Why did the Titanic tour submarine implode?

Did the Titanic tour submarine undergo rigorous testing?

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no

 

Edited for edits

Not enough; it seems.

The vessel needed to be tested to failure; an expensive proposition. But cyclical failure needed to be well understood.

 

Implode, not explode. And I agree with Fallguy; this should have been tested to failure. Multiple times. Especially in a situation where lives are on the line.

 

"should have been tested to failure, multiple"
Not necessarily, many of the pinnacles of engineering accomplishment are created without a "tested to failure" process. Certainly 90% of the space vehicles, submarines, surface ships etc and tens of thousands of other
mechanical systems

It is doubtful that they would built several Titanics and run them into various icebergs to be tested to failure.

There are literally hundreds of books which describe "Non-destructive Test Procedures", and I would imagine the Titan would have undergone such procedures as somewhere a group of engineers applying Generally Accepted Engineering Principals, would have had to sign off on.

Certainly errors are made, the seal failures on Challenger being a history making event where in the investigation afterwards, found that the engineering group notified management that these seals had never been tested
at lift off temperatures.

My only point here is that Testing to Failure is often not feasible in many circumstances

Perhaps a giant skid ?? Just joking

 

I beg to differ.
This is a submersible, therefore the shell is subjected to many cycles during its life time, fatigue.
Fatigue of isotropic materials is well understood and documented.

But composites not so.
And with composites, you need seriously strict QA to ensure you get the same final laminate each and every time.

This can only be done via testing, and rigorously to failure to ensure the whole mechanisms of the stress-strain and CTOD is fully understood.

 

Why did it Implode ?
Um, Intense Hydraulic Pressure, surely ?
For the sake of painful accuracy, I think you mean "Why did the Hull fail to resist the Pressure, on this occasion, after so many successful tests", as the other answers have assumed.

My Google search came up with Titanic sub: Safety concerns raised about missing submersible https://www.bbc.com/news/science-environment-65977432

"US court documents show that David Lochridge, the company's Director of Marine Operations, had raised concerns in an inspection report. In a May 2021 court filing, the company said Titan had undergone more than 50 test dives, including to the equivalent depth of the Titanic, in deep waters off the Bahamas and in a pressure chamber."

But, in the same article

"1) In the court documents, Mr Lochridge claimed the hull had not been properly tested - where it's placed under extreme pressures and analysed to look for potential problems.

He claimed that trials on a smaller scale model of the sub had revealed flaws in the carbon under pressure testing."

and

" 2) Mr Lochridge also raised the issue of the Titan's glass viewport. He claimed the company that made the material would only certify its use down to 1,300m."

and

"3) The hull of a deep-diving sub is usually spherical, which means it receives an equal amount of pressure at every point, but Titan's hull is tube-shaped, so the pressure would not be equally distributed.

"Titan is quite a different deep-sea submersible compared to those used in research," said Dr Roterman.

"Whether or not this design with composite materials represents a structural weakness would be for engineers to determine, however," she added."

So, Composite Fibre Recycling Stresses is just ONE potential culprit.

 

There are, indeed, some great difficulties to define and realize failure tests that trully represent real life cases. In the other hand, one should be aware that NDT -non destructive testing - is to be used in conjunction with DT - destructive testing -, so as to exploit the results of the NDT tests and decipher what is acceptable and what is not. Industries that are able to use only NDT for certain parts have got necessarily a QMS - quality management system - that one relies on to tell if NDT only is sufficient or not, based on comparison with previously made DT campaigns. Such a QMS is acquired by statistical sampling of DT results when a sufficient number of part is to be produced. If not, the part produced are at high risk. This happens to be the case for every prototype, made using new materials, new building technics, or new architectural designs. Unfortunately, some saddest part of the history of transportation shows that, at one point or another, failure analysis has always been part of the product development.

Composites are very difficult materials to work with. The introduction of composite parts in the AIRBUS airplanes and in the DASSAULT RAFALE jetfighters have required tremendous investissments and have been the cause of multiple and important delays in each project. For instance, at the beginning of the RAFALE production, at the start of the "S" curve so to say, 5 out of 6 structured wings were simply put to trash. 100% composite made, the building quality was just not enough to allow them to be mounted.

 

in risk analysis, it is oftenly refered to "T.O.P". Meaning that accidents generally occured, involving Technical, Operationnal and Personnal flaws, all together.

 

Yeahnah...

A couple of ideas, principles perhaps.

1. Not too difficult to test the vessel at 2x the intended pressure, unmanned.
2. Not too hard to repeat x 50; at least have this record and safety margin.
3. Make new vessel, repeat x1 at 120% of intended.
4. Check for fatigue etc and discard at < 50 cycles

Not foolproof, but for high risk activities....

 

What year was this?
The Dassault Rafale was developed along the year 1985- 1987 around the time of Beechcraft Starship, also a canard, at the time composite was at its infancy. To quote the article "The program was delayed several times, at first due to underestimating the developmental complexity and manufacturing learning curve of the production composite construction".

 

I wondered about one thing.

If there were a variation in the strength of the laminate; as we experience in boatbuilding; then over time; would that area move even the slightest bit? It seems like a no brainer to me that composites and this design would have the potential for serious shortcomings versus isotropic materials.

Or worse, a pinpoint or smaller sized bit of air, somewhere deep in the laminate that experiences pressures; just like a boathull bottom. The area, in cycling, would change in size, shrink and re-expanding and potentially starting some ultra small shear. Then on each subsequent use; that shear could grow. The famous David Pascoe rip on cored composites and simple hydraulic erosion of cored bottoms comes to mind.. Maybe any air would be fatal always and revealed in regular testing..or maybe the processes used are better, but I produced laminated parts yesterday under 30" of Hg and they have a couple spots of air..

The only way to validate the integrity of the existing hull would be perhaps some form of xray or other; because pressure testing the ship (in use) would add cycles.

it seems fair to say; mistakes have been made and the court case points to them

 

How would you test a 30 cm thick hull to withstand 6000 psi

 

Sounds pretty expensive, especially since the target depth was about 3700 meters. And you need very strong cables to lower an unmanned sub to 7400 meters.

I'm sure you guys all know or know of people who enjoy taking extreme risks, which sometimes kill people. E.g., first runs of extreme whitewater rivers, surfing giant waves, climbing dangerous mountains. People figured out the diving tables, because of other people who died. Astronauts. Early parachute and wing suit users. Etc. Ice climbers and arctic explorers. Trans oceanic single ship sailors. For that matter, people who fly ultralight composite material aircraft, while presumably safer commercial aircraft are mostly metal.

You could make similar comments about them, and the people who make their equipment.They all do things without "adequate" testing.

Do I remember reading the cost of these trips was already about $250,000? Imagine the cost if you tried to make them as safe as your average cruise ship, like the Titanic, tries to be.

Though maybe the Titanic isn't the best "safe" example. Though it passed the safety certification tests that ships of her time were required to pass. The safety certification rules were altered in light of her failure.

AFAICT, engineering often advances through studying failures. E.g., bridges, dams, buildings... Will that happen here?

Here is a cool article about DIY submarines:
The Wacky, Risky World of DIY Submarines https://gizmodo.com/the-wacky-risky-world-of-diy-submarines-1827864616

 

Why use carbonfibre? It only works in tension while the epoxy handles all the compression load, so he essentially built the thing out of epoxy instead of titanium. Is that a sane choice? The tube shape does mean that some of it was under tension along the length of the tube, but only once it started to buckle inwards around the middle, by which point it would have failed anyway, so the carbon fibres were redundant. Maybe using that material made it sound stronger to customers so that they would feel more confident.