[lgalla]

Zunba hope you don't mind me asking direct questions,but you seem to have good answers.On tube filling and deflection.Does the modulas of each material really addup?Example from only a hands on experience.If I fill a 4"X1/16"wall aluinium tube with lightweight urethane foam,you can drive your car over it and not crush it.I would guess the defection is less although the urethane foam only is 15psi.Joining 4 walls of tubing with lightweight filler appears to increase the moment.Any thoughts on the subject?Thanks
Larry

[Zumba]

If I fill a 4"X1/16"wall aluinium tube with lightweight urethane foam,you can drive your car over it and not crush it.I would guess the defection is less although the urethane foam only is 15psi.Joining 4 walls of tubing with lightweight filler appears to increase the moment.Any thoughts on the subject?Thanks
Larry

That is interesting. In that particular example, I'm guessing that there are other factors coming into play. Perhaps the top face of the tube deforms, but at the same time, the car tire also deforms. At a certain point, the flat spot on the tire will be wide enough that the vertical sides of the tube begin carrying the weight. If this is the case, then the foam actually has no effect.

As for your main question, "On tube filling and deflection.Does the modulas of each material really addup?", I think yes.

The easiest way to test this would be to get a piece of steel pipe and an aluminum solid round. Turn the aluminum solid so that it fits snugly in the steel pipe. Then perform basic beam deflection experiments and compare to the calculated values. I think they'll match up pretty closely.

If you want to take it a step further, you could get a piece of aluminum pipe and steel solid round. Deflection should definitely be different. How much would depend on the wall thickness of the pipe.