Quote:
Originally Posted by JamesCH95
Plastics tend to have brittle failure modes in dynamic situations, which is why they generate shrapnel, and why they are generally a terrible choice for pressurized gas applications. Not to mention their sensitivity to temperatures, certain chemicals, nicks/scratches/gouges, over-tightening, etc.
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Exactly right about this: the ductile vs. brittle failure modes are a critical distinction between metal and plastic tanks. It would take an extremely (and unrealistically) high strain rate to cause an unhardened metal tank to fail in a brittle manner.
Quote:
Originally Posted by JamesCH95
The reason why teams use plastic tanks is because they are lighter than the stainless tanks from Clippard. Unfortunately, this low weight comes at the price of strength and durability. Stainless steel has a significantly higher strength:weight ratio than polypropylene.
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Incidentally, the carbon fibre skin on the Boeing 787 is (in some places) thicker than structurally necessary because it needs to be resistant to penetration by objects like baggage carts. Physical damage tolerance is often an application-specific requirement, and may not be adequately regulated in the FRC rules.
One can conceive of a similar situation with conventional ductile metal tanks: you could make them very thin and still strong enough to withstand the pressure load, but any damage could cause them to fail (albeit in a ductile way). (Contrast this with a hypothetical
hardened (i.e. not ductile) metal tank: paper-thin and very strong, but if damaged, it shatters. That would be a bad design in this application.)