On Thu, Apr 30, 2020 at 2:34 AM a8b7k57g@protonmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
12mm H80 pvc foam is ~$AUS25 per sqm and requires an additional 200 gsm ($2.40) of resin each side so it weighs 1.4 kgs per sq m and costs $27.40.To match the foam weight, the corrugations are 300 gsm (1.4/0.48). To match the cost, 650 gsm (27.4/4.1)wow < 1/10 the price, and 1/3 the weight.Plus the glue and the edges. And we have not got any properties yet. But worth a look..With the thickness we are talking, cheap 1/2" foam gives a 1" core, Which has to have hella shear, no?
Depends on the foam properties, not the thickness.. Although 1" core will be a lot stiffer.
If the corrugations are stiff enough not to need faces, they will be lighter and cheaper, albeit ugly (not a problem for hidden bulkheads and things like floors where either one side or neither side is visible), harder to build and challenging to fillet and tab.If you can source a vacable cheap foam (even EPS), and do a square corrugated, that you can infuse, you could have a whole system.I think H or VH would work.assuming VH you add ~0.35 KG/m^2These guys, and many others in Aus, blow the polystyrene. Assuming VH is the same from all suppliers, it squashes under vacuum.Not that big a deal for the foam, but the cloth wrinkles. The only foam to use is the extruded polystyrene. I will look into this, but from memory, Foamular Aus do not stock the higher densities.BAH! I assumed VH with it's 165kpa could hold 100kpa vac ok. I thought it might be perfect as it still might warp to a gentle hull curve under vac. If cheap enough vs XPS, hit it with a thin coat of resin/sealer?
Maybe. I suspect it would crack under vacuum as the core compressed. Another problem with blown polystyrene is that it soaks up water. Not a problem if it is treated right.
Foamular Aus has under concrete slab foam, so they must have something thats 170+KPA
Could be, but last time I asked, they didn't, but could get it if I ordered a truck load.
Square corrugated add 20.7% to the length, as supposed to the curved 10.5%How do you calculate this? Assuming the corrugations are one piece, I get a sine wave uses 1.4 * the width, semi circles is pi/2= 1.5ish and square corrugations are 2.Here are my thoughts. I assume errors. Pointing them out earns a cookie.The arc length of a sine wave2pi =~6.28, arc length to 2pi is 7.640395578~7.64/~6.28 = ~21.7% longerbut that is for a proper sin arc, the corrugated sheets are, typically 3" pitch and 1.5" depth, so the sin wave has been stretched, lengthwise, 50%, so only ~10.7% longer, which agrees with your assumptions, my assumptions, and the given rule of thumb for corrugated iron, right?
Maybe. My assumption was 40% longer, assuming height = wave length. This is what i cut the glass to and it was too long.. I trimmed it without measuring. A sheet of A4 is 295mm long, covers 265mm of the roofing iron, near enough 10%. I bow to your superior maths skills.
The glued together 400 gsm corro sheets are quite stiff. The 200 gsm not so much. Both are in the sun for a post cure, I will pronbably break them tomorrow. The sanding and spot gluing was a pain. Next test is one sheet of 12mm semicircular corrugated with a flat each side, all co-cured, 400 gsm double bias for the corro, 400 biax for the faces.
As an aside;Standing in the building supply I hear two guys discuss why everybody says 10% and not 10.7%. One of them suggests it's because contractors and roofers do not care about math. The old guy behind the counter speaks up and suggests it is because builders are considering significant figures, and since one buys a 4x8 sheet, 10% has only one significant digit. I don't know how that effects one in a SI state, with mm measures.
mm are for scientists and engineers. Real people tend to use centimetres and metres.
I will be here, inside, all week.Semi Circles is pi/2, as you said.Calculating square corrugations.I guessed a flat and a slat ratio of one to one. so, ( \_ ). This is, of course configurable.But the slant portion of the square corrugated would be the hypotenuse of a square, which is sqrt(2) = ~1.4, which is also how long it is vs mold length. so just slants, and only glue at just points ( \/\/ ), would be 40% longer. any flats would make it proportionally less.
Got to have the flats, and the slant angle has to be slightly rounded. How much of each needs testing, but probably not much, if it is reliable.
If you have a way of determining how big the core interface, and the face interface, should be vs slants, I would love to hear your thoughts.
If it looks right, it might be. ;-) 45 degrees is the optimum angle for sheer properties, more than that, i do not know.
Perhaps at this point it would be neat to take it to a composite engineer and see what shapes would give optimal outcomes? Could someone on boatdesign help?
Maybe. The deal i have with the prototype cargo proa includes access to some of the best engineers and testing equipment in the country. More on this in the next week or so, but sailing by Xmas is back on the agenda.
My questions:I had heard you suggest infusion will generally travel 8" along glass? If you had to guess, would you think you could infuse a stack of outside skin, outer corrugated foam and glass, inner corrugated foam and glass and upper skin?
Sure, but I would test it first. If not, some holes in the foam would be required. These would add to the core properties, but no idea how much
Would the slants give a natural infusion path? Or would you still need to groove the foam?
Not for the test.
Is there some ratio of slant to flat that would eliminate the need for a second core?
No idea. Will have another data point after the semi circular, single coor test piece..
Is a single core more infusable?
Than 2 cores? Yes. Than no core? No.
What properties would you look for/test for? Layup a length of h100 and the corrugated core and look at yield? yield to failure? Hit it with a hammer?
All of those, except I don't have any foam will cut a piece out of some scrap and see how they compare.
When can I build my E25 with this?
When we have some suitable properties. Making some samples beats the hell out of Netflix for passing Iso time.
Even more excited.
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Posted by: Rob Denney <harryproa@gmail.com>
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