With respect to the test data below, the loss of shear strength after impact is to be expected and this data is applicable to hull skins. On the other hand a 2mm (about 1300gsm) skin is a heavy layup for a Harry. You would need to look at the details of the impact test to see relevance to a boat hull.
Making good hull panels requires having a proven process with the materials being used The best way of proving a process, short of making a boat and testing it to destruction, is to make test pieces using the proposed materials and process then test to destruction. The two easy tests to perform are bending and tensile adhesion. In the bending test I have found that the compression skin fails in buckling at about half the rated compressive strength of the cloth when epoxied to H80 core. That means the tensile, or inner skin, of a hull panel can be half the weight of the outer skin for similar performance of both skins. That is also consistent with the outer skin taking direct impact load.
The PET armacell appears to be an interesting product. Not sure how PET foam performs in a sun exposed water environment but it should be good given the durability of PET bottles in the ocean. I would look for examples of its use in the marine environment. I would get a sample and layup sample pieces to test in bending and adhesion. I would compare the results with H80 PVC core in the same layup.
In the table below the Balsa core performs the best in these tests. That is a reminder of another important factor; water absorbency and resulting degradation through biological attack. In my view Balsa is not a good core for underwater panels.
On 4 May 2018, at 12:00 am, Björn bjornmail@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:I have found more info about the shear strength of PET foam. See the report DEVELOPMENT OF DURABLE TRAIN FLOOR COMPLIANT WITH EN 45545-2It compares the shear strength to Nomex honeycomb (of unknown type), and balsa (of unknown type) in both undamaged and slightly damaged state in 4-point bending."The targetthickness for the panels was 19 mm with a corethickness of 15 mm and skins of 2 mm on eachside. The manufacturing method was wet preg withvacuum consolidation due to the high level of fillerand thus viscosity, especially for the epoxy system."
Core Resin system Panel weight [kg] Shear strength [MPA] Shear strength after impact [MPA] Nomex HC Phenolic 8.3 0.75 0.49 PET 80 kg/m³ Phenolic 7.75 0.77 0.42 Balsa Phenolic 9.6 2.16 1.88 Nomex HC Epoxy 9.4 1.21 0.61 PET 80 kg/m³ Epoxy 8.86 0.64 0.44 PET 100 kg/m³ Epoxy 8.8 0.89 0.71 Armacell also makes a foam with variable density - high density on the surface, and lower density in the core. For example 200 kg/m3 on surface, 70 kg/m3 in core.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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