Delamination is right on the point. XPS has a tensile strength of 0.4MPa. H80 PVC foam has a tensile strength of 2.5MPa. That is a massive difference as it relates to delamination.
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.
XPS is a lower cost means of quickly building a disposable hull. PVC H80 is good for a durable hull that will give years of service.
Rick W
On 3 May 2018, at 7:21 am, mcrawf@nuomo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:So the design criteria aren't just bending and shear given sailing forces, but also the ability to remain laminated after an impact that deforms the sandwich. Some core materials remain stuck to their skins, others are more brittle and can experience large areas of separation.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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