4 ms·
The hull imploded, not the window, but the shockwave probably pushed the window outward or shattered it, as it was only held strongly against moving inwards. P
by _yb2s 3y ago
The hull imploded, not the window, but the shockwave probably pushed the window outward or shattered it, as it was only held strongly against moving inwards.
People make a big deal about the acrylic glass not being rated for the depth, but I think it's almost impossible that it was the window, and think it must have been the hull:
* The properties acrylic are well understood, and the strength of an acrylic disc is trivial to calculate, even if not "rated" you can easily calculate if it's strong enough
* The window should fail visually with a lot of warning before rupture
* If the window failed with the titanium end cap, there would be no reason for implosion of the carbon fiber hull
The hull on the other hand is an irregular/non-homogenous part that is impossible to model accurately. There was no way to know how strong it was without extensive testing on a number of identical hulls- which they never did. The solidworks modeling method they used to give a ~2x margin of safety was nonsense as it ignores the realities of stress cycles, defects, etc.
- TechBro8615 3y agoHow was the window "connected" to the hull? Would that be a weak point?
- Wojtkie 3y agoDeep sea portholes are usually cones of acrylic that seat right into a port in the hull [0] [0]https://www.researchgate.net/publication/340442621_Prediction_of_the_service_life_of_deep-sea_conical_acrylic_portholes_at_designing https://www.researchgate.net/publication/340442621_Predictio...
- EA-3167 3y agoThis sub was a carbon fiber cylinder with two titanium end-caps, and the porthole was fitted into the forward end-cap.
- _yb2s 3y agoThey machine a wide ledge on the titanium, so the window is pushed into the groove/sill under pressure, basically a large window that is covering a smaller hole that it can't fit through. For all practical purposes, it justs sits on there and the pressure holds it on. It would also have bolts and/or sealant to keep it in place when not diving.
- zardo 3y agoThe monitor mounts screwed directly into the hull seem a likely starting point for the failure.
- akiselev 3y agoIn the photos I've seen, it was pretty clear that they had a separate inner hull for mounting stuff. If they really drilled into the outer hull, it wouldn't have survived the first trip as that would have certainly caused matrix cracking that propagated to the skin. It would have failed in the first 1000 meters.
- AlbertoGP 3y ago> The monitor mounts screwed directly into the hull seem a likely starting point for the failure. Nothing was screwed directly into the hull: > These handle-lights aren’t attached to the carbon fiber. The sub is lined with a big insert, a perforated metal sleeve, that fits snugly against the carbon fiber, like a rolled-up poster in a mailing tube. “The thing with carbon fiber is you can’t cut holes in it. It doesn’t like that,” Rush says. “Nothing touches the carbon fiber.” — David Pogue in “What I Learned on a Titanic Sub Expedition” https://nymag.com/intelligencer/2023/06/what-i-learned-on-a-titanic-submarine-expedition.html https://nymag.com/intelligencer/2023/06/what-i-learned-on-a-...
- soligern 3y agoThat’s just random 4chan speculation passed off as fact.
- nomilk 3y ago> The hull on the other hand is ... is impossible to model accurately. Why is the hull difficult to accurately model? (assuming the exact materials and precise dimensions were known).
- akiselev 3y agoCarbon fiber can't be inspected like metals can using radiographic, liquid penetrant, or magnetic particle testing, so even if we did know the exact materials and precise dimensions [1], it's very hard to characterize them and how they responds to stresses. [1] composite materials are not as homogeneous as metals are, so most of the time we actually don't know the exact materials and precise dimensions. Only manufacturers that make enough parts to afford to do destructive testing can characterize the process enough to make reliable guarantees about part strength.
- sottol 3y agoThere are a variety of non-destructive inspection and testing methods for composite, like ultrasonic c-scans and pulsed thermography that I know of. And you can produce reliable composite parts (you don't want homogenous, but them to come out exactly as spec'ed) under strict control, but it doesn't look like they necessarily did that here. They seem to have eg foregone autoclave curing of the tube section probably due to cost.
- _yb2s 3y agoThey could have identified defects with non-destructive testing, but they almost certainly would have found a huge number of them, and had no way to reliably model the importance/potential impact of them.
- _yb2s 3y agoWe're talking about a bunch of layers of fibers, and woven cloth impregnated in epoxy. It's a pretty messy, irregular thing with voids, gaps, broken fibers, etc. even if you lay it up robotically (as they did). The modeling they did assumes a perfect material, and then adds some arbitrary factor of safety that will hopefully account for imperfections. It probably would have been fine if only used for one dive, but not after a substantial number of fibers had snapped as the hull flexed across numerous dives.
- zaebal 3y agoCan we assume that if the acrylic was a point of failure, then the whole titanium end cap section would appear much more damaged, than what we can see on those pictures?
- postmodest 3y ago> The window should fail visually with a lot of warning before rupture The window would deform up to 2" during dives, according to passengers.
- _yb2s 3y agoThat does sound pretty sketchy... but from what I've heard, acryrlic should start to fracture in a way that makes it opaque before it catastrophically fails.
- wumms 3y agoThe time between opaque and failure might be little at that pressure. Somewhat related (possible material fatigue): A 16-meter (52-foot) high aquarium has burst at a hotel in downtown Berlin (2022): https://www.dw.com/en/berlin-massive-aquarium-home-to-1500-fish-bursts/a-64119337 https://www.dw.com/en/berlin-massive-aquarium-home-to-1500-f... Manufacturer: https://www.reynoldspolymer.com/projects/aquadom/ https://www.reynoldspolymer.com/projects/aquadom/
- deleted 3y ago[deleted]
- scotty79 3y ago> If the window failed with the titanium end cap, there would be no reason for implosion of the carbon fiber hull I feel like if the window failed then the sheer momentum of inrushing water could detach titanium cap on the opposite end of the sub. A bit like you can break the bottom o a glass bottle by hitting the bottle from the top which causes the water in the bottle to separate from the bottom of the container and then come back down with enough momentum to break the bottom.