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Let's say I have an iron cube of 1 cubic meter and I want to make an aquarium out of it.

To hold water I want to wind stretch plastic film around the walls of that experimental aquarium.

Let's assume that fish and water are harmless for the plastic film, and that the water level is H from the bottom. There is also no leakage because stretch film has been smartly applied, and a rock solid table with concrete feet is carrying the aquarium. So nothing except the water pressure on the side can damage the aquarium walls.

I need to know how many revolutions I have to make around the side walls so that the stretch film does not break.

I am also trying to compute this value (number of wraps) theoretically but it gives me headaches.

That's why I am planning to measure it on a mock up wall as small as possible to save plastic film because I don't want to waste it since I don't have much.

  1. If I create a mock up of the frame of 30 cm x 30 cm, put a 10L bucket (base diameter 28 cm) full of water on it and if the plastic film does not break, can I deduce from this experiment that the film can sustain a pressure of 10 x 9,81 / (π x 0.14²) ~ 1500 Pa ?

  2. So on the lower part of the side walls the water pressure will be $\rho_{water} \cdot g \cdot H$ ~ 1000 x 9,81 x 1 ~ 10kPa when the aquarium is full.

Consequently the 40 cm wide stretch film will have to resist a pressure of 10 kPa on the lower winding.

So in that example I will have to do at least 10 /1,5 ~ 7 wraps to allow the walls to resist the water pressure.

Is my experiment process correct, can I follow it and be sure the walls won't break?

ChewingGumXpert
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  • Worth looking at this: https://engineering.stackexchange.com/q/52152/10902 – Solar Mike Aug 16 '22 at 21:30
  • Also think about the pressure on the walls varies with the depth of water. Also, if you wrap around the frame the force of the water will push the film off the frame, so perhaps some inside layers... – Solar Mike Aug 16 '22 at 21:32
  • Are you and @ChewingGumExpert the same? – Solar Mike Aug 16 '22 at 21:33
  • @SolarMike Yes we are ! Just a login problem! Right, the water force will be on the plastic enveloppe. Maybe it should be wound differently or an external layer may be required. – ChewingGumXpert Aug 17 '22 at 04:56
  • Re, "...a rock solid table with concrete feet..." How about the floor beneath those feet? How strong is that? Just the water alone is going to weigh a ton. Add the weight of the iron frame, decorative rocks and gravel, and the concrete table itself... Where I live, the local building code only requires the floor in a residential building to withstand $40\text{lb}/\text{ft}^2$. That means, I'd either need to evenly spread that load over an area greater than $55\text{ft}^2$ ($5.1\text{m}^2$,) or else I would have to reinforce the floor under the table. – Solomon Slow Aug 17 '22 at 14:13
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    @SolomonSlow good point to pay attention to in a flat but here aquarium is laid in a garage with a floor made of 20 cm reinforced concrete. So it should be ok in that case. – ChewingGumXpert Aug 17 '22 at 15:43

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