Teardrops n Tiny Travel Trailers

Guy , hot as it is here we still have to search for the good stuff … Not as common as we’d like …

And running the math on composites is a pain even when you have proper material strength charts; it’s not even possible to do more than ballpark with ad-hoc materials! The good old test a sample and go from there is by far the best way until you are trying to optimize or plan for mass production.

Do you not get PIR (polyisocyanurate) insulation in the US? The leading brand name over here is Celotex. It is so much stronger, and so much better an insulant than either variety of polystyrene that nobody here uses anything else. It strikes me as an ideal material for the use you guys intend.

X, individual testing was the most convenient and friendly method …

Mike , some people have used it … But we found it was more questionable , health wise … https://foursevenfive.com/blog/why-foam ... gredients/ and it’s brittle ...

My house is insulated with polyiso because I got it cheap from overruns and seconds. I think it’s too pricey for its small gain over other foams. Specifically the fact in immobile construction the use of cut and installed panels defeats the great advantage of foam and that’s the continual barrier by use of a gap filling air inhibitor. CCSPF (closed cell spray polyurethane foam) is better at one inch over three inches of other materials based solely on the air blocking, vapor control, and stiffening of the structure. R-value (or the U-value for ones across the pond) is poorer (by just a little) than polyiso but cutting and installing is the issue with regular insulation for the most part, where 50% (or more) is installed incorrectly and won’t match the predicted K value of the envelope anyhow.

Also, Polyiso is very brittle without skins. It sands down beautifully, and would be great for stack and shaping, It also doesn’t come back from minor indentations as easily, it likes to stay deformed. But if i found a supply of it for cheap I would use it again. A mobile camper included. But I wouldn’t pay more for it.

Doesn't polyiso also tend to absorb water after a long period? I feel like I have seen a saturated piece of it at some time in the past.

I can’t recall definitively but I believe it absorbed some. I left a few scraps around and after the snow melt I know their skins were ruined but think it only penetrated water 1/4” or so; not like a sponge. Admittedly, this is just a little bit, but more than a teardrop should see in its lifetime so should be fine. I never did a submersion and weight test...

If you can only get 1" locally, you can easily laminate sheets together with gorilla glue, using an overlapping pattern of loops

I built a camper out of 1" XPS. With a nice curve. It will span 5' on the roof. XPS is a lot stronger then EPS. If you want reinforce the roof. You could run a couple tubes(closet tubes) across the roof with a 1/2" space and a couple spacers between the pipe the the roof to supporting the roof and to hanger cloths on.

Xanthoman wrote:As far as the squared vs cubed strength; the equation for moment of inertia, I,which dictates bending max strength,Mc/I, is geometrically: bh^3, so yes it is cubic. But when you account for shear and other things it doesn’t translate exactly. .

Its been many years but I think you're considering deflection and I was addressing simple bending moment, which I'm pretty sure is proportional to the square of the depth.

I am not sure what you mean by simple bending moment...simple bending moment is just force,F, by distance,d, of moment arm. M=Fd. The way an object behaves has nothing to do with the moment as it deals with its own geometry, thus converting the effects of the moment, torsion, shear forces into stress. The greater the moment of inertia, I, the greater resistance to deformation geometrically. Material properties then come into play such as Young’s Modulus, E, (modulus of elasticity) which will dictate the deflection based on loading, P. Often the goal in design is to find a maximum acceptable deflection and then work to find the minimum deflection based on material and geometries involved and adjust to be within desired parameters. All these work down from total yield strength and making sure the combined stresses don’t deform the object or deflect it beyond the bounds. And I forgot the 1/12 value in my last equation for I of a rectangular cross section, I will edit that. I’m not sure exactly what you are referring, but I don’t recall anything being a simple square as you suggest...And without diagrams none of this mumbo-jumbo will mean anything to anyone who hasn’t taken a statics or strengths course at some point...haha

And to simplify things , When in doubt make the Foam THICKER …. We used EPS ( bead foam) that was 3.5” Thick ! And that over an aircraft style rib and stringer frame … Plenty strong … over 5 years now living Outside in the open …

The original intent of a Foamie … a basically Inexpensive, very Low maintenance travel trailer ...