Björn:
I haven't found the time to read the whole thread yet unfortunately. I will say however that I have not EVER advocated using XPS below the waterline or where there is significant impact or abrasion. The surface presented to the epoxy is important, which is true of any foam. I should have qualified the statement you quoted. A "peeling force" should not be present where foam sandwich used in a properly engineered. The bond should only be subjected to a shearing force. The penetration and pumping effect described should never be present for several reasons.
In any case did my peel and impact tests on the third sample, that was flashed with aggressive blasting sand, and was not happy with the results. While the peel brought foam with it, as it should in a good bond, and left me confident that a in a beam situation the ultimate failure mode would NOT be as a result of delamination, the impact and compression results made it clear that it would be suitable in only a relatively few applications in boat construction. While the low density, allowing for a thicker sandwich for the same weight could for example give a lighter stiffer deck in theory, the surface would not take the pressure of walking on it without deforming the foam itself, and would thus require a thicker top surface layup, or a flooring overlay to distribute these loads out over a larger area. Where teak is being laid over the fiberglass, or something like a laminate flooring is going to be used over it there should be no problem. The weight of even a single additional layer of glass / resin negates any weight benefit, and after all, weight is one of the primary considerations in my book. For vertical surfaces such as bulkheads, there should never be the kinds of loads that will fail an XPS cored sandwich construction.
The conclusion....... my conclusion, is that a lot of careful thought and engineering needs to go into working XPS core into boat building, with consideration for it's benefits and liabilities to determine how and where it is appropriate. The amount of weight savings it can offer in the limited applications where it can be used probably do not justify it's use. It's only real value is to make a thicker core for more stiffness without the increased weight of H-80. Stiffness should be directly proportional to core thickness. Using H-80, stiffness can be achieved by a thicker core or more layers of glass, the former being preferable. If we are using 6 oz cloth, it's fair to assume that the result of an additional layer will be about 12-16 oz per square yard including resin (infused) times 2 (each side)..(24-32 ounces per square yard total)..... correct me please. 1/2" additional thickness of H-80 is going to weigh 30 oz per square yard, not a lot of difference. Using 1" XPS, the weight drops by 36 ounces for a 1" core, but at least one additional layer of glass is needed unless some sort of overlay is used ...... assuming this is a deck we are talking about.
**** There really appears not to be any significant benefit if any of using XPS in boat building except perhaps for a very few applications. The weight and cost savings in light of this would seem trivial. And this does not take into account weather or not it would work well with infusion............ It's just not worth the effort, which obviously is why it is not used.
I had planned to do some bend tests, but after running the extremely rough (verging on WAG) numbers, decided it was not worth the time.
H.W.
On 05/18/2018 04:28 AM, Björn bjornmail@gmail.com [harryproa] wrote:
I haven't found the time to read the whole thread yet unfortunately. I will say however that I have not EVER advocated using XPS below the waterline or where there is significant impact or abrasion. The surface presented to the epoxy is important, which is true of any foam. I should have qualified the statement you quoted. A "peeling force" should not be present where foam sandwich used in a properly engineered. The bond should only be subjected to a shearing force. The penetration and pumping effect described should never be present for several reasons.
In any case did my peel and impact tests on the third sample, that was flashed with aggressive blasting sand, and was not happy with the results. While the peel brought foam with it, as it should in a good bond, and left me confident that a in a beam situation the ultimate failure mode would NOT be as a result of delamination, the impact and compression results made it clear that it would be suitable in only a relatively few applications in boat construction. While the low density, allowing for a thicker sandwich for the same weight could for example give a lighter stiffer deck in theory, the surface would not take the pressure of walking on it without deforming the foam itself, and would thus require a thicker top surface layup, or a flooring overlay to distribute these loads out over a larger area. Where teak is being laid over the fiberglass, or something like a laminate flooring is going to be used over it there should be no problem. The weight of even a single additional layer of glass / resin negates any weight benefit, and after all, weight is one of the primary considerations in my book. For vertical surfaces such as bulkheads, there should never be the kinds of loads that will fail an XPS cored sandwich construction.
The conclusion....... my conclusion, is that a lot of careful thought and engineering needs to go into working XPS core into boat building, with consideration for it's benefits and liabilities to determine how and where it is appropriate. The amount of weight savings it can offer in the limited applications where it can be used probably do not justify it's use. It's only real value is to make a thicker core for more stiffness without the increased weight of H-80. Stiffness should be directly proportional to core thickness. Using H-80, stiffness can be achieved by a thicker core or more layers of glass, the former being preferable. If we are using 6 oz cloth, it's fair to assume that the result of an additional layer will be about 12-16 oz per square yard including resin (infused) times 2 (each side)..(24-32 ounces per square yard total)..... correct me please. 1/2" additional thickness of H-80 is going to weigh 30 oz per square yard, not a lot of difference. Using 1" XPS, the weight drops by 36 ounces for a 1" core, but at least one additional layer of glass is needed unless some sort of overlay is used ...... assuming this is a deck we are talking about.
**** There really appears not to be any significant benefit if any of using XPS in boat building except perhaps for a very few applications. The weight and cost savings in light of this would seem trivial. And this does not take into account weather or not it would work well with infusion............ It's just not worth the effort, which obviously is why it is not used.
I had planned to do some bend tests, but after running the extremely rough (verging on WAG) numbers, decided it was not worth the time.
H.W.
On 05/18/2018 04:28 AM, Björn bjornmail@gmail.com [harryproa] wrote:
Any pictures to share? =)
I think you should compare the results to some other core material (like wood to start with if you don't have any other foam), because otherwise the results becomes a bit arbitrary.
>> Peel strength is not really an issue in a sandwich construction.
Didn't you read the polystyrene thread on this list? It was started very recently and contains only 64 posts, so it really isn't that much to read. What is your reply to Rick W's post from third of May:"I made a long slender prototype hull from a block of XPS. The skin was 200gsm carbon fibre. Over a few uses water found its way through pinholes and some surface scratches and that initiated progressive delamination through various processes like handling and thermal expansion of the water including a few periods of ice in cold weather.
Once water can get in, it pumps the bond by forming a bubble under the skin. The temperature of the water in the bubble could range from 10C to 40C in a matter of hours. The expansion works away at the edges of the bubble and extends it.
A thin skin with pinholes on H80 PVC foam does not deteriorate the same way. The bond must be strong enough to prevent the thermal fretting of the bond."
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Posted by: StoneTool <owly@ttc-cmc.net>
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