SAN-PVC-PET foam core

Greetings to all, hope your doing well.

This is my first post in this forum after lots of time spend reading throught the forum before placing my question. Its not efficient to constantly ask the same questions over and over right ?

note: non english person so pardon my mistakes.

Anyhow, I was looking at these three foam core types (SAN-PVC-PET) and searching through their data sheets i made a table with their numbers shown at their advertised brochure so this is only based at the numbers that the manufacturers give.

I have checked the table but i am sure there will be some mistakes between them(i got crosseyes from looking at the numbers...)

That is why i add the pdf brochures as well.
https://local.armacell.com/fileadmi...T_website/Product_Flyer/ArmaPET_Struct_GR.pdf
https://www.tridentfoams.co.uk/pdf/TDS_AIREX_T10_E-Rev_4_external_1106.pdf
https://s3.amazonaws.com/cdn.fibreglast.com/downloads/00293.pdf
https://diycomposites.co.uk/products/datasheets/TDS/tds-airex-c70-e-04.2020.pdf
https://media.easycomposites.co.uk/datasheets/EC-TDS-EASYCell-40-75.pdf


There are ofcource the small letters were it says that the tests were done with 20mm-40mm etc so in generally i take the numbers with a grain of (sea)salt.

None the less, there are some questions that are raised.

From what i see in the numbers pretty much all have more or less the numbers are close to eachother with frew (VERY big) differences.
Biggest i could found (and if i understood the definition of sheer strain/elongation) is that PET foam has the lowest of them all.

In order to build a catamaran full of foam core, which would be be the best foam to choose from ?
Using different foam cores from the hulls and decks, might that be an option ?
Which properties are the most vital ? (all of them one could say) but for hulls which is by far the most importand, what would be the best option ?
I have seen that many of you have your own experiences and opitions about so if someone could shed some light, that would be much appreciated.

thanks in advance.

 

The ods file is not working. I prefer san first, then pvc.

 

Thanks fallguy, hope this one works.

 

Okay, so an obvious problem is you are comparing different density materials. It would be unfair to compare varying densities unless the lamination required was the same..or something on that order

Gurit M80, for example, cannot be fairly compared to Armacel Pet 150 because the pet is twice as dense.

 

Ah yes, that, i should of said that. I used the shear strength as basis , so i had to use higher density PET in order to be able to compare with the 80kg/m3 of the other foams.

 

I liked the PET due to 100% recycle, nice density, pretty much half the price of other foam but when i see the sheer strain, it is disappointingly low. So that is why i thought maybe use it in either the bulkheads instear of the hulls or other non structural uses.

 

I think you are approaching the problem from teh wrong direction.

First you should decide what the material has to accomplish in each area, then find a material to fulfil your requirment. That is essentially whay there are different materials available.

PVC foam works well for hull skins but it needs heat to bend it.

Airex bends and gives adequate strength but if it gets hot it flexes, so it's great for rounded hull bottoms not so good for decks are dark painted hull sides in warm climates.

SAN foam has some nice properties but it's expensive and if teh specs of PVC etc are adequate...the hulls skin will either delaminate or buckle or it won't. If it doesn't fail then spending half again or double on foam is wasted money.

Polyurethane foam is cheap but doesn't have the bond strength. It will delaminate. Don't use it in stressed areas.

 

Different foam types will give you different tenacity. But in choosing the "best" depends on what you want to achieve. Attached below are the different types of foam and their characteristics as it appeared in PB magazine a long time ago. The "best" from impact resistance came out to be corecell. Not too rigid and not to "stretchy". Others choose foam for specific strength. That is, how much load it can carry vs its weight (strength to weight ratio)

 

Good point, thanks for the explanation.

 

Laser focused on the issue Guzzis as always. If i understood correct, PET would be safer to be used inside in non stress areas. Cheers.

 

Actually, there is very little difference between corecell and PVC in terms of shear specific (shear to weight ratio) which is what you need in core sizing. The difference comes in impact resistance. Corecell is much more forgiving and deflects in unison with the FRP panel. PVC is much more stiff and transfer the load from impact point to opposite side causing delamination. Good practice is to use corecell at the bottom and all above waterline, use the much cheaper PVC.

Theoretically, you can use a higher modulus face such as carbon fiber and soft core. High modulus carbon fiber is stiff, deflects the load and transfer it a greater area. But that is economically not a good solution. Expensive face, cheap core.

 

Yes after putting all the (correct) data from the TDS of all the foam cores i do see that they have many similarities (check the foto)

EDIT : The tests of every brand are done with different thicknesses from 10mm till 40mm so i take the TDS with a grain of salt.

About the carbon fiber, (or carbon/kevlar) i did thought about using carbon fiber under the waterline, but then i saw this video

so that made me question my original idea. There are many objects underwater that are not visable so i wanted some strong underwater protection... but if i use carbon fiber, do you use 1 layer or more ? which weight ?

 

Carbon fiber is good if not mixed with other material. It has a very low strain, 1 to 1.5%, meaning, it does not like to stretch. It is also very poor in compression, about 60% usable. High modulus category, it is brittle.

Mixing it with Eglass leaves you with very little usable strength (or strain) in Eglass because Eglass laminate can stretch up to 5%. You will break the carbon fiber first (in terms of stretch) before you reach the ultimate failure of Eglass. In short, you are wasting your Eglass capability.

 

Here is an image from our recent discussion on Basalt fiber. Note the low strain of carbon fiber. Long after the CF has reached its ultimate strength and strain, all the other laminates are wanting for more stretch.

Or to put it another way, you can draw a horizontal line at 50% of the Eglass ultimate strength. Read where it intersect CF. You can only use that much strength from CF because you have reached the limit load on Eglass. It is called the limiting strain.

 

Put the carbon on the hull dreams away and use them as some decoration, unless you wsnt an ultralight boat with not great ability to bump anythin.

cf/aramid console