Deep water sub - carbon fiber question

Triathlon Forum
1

Per this article

I found this line curious as it goes against everything I hear about CF bikes… Plausable? Is it because the CF is completely different than on a bike/fork/stem/handlebar?

“No leak is tolerable. A leak would cut through stainless steel or human flesh and mean certain death,” he said. "The depth is beyond the capabilities of any other craft, so rescue is impossible.
“It’s like being on the dark side of the moon,” he added.
Branson – who has coined the term “aquanauts” for those who go below 20,000 feet – was sanguine about the dangers.
“It’s very important if you do adventures that you do think about the worst eventualities that can happen,” he said, saying these included the pressurization system going wrong.
"We’re hopeful that, if that happens, because it’s made of carbon fibre, we won’t have a catastrophic failure, we’ll start hearing pinging sounds as the carbon starts to break.
“If that happens we will … come back up and go back to the drawing board,” he added.

2

My uneducated guess would be that in the past, vessels have been made of various metals that when put to failure at extreme depths will simply crush. There is no warning, once a tiny weak spot shows itself, it’s game over and the whole thing implodes. However, since CF is made of thousands (millions in their case), it “should” not simply implode, but will begin to fail more slowly since it is not all one single unit. My guess though is that if something starts to fail at 28k+ feet down, you don’t have too much time to boogy out of there before more failure occurs. The whole bike vs. vessel thing doesn’t correlate with eachother, bikes are faced with impact forces while this thing they built will have crushing forces from pressure.

3

No, it’s not. Filament wound composite pressure vessels have very different failure modes than, say, titanium pressure vessels. A carbon fiber pressure hull is susceptible to stress rupture, which is catastrophic - but as Branson is expressing, you MIGHT get some warning first. It’s unlikely that it would be enough at depth. This is what a composite pressure vessel looks like “naked”:
http://www.adoptech.com/pressure-vessels/main.htm
A Deep Flight Challenger hull was supposed to use similar techniques when it was first made public.

But no, this has nothing to do with bicycles. When your bike frame is pressurized to 15k-20k psi, then we’ll talk :stuck_out_tongue:

4

I would think that at those depths and pressures you would definately want some warning that the hull is about to breach. Ten minutes should allow enough time to drink a shot of whiskey and kiss your ass good bye.

Styrrell

5

You would have closer to a tenth of a second than ten minutes.

6

That is the sort of death that is best to happen suddenly and without warning. There is no hope, so no use having time to ponder it. Its the same rationale as not putting ejection seats on the space shuttle. You aren’t going to survive if it fails.

7

http://www.bathyscaphetrieste.com/bathyscaphe_deepest_dive.html

In all, Trieste’s descent to the floor of the Marianas Trench takes nearly five hours, passing from from the sunlit world, through the ‘twilight zone’, into the blackness of the deep-sea abyss. Finally the bathyscaphe enters the ‘hadal zone’ – unknown territory for any manned vehicle.

At 32,400 feet the bathyscaphe is shaken by a loud but muffled explosion, rocking Trieste’s cabin like a small earthquake. Has the bathyscaphe crashed into a rocky ledge on the trench wall? Has the float been punctured, causing Trieste’s precious gasoline buoyancy to leak into the ocean, dooming the Piccard and Walsh to an inescapable death on the deep seafloor? They don’t know it yet, but the explosion was caused by the cracking of a window in the bathyscaphe’s entrance tunnel.

Should they abort the bathyscaphe’s descent? According to the instruments, Trieste’s sink rate remains unchanged, suggesting damage is minor. Piccard and Walsh decide to continue to the floor of Challenger Deep, the deepest point in the Marianas Trench.

Nearly five hours after leaving the surface, the bathyscaphe Trieste settles on the bottom and comes to rest in a plume of pale mud. The depth is 35,813 feet. To his amazement, Piccard spots a flatfish scooting away across the seafloor, proving that life can exist in even the deepest recesses of the ocean.

After 20 minutes on the seafloor making scientific measurements and observations, bathyscaphe Trieste releases 16 tonnes of ballast and gently lifts off the sea bottom. The submarine breaks the surface at 4.56 P.M, and Walsh gently empties the entrance tunnel with compressed air. The cracked window holds, and the men breathe a sigh of relief – they are not trapped inside the pressure sphere.

8

Amazing that only 2 people have ever been to this depth. A truly unique achievement!

9

… A carbon fiber pressure hull is susceptible to stress rupture, which is catastrophic…

please expound on the term “stress rupture” you’re using here? This is a common metallurgy term and I think if you composite guys are using it too, they probably don’t have the same definitions as my field?

10

http://www.bathyscaphetrieste.com/bathyscaphe_deepest_dive.html

In all, Trieste’s descent to the floor of the Marianas Trench takes nearly five hours, passing from from the sunlit world, through the ‘twilight zone’, into the blackness of the deep-sea abyss. Finally the bathyscaphe enters the ‘hadal zone’ – unknown territory for any manned vehicle.

At 32,400 feet the bathyscaphe is shaken by a loud but muffled explosion, rocking Trieste’s cabin like a small earthquake. Has the bathyscaphe crashed into a rocky ledge on the trench wall? Has the float been punctured, causing Trieste’s precious gasoline buoyancy to leak into the ocean, dooming the Piccard and Walsh to an inescapable death on the deep seafloor? They don’t know it yet, but the explosion was caused by the cracking of a window in the bathyscaphe’s entrance tunnel.

Should they abort the bathyscaphe’s descent? According to the instruments, Trieste’s sink rate remains unchanged, suggesting damage is minor. Piccard and Walsh decide to continue to the floor of Challenger Deep, the deepest point in the Marianas Trench.

Nearly five hours after leaving the surface, the bathyscaphe Trieste settles on the bottom and comes to rest in a plume of pale mud. The depth is 35,813 feet. To his amazement, Piccard spots a flatfish scooting away across the seafloor, proving that life can exist in even the deepest recesses of the ocean.

After 20 minutes on the seafloor making scientific measurements and observations, bathyscaphe Trieste releases 16 tonnes of ballast and gently lifts off the sea bottom. The submarine breaks the surface at 4.56 P.M, and Walsh gently empties the entrance tunnel with compressed air. The cracked window holds, and the men breathe a sigh of relief – they are not trapped inside the pressure sphere.

i propose a challenge: sky-dive from the highest anyone has dove from, landing perfectly timed on the vessel and continuing your “free fall” to the bottom of this trench making the largest descent possible ‘on’ earth.

i don’t see any issues with that?

11

From those of us who have lived and worked in that arena…

When a submarine implodes no one gets wet while alive. The compressive forces (diesel effect) kills you before the water touches you.

However, many US submarines have suffered non-catastrophic flooding and lived to tell about it. Been there, done that. In those rare cases failure still occures in an instant, but not at the level that kills the ship. A 1/4 nipple blows off, a sea chest blow fails, a heat exchanged ruptures, those kind of failures. That type of failure, with all the safety systems and crew training, will still but the ship in danger if immediate actions are not carried out correctly instantly. Not to mention that there is an “operating envelope” of depth and speed that must be adhered to. That is why we consider ourselves a brotherhood like few other groups in the military.

This toy that is being discussed does not have the reserve ballast, safety systems, or operating envelope safety margin that would allow it to survive any abnormal/unexpected water intake. Simple as that. Either it works or no one know why it didn’t.

Real submarines (US and UK at least) are made of high yeild carbon steel, designed to compress and release with depth changes. (The USSR built a titanium sub back in the 70’s and it didn’t work so well for the opposite reason). Not being a materials engineer (ME barely) I have no idea what CF does under repeated compressive loads, but assume that it acts much like carbon steel in the respect of give and take without failure. Since it is lighter for the same strength it would have lots of benefits for use in a submersible. But giving you a failure warning is not going to be one of them.

MMCS(SS) Ret. Qualified on 637, 640, 688, and 671 class. ME/PE.

12

Kind off my point, did you think I meant a shot of whiskey, kiss your ass goodbye, then get out the tools and patch the hole? :wink:

13

Seems there would be quite a few advantages to composite hulls:

http://books.google.com/books?id=SjfgOfV8Am0C&lpg=PA90&ots=vFlOG_96ro&dq=carbon%20fiber%20submarine%20hull&pg=PA90#v=onepage&q=carbon%20fiber%20submarine%20hull&f=false

Fascinating stuff.

14

i propose a challenge: sky-dive from the highest anyone has dove from, landing perfectly timed on the vessel and continuing your “free fall” to the bottom of this trench making the largest descent possible ‘on’ earth.

i don’t see any issues with that?

Looks like someone tried 1/2 of that, grounded because of a lawsuit. Now, if he could land and jump straight into the submersible…

http://www.space.com/9338-record-breaking-red-bull-space-dive-grounded-lawsuit.html
http://www.space.com/9338-record-breaking-red-bull-space-dive-grounded-lawsuit.html
http://i.space.com/images/i/5724/i02/skydiver-supersonic-space-jump-100712-1-02.jpg?1292271417

15

I’ve got an interesting perspective on this one… I worked in a composites lab on an ocean floor depth (we were trying to break the record for autonomous vehicles) autonomous salvage and recovery robot. Pretty big vehicle, about the size of a delivery van. We used these 5gallon bucket sized unidirectional tow pressure vessels for the electronics. It was an computerized system to wind the tow (like a carbon tape of UD fibers) into the pressure vessels with a heat source hitting the tow right as it was joined to the vessel curing the and bonding the resin as we went. Walls were a good 1.5" thick, damn things looked likey’d survive a bomb attack.

Testing, I personally tested the smaller scale stuff down to 10,000 ft simulated depth. This was cameras and other smaller mock ups of the above vessel. We did this in a 2ft tall pressure chamber that we built that was charged with pneumatic brake fluid so that you didn’t get as much compression of the pressurized fluid and the danger was a bit less. Ever see a Jack antenna ball go in at 2" diameter and come out at .2…!

The larger chambers were tested in an underground pressure chamber. I remember when one of them failed at about 8,000ft simulated ocean depth. Felt like a small earthquake. Whole building shook and it sounded like a semi had just crashed into a brick wall. Based on examining the failure mode I believe (it’s been a while) that we decided that it failed all at once and not incrementally. Totall delamination and cracking of the vessel likely due to an inconsistancy in curing. Granted this is a failure mode that is likely less likely in say a quasi-isotropic fabric type layup but I still wonder about the failure mode on the sub.

ok, back to work.

16

Look up leak before break design. It is common that any pressure vessels have this criteria. It may be that in some instances (I am just speculating) composites are easier to design in this manner.

17

He can hope but it won’t happen. CFRP doesn’t fail like that. It fails catastrophically. Once the matrix cracking gets beyond a certain percentage it lets go, it’s done. The only way that this could happen is if they overbuilt it with XX times the strength required to hold the pressure. Remember that this is a *reverse pressure vessel. *The load is compressive and standard winding plies won’t work the same way. If they make it super strong, it will be very heavy, and the inner plies will probably not be fully engaged in the load.

We did a similar test for the 787 Dreamliner. We designed a joint in the fuselage, and then did a compression test to failure on it. At 100% it held, at 150% it held and the test was successful, but we kept going, at 200% it held. At 263% it failed suddenly and shot fasteners across the room. No cracking was heard, no indication of failure or location or manner of failure. The 100% load, on the order of 2.7 million pounds was equivalent to pulling a 9g turn on an airliner the size of a 767. There’s no way to actually do this in reality. The engines aren’t poweful enough, and the plane’s aero package keeps it from going faster, so there’s not enough energy even in a dive to pull this off. Boeing has airliner design *down. *
**
Steel has a particular advantage here: it will work harden when it starts to fail. Once a steel hull starts to go, it’s actually a little tougher than when it started. AND, the steel hull has a much greater ability to accept strain. There are very few materials that are tougher than high carbon steel, or high quality stainless steel.

18

Quick, someone design a whiskey injection system that shoots whiskey into my mouth at the first sign of a hull breach.

Maybe they could line the inside of the hull with a whiskey layer so that if the hull collapses you’re almost instantly surrounded by whiskey. I could die like that.

19

Composites are much more difficult to do leak before fail design. The K factors have to be experimentally determined based on the location’s individual geometry, unlike metals where material considerations drive the equations. It’s not impossible, but it’s very difficult.

And, again, this hull is under positive pressure. It wants to close the crack, not open it up. The failure mode is typically cross fiber shear, which composites are generally very bad at resisting.

It’s a really interesting design question.

20

what if its… carbotanium?