Extruded Polystyrene (XPS)

You should not limit yourself to simplified formulas as there are more sophisticated formulas available to predict composite performance.

If you will search this forum, you will find that a lot have been discussed about composites.

 

ive spent 30mins searching the forum and google.... i still cant find anything that suggests skin modulus will have anything but an infinitesimally small influence on core shear stress. This is the reason it is ignored along with many other things in simplified equations, we also combine this with a few assumptions for sandwich structures. We are well within these boundaries for our discussion purposes here...

 

Well good luck to you if you insist.

 

Finn foam in USA?

Another reply from Finnfoam when I made a recent inquiry as to whether their product was available in USA?

 

In another application, I built a bench seat that unfolds into a sun platform using 1.5" XPS foam panels skinned with 1/8" Meranti. Adhesive used was 3M Fastbond 30 water based contact cement.

This is a very stiff, light structure that is not expensive to produce.

 

I was wondering if XPS was anisotropic due to the extruding and stumbled on these as specific examples of XPS cored sandwich construction. I am not building concrete boats, so the second PDF is a bit more relevant...

ww2.integer.it/.../261%20490%20217%205%20Muller%20SE.pdf
http://www.ave.kth.se/polopoly_fs/1...tachment/David Wennberg Literature study1.pdf

 

I known the thread is ancient, but just for the record. I'm doing research into the same subject. I had overlooked this thread, so I started a new in "materials" forum.
Firstly, Groper, love your work and posts! Secondly I think there could be some use for XPS, in smaller boats, and with some limits. Ply skins should mitigate low impact resistance.
Unfortunately, the mentioned finnfoam all have the same low 300kpa shear strength, regardles of density, f-200 up to f-700. 27-42kg/m3. Still, it should be possible and in some cases make sense. I'll try and run some numbers. Mostly thick foams are regarded intrusive. But in northern Europe, 2" (50mm) insulation would be a good thing. (Disclaimer, I'm a total amateur).

 

I'm using 50mm in my boat Niclas.
When are you starting your build?
Do you have a proposed completion date?
What's the budget?

 

The biggest problem for me with xps is the hdt is only 165F.

Basically this means you better not use the boat near the equator; ever. Or paint it a dark color, etc.

Corecell M was specifically designed to have a higher hdt from what I have been told n read. The HDT is 230F or 65 degrees higher than xps.

Not a problem until it is and then it is a disaster.

 

This System 3 General Purpose Epoxy Resin has a heat deflection/distortion temperature of 119 degrees F and a Maximum Service Temperature of 160 degrees F.
https://cdn.shopify.com/s/files/1/1...d7a-a1a7-13c48d32fb9e.PDF?4145922552712269764
These are all in the 115-125F HDT range...
https://entropyresins.com/wp-content/uploads/2014/03/TDS-CLR-System.pdf
https://www.westsystem.com/wp-content/uploads/105-205-Epoxy-Resin.pdf
https://www.westsystem.com/wp-content/uploads/105-206-Epoxy-Resin-1.pdf
I don't know, but is a foam HDT of 160F much of a problem when the resin HDT is much lower?

 

I am only mentioning reality.

If the epoxy gets soft in the laminate; that is far different from the foam distorting. The epoxy can soften and return, but if the foam softens it does not return. So there is a bit of a difference.

Even I am tempted to try some 1/2" xps for internals in my build...like benchtops or tabletops and other nonstructurals.

 

I marvel at the attraction that polystyrene exerts, for some people, its like kids with "fairy floss", ( cotton candy, I believe the Americans call it) for them, it has a magic about it ! Sadly, both have little real substance.

 

It all comes down to money.

12mm Gurit core is 150-200$ a sheet

1/2" pink polystyrene is about 15-20$

At 10% of the cost; finding a way to make it work seems wise.

When I ordered 60 sheets of corecell M; I immediately pondered xps. I thought 1200 vs 12000!

For a tender or a small skiff, I'd be tempted to use xps.

I have used it once. I built outriggers for a canoe as spending 150 for float foam seemed foolish.

For something like wall/door for a head; they would deaden sounds. And, of course insulation for ceilings.

I'd say it has a place, but it is not as large as many hope.

 

The problem is that people fancy it might be a worthy replacement for those more expensive foams in structural applications, it is not suited to. It is, as you say, the $ aspect, that causes people to entertain such ideas.

 

I'm not very versed in the subject and was trying to stick to reality also.

I was thinking the HDT of foam and the HDT of resin might somewhat/somehow be related. So if the foam had an HDT of 165 F and the resin had an HDT of 119 F, I'd think the resin would be the thing to worry about as far as HDT. That the resin would have reached it's Maximum Service Temperature at 160 degrees F, and the foam had not even reached it's HDT at that temp, seemed to reinforce that idea. BASF has some XPS with an HDT of 220 F.

It gets warm for an airplane sitting on the tarmac.
Styrofoam On Wicks Aircraft Supply http://aircraftproducts.wicksaircraft.com/viewitems/aircraft-foams/styrofoam


Another cheap foam is polyisocyanurate. You can get a 2" x 4' x 6' piece from Fibreglast developments for $80 or go here INSULATION- 4' X 8' Sheets NEW- Various Sizes| repurposedMATERIALS https://www.repurposedmaterialsinc.com/poly-iso-insulation/dfw-insulation-4-x-8-Various%20Sizes-cheap-used-salvage-surplus/ and get the equivalent for $12.50. Or go to any wholesale commercial roofing supply and get it at their prices, as it's the most common foam sheet roofing insulation sold.

I imagine the vast majority of products used in boat building were discovered/developed for other uses (or no uses at all) and were found to work for boats so they become very useful in boat building. Wood comes to mind, and resins and foam too. Fabrics. At the moment, I can't think of anything that was directly 'invented' for boats, other than a market, but there are probably a bunch.