Subject: Re: extruded polystyrene core questions
From: Mike Crawford
Date: 5/2/2018, 3:57 PM
To: harryproa@yahoogroups.com.au

<<But, of course, a plane does not see anywhere near the forces a boat does. >>

  Definitely.  That airframe is highly unlikely to be stressed by hitting a lot, container, whale, or sand bar, particularly in a location the designer didn't plan for.  Assuming the incident didn't sink the boat, we'd want it to be either undamaged, or have the damage localized, but have the rest of the structure continue to work.

  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.

  I'd probably go with a linear PVC, like Airex R63, known for its impact resistance, even if that meant a tad more weight.   Or Corecell's A series, which is supposed to be more resistant to higher temperatures.

    https://netcomposites.com/guide-tools/guide/core-materials/other-foam-cores/
    https://www.compositesworld.com/articles/getting-to-the-core-of-composite-laminates

  (I saw some great destructive testing photos of delamination of different core materials a few years ago, but I can't find them right now).

  For a 40' proa, in terms of percentage of the project cost, what do you think the cost savings would be for going with a cheaper core, including the labor and machine?

  I'm perhaps too conservative in a design sense, and while a proa causes no problems for me engineering-wise (the numbers speak for themselves), I'd be hesitant to make the leap with a core material that hasn't been beat upon in the marine world for a few years.  There would have to be a very significant savings.

  That said, no one proves the value of a new core material without using it.

  It would be great to see what happens to a few test panels of different core materials, including some controlled impact testing, before building a boat.

    https://www.practical-sailor.com/newspics/BOAT_BUILDING_1007.pdf

        - Mike



'.' eruttan@yahoo.com [harryproa] wrote on 5/2/2018 2:42 PM:
 

I am interested in your results!

But, are we sure we are solving a problem?

I am not sure there is an adhesion problem. Yes, Rob noted delamination in the skiffs, but, imho, that was because the laminate was damaged when over stressed.

I know all the Rutan plans planes were built out of glass over XPS. As well as the many derivative planes. They did not have a delamination problem generally. But, of course, a plane does not see anywhere near the forces a boat does. Air is much less dense.

I am not sure anyone has discussed a case where the laminate and core was up to the job, and stressed as expected, and the problem was narrowed down to a skin core adhesion issue.

Also Björn, i am working on a reply to the stiffness thickness core question. It is more in depth, so i beg Indulgence.



On May 2, 2018 11:56:13 AM UTC, "Björn bjornmail@gmail.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
 
Check out this stuff!

"Optimized waffle structure with very good adhesion properties for concrete, adhesive mortar and plasters"

This special textured surface, would it solve the issue of bad adhesion?
And would it help the infusion?!

I'm getting exited.. I might order some samples and try it out!