Extruded Polystyrene (XPS)

Great! Thank you. Can't wait to see the tests. I was thinking of getting a sheet just to throw some biaxial on and see what it comes out like. I'll wait until after your tests and do a few of my own...

 

I assume you mean Rectangular Hollow Section by RHS. A RHS has the side walls connecting the top and bottom walls and the side walls will have shear stresses. Likewise with an I-Beam the web has shear stresses.

"Using a thick piece of XPS in a bulkhead laminated with glass on all sides, would behave in a similar fashion to a box beam no?" Depends on the geometry of the beam, in particular the width to thickness ratio and length to thickness ratio.

 

Houses are built with walls and roofs of Structural Insulated Panels (SIPs), consisting of OSB (Oriented Strand Board) skins sandwiching a core of XPS, EPS, or polyurethane foam. The panels are engineered and tested.

 

So... what do people currently build cabinets out of that isn't heavy?

 

Locally can get balsa ply 12mm 10.5-12kg 1.2x2.4m $66 sheet
Plascore 10mm ~$45 sheet, face this with 600gsm biaxial glass or 1.5-2mm ply if you can get this cheap.

Personally I think you could use XPS for cabinetry and bunk tops in a catamaran.
But give some thought to your testing, look at the ASTM test methods. While ago in the Australian Multihull World there were a number of articles written by a guy who made styrene and ply panels and tested these himself. He convinced him self that the panels were fit to build a 9m catamaran, which he did. I think there was an article on the finished boat and it was a reasonably good looking boat. But 6-12 months later a reader sent in a photo to the magazine showing himself holding a piece of wreckage on a beach showing the mentioned boats name on it.
So did the boat brake up due to core failure?? unfortunately the magazine did not follow it up.
All the time and money spent on building a boat, was saving $15K on core worth it ?

 

I wouldn't use it in structurally critical areas if the properties of the material were not upto a required level for its intended use in an engineered structure, but we need to remember this XPS foam does have reasonably strong properties for a foam core material. it's core properties lie between h45 and h60 PVC foam, so we should be fine to use it where you might find a use for the lightweight cores such as interior furnishings etc . I think it maybe good enough for use in hull stiffening bulkheads and stringers if it used in manner whereby you are simply using this foam as a forma for laying glass over. In other words, creating a structure whereby the glass skins are taking all the load such as in a rectangular hollow section beam. Think about the way aluminum boats that are constructed in this manner where they are using HAT sections and RHS... Traditionally, composite boat builders seem to use PU foam for this, but XPS seems like its a better choice for its properties and low cost...

 

The balsa ply sounds ok Andrew, but it's still over 7 times the weight of XPS and about 5 times the price for the same volume of material... Still I'm sure I can find a use for some of it I've been
Wanting to ask where you get that balsa ply?

 

This stuff looks Interesting too btw - http://www.3d-core.com/en/index.html

I recommend checking it out, there maybe an easy method of achieving the same thing...

 

This stuff costs the same as Corecell, just got a quote yesterday for CORE-CELL M-Schaum 85 kg/cbm, 1220 x 2440 x 10mm (2,98 qm) € 30,07 p/qm ex VAT. 86 qm available

Bob

 

thats dissappointing... however it does show that its being used in boat hulls, not small boats either, i wonder if its XPS or the other foams they produce? http://www.3d-core.com/en/applications/marine.html

According to the tests http://www.3d-core.com/pdf/ESC_Measurement_10_2009_ENweb.pdf - the shear and compressive strengths exceed that of commonly used PVC structural foams. Obviously its from the channels forming a honeycomb resin web between the skins to enhance the properties... maybe a print thru problem with this, i dont know...

Im thinking, simply build a stamping device to punch this type of pattern into cheap XPS sheets to achieve the same type of effect...

 

Got further info on that, cant say I have heard of it.

 

I have been using 6mm gaboon with 42x16 kiri (my hull planking) as stiffeners

 

Groper & Sabahcat, the balsa ply known as E Ply is available locally on the north side of Brisbane from Revolution Wood Panels and Janden Plywood, couple of local mobile home and caravan builders are using it.

Groper; structurally I guess it would be no better than XPS cored panel of same thickness as its long grain balsa not edge grain and only thin hardwood faces. But it is a finished product not just a core only requires sealing, in some cases I have covered it with 145gsm plain weave glass.
At 3.7kgsm for $23 it is hard to beat, have you calculated the weight and cost of producing your XPS panels?

 

Andrew, i have now

A 25mm thick XPS panel infused with 600gsm double bias both sides weighs 2.9-3.0kg/m2. The cost of producing it per m2 is $55 via vacuum bag, or $73 via infusion due to consumables.

Its not as cheap as the balsa ply, however i would say its not a fair comparison... The XPS sandwich would be a hell of alot stiffer @ 25mm thickness, and probably alot stronger too. If we reduced the core thickness to 12mm, we loose 0.4kg weight and save $5 per m... so there is little point, you might aswell enjoy the thicker/stiffer panel... We never have the luxury of doing this with PVC foam cores as they are just too expensive when using anything but the bare minimum thickness you need...

 

Your weight may be a bit optimistic, what XPS density are you using? and are you allowing any resin to fill the surface? I know it is smooth compared to PVC.
Balsa ply is definitely for non structural work but cheaper and ready made.