) Appropriate adhesive for the job, 5) Appropriate adhesive thickness to allow for the expected movement / thermal expansions.
Some people make the mistake of only using the strongest/stiffest adhesive that they can find. The higher the tensile of single pack urethanes, the lower the elongation before break.
The best adhesive is the one with the lowest tensile that will do the job because it will have the highest elongation before breaking, which gets back to maximising the surface area.
Cheers,
Peter
OKA196 motorhome

Reminds me of the Lotus Elise chassis adhesives. The entire frame was glued together with a special adhesive. Ended up being amazingly strong and accident resistant.

 

[rruff]

The bond between the FRP and the foam is the weak spot. This is why panel mfg will use plwyood/luan but you want to avoid wood that can't (inside the panels) be serviced.

I don't think it has anything to do with the bond. They use very thin FRP and cheap light foam, and need the ply as an intermediate layer... to protect the foam and FRP, and keep the finish flat and smooth. If you make some samples, you'll see why it's necessary.

With stronger and stiffer foam and thicker skins, the ply is no longer needed.

 

[rruff]

We have a quality panel supplier in Oz, which must be a tiny market compared with the USA?

I hear overlanding is a bigger market in OZ than the US, despite the much smaller population. Seems impossible, but... 🤷‍♀️

The US has a big market for very cheaply built campers that aren't made for going offroad.

 

[Alloy]

I don't think it has anything to do with the bond. They use very thin FRP and cheap light foam, and need the ply as an intermediate layer... to protect the foam and FRP, and keep the finish flat and smooth. If you make some samples, you'll see why it's necessary.

With stronger and stiffer foam and thicker skins, the ply is no longer needed.

When testing a panel where does it fail?

 

[simple]

Depends on the test and panel matrix. Big loads in bending and axial compression, the skins buckle. Tensile, the skins tear apart. Normal compressive load the foam gets squashed and the skin eventually tears or punctures. Fatigue, the foam core can turn to dust. Environmental, thermocycle, UV, moisture...

 

[rruff]

When testing a panel where does it fail?

Light impact cracks the FRP and dents or cracks the foam.

Except for the "rotting when wet" aspect of ply, it's a great material to use for sandwich panels skins, especially with a hard exterior layer of fiberglass.

Wood is quite a bit stiffer than FRP by weight, and of course much less dense. This makes it a good weight efficient intermediate layer because it spreads out loads.

 

[mog]

Wood is quite a bit stiffer than FRP by weight, and of course much less dense. This makes it a good weight efficient intermediate layer because it spreads out loads.

100% My cabin made with FRP-plywood-foam (photo post #23) racked off a of 4 foot high storage support hitting the front of my Fuso on the way down . The Fuso was dented and bent, the cabin had a slight paint scratch.

 

[rruff]

I made a camper 22 years ago that had a 2.7mm luan skins, 3/4" XPS and wood core, with FG on the outside. I was very happy with the durability and weight. The floor/base (no flatbed) was 5.2mm luan on a 1.5" foam and wood core and no FG. It would have been smart to FG both sides of the floor/base, but I didn't have any failures in the ~50k hard miles I put on it. It you want to make a light and cheap camper, I think this is a good way to do it.

My current camper is 1.5" 4lb PVC foam, and 32oz FG-epoxy layup on most of it. The floor/base (no flatbed again) is 2" 4lb PVC, with 33oz carbon and 23oz FG layup on both sides. The big hatch in the back is 1.5" PVC, 22oz carbon, and 17oz FG. Carbon is for when you need something to be stiff... it's ~3x the stiffness of FG. Most of the time the flex of FG is fine.

 

[CoyoteThistle]

I'm having the same challenge as the OP. My current thinking is to build the box with honeycomb core panels, which are lighter and stronger than foam-core panels and reasonably priced (including shipping) from Carbon Core. Insulation will then be added that is non-structural to achieve my desired R-value. Adds some steps to the construction process but will be much cheaper and lighter than any foam-core panels I have been able to find.

 

[rruff]

^ Those won't be very light once you add foam and an interior skin. No interest in doing it yourself?

You can by strong 4 lb PVC foam from Carbon Core, and Terra Ops used the skins shown below.

 

[CoyoteThistle]

That's definitely a viable approach. However, the cost of foam, adhesive and those FRP sheets is much higher I would bet. Also, need to make the panels which is more work. 1.5" honeycomb core with FRP faces is less than 1 lb per sq. ft. 1" foam board is like 0.15 lb per sq. ft. 1/8" luan for the inner wall panels is about 0.35 lbs per sq.ft. Gives an R-value of maybe 8 or 9 at less than 1.5 lbs per sq. ft. at a cost of around $10 per sq. ft.

Could use the thinnest of the FRP skins in the table you showed to avoid use of plywood with minimal weight penalty. Curious about cost on those skins as I like that idea.

And as stated earlier in this thread, honeycomb core composites are proven technology and very strong. This approach also allows for using different insulation thicknesses in different areas (e.g., 2" foam board on the ceiling maybe).

Not the perfect solution, just another approach to consider given the lack of easy to acquire, high quality, reasonably priced foam core panels for true DIY builds.

 

[sprocket3]

I found a US company that will make the panels to spec, but wanted a LARGE order. If there's enough interest i can place a bulk order for panels. It would take about 6 16' habitats to get an order going with them. How much interest is there for quality foam core panels?

 

[rruff]

That's definitely a viable approach. However, the cost of foam, adhesive and those FRP sheets is much higher I would bet. Also, need to make the panels which is more work. 1.5" honeycomb core with FRP faces is less than 1 lb per sq. ft. 1" foam board is like 0.15 lb per sq. ft. 1/8" luan for the inner wall panels is about 0.35 lbs per sq.ft. Gives an R-value of maybe 8 or 9 at less than 1.5 lbs per sq. ft. at a cost of around $10 per sq. ft.

You are definitely building something there also! I think CC uses 17oz skins which is why they are light. Mine are >30oz hand laid, and with a 1.5" PVC core they are right at 1.5 lb/sq ft... which I think is fine. In the grand scheme I think it's best to not go too light.

Building mine was more work than I expected and messy, and I got tired of it. I can definitely relate to making it as easy as possible.

I don't remember what he paid for those skins... but I think it's early in his big thread. If you can get good skins for a reasonable cost, I think gluing to the foam to make panels is pretty trivial. Ask what they recommend for glue and do some experiments with different adhesives if you go that route.

 

[Peter_n_Margaret]

Be aware that there is a dramatic difference between panels made by sticking pre-made skins onto a core compared with those apparently same material panels being laid up wet-on-wet and then vacuum bagged.
The only delamination issues I have ever had were with the former construction. They are also typically heavier.
Cheers,
Peter
OKA196 motorhome

 

[Victorian]

HC is 1/3 heavier than any type of foam core panel (same thickness) with virtually no insulation value. It's true that they are stiffer and overall more resistant to impacts but why construct with composite panels in the first place?