[PSUBS-MAILIST] syntactic foam.

Sun Jun 11 12:19:14 EDT 2017

Composite material performance can be approximated by weight averaging the mechanical properties of each component in proportion to its volume fraction within the composite. In general, it is advantageous to minimize the matrix (resin) volume in a composite, whether fiber or micro/macro sphere reinforced. This is why multiple sizes of spheres are recommended - to preferentially fill the interstitial spaces between the largest spheres with additional spheres and not simply matrix material.

The spheres provide the required density reduction, but are brittle. The resin adds ductility / toughness to the composite, to carry mechanical loads applied to the composite part, and distribute the load across the sphere surfaces. Packed spheres with no matrix material would still withstand the hydrostatic pressure loads,  but any additional mechanical loading would point-load the spheres at their points of contact.

The requirement for glass spheres is really only derived from the strength and density requirements of the application. Using an air entrained resin exclusively may be sufficiently strong, but you may find it difficult to achieve a low enough density, both because of the maximum possible bubble size you can manufacture, and because of the fact that consistently sized air bubbles will never pack as densely as using various different sizes of e.g. glass spheres.

Sean

On June 11, 2017 8:24:36 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Greg,There has to be good reason to make foam by other means than
>standard practices.   Cost would be the biggest reason, and using wax
>will probably work, but is there a saving?  Using wax means you have to
>use a deeper rated sphere to offset the loss of reinforcement provided
>by the resin.  I have no idea what the cost difference would be.  Maybe
>the cost is still much better.  When I look at Cliff's report, the
>resin is not the expensive part.  Perhaps the direction should be, to
>look for a replacement for the spheres.  In Cliff's report it shows the
>resin triples the sphere's performance.  That implies that the true
>strength comes from the resin.  Maybe a sawdust resin or a styrofoam
>granule resin is worth looking at also.  Maybe it is a simple as air
>entrained resin?Fun to think about anyways.Hank 
>
>On Sunday, June 11, 2017 6:22 AM, hank pronk via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
> 
>
> Hi Scott,Thanks for the offer, but I need foam for 3,000 feet.Hank 
>
>On Saturday, June 10, 2017 9:03 PM, Scott Waters via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
>
> Hank,
>Hola from Costa Rica!
>Depends on if they are glass or carbon fiber spheres and what size they
>are. They are all pretty durable. We are actually cutting up the foam
>on Pisces and reattaching it to get the shapes we want. 
>I do have a ton of syntactic foam that is cert to 400m that I'd sell
>you for super cheap. Like all of it for $200
>Thanks,Scott Waters
>
>
>Sent from my U.S. Cellular® Smartphone
>-------- Original message --------From: hank pronk via
>Personal_Submersibles <personal_submersibles at psubs.org> Date: 6/10/17
>12:38 PM (GMT-06:00) To: Personal Submersibles General Discussion
><personal_submersibles at psubs.org> Subject: [PSUBS-MAILIST] syntactic
>foam. 
>I have an idea, but not sure if it will work.  My idea is to fill a
>neutrally buoyant container with macro and micro spheres.  After the
>container is as full as possible, then fill with an environmentally
>friendly oil.  This would be more buoyant than using a resin and less
>complicated and cheaper.  My concern is, how well will the spheres
>stand up against breaking from being in contact with the other spheres
>and the container.   Are these spheres delicate?
> Hank_______________________________________________
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