Tourist submersible visting the Titanic is missing 101

[Tomfh]

Yes, some experience with externally pressurized cylinders; lots of experience with compression loaded structures in general

How about the fatigue and toughness performance?I hear they said the Titan hulls have been getting cracks in prior missions.

In the paddling world carbon-kevlar hulls are often more popular than pure carbon, because the carbon hulls, whilst stiffer and stronger, are far less tough. Carbons hulls simply break if you hit things. I’m not entirely sure if this is because they use less material in pure carbon hulls, or if it’s because carbon is inherently more brittle?

 

[enginesrus]

RIP to all, sad deal.

I'm thinking this is why submarines are not made from carbon fiber?

 

[JLNJ]

Maybe they found some parts floating.

 

[SWComposites]

Carbon composites generally have good fatigue performance. A 5 inch thick composite cylinder doesn't have a "toughness" issue for impact damage that a thin kayak hull has. Kevlar has higher toughness for impact, and higher strain to failure - that's why it is used for ballistic protection vests, and also for thin boat/kayak hulls. Kevlar is crummy in compression.

Titanium can develop fatigue cracks, similar to other metals. Its highly design dependent (stress concentration areas are critical).

 

[DrZoidberWoop]

This story gets more and more infuriating as the details about the company and CEO keep coming out. It's a bit hard not to make a mockery of the complete stupidity. What a perverse case of "trust the experts" this turned out to be. Props to that guy who backed out.

 

[KevinK2]

In one posted article about the emplyee who was fired because he was critical of the design, it was mentioned he wanted ND testing to be done and was denied. On the 3 spoke CFE Specialized wheel used in the TDF that I did the structural design for in 89, I used acoustic emission testing effectively during the testing part of the design. In hindsight, this aparently bright guy had false confidense in his design. The multiple titanium composite interfaces scared me, as dis the custom alternating wet hoop windings with axial prepreg .. starting and stopping filament winding? And under rated viewing port? He needed a real competent 3rd party design review, obviously. Sad day.

Kevin Kelleher, P.E. (retired)
Internal Mechanical Eng'g Consultant
DuPont ESD Specialists

 

[SnTMan]

It would be interesting if they could recover the view port, if nothing else.

Or, rather, the end containing it.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Tomfh]

Yes hopefully they retrieve enough to discover the root of the failure.

 

[JStephen]

One question answered, at least the US Navy heard the "ploop":

https://www.yahoo.com/news/navy-first-detected-titan-subs-221226319.html

 

[FacEngrPE]

Shells under external pressure are often buckling critical long before they reach the material compression limit.

https://youtu.be/CJSaAjJMK5w

ASME code may be considered overly conservative, but you really really do not want to operate near the structural buckling limit in any design.

Addition
Here is a video from WABASH using a tanker trailer, a shell with stiffener rings which shows the speed and suddenness of a vacuume buckling failure.

https://youtu.be/0N17tEW_WEU

 

[1503-44]

They've got a bunch of arrays out there listening 24/7

Dik, Attached the spreadsheet. The calculation goes something like this. Did it from FBD just now for a 6" ID to 24" OD cylinder, without looking in textbook, so might be just an approximation. Looks like it has enough curvatures.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Reverse_Bias]

Did the vessel have a black box or a voice recorder? If not it will be hard to figure out exactly what happened beyond an implosion.

 

[verymadmac]

https://preview.redd.it/1a9ml4czve7...ed&s=544f11c48f19a2970efc0282b54a486a395960a4

The off yellow boxes are buoyancy foam are they not, and if memory serves me right offer something of the order 50 to 100 kg per cubic meter of foam. There doesn't appear to be much payload for systems.

I note they talk about acoustic condition monitoring, is it of value in these loading cases.Is there any indication of pending failure in thick composites where the failure case is stability driven.

 

[SnTMan]

It would seem that if the view port failed, the composite cylinder would be fairly intact?

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[TugboatEng]

That is my thought as well. They said it broke into 5 major pieces. That would be 2 end caps, the tail section, the landing struts, and the cylinder. For all of these things to separate I believe the cylinder they're all attached to would have to fail.

 

[dik]

Thanks... I'll take a gander.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Reverse_Bias]

All Stockton Rush's interviews sounded almost comically negligent. Bragging about cutting corners to save costs, breaking rules, and hiring young inexperienced yes people. Some more comments about how safety isn't always practical. That attitude alone is worthy of a whistleblower no matter what industry you work in.

 

[jhardy1]

If the viewport failed first, wouldn't the sudden in-rush of water at 400 atmospheres over-pressure lead to some dramatic "water hammer" effects, which could lead to a subsequent failure of the CFRP cylinder or the titanium end rings?

Pure speculation - but I think that unless / until some major pieces of debris can be retrieved, we may not know the definitive failure sequence.

http://julianh72.blogspot.com

 

[KevinK2]

I wonder what FEA they did for the anisotropic material at the shell? I guess elastic buckling would work, for just the brittle composite shell, non-linear if the ductile titanium ends are included.

Kevin Kelleher, P.E. (retired)
Internal Mechanical Eng'g Consultant
DuPont ESD Specialists

 

[SnTMan]

Spitballing, but:

View port fails, opposite end bond holds, cylinder explodes

Or: opposite end bond fails, cylinder survives

??


The problem with sloppy work is that the supply FAR EXCEEDS the demand