I think one thing they missed here is pointed out by this statement in the article:
"[...] in less than two years, and, says Brandt, require fewer support pylons. “Elon’s estimate calls for about $2.6 billion for concrete, but we’d get that down to more like $1.5 billion,” he says."
The pylons aren't purely for lifting the steel, they're also for distributing the weight of the Hyperloop cars. If anything, an equal length of carbon fiber tube would be more flexible (not less) than the same length as steel and would potentially require the same number or more of pylons.
The air that these cars float over does not negate gravity or the effect of their weight on the tunnel that they travel through.
All that being said, it looks like our current carbon fiber pre-preg (http://en.wikipedia.org/wiki/Pre-preg) production is currently able to handle a construction project like this. According to Wolfram Alpha, a cylinder 9 feet in diameter from Los Angeles to San Francisco would have a surface area of approximately 52 million square feet.
According to the book "Boeing 787 Dreamliner" by Mark Wagner and Guy Norris, in 2007 Boeing actually expanded the capacity of carbon fiber plants they had access to in France, Japan, and the US from 125 million square feet per year to 363 million square feet per year. I would hope that 6 years later we would be able to produce 52 million square feet.
I have a few questions stemming from ignorance. These aren't meant to me rhetorical in any way. I'm just curious how my understanding is incorrect.
I was under the impression that carbon fiber was "stronger" than steel. I understand that stronger doesn't always mean more rigid, but I was also under the impression that carbon fiber could be woven in different ways to offer greater rigidity on a desired axis. Is it possible to construct carbon fiber in a way that is more rigid than steel?
Couldn't they also increase the amount of material used, or does that not increase rigidity? I'm thinking something like 8-ply vs 6-ply, or something like that. I'm speaking entirely from a layman's view, so I'm curious why increasing the number of plies wouldn't work.
This is interesting because they could potentially avoid the thermal expansion problem that would otherwise sink the hyperloop. Carbon fiber has a negative coefficient of thermal expansion in its axial direction, and you can pair it with a metal to get a net zero expansion structure.
That is a really good idea. But I wonder if carbon fiber wouldn't be very expensive for a static structure like that.
Why not use much less expensive glass fiber? Compared to steel it would still be much stronger, lighter and be manufactured in one piece, without welds.
Perhaps glass fiber is not rigid enough? Also, I think the only reason carbon fiber is so expensive is the manufacturing cost, if you're paying for the machines anyway, perhaps the cost isn't that much higher.
I'm not sure there is that much production capability for Carbon Fiber. Back in 2011 Audi attributed the delay in the Debut of the Audi R18 LMP as being due to the global shortage of Carbon Fiber caused by the 787 Dreamliner program(Not to be confused with the Mazda 787B).
This makes the Hyperloop concept feel vastly more feasible. And manufacturing carbon fiber at those scales will open up all kinds of new infrastructure/architecture possibilities. The biggest question on my mind is: how does one continuously infuse/cure epoxy?
Hmmm. I'd have to see this run through an earthquake model. It seems to me that having them stacked/connected vertically would cause problems during an earthquake.
Think about those coffee stirrer straws that look like a figure 8 (it's a single straw pinched in the middle): if you hold one between your fingers the range of movement left/right is easy but an up/down movement is quite difficult (and if you push hard enough the straw buckles).
There's usually significant vertical and horizontal displacement during an earthquake. My thinking is that Elon's original design would fare better.
Regarding ground changes, we can look to current bullet-train rail systems. Nobody has ever died on a bullet train in Japan due to earthquakes. I saw on a documentary that Japan feed seismic sensor data into train control centers where any dangerous seismic event would trigger automatic stopping of the trains.
No passenger has ever died on the Japanese Shinkansen, but a train was derailed during an earthquake. The safety of high-speed trains, both in Japan and elsewhere, also relies on safety during a derailment by keeping the train rigid and having steel cars. In contrast, it seems to me that a breach of the integrity of the hyperloop tube would probably be fatal. Also, the higher speed of a hyperloop makes automatic stopping take longer.
In all, the hyperloop as it's currently being presented is much more dangerous than high-speed rail during an earthquake, and this is a legitimate concern.
It does require a near vacuum. At high speed, the tiny amount of air in the tube gets compressed to the point where it plays a significant role in the dynamics of the train's motion. So, both are true.
How are the safety aspects with steel or carbon fibers, considering that it will be close to roads and lots of people will have close access?
Could the (near) vacuum be compromised by any idiot with a hunting rifle and bullets optimized for piercing body armour? (At a minimum repairs and off time for a day or more.)
Can a kg of explosives put shrapnel through it and create a big crash? What is the safety distance for one of those Iranian self-fusing penetrators used in Iraq?
Also, railways are not really meant to be safe against attackers with physical access to it (so basically anyone). For example, the sensors/switches on a railway that cause a train to perform an emergency halt if the train driver misses a stop signal can be modified by anyone near it - no encryption, no locks (source: https://www.youtube.com/watch?v=xwaKYZfgY8k - only in German though).
You don't even need explosives, a simple wedge welded on a rail would be enough. In the end, I don't think it is economically feasible to secure a railway against that (as well as any other kind of track). You have to make sure that nobody does stupid things like these.
"[...] in less than two years, and, says Brandt, require fewer support pylons. “Elon’s estimate calls for about $2.6 billion for concrete, but we’d get that down to more like $1.5 billion,” he says."
The pylons aren't purely for lifting the steel, they're also for distributing the weight of the Hyperloop cars. If anything, an equal length of carbon fiber tube would be more flexible (not less) than the same length as steel and would potentially require the same number or more of pylons.
The air that these cars float over does not negate gravity or the effect of their weight on the tunnel that they travel through.
All that being said, it looks like our current carbon fiber pre-preg (http://en.wikipedia.org/wiki/Pre-preg) production is currently able to handle a construction project like this. According to Wolfram Alpha, a cylinder 9 feet in diameter from Los Angeles to San Francisco would have a surface area of approximately 52 million square feet.
According to the book "Boeing 787 Dreamliner" by Mark Wagner and Guy Norris, in 2007 Boeing actually expanded the capacity of carbon fiber plants they had access to in France, Japan, and the US from 125 million square feet per year to 363 million square feet per year. I would hope that 6 years later we would be able to produce 52 million square feet.