The factor of three
A tank's job is to hold pressure times volume. Physics fixes the minimum material for that job: a vessel whose load is carried by fibres in tension needs a fibre volume of 3PV/σ, whatever its shape, while an ideal metal sphere, loaded the same in two directions at once, needs only 1.5PV/σ. So fibre starts at a factor of two disadvantage, about three once resin and real-world losses are counted, and still wins, because per kilogram it is ten to twenty times stronger than steel.
Predict · at 1:11 in the video
Now build the tank from fibres instead, carrying load only along their length. Give them the same strength per kilogram as the steel. Lighter, the same, or heavier?
Heavier. Twice as heavy. There is a neat result behind this.
This course is our own. These books go deeper.
- Composite Filament Winding, S. T. Peters (ed.), ASM International, 2011
- Filament Winding: a Unified Approach, S. Koussios, Delft University Press, 2004
Simulations in this lesson are our own. Where a number rests on an assumption, the video marks it with an asterisk and says where it comes from.
