Technical Analysis on Titan Sub (Titanic Sub)

[russ_watters]

I was trying to find a source to confirm this and haven't spotted one yet. However an engineer from the submarine community stated in an interview that carbon fiber has already been ruled out as unsafe for salt water submarines [at least]. The claim was that where you have a joint between carbon fiber and titanium, as at the end caps, because carbon is a metal, you get current flow between the dissimilar metals. This in turn starts to break down the epoxy used in the carbon fiber, which eventually begins to delaminate.

The claim was that this was clearly established some years ago. Additionally, carbon fiber is appropriate for tension, not compression. And lastly, cycle testing was refused. And that is where the problems occur. It isn't just the pressure. It is the number of pressure cycles that causes problems.

I'm not sure if galvanic corrosion has been mentioned in the thread before, but yes it is a known issue correction; not with titanium:
https://www.corrosionpedia.com/galv...ed-to-carbon-fiber-reinforced-polymers/2/1556

The other two issues ("fibers" do nothing in compression and cyclic pressure changes cause fatigue) have been discussed in the thread in some detail. Based on reports of loud cracking noises on prior dives, it's likely those two issues are the ones that doomed the sub.

 

[snorkack]

Another video related to sub implosions and sub rescue operations:

Stupid question: how can a submarine implosion have a bubble pulse frequency or it be usable to determine the depth?

 

[pinball1970]

Stupid question: how can a submarine implosion have a bubble pulse frequency or it be usable to determine the depth?

Thinking same. I can get the note part, Bigger the vessel the deeper the note, longer the wavelength.
(quick google) Translate to depth, deeper it it is, the higher the pressure, higher energy so higher amplitude? Louder? Mind you deeper it is the fainter the signal.
Need a physics/acoustics guy.

 

[snorkack]

Thinking same. I can get the note part, Bigger the vessel the deeper the note, longer the wavelength.
(quick google) Translate to depth, deeper it it is, the higher the pressure, higher energy so higher amplitude? Louder? Mind you deeper it is the fainter the signal.
Need a physics/acoustics guy.

Well, I have the issue with "bigger"/"known volume" here.
For explosion, the pulse frequency is easy. Underwater explosion in homogenous, spherically symmetric water would create a spherically symmetric bubble, apart from the pressure gradient, and that would still leave the axial symmetry intact. One bubble pulsing at one frequency that depends only on explosion power and depth.
But a submarine? Cylindrical vessel full of contents?
If the cylinder fails first at one end, the water hammer would then travel along the cylinder, break the waterproof bulkheads in succession and leave the bubble at the other end. But if the cylinder fails somewhere near the middle but not exactly in the middle then the water hammers travel from the middle towards both ends, creating two bubbles of different sizes and periods. Plus the large internal structures which have further potential to alter the bubble behaviour and split them. Bubbles with similar but different periods, close enough to each other to modify each other significantly...

 

[pinball1970]

Well, I have the issue with "bigger"/"known volume" here.
For explosion, the pulse frequency is easy. Underwater explosion in homogenous, spherically symmetric water would create a spherically symmetric bubble, apart from the pressure gradient, and that would still leave the axial symmetry intact. One bubble pulsing at one frequency that depends only on explosion power and depth.
But a submarine? Cylindrical vessel full of contents?
If the cylinder fails first at one end, the water hammer would then travel along the cylinder, break the waterproof bulkheads in succession and leave the bubble at the other end. But if the cylinder fails somewhere near the middle but not exactly in the middle then the water hammers travel from the middle towards both ends, creating two bubbles of different sizes and periods. Plus the large internal structures which have further potential to alter the bubble behaviour and split them. Bubbles with similar but different periods, close enough to each other to modify each other significantly...

Ok. The physics is beyond me here.

 

[Vanadium 50]

I'm out of my depth here.

Pun intended?

 

[pinball1970]

Pun intended?

Possibly yes. That's bad. Apologies to the people who are human beings on the site.

 

[berkeman]

Possibly yes. That's bad. Apologies to the people who are human beings on the site.

Hey, waitaminute. What about the rest of us?

 

[jack action]

If the cylinder fails first at one end, the water hammer would then travel along the cylinder, break the waterproof bulkheads in succession and leave the bubble at the other end. But if the cylinder fails somewhere near the middle but not exactly in the middle then the water hammers travel from the middle towards both ends, creating two bubbles of different sizes and periods.

When the structure fails, I would expect it to fail everywhere pretty much at the same time.

​

 

[Frabjous]

When the structure fails, I would expect it to fail everywhere pretty much at the same time.

​

I disagree. The composite probably failed at the largest flaw resulting in asymmetric failure.

 

[DaveC426913]

When the structure fails, I would expect it to fail everywhere pretty much at the same time.

Only on the time scale of human perception.

The fail started somewhere. That led to other failures in very short order.

 

[jack action]

What I meant is that I don't expect the water to "come from one end and reach out the other". Once the initial failure occurs, the rest of the structure collapses almost instantly and water comes in from everywhere. Something like this (in reverse):

​

 

[snorkack]

For Titan, there are, it seems to me, three relevant speeds.
First is the freefall speed from the 4 km height. Which is a bit under 300 m/s. Because this is the speed to which the pressurized water can accelerate itself under its pressure.
(Speed of sound in air is irrelevant because the density of air is too small compared to water).
Second is the speed of sound in water - about 1500 m/s. Because the water needs to be accelerated, and the unloading signal for water to accelerate must reach water for the water to start moving.
And the third is the speed of sound in the hull. In steel it is about 5000 m/s; but in carbon fibre, it is grossly anisotropic.
How does a failure propagate in the hull, compared to the propagation of the products of failure (inrushing water and the hull pieces it pushes ahead)?

 

[jedishrfu]

Here's a video discussion on a transcript believed to be from the Titan sub to its base ship:



The presenter stresses that since there has yet to be released a formal transcript that this may be a leaked version of it. He said the sub community is very tight and that it could well have been passed from expert to expert as James Cameron seemed to know details of the sub journey within a day of the disaster.

They mention the cracking sounds heard in the aft compartment where the equipment was stored. The passengers were walled off from it. The transcript implies a faster rate of descent than was in their planned descent and that they may have known for roughly 20 minutes that they were in trouble and couldn't ascend fast enough even after dropping ballast and their sled frame.

If true its a very sobering and sad transcript to witness.

In some way, it reminds me of the Challenger disaster.

 

[Rive]

The transcript implies a faster rate of descent than was in their planned descent

Assuming it's real that alone should have triggered an abort on the mission, right after the start
A submarine/submersible way over the specified mass (that's what the faster descent implies, I think) yet they kept on going...

 

[NTL2009]

Thread has died down, but I saw this (from an email update I think). Found it interesting. This company uses composites for their (unmanned) submersibles - but they appear to use sound engineering principles, including testing to failure.

https://www.designnews.com/industry/carbon-fiber-safe-submersibles-when-properly-applied

But with appropriate construction, that’s not a problem, CET asserts. To prove it, Hogoboom points to the record of his company’s products in deep-sea applications. “We’ve built vessels that we’ve cycled 200 times (to deep-sea pressures) and then brought to implosion and those fail at the same depth as new ones.”

The key is diligence in designing and testing the composite structures, Hogoboom explained. “We have a very high confidence in the strength of what’s been built,” he said. “We use engineering models, but we test to failure to validate what’s been modeled. That’s a crucial step that OceanGate has skipped," according to Hogoboom. “They never brought an exact clone to failure.”

 

[gmax137]

Link from another forum, no real surprises, but an interesting read.

The ‘Titan’ Submersible Disaster Was Years in the Making, New Details Reveal
https://www.vanityfair.com/news/2023/08/titan-submersible-implosion-warnings
To many in the tight-knit deep-sea exploration community, OceanGate’s submersible dives were reckless and often dangerous, writes best-selling author Susan Casey.

 

[Vanadium 50]

writes best-selling author Susan Casey.

Which makes her an expert exactly how?

If I were to use best-selling author Michael Crichton as a source on climate change, the Mentors would rightly beat me up on this.

 

[gmax137]

I understand your point, but her article is pretty good. I thought the read was worth the 10 minutes. EDIT The text in my post was just copied over from the other forum. Actually I think it is Vanity Fair's blurb.

 

[Astronuc]

Which makes her an expert exactly how?

Apparently Susan Casey writes non-fiction books on topics related to the ocean and ocean life. She is a diver, and she has participated in several deep sea expeditions. From the article, it looks like she did her homework. It appears she knows some of the experts, and she interviewed many experts in the field.

Casey is not writing a scientific or technical article, but a story (an account) about what went wrong with OceanGate, the consequences and some of the people involved.

Maybe someday Lochridge will publish his account, once all of the legal matters are resolved.

Meanwhile, Rush did develop an innovative way to commit suicide and homicide.

If I were to use best-selling author Michael Crichton as a source on climate change, the Mentors would rightly beat me up on this.

Although Crichton has written 4 non-fiction books, he did write on climate science, or climatology. Crichton wrote mostly fiction novels.

 

[Vanadium 50]

I agree it is a story. It has a hero and a villain and everybody wears either a black or a white hat.

However, I do not think that swimming with dolphins and writing for Oprah gives someone a deep insight into mechanical engineering and naval architecture.

 

[jedishrfu]

One other thing to note is that Michael Crichton has an MD degree from Harvard, which I'm sure educated his writing on Jurassic Park and other novels with biomedical lore and technology:

https://en.wikipedia.org/wiki/Michael_Crichton

He did run afoul of the climate change folks in his book State of Fear, where he cited evidence of Antarctic cooling as a counter to global warming.

 

[hutchphd]

On the other hand I don't think this is fundamentally a technical question. I am satsfied that lack of "testing to failure" of a design that was radical in both conformation and materials is simply nuts. Oprah understands nuts.

 

[Astronuc]

gives someone a deep insight into mechanical engineering and naval architecture.

She's not imparting some deep insight (of her own), but rather relating the opinions and actions of experts in the field:

Senior inspection engineer Jonathan Struwe from Det Norske Veritas (DNV), a Norway-based international marine classification society that is the gold standard for safety,
Captain Don Walsh, Navy deep submergence pilot number one. Walsh commanded the bathyscaphe Trieste in 1960.
Terry Kerby, veteran chief pilot of the University of Hawaii’s two deep-sea subs, the Pisces IV and the Pisces V,
Marine engineer Will Kohnen, chair of the Marine Technology Society’s Manned Underwater Vehicles Committee,
Rob McCallum, cofounder of EYOS Expeditions,
Patrick Lahey, an experienced submersible pilot,
Karl Stanley, a seasoned submersible pilot,

several of who apparently warned Rush. Perhaps they should have warned the larger community. Apparently some customers of OceanGate were warned and heeded the warning. Others apparently didn't get the warning about the danger of an unclassed, untested submersible going to depths of 3.8 km.

Certainly, writing for Oprah is not a qualification for scientific journalism. Casey however did talk to the right people, and she had some first hand experience with deep sea exploration.

 

[pinball1970]

I understand your point, but her article is pretty good. I thought the read was worth the 10 minutes. EDIT The text in my post was just copied over from the other forum. Actually I think it is Vanity Fair's blurb.

I read it too. Pretty damning.

I agree it is a story. It has a hero and a villain and everybody wears either a black or a white hat.

However, I do not think that swimming with dolphins and writing for Oprah gives someone a deep insight into mechanical engineering and naval architecture.

Gosh sir it is Vanity fair and she is a journalist reporting on the deaths of five people.
I don't think she is claiming to give extra insight just putting the info together into one article.

 

[Astronuc]

NTSB to Investigate Titan Implosion with Coast Guard
https://news.usni.org/2023/06/30/ntsb-to-investigate-titan-implosion-with-coast-guard

The National Transportation Safety Board will investigate the implosion that killed five people death aboard the Titan submersible as part of the Coast Guard’s Maritime Board of Investigation.

The U.S. Coast Guard, which served as the lead agency on the recovery efforts for Titan, opened a Maritime Board of Investigation June 25 to look into Titan’s last dive, which ended in the death of the five passengers aboard, including OceanGate CEO Stockton Rush.

As part of the NTSB’s investigation, it will determine probable cause and any applicable safety recommendations, according to a news release from the agency. The report is expected in the next year or two.

As with all such investigation, the authorities will seek to identify the proximate cause. Design, construction and testing (part of quality assurance) of the system will be another part of the investigation. I would expect part of the investigation will involved the same people interviewed by Casey.

 

[Vanadium 50]

I look forward to the report. I've read a few of them (OK, I am a nerd) and find them much more nuanced than other reports, Yes, you usually don't get the mustache-twirling villain, but you might get some insight.

Do you understand how they got jurisdiction? This is in Canadian waters. Sure the sub was manufactured in the US, but if a plane crashes in a foreign country, usually that country is responsible for the investigation, even if the plane was built in the US.

 

[pbuk]

Do you understand how they got jurisdiction? This is in Canadian waters.

The wreck of the Titanic lies in international waters.
https://en.wikipedia.org/wiki/Agreement_Concerning_the_Shipwrecked_Vessel_RMS_Titanic

The Maritime Board of Investigation doesn't have any jurisdiction: its role is to investigate and make recommendations, not to make judgements.

 

[Astronuc]

The wreck of the Titanic lies in international waters.
https://en.wikipedia.org/wiki/Agreement_Concerning_the_Shipwrecked_Vessel_RMS_Titanic

The Maritime Board of Investigation doesn't have any jurisdiction: its role is to investigate and make recommendations, not to make judgements.

Nevertheless, the Canadian Transportation Safety Board (similar to US NTSB) has launched an investigation and they will be cooperating with the US, UK and France as interested parties. The support vessel, Polar Prince, and Titan, left from a Canadian port, and returned to St Johns, Newfoundland.
https://www.tsb.gc.ca/eng/enquetes-investigations/marine/2023/m23a0169/m23a0169.html

the wreckage from the submersible Titan recovered by the United States Coast Guard (USCG) arrived in St. John’s Port. The TSB has inspected, documented, and catalogued the materials for its safety investigation. The materials are now in the possession of the USCG.

Canadian citizens provided support and the occupants of Titan were citizens or residents of US, UK, France, and Pakistan. Apparently Shahzada Dawood had citizenship in Pakistan, UK and Malta.

The TSB will continue to cooperate with the United States, United Kingdom, and France, in accordance with international agreements, as they are “substantially interested states” under the International Maritime Organization Casualty Investigation Code.

 

[Swamp Thing]

It's good to know that testing to destruction can empirically lead to a safe design.

But it has been pointed out (on this thread, I think) that carbon fibers don't contribute anything at all to a shell under external pressure -- at least when used in the conventional way. Have these people found a way to make the carbon fibers more effective under compression? Or does it just show that the epoxy alone can be strong enough if designed and tested properly?

Edit: Or have they disproved the idea that carbon reinforcement is not effective under compression?

 

[NTL2009]

It's good to know that testing to destruction can empirically lead to a safe design.

But it has been pointed out (on this thread, I think) that carbon fibers don't contribute anything at all to a shell under external pressure -- at least when used in the conventional way. Have these people found a way to make the carbon fibers more effective under compression? Or does it just show that the epoxy alone can be strong enough if designed and tested properly?

Edit: Or have they disproved the idea that carbon reinforcement is not effective under compression?

From the article I linked, not much detail, but:

https://www.designnews.com/industry/carbon-fiber-safe-submersibles-when-properly-applied

Some important aspects of the manufacturing process include the layout and fiber orientation of the carbon fiber cloth used.

 

[256bits]

It's good to know that testing to destruction can empirically lead to a safe design.

But it has been pointed out (on this thread, I think) that carbon fibers don't contribute anything at all to a shell under external pressure -- at least when used in the conventional way. Have these people found a way to make the carbon fibers more effective under compression? Or does it just show that the epoxy alone can be strong enough if designed and tested properly?

Edit: Or have they disproved the idea that carbon reinforcement is not effective under compression?

Disproved is a bit strong. They are tricky-er to produce a final compressive product due to the many manufacturing defects that can arise, such as voids, delamination. In addition, the destructive test sample of the material does not in and of itself does not lead to a "safe design" - simple reason being that the test sample does not completely give a realistic representation of how a finished product will act as a whole under use. And not just for composites anyways - if it was true for any material, an new airplane design could be does in months rather that years.

Following the thinking that "you cannot push a rope" is flawed, as a rope acts as a non-rigid material, not in itself designed for being pushed. Add a a hardening resin and the rope will have an increased capacity to withstand compression. Note that any long thin material whether it being a steel rod, or rope, will fail by buckling, Simply a baseless argument being put forward.

Compressive strength of composites is mainly not available in the literature, as most applications would involve the material being under tension, so why do the test.

the below is from
https://ieeexplore.ieee.org/document/9856658
with explanation
Two main issues were faced during the literature review of the material to know its mechanical properties. The first one is that although the composite chosen is very popular and used widely in many industrial and research applications, a wide range of the values of the mechanical properties was found with huge differences in comparison to the datasheets and other research work. The second problem is that some of the parameters do not exist neither in datasheets nor in scientific articles. Most of the parameters stated are in tension, while most of the compression values were missing. Table 1 shows a comparison between “Toray” T-300 composite and fiber properties from different resources. It is obvious that not only does a wide variation exist between the values of the properties, but also many properties are missing (the shaded cells) which are important to the design. These values, even if assumed, will result in completely wrong predictions of the stresses and the strains in the laminas, which led to the necessity of the experimental tests performed and explained in the following section.

One can see for the references given for the material, that is does have a compressive capability.
Note that the material datasheet does give only the tensile capability.

 

[pinball1970]

This today.

https://www.independent.co.uk/news/...plosion-human-remains-oceangate-b2427611.html

The investigation/inquest is to come.

 

[DaveE]

This today.

https://www.independent.co.uk/news/...plosion-human-remains-oceangate-b2427611.html

The investigation/inquest is to come.

"The Coast Guard reported that they also recovered additional presumed human remains from within the Titan’s wreckage, which were subsequently sent for analysis by US medical experts."

Um... Why?

 

[pinball1970]

"The Coast Guard reported that they also recovered additional presumed human remains from within the Titan’s wreckage, which were subsequently sent for analysis by US medical experts."

Um... Why?

DNA profiling perhaps?

 

[snorkack]

DNA profiling perhaps?

The highlighted word was "US".
So, why US medical experts, not Canadian medical experts?

 

[pbuk]

So, why US medical experts, not Canadian medical experts?

Because the US Coast Guard is leading the investigation. Why do you think Canadian medical experts should be involved?

 

[pinball1970]

The highlighted word was "US".
So, why US medical experts, not Canadian medical experts?

As opposed to the Canadian coast guard?
I do not know, the vessel was lost in Canadian waters?
This was in in the Guardian 10th Oct

The salvage mission conducted under an agreement with the US navy was a follow-up to initial recovery operations on the ocean floor roughly 1,600ft (488 meters) away from the Titanic, the Coast Guard said.

 

[pbuk]

As opposed to the Canadian coast guard?
I do not know, the vessel was lost in Canadian waters?

The wreck of the Titanic lies in international waters.
https://en.wikipedia.org/wiki/Agreement_Concerning_the_Shipwrecked_Vessel_RMS_Titanic

I don't know where this idea came from, it's more than 300 miles away from Canadian waters. Edit: and more than 100 miles outside the Exclusive Economic Zone where Canada has rights and jurisdiction over e.g. exploration and environmental matters (200 nautical miles).

Another edit: in December 2022 Canada lodged a claim under the United Nations Convention on the Law of the Sea (UNCLOS) to claim certain rights over part of the continental shelf including the location of the Titanic, however (i) this claim has not been ratified (or denied) and (ii) the main aims of the claim are to protect mineral rights and the environment, not to be responsible for investigation of marine incidents on the High Seas.

 

[DaveE]

Canada was involved because it left from a Canadian port, I believe.

 

[Tom.G]

There is a youtube video dated Oct. 19, 2023 and a comment by an aeronautical engineer about carbon fiber construction.

The comment is #2005 by @airas, at the top of the comment list as of this post.

The claim is faulty lay-up of the Carbon fiber during construction. Looks plausible.

Cheers,
Tom

 

[Vanadium 50]

Excellent video.

I disagree with the idea that one must test to destruction. (Although one could argue that's what this dive was) It is often impractical, and evem the US Navy doesn;t do this. I also question what would have been learned - if the first dive had 50% margin, wouldn't they have said "Great! Now we know we have no problem!"

I know little about winding CF, but a little about winding SC magnets, Now that I have, albeit briefly, seen how this is wound, I'd be worried about torsion. If the layers aren't perfectly straight, this will turn the water pressure into a twist.

 

[jrmichler]

I disagree with the idea that one must test to destruction. (Although one could argue that's what this dive was) It is often impractical, and evem the US Navy doesn;t do this.

Neither does the FAA. Transport category aircraft have a design limit load factor of 2.5 without significant damage, and ultimate load factor of 3.75 without catastrophic failure. They do a static test, and if it passes, it's strong enough. This is a photo of the Boeing 787 wing static test. If you are ever in one of those airplanes in severe turbulence, now you know how far the wings can flex.

 

[Baluncore]

I cannot get my head around the compressive strength of tensile fibres. It seems to me that the compressive strength comes from the epoxy binder, and that the fibres reduce that section.

All fibres in that layup are running in the plane of the cylindrical surface, none are radial. Radial fibres are needed to prevent spalling or delamination of the epoxy under compression.

So why are the fibres there? Would it not be stronger if the CF was replaced with epoxy?
I would expect better results if the pressure hull was cast with epoxy, loaded with short randomly oriented Kevlar or CF designed to prevent delamination.

 

[russ_watters]

Neither does the FAA. Transport category aircraft have a design limit load factor of 2.5 without significant damage, and ultimate load factor of 3.75 without catastrophic failure. They do a static test, and if it passes, it's strong enough. This is a photo of the Boeing 787 wing static test.

777 though:

 

[Vanadium 50]

All fibres in that layup are running in the plane of the cylindrical surface, none are radial.

There is a cabin in the way.

The radial forces are transferred to the collar of the hemispheres and to some degree the hoop fibers.

And epoxy is strong stuff as well.

 

[Baluncore]

The fibres used should have the same temperature coefficient, young's modulus, and speed of sound as the epoxy filler.

There is a cabin in the way.

The radial fibres should cross the wall, stitching the layers together, to prevent delamination.

And epoxy is strong stuff as well.

Then why use the carbon fibre in a compressive orientation. It would be better to avoid the fibre which will progressively delaminate if the temperature coefficient, modulus of elasticity, or speed of sound are different to the epoxy.

 

[Vanadium 50]

It may not look it, but tensile strength is critical. Compression is not the whole story.

The problem is not that the hull might evenly shrink under pressure, killing the passengers. The problem is that it might buckle. That has compression on one side and tension on the other.

This is why the US Navy uses high tensile strength steel for its submarines. They have not lost a submarine in over 50 years, even after driving at least one into a mountain.

 

[jrmichler]

I used a unidirectional carbon fiber rod in an application where we needed light weight, high stiffness, and Euler buckling for overload. Since a design review raised concern about it breaking when buckling, I ran a test. A 15" length of rod needed to buckle sideways about 3", and it did not fail until bent far enough that the free ends almost touched. It failed in tension. The failure was a sudden brittle fracture with a loud noise and pieces flying across the room. The test was repeated several times, and each failure was on the tension side. The tensile failure was interesting because the specifications for the rod call for it to be stronger in tension than compression:

The rated compressive strength of the rod is almost two orders of magnitude larger than the compressive strength of epoxy. I believe the compressive force are supported by the fibers, while the epoxy prevents local buckling of the fibers.

Since we needed to convince a number of people, we made a video of the test. I knew that it would shatter, so was wearing goggles and heavy leather gloves. I did not realize that I was standing under a bright light that made me look like some sort of demented mad scientist on the video. Several years later, that video was still being shown to new engineers, apparently to warn them about the guy in that office over there.

 

[gmax137]

I did not realize that I was standing under a bright light that made me look like some sort of demented mad scientist on the video.

Any way you can share the video, or at least a still frame?