Subject: Re: [harryproa] Peel Strength
From: "StoneTool owly@ttc-cmc.net [harryproa]" <harryproa@yahoogroups.com.au>
Date: 5/18/2018, 1:11 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 

    Cost and availability is an issue here in the US...... we don't have Finnfoam, we have Dow Corning, etc XPS insulation foam at 2 pounds per square foot density readily available.   The problem is always what is available locally or shippably.   If more suitable XPS foams exist, they are not readily available, and cost quickly becomes prohibitive.    There clearly is a place for lower density foams than H-80 and H-100, but again availability is a problem.   Like fiber, there is a place for E glass and for S glass, and for kevlar and carbon fiber.    Only the racers with deep pockets can build with optimum materials all the way through.   The rest of us have limited choices to go with our limited budget.  One of the most indisputably best places for blue or pink 2 pound XPS is as a crush structure in the bows.   Just as in an automobile, where the forward structure is designed to crumple and absorb the kinetic energy, XPS seems a nearly ideal crush material to absorb a bow on impact and prevent real structural damage.   It also appears to me to be a good core in very specific locations such as bulkheads, or decks that will be overlain with material that will distribute impact and compression loads.  
    Most of us will stick to H-80 and H-100 because the weight benefits are small enough that it simply is not worth using a foam that is not designated as a marine structural foam, not knowing what the longevity will be and how well it will perform.  It would be nice to be able to buy H-40 locally, better yet to be able to buy a product that had the density of H-100 at the surfaces tapering off to a far lower density at the neutral axis (center).   But that's a pipe dream ;-)

                                                                                                                                            H.W.



On 05/18/2018 09:19 AM, '.' eruttan@yahoo.com [harryproa] wrote:
 



|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.

If the strength of a composite sandwich does not depend on peel strength, why are we measuring peel strength?

Is it just fun?

|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."

As noted there, Rick has no idea what the compressive strength of the core was. Assuming Rick did the composite under vac, the 15psi XPS(cheapest XPS insulation) was already compromised. Also note that no other source has suggested water harms the XPS fiber bond. Rob Denny stated he only had delamination in wet layup XPS skiffs where they were walked on. Also note that the cheap 'sawfish' (youtube) XPS kayak/boats are just cheap random XPS and wood glue and polyester bedsheets as skins, have been used for nearly a decade and no delamination noted. Also Rutan planes.

So the idea that water destroys the cheap XPS laminate interface is contradicted by solid data.

Also, can we clarify what grade of XPS we are talking about. Generally there are 2 grades commonly available in the US. The 15psi grade is entirely unacceptable in laminates, IMHO. The 25psi grade is marginal at best, but seems to have been used in many hobbyist projects. Its 170% stronger than the 15psi stuff. The densities are nearly identical, so we can't just call it 2 pound sq foot XPS.

The 40, 60 and 100psi grades are a very different animal. Please don't confuse them.


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Posted by: StoneTool <owly@ttc-cmc.net>
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