Oceangate

[johnb2713]

At that depth, if the design wasn't good, it wouldn't have survived one trip, never mind 40.

The design must have had some merits but the longevity of it wasn't correctly considered, it's nigh on impossible to check carbon fibre for fatigue, it doesn't give you any warning of failure. It's possible that the craft was inadvertently damaged during launch, recovery, transport or maintenance.

 

[binky]

The design must have had some merits but the longevity of it wasn't correctly considered, it's nigh on impossible to check carbon fibre for fatigue, it doesn't give you any warning of failure. It's possible that the craft was inadvertently damaged during launch, recovery, transport or maintenance.

I was thinking the carbon fibre is probably what gave. It's strange stuff, super strong but, as you say, when it does fail, it seems to do so in a spectacular fashion.

 

[johnb2713]

I was thinking the carbon fibre is probably what gave. It's strange stuff, super strong but, as you say, when it does fail, it seems to do so in a spectacular fashion.

Its super strong in tension, not as good in compression, when it fails it's like glass, it shatters.

 

[Andy™]

At that depth, if the design wasn't good, it wouldn't have survived one trip, never mind 40.

every trip is destroying the carbon fibre internally. but unlike steel, you can't easily detect it

 

[Andy™]

I was thinking the carbon fibre is probably what gave. It's strange stuff, super strong but, as you say, when it does fail, it seems to do so in a spectacular fashion.

someone on reddit compared it to a rope

if you have a round loop of rope and try and expand it, it will take a lot of force before it breaks. force pushing it together it will give easily. put glue on the rope and it will still have excellent properties holding force in trying to get out, and it will give better properties holding force out, but it will still give, just a matter of how many cycles to break the adhesive between layers

it would also not take much for a single spot to collapse in slightly. as soon as that happens its not a perfect circle distributing the load equally any more and its gone. same would also apply to steel but it would take more force to do so

 

[Andy™]

At that depth, if the design wasn't good, it wouldn't have survived one trip, never mind 40.

can't remeber the flight number, but basically a 747 (i think it was a 747?) was damaged in a tail strike. it was repaired but they didn't do it properly. it survived another 20 years before it failed. the repair design wasn't good (just like the sub). but it did survive many flights before a failure. just because its survived a few trips doesn't mean all is well

 

[binky]

someone on reddit compared it to a rope

if you have a round loop of rope and try and expand it, it will take a lot of force before it breaks. force pushing it together it will give easily. put glue on the rope and it will still have excellent properties holding force in trying to get out, and it will give better properties holding force out, but it will still give, just a matter of how many cycles to break the adhesive between layers

it would also not take much for a single spot to collapse in slightly. as soon as that happens its not a perfect circle distributing the load equally any more and its gone. same would also apply to steel but it would take more force to do so

This what I was thinking, stress fracturing of the carbon. Add to that the extremely aggressive nature of the marine environment, and it didn't strike me as a good material to use. The guy who designed most of the sub was an aerospace engineer, wrong discipline no matter how talented an engineer.

True story from my days of building Naval weapons. For some reason the Army weapons department got the job of designing a piece of kit for frigates, to cut a long story short it rusted solid in a short space of time. Horses for courses...

 

[kerching]

When I was diving we regularly did 100/110m dives. Pressure at these depths is 11/12 times the pressure on the surface, but as the human body is mainly water the effects were not that great as long as you equalised and had the correct gases with you.. however we had a couple of goes in a recompression chamber. Took a polystyrene cup in, blew us down to 40m (5 bar pressure) poly cup compressed to thickness of a piece of paper!

Just my ha'porth of input

 

[UNG]

While the loss of life is a sad event the loss of this submersible is looking more like a case of the luck ran out and add into that a company CEO who apparently shunned any safety protocols because safety was a dirty word that slowed or stopped development.

Given the pressures involved at the depth the Titanic is at being around 400 times greater than the ambient surface pressure how would you and how did they verify the submersible was good for continued use after each dive as the pressure stress involved must have had an ongoing effect on the components used which ultimately resulted in the catastrophic failure during the latest dive

One I always remember back in the days when I was diving a mate of mine had a dive shop in Manchester and his cylinder test rig was able to reach higher test pressures than most rigs he was asked by another dive shop owner if he could test a cylinder as his test rig couldn't get it to the required test pressure, for those who are not familier with cylinder testing this is a hydrostatic test so water is used rather than air would would be very dangerous if the cylinder burst. So a cylinder rated to 3000 PSI would be tested to 5000 PSI the cylinder in question had already been on a test rig which could hit just under 10,000 PSI and the cylinder was showing signs of expansion so it was put on my mates test rig which could hit 20,000 PSI so more water was pumped into the cylinder and it was still well under the required test pressure when it burst at an equivalent test pressure of 18,500 PSI, when the cylinder burst it was quite spectacular with water everywhere and for safety nobody was in the room but watching through a window with a camera, I believe when the customer was told his cylinder had failed the test and shown the result he was quite upset and annoyed that his cylinder was destroyed. This cylinder was made of aluminium and quite old and had been tested many times before and had been filled and emptied many times over and the stresses involved had obviously taken their toll on the aluminium

There are certainly going to be a lot of questions asked in the aftermath of this loss and while a lot of what caused the loss is speculation at the moment I wonder how much of this submersible will be recovered for forensic examination to determine the cause but it is unfortunate that the company CEO will not be around to answer any of the questions that arise from this sad event as I suspect people involved in the company will be distancing themselves from his ideals

 

[johnb2713]

The situation with the sub is very different to testing a cylinder, the pressure is on the outside trying to collapse it. The slightest imperfection be it a scratch or gouge in the carbon fibre would cause a weak spot in the circle, once that occurs delamination follows shortly after and the aftermath we know.
Andy in post #45 has a great analogy which demonstrates carbon fibre in tension is excellent, very much like the divers air cylinder, it's very different situation in compression.

 

[Andy™]

I wonder how much of this submersible will be recovered for

considering carbon fibre shatters id expect them to find the titanium ends but the main carbon fibre tube will be in a few million shreds and mostly washed away. i don't think there will be much of it to recover

 

[apprentice87]

This cylinder was made of aluminium and quite old and had been tested many times before and had been filled and emptied many times over and the stresses involved had obviously taken their toll on the aluminium

So far as i can remember from the time i studied such things steel has a fatigue limit, that is, below a certain stress level, you could subject it to limitless reversals with no fatigue problems. We were taught that aluminium does not have a fatigue limit, so when subject to cyclic loading, will fail at some point.. That might have been pure aluminium though, the various alloys might be different..

john..

 

[binky]

So far as i can remember from the time i studied such things steel has a fatigue limit, that is, below a certain stress level, you could subject it to limitless reversals with no fatigue problems. We were taught that aluminium does not have a fatigue limit, so when subject to cyclic loading, will fail at some point.. That might have been pure aluminium though, the various alloys might be different..

john..

Aluminium work hardens, although I forget the details of how it works.

 

[johnb2713]

Aluminium work hardens, although I forget the details of how it works.

It does indeed as do most metals that flex. The problem with carbon fibre is it doesn't flex very much, it is strong but extremely brittle so when it fails it's glass, it shatters into small pieces. This may have been a small comfort to the passengers of Titan, according to a Royal Navy medical expert, the human body takes 150 m/Sec to respond to pain. The failure of the carbon fibre would have taken less than 1 m/Sec to elevate their pressure to the 5600 psi, they wouldn't have felt anything. Furthermore, the air when compressed to this pressure at this rate would instantly combust reducing their bodies to ash immediately. Amazing forces down there for sure.

 

[Andy™]

even if it was a steel hull that failed, death would have happened faster than they would know

compression would have raised temperature signaficantly (just like in a diesel engine), however the time frame woudlnt really allow their bodies to turn to ash. outer skin may have started to burn but the 350-400 bar (not sure on depth of failure) of water hitting them at high speed, complete with bits of carbon fibre, would have oblitered their bodies into nothing more than mush and they are now fish food

steel sphere, but being inside would be pretty much same result

 

[johnb2713]

even if it was a steel hull that failed, death would have happened faster than they would know

I suppose that is some comfort to the families.

compression would have raised temperature signaficantly (just like in a diesel engine), however the time frame woudlnt really allow their bodies to turn to ash. outer skin may have started to burn but the 350-400 bar (not sure on depth of failure) of water hitting them at high speed, complete with bits of carbon fibre, would have oblitered their bodies into nothing more than mush and they are now fish food

Well the naval medical professor expert chappie thought differently, it doesnt really matter really. There is both the temperature increase of the air and the bodies themselves when compressed I suppose.

steel sphere, but being inside would be pretty much same result

Thats pretty impressive

 

[Andy™]

Well the naval medical professor expert chappie thought differently, it doesnt really matter really. There is both the temperature increase of the air and the bodies themselves when compressed I suppose.

too many different things all going on at the same time. end result is still the same though

out of all the failures that could occur and ways to die through them, implosion was the best

 

[johnb2713]

too many different things all going on at the same time. end result is still the same though

out of all the failures that could occur and ways to die through them, implosion was the best

For sure, the number of people who had been invited on a dive but for various reasons didnt go are thanking their lucky stars now. It's not something I would want to do for sure.

 

[binky]

For sure, the number of people who had been invited on a dive but for various reasons didnt go are thanking their lucky stars now. It's not something I would want to do for sure.

especially not as they have completed a high def 3D scan of the wreck quite recently.

 

[apprentice87]

Aluminium work hardens, although I forget the details of how it works.

It does indeed, but work hardening would require that you be able to plastically deform the material. Obviously you could not do this with a finished fabrication.
The material hardens as a result of the distortion and deformation of the slip planes in the material [the creation of dislocations] that the material distorts along as you deform it. This means that the stuff basically "locks up" and so get harder in that further deformation is more difficult..

The other way to harden aluminium is to introduce something that will precipitate out of solution either as it cools, or in the days after, or as a result of heat treatment. The precipitated second phase fits in the interstitial spaces between the atoms of the aluminium, and once again, blocks the movement of the material along its slip planes.

Now, if you heat the aluminium, more and more of the alloying element will try to precipitate out. This means that the second phase material that was in the interstitial spaces in the space lattice of the aluminium will form larger crystals that will "pop out" of the space lattice, so now, instead of a true alloy, you will have a mixture in the way that you would have if you mixed dried peas with sand. This means that all hardening and strengthening is lost..

This is why only an idiot tries to "repair" alloy wheels, or indeed, powder coats them.. Unless you know EXACTLY the alloy and the heat treatment that is has [or has not] recieved, you can have no idea at all, as to what will happen..

Here i have something you will all like!! Make yourself a reinforced plastic sub, then screw your monitor to the pressure hull with self tapping screws..

john..