Carbon fiber, one of the Titan submersible's experimental materials, comes under scrutiny

AOL ^ | June 23, 2023 | TOM COSTELLO AND MELISSA CHAN AND MARLENE LENTHANG

[xxqqzz]

The one-of-a-kind Titan submersible that imploded on its descent to the site of the Titanic this week, killing all five passengers, was made with experimental materials, including carbon fiber, which experts say has not been pressure-tested over time in such extreme depths.

Since the fatal dive, the innovation behind the Titan and OceanGate Expeditions — the company that owned and operated the vessel for paid tours to the Titanic — has come under increased and intense scrutiny.

Days after the Titan was reported missing, sparking a frantic search, the U.S. Coast Guard said Thursday that the 22-foot craft imploded, though officials do not yet know when or why.

[rdcbn1]

If the reports are true, the vessel was almost completely hoop wound carbon fiber tows, which means the vessel had virtually zero strength in the longitudinal direction because there were no carbon fibers in that direction to hold it together. only weak epoxy type resin.

It worked for a few dives because the loads were mostly all in compression but eventually matrix cracking caught up and caused a failure. Had the vessel been subjected to positive internal pressure it would have exploded at a very low pressure

Back in the days when boring 50 year old white engineers were still 20 year old innovators, carbon fiber filament wound pressure vessels were the state of the art for solid fuel rocket motor cases.

They had to be pressure tested before filling with the solid fuel so they were filled with water and pressurized to a thousand or so psi. They had so many leaks due to voids and air pockets from the winding process that some looked like sprinkler heads.

No big deal because they used a rubber liner to seal the leaks which was adequate because the vessels only saw positive internal pressure and they only had to live for a couple of minutes.

[griffin]

It’s just fine, if used correctly in the right application.

The long strands run one way in any particular ply. You pile up the plies an proportion to the loading direction magnitudes for your application. It’s like plywood.

Just because someone uses 1/4 inch plywood, or thinner, instead of 5/8 for flooring....and an elephant falls thru after 5 jumps....doesn’t make it the plywoods’ fault. It’s the builders fault for not using the proper laminate layup.

[ProtectOurFreedom]

1. It is impossible to use non-destructive testing (NDT) on composite materials and get useful results.

2. The carbon fiber was wound onto the mandrel without using a criss-cross pattern which results in a weaker pressure vessel.

3. Carbon fiber is a very brittle, not ductile, material. Look at the mess on the track after any Formula 1 crash.

3. You have the differential thermal expansion problems you mentioned as well as differential strain caused by pressure.

4. Carbon fiber suffers its own type of cyclic fatigue and this submersible had been through quite a few cycles.

5. The manufacturer of the acrylic viewport would not certify it for 4,000 meters. It was apparently certified for only 1,500 meters depth.

Other than those few minor things, it was a safe vehicle.

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I had not read that Rush bought old carbon fiber at a discount. Is there really an age limit on CF for aircraft usage?

[catnipman]

working link:

https://www.nbcnews.com/news/us-news/carbon-fiber-one-titan-submersibles-experimental-materials-comes-scrut-rcna90856

[butlerweave]

I read someplace yesterday that the sub only had about 20 hours of oxygen not 90

[Big Red Badger]

“It’s What Plants Crave!”
.
Yuppers....
I worked Indycars to Government Drones
total of 30yrs and Carbon Fiber has It’s place and the ‘To Old’ for use is True.

[rdcbn1]

That was one layer of of many, but it does seem that the vessel was designed and fabricated entirely made from hoop wound tows.

That constitutes engineering malpractice and criminal negligence.

I can't believe that the company that wound the vessel knowingly fabricated such a crime against nature.

Heck, I'm surprised that they were even able to pull the vessel off the mandrel it was wound on without breaking it in half if it was totally hoop wound

[griffin]

for long-fiber composites, I don’t THINK the matrix is designed to carry any load. That should not be going into any stress calc. Maybe in short-fiber...but I am less familiar with them.

Iirc the matrix only supports the long fibers - keept them in place and oriented. Kinda like a web of an i beam. I could be incorrect.. The main concern is the fiber in the geometry of the layup that are most stressed starting to fail, which in turn transfer the load to the next fibers, which are in a slightly less mechanically advantageous position to bear the increasing stress due to reduction in stress bearing area...it cascades until catastrophic brittle failure.

[butlerweave]

and no voice communication only text because they wouldn’t be heard over carbon fiber snapping

[griffin]

seems like something an over-egoed business guy would do. I am always disgusted that some people think they know better than a qualified, experienced engineer...especially when death is on the line.

[KC_for_Freedom]

I would add from experience that getting repeatible mix quality with resin materials is very difficult, our resin work in the defense industry was highly variable.

A number of missiles with fiber wound resin shells dis not perform well and had to be culled from the fleet. (Mix was inconsistant for a while, til we learned how to do it.)

[catnipman]

“But carbon fiber is inspiring to 20 something engineers.”

especially appealing to non-white male 20 something engineers?

[Big Red Badger]

“Use By Date”-———Yuppers.

[griffin]

BINGO

[griffin]

BINGO

[Abathar]

I own a tool and die company, I make the tools that make the rubber liners too. :)

[buridan]

Here’s an excerpt from a CBS interview with Rush, the OceanGate CEO and Titan pilot:

Rush: . . . We have eight acoustic sensors in there, and they’re listening for this. So when we get to 1,000 meters, if all of a sudden we hear this thing crackling, it’s, like, “Wait, did somebody run a forklift into it? You know, has it had cyclic fatigue? Is there something wrong?”

And you get a huge amount of warning. We’ve destroyed several structures [in testing], and you get a lotta warning. I mean, 1,500 meters of warning.

It’ll start, you’ll go, “Oh, this isn’t happy.” (LAUGH) And then you’ll keep doin’ it, and then it explodes or implodes. We do it at the University of Washington. It shakes the whole building when you destroy the thing.

So that’s our backup for the hull. And we’re the only people I know that use continuous monitoring of the hull.

POGUE: So if you heard the carbon fiber creaking—

RUSH: If I heard the carbon fiber go pop, pop, pop, then the gauge says, “You’re getting a whole bunch of events.”

POGUE: Could you get three hours back to the surface in time?

RUSH: Yes. Yes, ‘cause what happens is once you stop going down, the pressure, now it’s easier. You just have to stop your descent. And so that’s what we did a lotta testing on. You know, what kinda warning do you get?

And as I said, the warning is about 1,500 meters. It’s a huge amount of pressure from the point where we’d say, “Oh, the hull’s not happy” to when it implodes. And so you got a lotta time to drop your weights, to go back to the surface, and then say, “Okay, let’s find out what’s wrong.”

I read speculation somewhere that the submersible was on the way up when disaster struck. I wonder if the ship monitoring it knew of problems and of a possible return or if it detected the noise of the implosion.

[butlerweave]

Hoop wound carbon fiber and glued to the titanium endcap.

In a filthy warehouse

[griffin]

beams have a tension side and a compression side. I bet they fail at the compression side, or at attachment points or at stress concentration points, no?

[catnipman]

“Still trying to imagine how they laid it up”

there’s a video of them laying it on that looks like a giant phonographic wax cylinder spinning slowly while a shuttle goes slowly back forth while the spinning cylinder pulls the fiber from a reel glue while glue coats the fiber ...