Oceangate sub allegedly used carbon fiber already past its service life

[da na]

Summary

It has surfaced (unlike the Titan submersible) that the hull of the ill-fated submarine was constructed from "cut-rate carbon fiber" deemed unusable for aircraft. A would-be passenger has alleged that the missing Oceangate submarine, already the subject of much scrutiny due to its poor build quality, had been constructed from carbon fiber sourced from Boeing. This carbon fiber was deemed to not be able to withstand sustained use in aircraft. This passenger alleges Rush, the CEO of Oceangate, says the carbon fiber was obtained at a "big discount". 

 

Take this with a grain of salt, since Boeing has not disclosed any sale made to Oceangate.

 

Quotes

Quote

Rush told Weissmann that "he had gotten the carbon fiber used to make the Titan at a big discount from Boeing because it was past its shelf life for use in airplanes," Weissmann wrote.

In his recollection, he asked Rush whether that was a problem, but he said he was told that the shelf-life dates "were set far before they had to be."

 

My thoughts

At the typical cruising altitude of 30,000 feet, an airplane has to endure from 4-5 PSI of pressure. The cabin is kept pressurized from 18-25 PSI. 
The CEO of Oceangate claimed the sub could travel up to 13,000 feet below sea level, subjecting it to around 1,300 atmospheres worth of pressure. One atmosphere is equivalent to around 14.7 PSI, meaning the sub should be able to withstand over 19,000 PSI to safely travel at such a depth. TL;DR, a very, very bad idea.

I may have done this math wrong. I am no expert on these formulas.

 

Sources

https://www.insider.com/oceangate-ceo-said-titan-made-old-material-bought-boeing-report-2023-6?amp

[Skiiwee29]

<-- Moved to Off Topic -->

[Supersonicwolfe]

8 minutes ago, da na said:

Summary

It has surfaced (unlike the Titan submersible) that the hull of the ill-fated submarine was constructed from "cut-rate carbon fiber" deemed unusable for aircraft. A would-be passenger has alleged that the missing Oceangate submarine, already the subject of much scrutiny due to its poor build quality, had been constructed from carbon fiber sourced from Boeing. This carbon fiber was deemed to not be able to withstand sustained use in aircraft. This passenger alleges Rush, the CEO of Oceangate, says the carbon fiber was obtained at a "big discount". 

 

Take this with a grain of salt, since Boeing has not disclosed any sale made to Oceangate.

 

Quotes

 

My thoughts

At the typical cruising altitude of 30,000 feet, an airplane has to endure from 4-5 PSI of pressure. The cabin is kept pressurized from 18-25 PSI. 
The CEO of Oceangate claimed the sub could travel up to 13,000 feet below sea level, subjecting it to around 1,300 atmospheres worth of pressure. One atmosphere is equivalent to around 14.7 PSI, meaning the sub should be able to withstand over 19,000 PSI to safely travel at such a depth. TL;DR, a very, very bad idea.

I may have done this math wrong. I am no expert on these formulas.

 

Sources

https://www.insider.com/oceangate-ceo-said-titan-made-old-material-bought-boeing-report-2023-6?amp

Aerospace Engineering (B.S.) and Mechanical Engineering (M.S.) here

 

A bigger problem is carbon fiber have been proved to work great in an environment that have expansion forces. E.G. Something high pressure inside, low pressure outside. Examples are: Scuba Tanks, Rocket propellent tanks, Aircraft fuselage.

 

This is quite a bit different when the outside pressure is higher than inside. Compression forces makes delamination between carbon fiber layers a lot more likely.

 

It's similar to concrete but in reverse. Concrete is very good at handling compression forces, but terrible at handling expansion forces (very easy to crack). This is why in reinforced concrete, steel rebars are used to help concrete to withstand the expansion forces, and other methods like pre-tensioned concreate are used to avoid the short comings.

[brwainer]

Regarding your PSI comparison: the sub’s carbon fiber walls were 5” thick - I don’t know about a Dreamliner’s walls but way less. I don’t think the PSI difference is what immediately makes this a bad idea. The sub had dozens of successful dives. It is the mechanical properties of carbon fiber overall that make it a poor choice for repeated cycles of compression and decompression - too stiff and not a homogenous material.

[Arika]

Quote

The CEO is one of the five passengers that floated down into the depths of the ocean towards the Titanic wreck.

In the interview in November 2022, he said: , "You know, at some point, safety is just a pure waste. I mean, if you just want to be safe, don't get out of bed, don't get in your car, don't do anything.

 

[Needfuldoer]

 

[12345678]

Why is this news making such hype?

[freeagent]

1 minute ago, 12345678 said:

Why is this news making such hype?

Because many other newsworthy things happened at the same time, this was chosen to keep the masses occupied.

[Supersonicwolfe]

17 hours ago, brwainer said:

Regarding your PSI comparison: the sub’s carbon fiber walls were 5” thick - I don’t know about a Dreamliner’s walls but way less. I don’t think the PSI difference is what immediately makes this a bad idea. The sub had dozens of successful dives. It is the mechanical properties of carbon fiber overall that make it a poor choice for repeated cycles of compression and decompression - too stiff and not a homogenous material.

You are right about the biggest problem with carbon fiber COMPOSITES. It's not homogenous material, making FEM analysis difficult and failure perdition much harder to do.

(We actually have formula and tables for load cycle/crack propagation prediction for metals. This is how we come up with when to inspect an airplane to do tear down "C check" and "D check" where an aircraft is taken all apart, takes weeks to complete.)

You mentioned it had successful dives, that is actually where thing start to fall apart.

 

Carbon fiber are sheets of material that is very good at horizontal strength. It needs resin to bond sheets together, which made it stiff. It's still very light, and more flexible than steel/aluminum even titanium. (Just look at how much a Dreamliner's wing 787/A350's wings can bend) Carbon fiber can deform more without going into plastic deformation.

However Carbon fiber is also not so predictable, number or layer, direction of layer, type of resin, autoclave temperature/vacuum pressure all affects strength/flexibility. Sometimes metal mesh is also layered into carbon fiber to reinforce them.

 

My point is:

When bending or expansion, the outer layer tends to delaminate earlier than deeper layers in the material, easier to pick up during an ultrasonic or even visual inspection. But under compression, the inner layer underwent stronger internal stress and delaminate INTERNALLY first...I also heard the company didn't even do ultrasonic inspection after dives...

 

Successful dives without visible external damage? That would give the people a false sense of success/safety.

 

The problem with carbon fiber is also not just my grudge. James Cameron (one of the few explored the deep sea, went to the Challenger Depth with sub he designed himself) said he and few other deep sea diving export had warned the company against using carbon fiber hull, but their warning was ignored.

 

It's just like the de Havilland Comet jet liners, the very first time engineers like me start to notice the significance of fatigue cracking and micro cracking.

 

One more thing: Thickness actually isn't be-all end-all. Do you know that we have discovered bottles of wine and champagnes from the Titanic? Titan (the sub that imploded, actually have 7inch thick walls, but like like I already stated, thickness is not the problem)

 

In the end, unlike aircraft manufacturing, which have a tight certification process (The Chinese C919 notoriously took 7 years to get certified by the Chinese themselves). Submersible on the other hand, is not well regulated and I hope in the future that can be changed.