In the article Hyperloop: the doubts persist, it is claimed that the hyperloop could implode due to a crack in the tunnel wall. The argument is supported by the claim that air would rush in at the speed of sound.
The atmospheric pressure on the tubes under vacuum would be 10 tonnes per square metre, basically the weight of a lorry. With just the slightest crack, outside air would enter the tubes at the speed of sound, and the infrastructure would implode.
I fail to understand how an increase in internal pressure, (1.)assuming it's still below the external pressure) would cause a tubular structure to implode, since (2.)generally at an implosion, the external pressure generates a failure mode of the structure.
What I can imagine is that the relatively (w.r.t. the structural design) large forces and intense aerodynamics create resonance which could trigger a failure mode, which in its turn could lead to failure of different sections in the form of an implosion, but it seems to me that such a conclusion would require very detailed (computational) analysis, something that is not referenced. On top of that it would (3.)likely also depend on design details/iterations which appear to not yet be available.
Discussion of assumptions:
- Due to the large velocity of the incoming airflow, it could be possible that locally the internal pressure could temporarily exceed the external pressure, but I do not have any reasons to assume that would be the case.
- Theoretically a design which experiences buckling under external pressure and a different failure mode such as "tension failure"/yielding under internal pressure and a material could perhaps be selected to fail in failure mode 2 with very low stresses compared to the stresses required for failure mode 1. Though this seems irrelevant in this discussion.
- If it is a known phenomena for just 3 single plain cylinders in series to all implode if 1 suffers a leak/crack under a vacuum, then it might not be necessary to have a complete analysis of the tubing system.
So in order to verify this claim based on empirical evidence, my question is: is it a normal/known phenomenon for vacuum tubes/spaces to implode when they get a single crack?
Up till now I have not found documentation of such events, when searching on tags: implosion, leaks, cracks.