Tourist submersible visting the Titanic is missing 101

[TugboatEng]

For such a critical joint I see some questionable prep work in the video.

-Bare hands touching the bond surface.

-Solvent wiping used instead of caustic degreasers.

-Poor wiping technique

-no surface profile/grit blast immediately prior to fixing.

My understanding of adhesives is general. The metallic component is to be assembled as quickly as possible after surface treatment (usually grit blasting) or primed. Titanium oxidizes very quickly in air. Adhesives form weak bonds with metal oxides. Over time, exposure to water forms hydrates with the oxides which breaks the bond with the adhesive. This caused joint failure.

 

[Cool_Controls]

Tug, I saw that too. The guy is wiping with bare hands and puts his ungloved hand on the joint face probably where he just wiped, I have also read pickling of the titanium is done some cases before bonding.

 

[JStephen]

Something I'm curious about- they have mentioned having oxygen cylinders onboard, etc. But they don't have any way to eject air from the sub when submerged- so if they start using oxygen cylinders, don't they build up more and more pressure inside there? Then what happens if they open the sub up again?

One of the videos I was watching just now said they had a timed-release sandbag that released after 14 hours no matter what, so if it's not flooded or imploded or hung up, it should be on the surface. And doesn't seem to be.

 

[Murph 9000]

I don't know who would pony up the cash to look for it. Also, It's doubtful to even be in the immediate vicinity of the Titanic, or it could be right on top. Who knows? If it's not, then due to it's small size, would be kinda like looking for a piece of a needle in a haystack.

One of the navies might decide to do it as a type of training exercise. Both Petrel and Proteus are new acquisitions, and a new type of ship for both USN and RN; they will be spending money on commissioning and training anyway, so it might not be a significant additional cost to do some of that in this area. Government spending can be a strange thing.

The Canadians also have a new survey vessel due in 2024, having just scrapped an older vessel of this type. I couldn't find much detail on it from a quick search, so not certain if it will be something suitable for this type of deep ocean work.

 

[LittleInch]

This gives you the best view I've seen of the inside etc and the rather errr off the shelf nature of some of the components.

https://youtu.be/29co_Hksk6o

CBS reporter who went dived down.

There really isn't a lot of vision down there....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ldeem]

I was looking around and found this article on the carbon fiber hull maker.

https://www.compositesworld.com/articles/composite-submersibles-under-pressure-in-deep-deep-waters

Link

Quite a read, delegated design and six weeks to do it. I assume that is design and fabrication. Now I am wondering if anyone looked at how the Ti ends and carbon fiber middle section would function together.

You would think the billionaire passengers would have someone perform due diligence on a craft like this risking their life.

 

[SWComposites]

“ Thickness, he says, was estimated using micromechanics, and then verified with finite element analysis (FEA).”. Wonderful. That sort of maybe can work for tension stresses, but can be highly unreliable for compression loading.

And a combination of prepreg plies and wet winding plies. Ugh.

 

[SWComposites]

And what a nice clean room for bonding.

 

[Cool_Controls]

That bonding process was about 2 steps above me doing PVC piping.

 

[enginesrus]

Do they have any sort of radio or ? contact with the folks on the sub? Most always there is some method of contact, what happened there?

 

[spsalso]

I recommend watching this video on the subject by a real submariner:

https://www.youtube.com/watch?v=4dka29FSZac

spsalso

 

[Cool_Controls]

Additonal background information
Link

 

[thebard3]

Carbon composites have been around for decades. I don't think there were any design festures that would be outside of established standards or known values. If this guy is right, it should be easy to determine.

Brad Waybright

The more you know, the more you know you don't know.

 

[Cool_Controls]

The view port only being certified to 1300 meters by the manufacturer is pretty damning and should be easy to verify.

 

[GregLocock]

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[GregLocock]

We used to bond titanium to composites. Shot peen, ultrasonic bath, MEK wipe, primer, suitable epoxy. The main problem is creating chemical 'ends' to bond to on the composite/old epoxy.

Never had a failure, but we were dealing with small components in a reasonably clean facility, not a shipyard.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[hacksaw]

Contact was lost 45 minutes into the mission.

 

[hpaircraft]

On bonding the titanium to the carbon, I sure would have wanted to see a lot more squeeze-out in that joint, as evidence of full coverage. Also, I rather wonder about the fiber orientations in their layup schedule. All they showed in the video was circumferential windings. That's all well and good to resist hoop stresses, but what about the longitudinal stresses applied parallel to the cylinder axis by water pressure on the dome ends?

 

[SWComposites]

if you read the compositesworld article linked above, it states that prepreg tape plies were laid up in the axial direction, presumably interleaved between the wet wound hoop plies. So essentially a 0/90 layup in the cylinder section; but we don't know the percentages of hoop and axial plies.

but yeah, that bond joint and process looks a bit sketchy.

also, there is likely waviness/wrinkles in the hoop plies so the compression strength will be reduced from "theoretical". filament wound cylinders work great for internally pressurized bottle and rocket motors, which puts the hoop fibers in tension. External pressure loads are much trickier to design for.

 

[TugboatEng]

ultrasonic bath, MEK wipe

This is a very important detail that I see often missed. Solvents only smear the grease/oils around. The part has to be fully degreased before it is solvent wiped. The bath removed the greases, the wipe removed residual dust.