Comment by regularfry
4 days ago
Carbon fibre, maybe? You could get a high continuous fibre content without layer weaknesses. That's got to be interesting.
4 days ago
Carbon fibre, maybe? You could get a high continuous fibre content without layer weaknesses. That's got to be interesting.
Yes indeed.
In my other comment I suggested carbon fibre flywheels (for energy storage). A design that stresses the rotor uniformly to near it's breaking point would make a great storage device. If it's possible to add density to the fibres but without compromising strength, even better.
For a solid material with equal strength in all direction the optimal cross section is one with an exponentially decreasing thickness.
To give an intuitive reasoning, the more radially inwards you go there's is more material and velocity on the outside that's straining to break free, so you need larger cross-section to resist that. But now, this extra thickness too has to be supported as you move inwards. One can make this formal as a differential equation and the solution is an exponential profile.
Anyhow, for carbon fibres the optimal geometry will depend on the weave because a fibre has different strength along different directions.
AFAIK, carbon fiber flywheels that are levitated in vacuum and that exceed the energy density of the metallic flywheels have already been made and used in certain experiments, even if I am not aware of any such flywheel being available commercially.
There was also some research for using such flywheels for energy recovery in very heavy vehicles with electric motors, e.g. tanks with a turbo-electric generator, but the use in a vehicle has obvious difficulties. Even if the flywheels are paired, to avoid influencing the mobility of the vehicle, that still causes high internal stresses in the case holding the pair of flywheels when the vehicle rotates, which can lead to fatigue failures.
Right.
I chose it as my undergraduate project literally several decades ago.
3D woven ones might be stronger as they might resist laminar separation of circumferential layers more. Going by units, the product of stress and volume has the same units as kinetic energy. So it appears breaking stress and volume might be what limits the stored kinetic energy. This addresses doubt and curiosity raised by one comment (not yours).
Actually this should be a call-for-proposal for Y Combinator, demonstrating carbon fiber knitting.
Carbon fiber is typically woven in a simple fashion, to keep the strands straight because high tensile strength is the key.
But if it can be shown that knitted structures can preserve the tensile strength, that would be interesting indeed.
Think about the recent Titan submersible failure due to carbon fiber construction. What if instead of sheets of carbon fiber that could delaminate, you had a solid knitted carbon fiber shape? You might be able to demonstrate knitting that has more isotopic strength under both compressive and tensile loads.
Nice idea! Both for woven goods and I guess parts.