I noticed that when transporting the sub by crane, the straps were attached to the titanium end rings, so the whole 10,000kg weight of the sub was borne by the two parts which were glued onto the carbon fibre hull. That's surely got to have taken its toll on that questionable glue joint.
I wouldn't be too concerned about that. After all, entire airplanes are lifted up with wings that are glued to the fuselage. Also, 10 t is nothing in comparison to the forces applied a few km down below.
@@davidelliott5843 : What do you think of the multiple accumulative effects of saline deposits in combination with extreme pressure from opposing different ocean currents into epoxy and carbon fiber, also, which does not occur to aircraft. To think that epoxy and carbon fiber will not over continued use begin to deteriorate indicates poor judgment. Stockton Rush may have developed a suicidal tendency due to his goals to achieve more than his restricted budget could afford. He certainly was quite a salesman, however, with no regard for the lives that he was about to sacrifice with his own. Attorneys are about to win a case against Oceangate due to this carbon fiber that exceeded its shelf life-a true red flag of which Rush was aware. And to think that an epoxy bond on titanium would react over time and stress in the same manner as over carbon fiber.
to me, seeing that the end-domes and the titanium rings were recovered quite intact, and also noticing that the acrylic window was blown out inclusive the retaining titanium ring that held that window in its place and its bolts, that tells the story all to well. The carbon fibre part of the vessel crushed in on itself and then the air inside this compartment blew out the acrylic window from the inside out like a champagne cork. All that with such a force that it even dismounted the retaining titanium ring and the bolts holding it. What I really can`t get my head around is, that they did just parallel layers of the carbon fibre and not criss-crossed them. Most likely this wouldn`t be strong enough either, but it for sure would have increased the amount of pressure the hull would have been able to take by a lot.
Because doing criss cross patterns was more time consuming and expensive. It was another corner he felt he could cut . With his so called logic and good engineering. He was wrong.
I work with a lot of epoxy/urethane bonding to aluminum and we increase the surface area with media blasting the surface and roughing it with special cutters. I noticed the titanium end pieces had smooth machining work and the salvage photos you could see the bonding had detached cleanly from the surface for the most part.
Was it also a flawed process of having a gang of bods using decorating spatulas to hand coat the surfaces? I used to build small pressure housings for underwater flashguns as a kid, I was mortified to see the way this thing was put together, even with my extremely limited experience !!
@@CharlieNasty-cd5hu Yes, all formula 1 chassis are made of carbon fiber. I even believe I read recently that Alfa Romeo just built their entire chassis out of carbon fiber. Google it it looks very cool.
There are a lot of comment to reply to. I just got to yours. A new mic is on order with a pop filter. You very nice comment just shows what kind of troll you are.
"The titanium flanges are bonded with a type of epoxy...we don't know what type... it's proprietary" Yet somehow none of us would be shocked if there were a couple dozen of those side-by-side syringes from home depot sitting empty in the dumpsters out behind the shop where this thing was made...
I noticed too, that after the wrapped the mandril with 5 inches of carbon fiber they then routed out a 1/2 inch flange for the titanium rings to sit over when glued on, The bottom flange is just visible in the photo you show of the vessel hanging upright, so imagine that at both ends, Carbon fiber at any thickness does not respond well to the stresses introduced by any bladed machining process and would have developed micro fractures. Also no one seems to be pointing this out but in the video of the wrapping process you can clearly see quite large air voids being introduced during the wrapping itself and they just carry on wrapping, That was the first alarm bell that rang loudly for me when I saw that video and if i had seen that there is no way I would want anyone trusting their life to that cylinder, Let alone the madness of actually thinking a cylinder is a good idea for a pressure vessel at those depths! So not only did they have a crappy idea for the shape of the submersibles pressure vessel it seems to have be manufactured with very little care in the first place.
Yes, that was on an old sub. On the Titan, they used pregreg tape wrapped around a mandrel. But we do not know what orientation and what cure they used. Thanks for the feedback
Quote from composites world “The biggest challenge, Spencer reports, was developing a manufacturable design that “would produce a consistent part with no wrinkles, voids or delaminations.” And without use of an autoclave. Spencer opted for a layup strategy that combines alternating placement of prepreg carbon fiber/epoxy unidirectional fabrics in the axial direction, with wet winding of carbon fiber/epoxy in the hoop direction, for a total of 480 plies. The carbon fiber is standard-modulus Grafil 37-800 (30K tow), supplied by Mitsubishi Chemical Carbon Fiber & Composites Inc. (Irvine, CA, US). Prepreg was supplied by Irvine-based Newport Composites, now part of Mitsubishi Chemical Carbon Fiber & Composites Inc. The wet-winding epoxy is Epon Resin 682 from Hexion Inc. (Columbus, OH, US). The curing agent is Lindride LS-81K frLindau Chemicals Inc.cals (Columbia, SC, US).”
A cylinder is the optimal shape, for getting the most paying passengers, er, 'mission specialists' inside the pressure, er, 'pay' vessel. I doubt Stockton charged himself, or PH. So really only 3 paying customers, so only $750K per run, and Stockton had complained that bunker (fuel) to the dive site & back was $1 MIL. So... I guess he really needed a longer submersible. Titan 2.0 might have resembled a paper towel roll. Oh dear. So where were all these carbon fiber specialists/commenters warning Stockton before this happened? In your industry, surely you would have heard of this singular application - so why didn't everyone in the carbon fiber industry warn him that he's doing every thing wrong that can be done wrong.
Colonel Phillip Corso said carbon fiber was back engineered from crashed alien spacecraft. His job was to seed different materials from the crashed saucers into industry to let them figure out how to back engineer them, because the military was not having any luck. For the things that were used by the military, the companies had an agreement to only make it exclusively for the military. When Corso said this, it reminded me of witnesses to the Roswell crash who said there were beams in the structure of the crashed craft that were real lightweight, but stronger than steel. It was probably carbon fiber or carbon nano tubes, which I read is 20 times stronger than carbon fiber. Anyway, thanks for the great video. I learned alot about carbon fiber from watching it.
Thank you, Joe. Great to get an engineering perspective on this totally preventable tragedy. One request and this is kind of minor but as a headphone user I'd recommend a pop filter on your microphone, please. All the best.
Just to clarify, Spencer Composites(not located in the Pacific Northwest, btw) only created the prototype tube not the one that imploded. The image at 12:05 is not the Spencer Composites facility.
Thanks for the clarification. Another Engineer indicated that the later sub did not use filament winding, but tape winding. So not sure who did the original filament winding then.
@@JoediyLab I work at MAF in New Orleans La. There is an old Autoclave that gets alot of use on rocket parts. There is also a very big Ingersoll fiber placement machine here. mafspace.msfc.nasa.gov/
Thank you for your information , I can see this accident giving engineers food for thought, I do feel for the young lad That he likely heard the Fiber Delaminate by way of cracking Right up until it failed ,It had dropped the weights apparently ! . Mayr they all Rest In Peace
@@JoediyLab Anytime! Yours is the first channel I've been able to find where someone who knows their stuff is discussing it without getting into the weeds with the conspiracy theories. I'm not saying some of their ideas are wrong but they tend to make a lot of assumptions based on shaky reasoning. I like your approach of more strictly sticking to the physics and engineering. Anyways keep up the great work!
Carbon fiber has a good tinsele strength, but it's not very good for compression or shear strength, if you want a scuba tank where you're holding pressure within a multi directional weave would be great. But horrible at trying to keep pressure out.
@@N4CR5the cf filament itself is flexible line, like a high test fishing line. The cf wound in a multi directional pattern on an air tank acts as a woven sack that resists expansion with its tensile strength, with the resin added to help hold its desired form (including keeping it from collapsing from external force), and prevent the air from escaping through the cf woven structure. The two combined are a composite but also referred to as cf. The cf filament by itself won't stretch and doesn't snap easily, but it is still a flexible line. If you have a loop of cf or any flexible line/rope and pull outward from the center of the loop with equal pressure it will hold until you reach the strength to snap it. But take that loop and push inward and it collapses. That's why a cf composite works for holding greater internal pressure from expanding outward but not the inverse. When you squeeze the cf composite tank with greater external pressure the woven sack doesn't add much of, if any of its properties so all you're relying on is the resin's ability to resist compression (hold its form) so they were basically in a 5 inch thick walled epoxy resin tube/ jar with two metal (titanium)end caps and nearly 6000 psi squeezing it from all directions. It's amazing they got away with it the first few times. Sorry this is so long but wanted anyone else reading it to understand what the cf filaments & the resin's contribution to the cf composite are. Apparently it was rocket surgery to OceanGate's brilliant college educated "engineer" Stockton Rush and his college student interns (apparently just yes men).
Thanks Joe. I am so very interested in the mode of failure of Titan. Rush was certainly a maverick & paid the price for his efforts. Problem is, he took folk with him !
Thing is...where the glue the CF and the titanium end caps meet...all it would take is crack between the materials that woould pop that whole ring mount off. Thats what i think happend. It worked for a few dives but it was just that one compression cycle too much for this tourist sub to take. Im not an engineer but ive watched enough YT vids to think this was a bad idea...i didnt even know this sub existed but I'd of had the same feeling and thought process.
I feel i have been well informed to the best of your knowledge by your video .Thanks Joe for sharing what you know .Great help in understanding more than what has been said recently. I kept asking myself what is the cylinder under the carbon cylinder they are weaving onto ? is it just the mandrel or a titanium inner sleeve to go with the wound carbon hull ?
Yes you are correct the metal cylinder is a mandrel, once cured the carbon fiber is pulled off of the mandrel, then the flanges are glued onto the carbon fiber tube. Thanks for the feedback
@@JoediyLab I want to see a very thin steel or titanium mandrel removed from the CF hull of that size. After curing both parts are glued together, if not realy, friction between parts is terrible. It is possible if you contract the inner mandrel by freezing but what influence on CF caracteristics?????
Thank you for a very informative video. So many things that I did not know about carbon fibre. You brought up F1 and from various videos I have seen they appear to use a clean room environment and they are only driving round a field. This is not to denigrate their skills. Oceangate appear to be constructing the pressure vessel in an airy warehouse/workshop for a far more extreme enviroment. It also appears that the titanium end is only held on with adhesive from an open bucket. Unless there is an inner ring it is only that bond resisting external pressure. From the recovered ends they appear to have come out devoid of any carbon fibre.
Yes I would love to see the results of the investigation. Epoxy bonding with composites is common, but I do not think anyone has tested at these pressures.
From the materials-science perspective... Once upon a time, kayaks were made from fiberglass. A guy named Chan Zwanzig figured he could roto-mold better kayaks, and that's how kayaks are made now. Not carbon fiber, for kind of the same reasons fiberglass is best used for boat hulls. Internal-pressure vessel, CF's great, but external pressure? If you think so, I have a carbon-fiber kayak to sell you. Or a fiberglass submarine...
I saw something on Wikipedia about how the pressure vessel on the accident craft was already the second pressure vessel because the first showed indications of weakening after its second test dive. Don't know if they changed the design, but I guess that might tell you how error-prone the manufacturing process was. Edit: It seems to have been more than two dives and it seems unclear whether it was repaired or replaced.
Yes the first pressure vessel was filament wound and pregreg wrapped. The Titan pressure vessel was tape wrapped with pregreg. Pacific Coast Composites has the details. Thanks for the feedback
Just a quick question about the difference in hull strength if the CF was used differently. Instead of axially wrapping the CF around the inner titanium tube the way OceanGate made the Titan hull, what if instead the CF was 5" (or whatever hull thickness) wide factory finely woven into a curve that exactly matched the curvature of the inner titanium tube, in one single piece thousands of metres long? So in other words, wrapping adjacent to the flanges and gradually building up to the full length of the hull, with the woven CF perpendicular to the inner titanium tube external surface. I imagine quite expensive, far more difficult, would need to be compressed as it was wrapped, and may require some new tech to achieve, but in theory this way the CF wouldn't be as likely to delaminate since the pressure from the titanium bulkheads would press the spiral laminate tightly together. Obviously the design would need to allow for some longitudinal compression and expansion (possibly with bellows to allow for this on the inner titanium hull), but at least with the radially woven CF, then in theory there would be much greater compressional strength that would take greater advantage of the tensile strength of CF. I'd have thought it would be more ideal to design the CF hull so it could be easily removed (for reduced maintenance costs) in one cylindrical piece from the titanium hull, for testing/scanning from both the exterior and interior surface for better resolution. Obviously the above would require a lot of work and engineering, far easier said than done. If the Titan could even survive one trip to the Titanic with that crude axially wrapped wrapped CF hull (which I find quite surprising) then I'd have thought a far better way of using CF more suited for compressional loading might hold some promise, at least for the testing phase and unmanned trials. What are your thoughts?
Great question, In the video of the earlier sub it only show the hoop wrapping. I understand that in a later process they wrapped pregreg in a more axially orientation in the long direction. But the older sub did still fail. On the titan sub they used pregrep carbon through out the entire sub and used a tape wrapping machine. I was told that they wrapped in the hoop orientation and in the axial directions. I heard that they wanted 7" of thickness, but for some reason they received 5" thickness. Not sure why, Maybe a cost situation that Stockton Rush later decided. But that is just a guess based on his logic of using acrylic viewing port rated only to 1300 meter instead of 4000 meters. I have also read that carbon fiber can be constructed for strength against compressive forces. I am anxious to see the findings that the Canadian NTSB comes up. Based on the images of the recovered sub it appears that the titanium flanges popped out with little trace of either adhesive or carbon fiber remains attached to the flange. Thanks for the great question.
If all the fibers are going in a circular direction around the tube, and they don't have any layers going the length of the thing, then there's nothing other than resin resisting forces in the axial direction. They built a cylinder that's weak in what's usually the strongest direction. The hydraulic press channel has a video of carbon failing in this direction. It doesn't just shatter, it totally disintgrates into almost dust. If it failed like that, it would explain why they didn't bring up any shattered carbon pieces.
Correct, The video does not show a later process of wrapping carbon in the axial direction. The Titan sub was actually wrapped using pregrep and a tape wrapping machine. Totally different than filament winding process. Thanks for your feedback
Carbon fiber for compression (pressure typical) applications a pretty strict no, no - universally. CEO of OceanGate, Mr Rush, was in an oxygen deprived state, on top of Mount Stupid. (Kruger-Dunning effect)
Exactly! It's tensile strength vs it's weight is incredible, but it's not a good choice for this application. It would be well suited for containing internal pressures, but not at all suited for dealing with external pressure.
One YTer speculated that the viewport might have been removed after recovery for trigger reasons … might have been “red.” Your explanation makes more sense. Another YT analysis says the water rushing in does so at the speed of sound at 1 atm pressure (assuming inside was at 1 atmosphere). This is 340+ m/s (standard atmosphere press & temp.). So, the pressure front would hit just before the water. Either way, the viewport and end caps are subjected to forces beyond the structural limits. That the titanium parts survived relatively intact is not surprising for such a relatively (to the carbon fiber comp) ductile & elastic and much more shock resistant material. The acrylic viewport is another matter. The carbon fiber is likely in millions of shards or a crunched mass ….
A RUclipsr scientist called “thunderfoot” done a very good vid the other day about the pressure. About how water does actually compress, very little of course ( about 1% at that depth), and how its basically like a massive infinate spring surrounding the sub. When exposed to one atmosphere, like a leak, the spring desprings if you like, at something like 4x speed of sound. When the water hits an object, the energy smashes it apart in micro seconds. The vid is well worth looking for 👍
Oh and btw the hull wound by Spencer composites was wound with a wet winding process. This hull made loud cracking noises in service and so it was retired. The hull that failed and killed 5 people was wound using prepreg.
GREAT tutorial Joe ... nicely explained and bookmarked accordingly. And also thanks for confirming what I suspected ... no Auto-Clave used; the part that pisses me off ("Old White Guy" with 40 years experience building composite structures (38 Countries) for the World's largest Defense Firm) to no end is lack of a "Clean Room" or Ultrasonic NDI (after EVERY dive) ... pity that Rush didn't follow his 20 years of experience building the F-15 and knowing it would need to be done per AS9102 with SOF/QUAL/HALT requirements from "Engineering". BTW ... stress software loaded with the dimensions, material type, tape laying method shows that the pressure hull would need to have been 17.6 inches thick to withstand 6,000 psi ... far more than the 5 inches Rush and his Team came up with. Installation of the Titanium flange to CF Hull is the most probable failure point; expansion/contraction differentials between Titanium and CF result in a 1mm "gap" ... which is why Rush used his "Secret Sauce Adhesive" to cushion the different rates. And as you and I know ... if you take a smooth, steel rod and dip it in liquid silicone or "adhesive", let it cure ... you can pull it off the rod like it was a rubber glove. He would have been better off using a “Thread Laying (TOWS) machine and certainly an Auto-Clave. This thing was doomed from the get go. Saddest part is the kid that didn't want to go but it was "Father's Day" ... breaks my heart !
The Oceangate Video of winding the hull says it was for "Cyclops 2" which they eventually changed to "Titan." That video could be the very same hull that failed. I heard they did one change to the titan hull after around 2-3 dives because how loud and often they heard the carbon cracking and popping. Not sure if they made a new hull or just did some re-enforcing. Very curious on exactly what they did. Would love to hear your opinion.
The video is winding of an older pressure vessel. I spoke with an engineer that indicated the Titan use tape winding and not filament winding. Tape winding would be better as they could use prepreg tape and avoid the wet layup. It could also then be cured in an autoclave. But as far as we know they cured in an oven and not an autoclave.
The connection from titanium end plates and composite pressure vessel under pressure will compress at different rates. I have trouble believing it was material fatigue.
great for people want a more depth review of the accident from a engineering perspective. Thank you! To sum up the pitfalls of the strength of carbon fiber, "you cant push a rope" Tensile vs Compressive strength.
Interesting stuff. I dont know about CF, my training is in metals. What I have not seen as I go through the vids is any mention on the expoxy curing. You mentioned the degassing here, but do you have any thoughts on epoxy being an exothermal curing reaction ? If thats the case with CF that is. When I have used epoxy it gets hot and cures fast. For such a thick wall, I wondered how they would avoid thermal stress during curing. Or would this be an oven cured plastic ?
Yes in wet layups some epoxy can have exothermic reaction if applied too thick. On prepreg that have to be cured at higher temps, they are designed for the higher cure temps as long as you follow the specs. Good question
Very good and interesting. Most "experts" only say it wasn't good but you explain possible reasons why it wasn't good. Just one thought; You talk both about out of date pre-preg and dry fiber. I guess they didn't ad more epoxy to pre-preg so are we then talking about two different hulls made with different methods?
One good thing is that both Oceangate & Boeing are in Seattle Washington & the litigation lawyers won't have far to travel when issuing the court papers.
Cylinders have to be compacted layer by layer. Hoop tow tension is not enough radial pressure to compact broadgoods. I was a manufacturing engineer on filament wound cases designed for space shuttle boosters. They are now at Huntsville Alabama. The program ended when the director of NASA blew up the Challenger shuttle. The vacuume bag after winding does more to wrinkle hoop layers that are not compacted. They achieved low void content by drowning it in epoxy. You can see them scraping off the excess resin while winding. That is not resin control!
@@mycammedia Yes the NASA booster cases are steel 1/2” thick DCAC tool steel. Before the Challenger was destroyed by the director of NASA the Air Force wanted to do a polar launch.Filament-wound cases were manufactured by Hercules Inc. I was the senior process engineer. Edit “In order to provide the necessary performance to launch polar-orbiting shuttles from the SLC-6 launch pad at Vandenberg Air Force Base in California, SRBs using filament-wound cases (FWC) were designed to be more lightweight than the steel cases used on Kennedy Space Center-launched SRBs.[30] Unlike the regular SRBs, which had the flawed field joint design that led to the Challenger Disaster in 1986, the FWC boosters had the "double tang" joint design (necessary to keep the boosters properly in alignment during the "twang" movement when the SSMEs are ignited prior to liftoff), but used the two O-ring seals. With the closure of SLC-6, the FWC boosters were scrapped by ATK and NASA, but their field joints, albeit modified to incorporate the current three O-ring seals and joint heaters, were later (after STS-51L) incorporated into the field joints on the SRBs used until the last flight in 2011.”
@@oneskydog6768 Really - didn't know about that - why was it not really common knowledge - I only ask because I never saw any reference to anything like that. That must have been some amazing set up in terms of size - any special arrangement for the interface of the segment 'body' to the steel joints? just curious. I was interested in all the issues surrounding the field joint design - rotation of the joint, etc. I also was deeply interested a long time ago about AA587 - the public hearings about engineering issues and the differences of approach / philosophy between Boeing and Airbus about what each was willing to do when it came to using carbon fiber. Airbus pushed the issue much further towards making moutings from cf - but Boeing were way more conservative then and were unhappy to make the actual mountings from cf. At that time, they wanted to stick to an experience base of 70 years around the fatigue issue with metal.
You mentioned unidirectional fibers. I wonder what impact if any the unidirectional construction (no fibers along the length) had on the strength of the pressure vessel..
It appears carbon fiber and titanium have different rates of thermal expansion. Therefore, the materials would not expand and contract at the same rate thus opening up a mode of failure entirely based on exposure to temperature exposure differentials, entirely leaving the pressure exposure issue outside of the equation. From approximate surface (June 2023) to subsurface temperature differential is about 8 Deg C, estimated. The delta is not zero. Repeated cycling (outside of pressure delta) seems to show an issue.
wonder what kind of seal they have on the front dome closing onto the titanium ring. looks like a smooth surface, then any seal when the front hatch is closed ?
The threads are called filaments. Filaments are combined together to form a yarn. There are continuous filament yarns and “staple” filament yarns that are twisted together to form a yarn. The yarn is measured in “denier”.
You are a genius to explain this process. I listen very closely what you were saying. I respect everything you talked about. This Stockton rush would have called you a dirty white male over fifty who doesn't know anything. Thank you sir for explaining all this.
Looking at the recovery images, the titanium flanges were shown separated from the carbon fiber cylinder. It appears that when the carbon fiber section crushed, the titanium flanges were pushed out. There appeared to be no carbon fiber attached to the flanges that I could see.
I assume the thicker the lay up and the greater the number of plies, the greater the pressure in the autoclave to compact the layup as it cures. This might have made a difference between disaster and returning to the surface.
That is a very complex question. There are several variables involved. Temperature, pressure, vacuum (yes you vacuum bag when using an autoclave) There is also temperature ramp up and ramp down times and how the resin flows with in the laminate. I am not a mechanical engineer. I would have to do alot of research on this topic. Sorry.
I’ve been asking this question since the incident with no answer. I get that carbon fiber was the mistake…WHY would Stockton Rush make that mistake when there was 60 years of no fatalities and proven materials for deep dives? My assumption is carbon fiber is cheaper than titanium and he excused it for this reason. Why else would he insist on reinventing the wheel?
Now that the 787 Dreamliner. The carbon fiber vessel, do we want to be traveling around in pressurized cabins high in the atmosphere as we have seen the response to stress over time?
The only vids Ive seen of the mid-section layup, shows fibers only laid in the hoop direction, however the Wikipedia description suggests that there are alternate axial layers of UND. So effectively (if thats true) it should have similar properties to a weave. Perhaps optimistically achieving 550 MPA in compression? A simple solidworks simulation, (not accounting for dissimilar materials or adhesive bonds) suggests a stress of 250MPA at 4000mts if the entire pressure vessel were homogeneous. That seems rather too close for comfort. I have also not checked for buckling failure mode (tin can collapse) which may be a factor. Also the highest stress area is exactly where the titanium ends would attach.
Learned something new. Always thought as the carbon fiber strands as “threads” but the actual “Tows” sound more like rods structurally stiff but as fail as a STRUCTURE by bowing. Bonus points for spelling out “TOWS” as the YT transcripts can be a bit quirky. So if all the possible faults (no preprog cloth, out of aerospace spec materials and vacuum bagging versus autoclave) the Titan’s hull sounds like it was made like a fiberglass recreational boat only using different fibers and resins and 5” thick. Would the Titan’s construction pass USCG standards for an ocean going lifeboat? My understanding of fiber reinforced resin composites is as you stressed: bonding between layers and between the fibers and resin matrix, and, avoiding voids in the matrix is critical. With metals voids, inclusions and microscopic cracks greatly reduce strength and operational life; the NDT/NDI methods for inspection are well developed. For a 5” thick cylinder walled pressure vessel what are the methods for inspecting for fiber-resin bonding??
There methods would not pass inspection. I spoke with a composite s engineer, he indicated that with a portable ultrasonic tester he could not get penetration in a composite that thick. Possibly with a larger unit. Thanks for the feedback
@@JoediyLab A larger ultrasound unit would not work well. The penetration of acoustic waves into materials is frequency dependent, not power dependent. The higher the frequency, the higher the energy loss through absorption and the less thickness your wave will be able to penetrate. Ironically you need to lower your frequency to penetrate a thicker layer. However this comes at the cost of spatial resolution, the lower your acoustic frequency the larger the feature need to be in order to be detected, also the thicker the material the higher the wave amplitude or the power you need to put into the signal to get a decent return signal through sound absorption. The wavelength of NDT ultrasound is anywhere between 200KHz to 50MHz, let's say they use a frequency of 5MHz. Wavelength is dependent on sound speed which is dependent on material density. A 5 MHz ultrasound signal in air has a wavelength of 0.07mm with a sound speed of 343 m/s. A 5 MHz signal in CF with a sound speed of 10000 m/s is 2mm, so anything smaller requires a higher frequency. If you went down to 1 MHz your wavelength increases to 10mm(1 cm). So any cracks smaller than the wavelength of the sound won't interact strongly with the wave to reflect a signal back, it's basically the diffraction limit as it's termed in optics. Ultrasound works very well because it can detect very small cracks within a relatively thin layer of CF, down to fractions of a mm but as you get thicker your resolution advantage is lost. Also because the CF hull is a curved piece there are geometry issues which can cause the ultrasonic beam to scatter and not properly reflect off any defects depending on how the defect is oriented. Because it's also a laminate these alternating layers of CF and epoxy will cause the ultrasonic waves to reflect and refract as well as diffract, this causes a lot of interference. Imagine looking through a curved window made of multiple alternating panes of glass and air and shining a flashlight through that stack to see any defects in the inner panes. Source: Not a materials engineer or a NDT specialist was trained in petroleum geophysics on how to interpret seismic wave propagation in the earth.
Very clear and consise video, it's well known how Aircraft Wings are created with multiple patterns laid under Computer control. The flexibility has to be carefully planned and calculated and tested before a safe structure is used on an aircraft. As you said "Stretch" is very strong but "Compression" is not so strong. I was not happy watching the video of the manufacturer of the cylinder. It looked very risky and almost at a "Home DIY" level of build.
I'm wondering... Since the assembly is under compression, wouldn't most of the load be supported by the resin, not the CF? What would have happened if they used 5" thick resin poured from a mold with no CF at all?
No you will still get support from the carbon fiber. the strength of the fiber is along the length of the fibers. So you orient the fibers along the areas of stress you need. If you cast structural resin that thick it would heat up to much and weaken. Even with slower curing resin it would shatter. The strength of carbon fiber is a combination of resin to carbon fiber matrix. Carbon fiber by itself is only good in tension. If designed correctly you can get good strength in both tension and compression, But more strength in tension. Thanks for the great question.
@@JoediyLab I work with CF on a very limited basis, what would happen when say hardware is screwed into the CF? I noticed the monitors being mounted. And the illuminated handles he used that he got from Camping world.
Ive read thay autoclaves are generallly not recommended for filament wound parts like this because it can cause the fibers to buckle. In this case its actuallyy the fiber tension during winding which compacts the layers.
@@JoediyLab there's an 18 minute video where Stockton Rush gives a talk and he shows a few photos from the process. You can see the machine used to lay the fiber. It was a more complex tape laying machine.
In college when we made parts like bulkheads and torsion tubed out of carbon fibre using prepreg we had to place the parts under vacuum wrapped in plastic and use an autoclave. Never did we orient at 90 0 for every layer.
What you're trying to say is "the resin has to be molecularly uniform throughout the fabric, without any air bubbles, which we all know is very difficult to achieve.
Getting all the air bubbles out of 5” of prepreg is a challenge on its own. The simple thickness precludes success because the vacuum simply would need weeks to pull the residual air out.
That looks like a 6 foot step ladder next to it which would put it at about 10 feet I think. The Titanium rings make it look bigger in other pic maybe. Lol I just noticed the 12 foot ladder on the right . ;-)
Perfectly safe. The pressure is the opposite way around. Carbon fiber is great at keeping pressure in, not so much at keeping pressure out. Tensile vs compressive strength.
Great question, Here is a quote from Composites World "The maximum compaction pressure available at sea level with a perfect vacuum bag is 14.7 psi (29.92 inches or 760 millimeters of mercury.) This maximum available pressure drops approximately 0.5 psi (1 inch or 25.4 millimeters of mercury) for each 1,000 foot gain in altitude. "
If you draw a perfect vacuum under the bag, then what is pressing on the other side is whatever the atmospheric pressure is. More in Death Valley, less in Denver. Putting the vacuum bagged part in a pressurized autoclave results in greater than atmospheric compression.
I noticed in one of ocean gates videos that both interior monitors were screwed directly to the composite tube. Now I wonder they screwed other components to the exterior of the composite.
What are your thoughts on the longitudinal compressive forces the cylinder was exposed to with each dive. Approximately 400 atm x Pi x Cylinder Radius ^2 = 14.7 x 400 x 3.14 x 48^2 = 42.5 million pounds of longitudinal compression in addition to radial compression. Longitudinal area = Pi X ( 48^2 - 43^2) = 1430 in sq. Therefore 29,720 psi cylinder wall longitudinal compression. I don’t think any carbon fiber runs in that direction; therefore must be carried by the epoxy resin?
I like reading comments like this. I am not scientific at all, and have a high school level understanding of math. But somehow I can infer the point you are trying to make.
@@JoediyLab I calculated that the composite carbon fiber cylinder would’ve experienced 29,700 psi compression in the longitudinal direction and 60,600 psi radial compression throughout the entire side wall at Titanic depths. I think Stockton felt safe with carbon fiber composite because it has a compressive failure pressure of approximately 250,000 psi if it’s not damaged. But fatigue cycling and differential strains between titanium and carbon fiber may have done him in.
@@jamesn3513 and just what if a horrible mistake was made an error in judgment that may very well not wish to get revealed RE: litigation; that Sunday noise was bottom brackets falling down, not any implosion. So rescue was not pursued underneath but above. Then when Canadian C-3 Orion plane heard 30 minutes of banging, is when those in charge rushed to have underwater ROV brought took hours to get there. All those days, nights, in ocean pressures, subjected to changing temperatures and freezing ones, Can be date of implosion as hull plus resin becoming more brittle to failure! Don’t be so positive on dates being thrown, consider there may become a hugh liability issue to develop, dates can make or break such possibilities!
Carbon fiber is infuse on the outer part of cylinder the problem is it 100% sealed? if water pressure find its way thru the fiber its useless and only the metal frame is holding the pressure.
Is 5 inch thick carbon fiber an issue? This doesn't seem like the optimal thickness for this material. Do the properties of 1/4" carbon fiber scale linearly to 5 inch thickness? All carbon fiber I have seen is relatively thin (< 1/2")
It’s a miracle this sub made of pure ramen noodles and Italian spaghetti held together by only a thin layer of glue, did not implode at the very first trips.
The repeated claim that carbon fiber fails suddenly depends on the type of fibers used. The stiffest lightest ones are like that, but you can opt for grades that have more given/flex in them. For instance people build mountain bikes out of carbon fiber, and they can handle impact damage better than their metal counterparts, because they are using slightly less stiff composites that can handle it. Just wanted to mention this nuance here as people often repeat this claim without being aware of that.
I noticed that when transporting the sub by crane, the straps were attached to the titanium end rings, so the whole 10,000kg weight of the sub was borne by the two parts which were glued onto the carbon fibre hull. That's surely got to have taken its toll on that questionable glue joint.
Good point, thanks for the feedback
Lifting it by the carbon fibre would apply even more force to the joint. But none of that matters because carbon is useless in compression.
I wouldn't be too concerned about that. After all, entire airplanes are lifted up with wings that are glued to the fuselage. Also, 10 t is nothing in comparison to the forces applied a few km down below.
@@jcsjcs2 Yeah, by designed and designated points! Also pressure at few km is uniform, and cat's cradle is not!
@@davidelliott5843 : What do you think of the multiple accumulative effects of saline deposits in combination with extreme pressure from opposing different ocean currents into epoxy and carbon fiber, also, which does not occur to aircraft. To think that epoxy and carbon fiber will not over continued use begin to deteriorate indicates poor judgment. Stockton Rush may have developed a suicidal tendency due to his goals to achieve more than his restricted budget could afford. He certainly was quite a salesman, however, with no regard for the lives that he was about to sacrifice with his own. Attorneys are about to win a case against Oceangate due to this carbon fiber that exceeded its shelf life-a true red flag of which Rush was aware. And to think that an epoxy bond on titanium would react over time and stress in the same manner as over carbon fiber.
Yellow is known to be a stronger colour for submarines
I guess the Beatles really knew something 😂
@@JoediyLab it was made of crayon much better than tape
Yellow definitely easier to find pieces of...
@@lostpony4885 yellow wax, straight from Crayola, no exceptions.
US marine corps owns the patent
The international silver string submarine band
This is the most detailed take on carbon fiber I've seen so far! Thanks!
Before this video I really knew absolutely nothing about carbon fiber this was very interesting and I learned a lot thank you
Thanks for the feedback.
@@JoediyLab the dolt who insisted on that material should have watched such a video instead of using earplugs and screaming "revolutionary"
to me, seeing that the end-domes and the titanium rings were recovered quite intact, and also noticing that the acrylic window was blown out inclusive the retaining titanium ring that held that window in its place and its bolts, that tells the story all to well. The carbon fibre part of the vessel crushed in on itself and then the air inside this compartment blew out the acrylic window from the inside out like a champagne cork. All that with such a force that it even dismounted the retaining titanium ring and the bolts holding it. What I really can`t get my head around is, that they did just parallel layers of the carbon fibre and not criss-crossed them. Most likely this wouldn`t be strong enough either, but it for sure would have increased the amount of pressure the hull would have been able to take by a lot.
Yeah that was a huge rookie mistake with the carbon fibre, even uneducated people can see that
there are not bolt holes on the end nose. it tell me it was glued. the bolt's was just another retaining ring of some sort
Because doing criss cross patterns was more time consuming and expensive. It was another corner he felt he could cut . With his so called logic and good engineering. He was wrong.
@vibratingstring thanks for your feedback
@vibratingstring yes in the titan sub they used prepreg, but do not know if they wrapped any axial orientation at all. Thanks for the feedback
I work with a lot of epoxy/urethane bonding to aluminum and we increase the surface area with media blasting the surface and roughing it with special cutters. I noticed the titanium end pieces had smooth machining work and the salvage photos you could see the bonding had detached cleanly from the surface for the most part.
Thanks for the comments, yes we use to use acid to etch parts for bonding.
A couple of cans of Flex Seal will seal it up real good.
Interesting and makes total sense, gives the epoxy something to grip onto.
Was it also a flawed process of having a gang of bods using decorating spatulas to hand coat the surfaces? I used to build small pressure housings for underwater flashguns as a kid, I was mortified to see the way this thing was put together, even with my extremely limited experience !!
And I’m sure you watched the video where that was described?
During Med school my professor would always say never trust your life on a piece of equipment. So far that's worked for me.
Never been in a plane or in an elevator or etc etc
In this case that is wise advice
You always walk, you don't go any structures of man-made, you swim through rivers?
What about cars
@@CharlieNasty-cd5hu Yes, all formula 1 chassis are made of carbon fiber. I even believe I read recently that Alfa Romeo just built their entire chassis out of carbon fiber. Google it it looks very cool.
Good info, Joe. DIY a mic blast screen by using a sock filled with cotton and put over the mic. The distracting pop will go away
Yes new mic with pop filter on order
There are a lot of comment to reply to. I just got to yours. A new mic is on order with a pop filter. You very nice comment just shows what kind of troll you are.
@@JoediyLab Excellent!
@@thadollagenerale Thanks
Very informative video! Investing in a pop filter would highly heighten the quality of your productions
AMEN !
Or a sock and cotton wool
For this video: High pass filter 200 Hz.
Mic is on order
Mic is on order
"The titanium flanges are bonded with a type of epoxy...we don't know what type... it's proprietary"
Yet somehow none of us would be shocked if there were a couple dozen of those side-by-side syringes from home depot sitting empty in the dumpsters out behind the shop where this thing was made...
Thanks for your comments
I would say they just used Gorilla Glue, but I think that was way to upscale for them.
I noticed too, that after the wrapped the mandril with 5 inches of carbon fiber they then routed out a 1/2 inch flange for the titanium rings to sit over when glued on, The bottom flange is just visible in the photo you show of the vessel hanging upright, so imagine that at both ends, Carbon fiber at any thickness does not respond well to the stresses introduced by any bladed machining process and would have developed micro fractures. Also no one seems to be pointing this out but in the video of the wrapping process you can clearly see quite large air voids being introduced during the wrapping itself and they just carry on wrapping, That was the first alarm bell that rang loudly for me when I saw that video and if i had seen that there is no way I would want anyone trusting their life to that cylinder, Let alone the madness of actually thinking a cylinder is a good idea for a pressure vessel at those depths! So not only did they have a crappy idea for the shape of the submersibles pressure vessel it seems to have be manufactured with very little care in the first place.
Yes, that was on an old sub. On the Titan, they used pregreg tape wrapped around a mandrel. But we do not know what orientation and what cure they used. Thanks for the feedback
Quote from composites world “The biggest challenge, Spencer reports, was developing a manufacturable design that “would produce a consistent part with no wrinkles, voids or delaminations.” And without use of an autoclave. Spencer opted for a layup strategy that combines alternating placement of prepreg carbon fiber/epoxy unidirectional fabrics in the axial direction, with wet winding of carbon fiber/epoxy in the hoop direction, for a total of 480 plies. The carbon fiber is standard-modulus Grafil 37-800 (30K tow), supplied by Mitsubishi Chemical Carbon Fiber & Composites Inc. (Irvine, CA, US). Prepreg was supplied by Irvine-based Newport Composites, now part of Mitsubishi Chemical Carbon Fiber & Composites Inc. The wet-winding epoxy is Epon Resin 682 from Hexion Inc. (Columbus, OH, US). The curing agent is Lindride LS-81K frLindau Chemicals Inc.cals (Columbia, SC, US).”
A cylinder is the optimal shape, for getting the most paying passengers, er, 'mission specialists' inside the pressure, er, 'pay' vessel. I doubt Stockton charged himself, or PH. So really only 3 paying customers, so only $750K per run, and Stockton had complained that bunker (fuel) to the dive site & back was $1 MIL. So... I guess he really needed a longer submersible. Titan 2.0 might have resembled a paper towel roll. Oh dear. So where were all these carbon fiber specialists/commenters warning Stockton before this happened? In your industry, surely you would have heard of this singular application - so why didn't everyone in the carbon fiber industry warn him that he's doing every thing wrong that can be done wrong.
@JoediyLab Great report Joe, in some photos you see contaminates in the winding. Shouldn't this be done in a clean?
@@glcanonHe was warned, and people quitted their job due to the construction.
I’m retired from R&D Composite design. This was a very good video on this topic. 👍👍👍😀
Thanks for the feedback
Thank you Joe for sharing this insight into carbon fibre product manufacturing.
Thanks for your feedback
Colonel Phillip Corso said carbon fiber was back engineered from crashed alien spacecraft. His job was to seed different materials from the crashed saucers into industry to let them figure out how to back engineer them, because the military was not having any luck. For the things that were used by the military, the companies had an agreement to only make it exclusively for the military. When Corso said this, it reminded me of witnesses to the Roswell crash who said there were beams in the structure of the crashed craft that were real lightweight, but stronger than steel. It was probably carbon fiber or carbon nano tubes, which I read is 20 times stronger than carbon fiber. Anyway, thanks for the great video. I learned alot about carbon fiber from watching it.
Thanks for the comment
Thank you, Joe. Great to get an engineering perspective on this totally preventable tragedy. One request and this is kind of minor but as a headphone user I'd recommend a pop filter on your microphone, please. All the best.
new mic and pop filter has been ordered, Thanks for the feedback
very interesting! Nice to hear some thoughts on the engineering .
Thanks for the feedback
Many thanks for making this video. It is extremely informative.
Just to clarify, Spencer Composites(not located in the Pacific Northwest, btw) only created the prototype tube not the one that imploded. The image at 12:05 is not the Spencer Composites facility.
Thanks for the clarification. Another Engineer indicated that the later sub did not use filament winding, but tape winding. So not sure who did the original filament winding then.
That is the best video explaining carbon fiber description and application. Thank You Joe. 👍
Thanks for the feedback 🙂
@@JoediyLab I work at MAF in New Orleans La.
There is an old Autoclave that gets alot of use on rocket parts. There is also a very big Ingersoll fiber placement machine here.
mafspace.msfc.nasa.gov/
@@forrestgumpv9049 thanks for the link, I will check it out
Thanks so much for the detailed explanation of the carbon fiber process.
Thanks
Brother please sit further back from the microphone!! Or get a guard for it. You have some great info but it's hard to listen to.
Thanks, Yes I need to get a pop filter.
Thank you for your information , I can see this accident giving engineers food for thought, I do feel for the young lad That he likely heard the Fiber Delaminate by way of cracking Right up until it failed ,It had dropped the weights apparently ! . Mayr they all Rest In Peace
I hope Stockton is suffering in hell.🏴☠
Excellent, well supported analysis Joe. Thanks!
Thanks so much 👍
Excellent video. Very informative. You sound very knowledgeable about the subject matter. 👍👍
Thanks for the feedback
@@JoediyLab Anytime! Yours is the first channel I've been able to find where someone who knows their stuff is discussing it without getting into the weeds with the conspiracy theories. I'm not saying some of their ideas are wrong but they tend to make a lot of assumptions based on shaky reasoning. I like your approach of more strictly sticking to the physics and engineering. Anyways keep up the great work!
Joe, very informative. AZ programmer here. AS400
Thanks, just retired, doing RUclips, currently a bit burned out on coding, but may do some in regards to composite failure.
This is exactly what I needed to know. Thank you this was excellent!
Thanks for your feedback
Carbon fiber has a good tinsele strength, but it's not very good for compression or shear strength, if you want a scuba tank where you're holding pressure within a multi directional weave would be great. But horrible at trying to keep pressure out.
Love the idea of tinsel strength. A useful standard, along with potato chip/crisp strength for bending, and meringue strength for compression.
@@timjackson3954Pasta has the same strength per unit weight and volume as concrete…
@@allangibson8494 pasta houses?
Many high end air guns use CF tanks and they last/do well. Almost never hear of failures.
@@N4CR5the cf filament itself is flexible line, like a high test fishing line. The cf wound in a multi directional pattern on an air tank acts as a woven sack that resists expansion with its tensile strength, with the resin added to help hold its desired form (including keeping it from collapsing from external force), and prevent the air from escaping through the cf woven structure. The two combined are a composite but also referred to as cf. The cf filament by itself won't stretch and doesn't snap easily, but it is still a flexible line. If you have a loop of cf or any flexible line/rope and pull outward from the center of the loop with equal pressure it will hold until you reach the strength to snap it. But take that loop and push inward and it collapses. That's why a cf composite works for holding greater internal pressure from expanding outward but not the inverse. When you squeeze the cf composite tank with greater external pressure the woven sack doesn't add much of, if any of its properties so all you're relying on is the resin's ability to resist compression (hold its form) so they were basically in a 5 inch thick walled epoxy resin tube/ jar with two metal (titanium)end caps and nearly 6000 psi squeezing it from all directions. It's amazing they got away with it the first few times. Sorry this is so long but wanted anyone else reading it to understand what the cf filaments & the resin's contribution to the cf composite are. Apparently it was rocket surgery to OceanGate's brilliant college educated "engineer" Stockton Rush and his college student interns (apparently just yes men).
This is fantastic! Thank you!
wow so informative, i knew so little about this process of making carbon fiber equipment
Thanks
Thanks Joe. I am so very interested in the mode of failure of Titan.
Rush was certainly a maverick & paid the price for his efforts.
Problem is, he took folk with him !
Thanks
Informative - Thanks for the upload.
Thing is...where the glue the CF and the titanium end caps meet...all it would take is crack between the materials that woould pop that whole ring mount off. Thats what i think happend. It worked for a few dives but it was just that one compression cycle too much for this tourist sub to take. Im not an engineer but ive watched enough YT vids to think this was a bad idea...i didnt even know this sub existed but I'd of had the same feeling and thought process.
I feel i have been well informed to the best of your knowledge by your video .Thanks Joe for sharing what you know .Great help in understanding more than what has been said recently.
I kept asking myself what is the cylinder under the carbon cylinder they are weaving onto ? is it just the mandrel or a titanium inner sleeve to go with the wound carbon hull ?
Yes you are correct the metal cylinder is a mandrel, once cured the carbon fiber is pulled off of the mandrel, then the flanges are glued onto the carbon fiber tube. Thanks for the feedback
@@JoediyLab I want to see a very thin steel or titanium mandrel removed from the CF hull of that size. After curing both parts are glued together, if not realy, friction between parts is terrible. It is possible if you contract the inner mandrel by freezing but what influence on CF caracteristics?????
Learned a lot. Great video.
Thanks
Hi Joe. Please Purchase a PoP filter!!! Thanks. I enjoyed your video, Possibly adjust the EQ to minimize the Poping for audio Pleasure!!! Rock on.
Already done thanks
Now, this video is more like it. It's technical and that's what we want!!
Thank-you sir for the feedback
Thank you for a very informative video. So many things that I did not know about carbon fibre.
You brought up F1 and from various videos I have seen they appear to use a clean room environment and they are only driving round a field. This is not to denigrate their skills. Oceangate appear to be constructing the pressure vessel in an airy warehouse/workshop for a far more extreme enviroment. It also appears that the titanium end is only held on with adhesive from an open bucket. Unless there is an inner ring it is only that bond resisting external pressure. From the recovered ends they appear to have come out devoid of any carbon fibre.
Yes I would love to see the results of the investigation. Epoxy bonding with composites is common, but I do not think anyone has tested at these pressures.
Bonding composites to metals is a tricky business. Preparation of the surfaces is very important, as is ensuring complete contact.
@@TricksterJ97 Good information, thanks
@@TricksterJ97 thanks for your feedback
From the materials-science perspective... Once upon a time, kayaks were made from fiberglass. A guy named Chan Zwanzig figured he could roto-mold better kayaks, and that's how kayaks are made now. Not carbon fiber, for kind of the same reasons fiberglass is best used for boat hulls. Internal-pressure vessel, CF's great, but external pressure? If you think so, I have a carbon-fiber kayak to sell you. Or a fiberglass submarine...
Thanks for the feedback
Nice to meet you. Best regards and kudus for your awesome videos. I subscribed from Portugal. 🇵🇹
Thanks
Very interesting video, many details about the material
Thanks
Great info on carbon fiber. Thank-you!
Thanks for your feedback
I saw something on Wikipedia about how the pressure vessel on the accident craft was already the second pressure vessel because the first showed indications of weakening after its second test dive. Don't know if they changed the design, but I guess that might tell you how error-prone the manufacturing process was.
Edit: It seems to have been more than two dives and it seems unclear whether it was repaired or replaced.
Yes the first pressure vessel was filament wound and pregreg wrapped. The Titan pressure vessel was tape wrapped with pregreg. Pacific Coast Composites has the details. Thanks for the feedback
Just a quick question about the difference in hull strength if the CF was used differently.
Instead of axially wrapping the CF around the inner titanium tube the way OceanGate made the Titan hull, what if instead the CF was 5" (or whatever hull thickness) wide factory finely woven into a curve that exactly matched the curvature of the inner titanium tube, in one single piece thousands of metres long?
So in other words, wrapping adjacent to the flanges and gradually building up to the full length of the hull, with the woven CF perpendicular to the inner titanium tube external surface. I imagine quite expensive, far more difficult, would need to be compressed as it was wrapped, and may require some new tech to achieve, but in theory this way the CF wouldn't be as likely to delaminate since the pressure from the titanium bulkheads would press the spiral laminate tightly together. Obviously the design would need to allow for some longitudinal compression and expansion (possibly with bellows to allow for this on the inner titanium hull), but at least with the radially woven CF, then in theory there would be much greater compressional strength that would take greater advantage of the tensile strength of CF. I'd have thought it would be more ideal to design the CF hull so it could be easily removed (for reduced maintenance costs) in one cylindrical piece from the titanium hull, for testing/scanning from both the exterior and interior surface for better resolution. Obviously the above would require a lot of work and engineering, far easier said than done.
If the Titan could even survive one trip to the Titanic with that crude axially wrapped wrapped CF hull (which I find quite surprising) then I'd have thought a far better way of using CF more suited for compressional loading might hold some promise, at least for the testing phase and unmanned trials.
What are your thoughts?
Great question, In the video of the earlier sub it only show the hoop wrapping. I understand that in a later process they wrapped pregreg in a more axially orientation in the long direction. But the older sub did still fail. On the titan sub they used pregrep carbon through out the entire sub and used a tape wrapping machine. I was told that they wrapped in the hoop orientation and in the axial directions. I heard that they wanted 7" of thickness, but for some reason they received 5" thickness. Not sure why, Maybe a cost situation that Stockton Rush later decided. But that is just a guess based on his logic of using acrylic viewing port rated only to 1300 meter instead of 4000 meters. I have also read that carbon fiber can be constructed for strength against compressive forces. I am anxious to see the findings that the Canadian NTSB comes up. Based on the images of the recovered sub it appears that the titanium flanges popped out with little trace of either adhesive or carbon fiber remains attached to the flange. Thanks for the great question.
If all the fibers are going in a circular direction around the tube, and they don't have any layers going the length of the thing, then there's nothing other than resin resisting forces in the axial direction. They built a cylinder that's weak in what's usually the strongest direction. The hydraulic press channel has a video of carbon failing in this direction. It doesn't just shatter, it totally disintgrates into almost dust. If it failed like that, it would explain why they didn't bring up any shattered carbon pieces.
Correct, The video does not show a later process of wrapping carbon in the axial direction. The Titan sub was actually wrapped using pregrep and a tape wrapping machine. Totally different than filament winding process. Thanks for your feedback
Very interesting.
Thanks
Greeting from France
Thanks for the feedback
Carbon fiber for compression (pressure typical) applications a pretty strict no, no - universally. CEO of OceanGate, Mr Rush, was in an oxygen deprived state, on top of Mount Stupid. (Kruger-Dunning effect)
Exactly! It's tensile strength vs it's weight is incredible, but it's not a good choice for this application. It would be well suited for containing internal pressures, but not at all suited for dealing with external pressure.
One YTer speculated that the viewport might have been removed after recovery for trigger reasons … might have been “red.” Your explanation makes more sense. Another YT analysis says the water rushing in does so at the speed of sound at 1 atm pressure (assuming inside was at 1 atmosphere). This is 340+ m/s (standard atmosphere press & temp.). So, the pressure front would hit just before the water. Either way, the viewport and end caps are subjected to forces beyond the structural limits. That the titanium parts survived relatively intact is not surprising for such a relatively (to the carbon fiber comp) ductile & elastic and much more shock resistant material. The acrylic viewport is another matter. The carbon fiber is likely in millions of shards or a crunched mass ….
A RUclipsr scientist called “thunderfoot” done a very good vid the other day about the pressure. About how water does actually compress, very little of course ( about 1% at that depth), and how its basically like a massive infinate spring surrounding the sub. When exposed to one atmosphere, like a leak, the spring desprings if you like, at something like 4x speed of sound. When the water hits an object, the energy smashes it apart in micro seconds. The vid is well worth looking for 👍
Oh and btw the hull wound by Spencer composites was wound with a wet winding process. This hull made loud cracking noises in service and so it was retired. The hull that failed and killed 5 people was wound using prepreg.
Yup, I said old sub was made wet layup new sum was prepreg and I mentioned Spencer Composites
@@JoediyLab Oh got it. I didn't notice.
Do you remember the source for that info?
@@eurotrashdude8484 Check the following wikipedia page on Oceangate en.wikipedia.org/wiki/OceanGate
Also there is a video Posted in the description from the Oceangate RUclips page showing the wet filament winding process.
Great CF info thank you!!
Thanks
Fascinating.
GREAT tutorial Joe ... nicely explained and bookmarked accordingly. And also thanks for confirming what I suspected ... no Auto-Clave used; the part that pisses me off ("Old White Guy" with 40 years experience building composite structures (38 Countries) for the World's largest Defense Firm) to no end is lack of a "Clean Room" or Ultrasonic NDI (after EVERY dive) ... pity that Rush didn't follow his 20 years of experience building the F-15 and knowing it would need to be done per AS9102 with SOF/QUAL/HALT requirements from "Engineering". BTW ... stress software loaded with the dimensions, material type, tape laying method shows that the pressure hull would need to have been 17.6 inches thick to withstand 6,000 psi ... far more than the 5 inches Rush and his Team came up with. Installation of the Titanium flange to CF Hull is the most probable failure point; expansion/contraction differentials between Titanium and CF result in a 1mm "gap" ... which is why Rush used his "Secret Sauce Adhesive" to cushion the different rates. And as you and I know ... if you take a smooth, steel rod and dip it in liquid silicone or "adhesive", let it cure ... you can pull it off the rod like it was a rubber glove. He would have been better off using a “Thread Laying (TOWS) machine and certainly an Auto-Clave. This thing was doomed from the get go. Saddest part is the kid that didn't want to go but it was "Father's Day" ... breaks my heart !
Thanks for the comments.
@@JoediyLab Welcome ... things to ponder.
The Oceangate Video of winding the hull says it was for "Cyclops 2" which they eventually changed to "Titan." That video could be the very same hull that failed. I heard they did one change to the titan hull after around 2-3 dives because how loud and often they heard the carbon cracking and popping. Not sure if they made a new hull or just did some re-enforcing. Very curious on exactly what they did. Would love to hear your opinion.
The video is winding of an older pressure vessel. I spoke with an engineer that indicated the Titan use tape winding and not filament winding. Tape winding would be better as they could use prepreg tape and avoid the wet layup. It could also then be cured in an autoclave. But as far as we know they cured in an oven and not an autoclave.
I hit wrong key on that date it was done 2020 to fall of 2021. On hull
thank you!
Thanks for your video!
Thanks
The connection from titanium end plates and composite pressure vessel under pressure will compress at different rates.
I have trouble believing it was material fatigue.
Not in the titanium, in the images from recovery they appear intact. But I have heard from seen images that the viewing port was blown out. Thanks
great for people want a more depth review of the accident from a engineering perspective. Thank you! To sum up the pitfalls of the strength of carbon fiber, "you cant push a rope" Tensile vs Compressive strength.
Carbon fibre composites are very good in compression.
Interesting stuff. I dont know about CF, my training is in metals. What I have not seen as I go through the vids is any mention on the expoxy curing. You mentioned the degassing here, but do you have any thoughts on epoxy being an exothermal curing reaction ? If thats the case with CF that is. When I have used epoxy it gets hot and cures fast. For such a thick wall, I wondered how they would avoid thermal stress during curing. Or would this be an oven cured plastic ?
Yes in wet layups some epoxy can have exothermic reaction if applied too thick. On prepreg that have to be cured at higher temps, they are designed for the higher cure temps as long as you follow the specs. Good question
You need a pop-filter for your microphone!
Crazy glued
Very good and interesting. Most "experts" only say it wasn't good but you explain possible reasons why it wasn't good. Just one thought; You talk both about out of date pre-preg and dry fiber. I guess they didn't ad more epoxy to pre-preg so are we then talking about two different hulls made with different methods?
Correct it appears that the later sub may have used prepreg, but we really do not know for sure.
One good thing is that both Oceangate & Boeing are in Seattle Washington & the litigation lawyers won't have far
to travel when issuing the court papers.
Thanks for the feedback
Very well presented an thanks for depth in feet an not Meters..
Thanks
Cylinders have to be compacted layer by layer. Hoop tow tension is not enough radial pressure to compact broadgoods. I was a manufacturing engineer on filament wound cases designed for space shuttle boosters. They are now at Huntsville Alabama. The program ended when the director of NASA blew up the Challenger shuttle. The vacuume bag after winding does more to wrinkle hoop layers that are not compacted. They achieved low void content by drowning it in epoxy. You can see them scraping off the excess resin while winding. That is not resin control!
Great information, yes the filament wound sub failed during testing. Yes it was pretty scary watching the first video.
yeah......except the space shuttle boosters were made from steel
@@mycammedia Yes the NASA booster cases are steel 1/2” thick DCAC tool steel. Before the Challenger was destroyed by the director of NASA the Air Force wanted to do a polar launch.Filament-wound cases were manufactured by Hercules Inc. I was the senior process engineer.
Edit
“In order to provide the necessary performance to launch polar-orbiting shuttles from the SLC-6 launch pad at Vandenberg Air Force Base in California, SRBs using filament-wound cases (FWC) were designed to be more lightweight than the steel cases used on Kennedy Space Center-launched SRBs.[30] Unlike the regular SRBs, which had the flawed field joint design that led to the Challenger Disaster in 1986, the FWC boosters had the "double tang" joint design (necessary to keep the boosters properly in alignment during the "twang" movement when the SSMEs are ignited prior to liftoff), but used the two O-ring seals. With the closure of SLC-6, the FWC boosters were scrapped by ATK and NASA, but their field joints, albeit modified to incorporate the current three O-ring seals and joint heaters, were later (after STS-51L) incorporated into the field joints on the SRBs used until the last flight in 2011.”
@@oneskydog6768 Really - didn't know about that - why was it not really common knowledge - I only ask because I never saw any reference to anything like that. That must have been some amazing set up in terms of size - any special arrangement for the interface of the segment 'body' to the steel joints? just curious. I was interested in all the issues surrounding the field joint design - rotation of the joint, etc. I also was deeply interested a long time ago about AA587 - the public hearings about engineering issues and the differences of approach / philosophy between Boeing and Airbus about what each was willing to do when it came to using carbon fiber. Airbus pushed the issue much further towards making moutings from cf - but Boeing were way more conservative then and were unhappy to make the actual mountings from cf. At that time, they wanted to stick to an experience base of 70 years around the fatigue issue with metal.
@@mycammedia operational security need to know basis
Very educational video on carbon fiber.
Thanks for the feedback
You mentioned unidirectional fibers. I wonder what impact if any the unidirectional construction (no fibers along the length) had on the strength of the pressure vessel..
Basically no bending or shear resistance other than the epoxy resin matrix.
It appears carbon fiber and titanium have different rates of thermal expansion. Therefore, the materials would not expand and contract at the same rate thus opening up a mode of failure entirely based on exposure to temperature exposure differentials, entirely leaving the pressure exposure issue outside of the equation. From approximate surface (June 2023) to subsurface temperature differential is about 8 Deg C, estimated. The delta is not zero. Repeated cycling (outside of pressure delta) seems to show an issue.
wonder what kind of seal they have on the front dome closing onto the titanium ring. looks like a smooth surface, then any seal when the front hatch is closed ?
No seal, at depth the pressure would keep water out. Just have to make sure surfaces are very clean. Thanks for the great question 😊
Good video, but heads up, I think you’re too close to the mic. Every time you say a word with the letter ‘p’, we hear a loud burst of air
The threads are called filaments.
Filaments are combined together to form a yarn.
There are continuous filament yarns and “staple” filament yarns that are twisted together to form a yarn.
The yarn is measured in “denier”.
Thanks for the comment
You are a genius to explain this process. I listen very closely what you were saying. I respect everything you talked about. This Stockton rush would have called you a dirty white male over fifty who doesn't know anything. Thank you sir for explaining all this.
I confess I am a dirty white male over 60. Thanks for the feedback
If the pressure makes the centre section of the tube compress would the ends distort?
Looking at the recovery images, the titanium flanges were shown separated from the carbon fiber cylinder. It appears that when the carbon fiber section crushed, the titanium flanges were pushed out. There appeared to be no carbon fiber attached to the flanges that I could see.
I assume the thicker the lay up and the greater the number of plies, the greater the pressure in the autoclave to compact the layup as it cures. This might have made a difference between disaster and returning to the surface.
That is a very complex question. There are several variables involved. Temperature, pressure, vacuum (yes you vacuum bag when using an autoclave) There is also temperature ramp up and ramp down times and how the resin flows with in the laminate. I am not a mechanical engineer. I would have to do alot of research on this topic. Sorry.
I’ve been asking this question since the incident with no answer. I get that carbon fiber was the mistake…WHY would Stockton Rush make that mistake when there was 60 years of no fatalities and proven materials for deep dives? My assumption is carbon fiber is cheaper than titanium and he excused it for this reason. Why else would he insist on reinventing the wheel?
Hubris
$$$$$$
@@ericpalmer3588 thats not really an answer though...
Very good technical informative Video, but you got a Problem with your Mic there, the Pops are very distracting and nerv racking.
Thanks, yes new mic is on order
Did you know the sub impacted the prop of titannic on a previous dive?
Now that the 787 Dreamliner. The carbon fiber vessel, do we want to be traveling around in pressurized cabins high in the atmosphere as we have seen the response to stress over time?
Inside pressure is in tension, outside pressure is in compression, Big difference. Thanks for the comment
The only vids Ive seen of the mid-section layup, shows fibers only laid in the hoop direction, however the Wikipedia description suggests that there are alternate axial layers of UND. So effectively (if thats true) it should have similar properties to a weave. Perhaps optimistically achieving 550 MPA in compression? A simple solidworks simulation, (not accounting for dissimilar materials or adhesive bonds) suggests a stress of 250MPA at 4000mts if the entire pressure vessel were homogeneous. That seems rather too close for comfort. I have also not checked for buckling failure mode (tin can collapse) which may be a factor. Also the highest stress area is exactly where the titanium ends would attach.
Yes I have not seen another video as well. I had heard that they wrapped prepreg in an axial orientation, but I cannot find any proof. Thanks
very interesting. is kevlar stronger or is it carbon fibre? I thought kevlar is stronger so why didnt he use this?
Carbon fiber is stronger, Kevlar is more abrasion resistant and impact resistant than carbon fiber.
Learned something new. Always thought as the carbon fiber strands as “threads” but the actual “Tows” sound more like rods structurally stiff but as fail as a STRUCTURE by bowing. Bonus points for spelling out “TOWS” as the YT transcripts can be a bit quirky.
So if all the possible faults (no preprog cloth, out of aerospace spec materials and vacuum bagging versus autoclave) the Titan’s hull sounds like it was made like a fiberglass recreational boat only using different fibers and resins and 5” thick. Would the Titan’s construction pass USCG standards for an ocean going lifeboat?
My understanding of fiber reinforced resin composites is as you stressed: bonding between layers and between the fibers and resin matrix, and, avoiding voids in the matrix is critical. With metals voids, inclusions and microscopic cracks greatly reduce strength and operational life; the NDT/NDI methods for inspection are well developed. For a 5” thick cylinder walled pressure vessel what are the methods for inspecting for fiber-resin bonding??
There methods would not pass inspection. I spoke with a composite s engineer, he indicated that with a portable ultrasonic tester he could not get penetration in a composite that thick. Possibly with a larger unit. Thanks for the feedback
@@JoediyLab A larger ultrasound unit would not work well. The penetration of acoustic waves into materials is frequency dependent, not power dependent. The higher the frequency, the higher the energy loss through absorption and the less thickness your wave will be able to penetrate. Ironically you need to lower your frequency to penetrate a thicker layer.
However this comes at the cost of spatial resolution, the lower your acoustic frequency the larger the feature need to be in order to be detected, also the thicker the material the higher the wave amplitude or the power you need to put into the signal to get a decent return signal through sound absorption.
The wavelength of NDT ultrasound is anywhere between 200KHz to 50MHz, let's say they use a frequency of 5MHz.
Wavelength is dependent on sound speed which is dependent on material density. A 5 MHz ultrasound signal in air has a wavelength of 0.07mm with a sound speed of 343 m/s. A 5 MHz signal in CF with a sound speed of 10000 m/s is 2mm, so anything smaller requires a higher frequency. If you went down to 1 MHz your wavelength increases to 10mm(1 cm). So any cracks smaller than the wavelength of the sound won't interact strongly with the wave to reflect a signal back, it's basically the diffraction limit as it's termed in optics.
Ultrasound works very well because it can detect very small cracks within a relatively thin layer of CF, down to fractions of a mm but as you get thicker your resolution advantage is lost.
Also because the CF hull is a curved piece there are geometry issues which can cause the ultrasonic beam to scatter and not properly reflect off any defects depending on how the defect is oriented. Because it's also a laminate these alternating layers of CF and epoxy will cause the ultrasonic waves to reflect and refract as well as diffract, this causes a lot of interference.
Imagine looking through a curved window made of multiple alternating panes of glass and air and shining a flashlight through that stack to see any defects in the inner panes.
Source: Not a materials engineer or a NDT specialist was trained in petroleum geophysics on how to interpret seismic wave propagation in the earth.
Very clear and consise video, it's well known how Aircraft Wings are created with multiple patterns laid under Computer control. The flexibility has to be carefully planned and calculated and tested before a safe structure is used on an aircraft. As you said "Stretch" is very strong but "Compression" is not so strong. I was not happy watching the video of the manufacturer of the cylinder. It looked very risky and almost at a "Home DIY" level of build.
Thanks for the feedback
Someone get this man a pop filter.
I'm wondering... Since the assembly is under compression, wouldn't most of the load be supported by the resin, not the CF? What would have happened if they used 5" thick resin poured from a mold with no CF at all?
No you will still get support from the carbon fiber. the strength of the fiber is along the length of the fibers. So you orient the fibers along the areas of stress you need. If you cast structural resin that thick it would heat up to much and weaken. Even with slower curing resin it would shatter. The strength of carbon fiber is a combination of resin to carbon fiber matrix. Carbon fiber by itself is only good in tension. If designed correctly you can get good strength in both tension and compression, But more strength in tension. Thanks for the great question.
If you haven't subsequently found the info, the CF hull was 66 inches OD and 100 inches long with 5" thick walls. Not 8 ft OD.
I thought the CF was wound on a titanium drum which formed the cylinder. Was this not the case? So it basically molded into the shape we see?
No the carbon was wrapped on a mandrel and pulled off when cured. Then the titanium flanges were bonded on.
@@JoediyLab I work with CF on a very limited basis, what would happen when say hardware is screwed into the CF? I noticed the monitors being mounted. And the illuminated handles he used that he got from Camping world.
That would cause isolated stress points around the area of the screws or bolts. I think they had s sub structure that they mounted hardware to.
Ive read thay autoclaves are generallly not recommended for filament wound parts like this because it can cause the fibers to buckle. In this case its actuallyy the fiber tension during winding which compacts the layers.
Yes would be interesting to see what method they used on the new sub with the prepreg, could not find any data on the method
@@JoediyLab there's an 18 minute video where Stockton Rush gives a talk and he shows a few photos from the process. You can see the machine used to lay the fiber. It was a more complex tape laying machine.
@@matthew4878 I will search for that, do you know if Spencer Composites has an autoclave?
@@JoediyLab Their website says that they do. I doubt it's big enough for this though.
In college when we made parts like bulkheads and torsion tubed out of carbon fibre using prepreg we had to place the parts under vacuum wrapped in plastic and use an autoclave. Never did we orient at 90 0 for every layer.
When the Russians produced the VAZ-2101 with aluminum brake drums, they also said it was revolutionary.
What you're trying to say is "the resin has to be molecularly uniform throughout the fabric, without any air bubbles, which we all know is very difficult to achieve.
Yes, using prepreg gets you close. Also resin to fabric ratio is critical to strong parts. Thanks for saying it so elegantly
@@JoediyLab you know. 👍
Getting all the air bubbles out of 5” of prepreg is a challenge on its own. The simple thickness precludes success because the vacuum simply would need weeks to pull the residual air out.
@@allangibson8494 is it fair to say Titan was effectively a toilet roll with a pair of glorified bottle tops at each end.
@@Stevie-P123 Pretty much, Yeah. I could have not put it better myself!
You never posted the link to the video you mention?
Check the description, should be there. Thanks, if not search Oceangate on RUclips there is a video on there site
That looks like a 6 foot step ladder next to it which would put it at about 10 feet I think. The Titanium rings make it look bigger in other pic maybe. Lol I just noticed the 12 foot ladder on the right . ;-)
how safe is it on airplanes then? as they are pressure vessels as well...
Perfectly safe. The pressure is the opposite way around. Carbon fiber is great at keeping pressure in, not so much at keeping pressure out. Tensile vs compressive strength.
Thanks for your feedback. Yes internal pressure is a different force.
Sylvester the Cat analyses the Titan tragedy.
If 14.7 psi is sea-level, could the elevation of a factory significantly reduce the available vacuum-bag pressure?
Great question, Here is a quote from Composites World "The maximum compaction pressure available at sea level with a perfect vacuum bag is 14.7 psi (29.92 inches or 760 millimeters of mercury.) This maximum available pressure drops approximately 0.5 psi (1 inch or 25.4 millimeters of mercury) for each 1,000 foot gain in altitude. "
If you draw a perfect vacuum under the bag, then what is pressing on the other side is whatever the atmospheric pressure is. More in Death Valley, less in Denver. Putting the vacuum bagged part in a pressurized autoclave results in greater than atmospheric compression.
Even gluing it together there was no press, just the weight of titanium ring. Is it important?
Check out the later video on adhesive, Some adhesives are very strong.
I noticed in one of ocean gates videos that both interior monitors were screwed directly to the composite tube. Now I wonder they screwed other components to the exterior of the composite.
There is more than likely an interior sub frame that they are using to mount hardware. Just like the flooring, a flat panel is used to sit on, thanks
What are your thoughts on the longitudinal compressive forces the cylinder was exposed to with each dive. Approximately 400 atm x Pi x Cylinder Radius ^2 = 14.7 x 400 x 3.14 x 48^2 = 42.5 million pounds of longitudinal compression in addition to radial compression. Longitudinal area = Pi X ( 48^2 - 43^2) = 1430 in sq. Therefore 29,720 psi cylinder wall longitudinal compression. I don’t think any carbon fiber runs in that direction; therefore must be carried by the epoxy resin?
I like reading comments like this. I am not scientific at all, and have a high school level understanding of math. But somehow I can infer the point you are trying to make.
I heard that in some data from Pacific coast composites that did run plys in the hoop and axial direction. But I have to confirm
@@JoediyLab I calculated that the composite carbon fiber cylinder would’ve experienced 29,700 psi compression in the longitudinal direction and 60,600 psi radial compression throughout the entire side wall at Titanic depths. I think Stockton felt safe with carbon fiber composite because it has a compressive failure pressure of approximately 250,000 psi if it’s not damaged. But fatigue cycling and differential strains between titanium and carbon fiber may have done him in.
@@jamesn3513 wow, very cool. Yes I agree with your thoughts.
@@jamesn3513 and just what if a horrible mistake was made an error in judgment that may very well not wish to get revealed RE: litigation; that Sunday noise was bottom brackets falling down, not any implosion. So rescue was not pursued underneath but above. Then when Canadian C-3 Orion plane heard 30 minutes of banging, is when those in charge rushed to have underwater ROV brought took hours to get there.
All those days, nights, in ocean pressures, subjected to changing temperatures and freezing ones,
Can be date of implosion as hull plus resin becoming more brittle to failure! Don’t be so positive on dates being thrown, consider there may become a hugh liability issue to develop, dates can make or break such possibilities!
PLEASE use an OMNIDIRECTIONAL mic. Your percussives are distracting! Love your content..
Mic is on order
Carbon fiber is infuse on the outer part of cylinder the problem is it 100% sealed? if water pressure find its way thru the fiber its useless and only the metal frame is holding the pressure.
Is 5 inch thick carbon fiber an issue? This doesn't seem like the optimal thickness for this material. Do the properties of 1/4" carbon fiber scale linearly to 5 inch thickness? All carbon fiber I have seen is relatively thin (< 1/2")
Good question, deformation doe not scale linearly. Yes most research has been don on thin walled cylinders. thanks for your feedback
It’s a miracle this sub made of pure ramen noodles and Italian spaghetti held together by only a thin layer of glue, did not implode at the very first trips.
The repeated claim that carbon fiber fails suddenly depends on the type of fibers used. The stiffest lightest ones are like that, but you can opt for grades that have more given/flex in them. For instance people build mountain bikes out of carbon fiber, and they can handle impact damage better than their metal counterparts, because they are using slightly less stiff composites that can handle it. Just wanted to mention this nuance here as people often repeat this claim without being aware of that.
Thanks for your input