Originally Posted by
Zumba
Martin, good point on the buckling issue. Similar to how a can filled with soda is is much stronger than an empty one, even though liquid clearly has zero structural properties. In the case of the soda can, the liquid has no place to go, and because liquid is not compressable, it acts like a bottomed out spring (after the co2 fizz has compressed).
The foam technique is very interesting because foam is filled with tons of air pockets. What prevents it from flexing just a like a seat cushion?
When filling a pole with foam, I'm guessing that the foam is basically there to contain air. The tiny pores of dense urethane foam act like damper valves to prevent the air from escaping to quickly. This would prevent the pole from denting (and consquently buckling) as a result of shock loads. But for rigidity under constant loads, I'm not sure how much it would actually do.