starting this to coincide with my board project question.
I m using 2lb EPS as the blank, in a effort to test in a manner of sorts the difference in weights.
thinking I have 1 lb, was wrong, its 1.5 lb or 15/20kg m3. so TESTING 1.5 and 2.0 lb , desiity per cubic square foot.

materials are the bomb, 2 tuna cans, 1 cat food a large shipping tape roll wrapped in duct tape, 0.936kg.Dropped from 3.6meters.

EPS 2.75 cm thick.

trying to drop the bomb the same each time, not happening, picked this shape, to impact in different angles, it would be easy to destroy the EPS, I wanted to damage to reflect the difference.

above is 2lb, this was a wicked angle to hit, worse possible, the half circle, the contact to the right , 3. Lines landed flat.

still with 2lb , but with a 5mm core cell cushion, fairly minimal denting

1.5 , straight down impact, spread out some cause its flat.

1.5 with 5mm Corecell

The 2.0 with Corecell , had little damage, dents yes. The 1.5 still went into the EPS with damage.

it is difficult to make a meaningful assessment , it's difficult reflect the damage in the photos.

i thought about a ball that would land the same each time, certainly more bombs would define things better,

its not the black and white results I expected.
no cats dogs or wallabies were harmed in this test.

You could always put a loop top and bottom and get it to slide down a pole. Same height and angle each time will give better results.

If you just put the corecell on top rather than laminating (gluing) it on then the result is not valid.
The slippage between layers allows for more deflection.

And if you haven't laminated the corecell with glass, it's not going to protect the eps as it would in real life.

I like the idea of a tow ball on a drill press and bathroom scales to measure pressure.

I'd much rather go with the 1.5lb foam, and use a bit of carbon and kevlar on the deck.

I think you should try actually laminating the 1.5 with different materials and see what happens then.

using a tow ball you only need foot square samples.

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Mark _australia said..
If you just put the corecell on top rather than laminating (gluing) it on then the result is not valid.
The slippage between layers allows for more deflection.

And corecell without some sort of cloth over each side, is going to bend a hell of a lot more than if it's part of a sandwich.

Had a look through my shed today and found some of my old tests.





Top left is a piece of my foam, looks like I was wrong about it being 24kg/m3 (1.5lb/ft3) I measure and weighed it, and it's come out at 34kg/m3, but my scales aren't accurate at such low weights, so it's probably 32kg/m3 or 2lb/ft3.
The rest are tests done with a one and seven eigth inc diameter tow ball connected to a drill press with bathroom scales underneath. I pulled all of them down to 100kg.

top right is 3 layers of plain 6oz cloth laminated to the foam. I don't remember how I measured the indentations now, maybe feeler gauges, but this says 0.8mm.

bottom right is one layer of 6oz carbon on 80kg d-cell, that says 0.4mm. Lower middle is a carbon, kevlar, carbon lay up straight on top of the blue foam, this shows no indentation, but it's possible the cracking of a few strands of carbon were heard. The last one is a thin veneer of pine on d-cell.

I can't remember what the weight if the okd XPS is but the new stuff varies from 32 to 35kg/m

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R1DER said..
I can't remember what the weight if the old XPS is but the new stuff varies from 32 to 35kg/m

Yes that's what surprised me, I thought I had the old light foam, but this is weighing in as the new heavy stuff. Perhaps I should measure a bigger piece, or maybe I bought the wrong stuff back then.

pleased to read all remarks.
in my closing paragraph I attempted, literary genius that I am, to reflect, without saying I were a dunce, that , due the midigating conditions the test, so to speak was inconclusive , but did produce results, hazy and all.

yes by fixing glass and the Corecell to the EPS, the outcome would probably be different. At which point do you stop ,or add additional glass carbon, paint ? the test was to do the difference in EPS DENSITY, not a full build up. I went so far to think about putting a wasted board in the dummy group, that I may yet. So now ..

onto a board hull, the bomb , showed a scuff that looks like a shoe scuff, it was hard to find .

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forceten said..

yes by fixing glass and the Corecell to the EPS, the outcome would probably be different. At which point do you stop ,or add additional glass carbon, paint ? the test was to do the difference in EPS DENSITY, not a full build up.

My point is that dropping onto styro, then dropping onto styro with PVC foam laid over the top, is a bit irrelevant, as in a real world situation the sum of the parts is much greater when they are bonded.
That's why we sandwich - to make it much stronger.
eg; plywood vs one solid piece of wood same thickness. We know the ply is better.
Your test is like comparing 1" wood, and then 1" of plywood but the layers have no glue.

i knew before I posted that the principle was flawed . In several key areas.
the addition of core cell , was a afterthought, much like the real board Test.

generally speaking some judgement , on the TEST. purpose , which was The DENSITYs of just the EPS , was presented, not the black and white I expected.

I agree it's a bit irrelevant, I would suggest OTOH it's a bit relevant, connected to the matter at hand.