Comment by hajile | Hacker News Reader

Comment by hajile | Hacker News Reader

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I've heard both assertions. I tend to believe that Carbon Fiber is a fine material to use.

This submersible used untested techniques. They didn't adhere the layers together properly and apparently never bothered to X-ray the tube as that would have shown at least some of the defects. It also seems like there were other design issues with how the tube was paired to the ends.

Most importantly, the deaths were caused by negligence during operation and maintenance. They had the data showing when the hull was damaged on the previous expedition, but either never did their due diligence and analyze it or ignored the results. Even during their last expedition, they may well have avoided death if the alarms had been heeded.

EDIT: to answer the people who seem skeptical, there are companies making carbon fiber vessels that have successfully gone much deeper than those Titanic dives. We're still in the learning stages with the technology, but we'll eventually find the combinations and standards that can make it safe to use (at which point, it may become better than our current solutions). Until then, maybe we shouldn't be shoving people into damaged experimental vessels to see what happens.

https://www.compositeenergytechnologies.com/underwater-carbo...

https://www.researchgate.net/publication/376273321_Carbon_Fi...

The Coast Guard report section “5.6 Insufficient Understanding of Carbon Fiber Material Properties for Deep-Sea Applications” addresses your arguments.

Yes. It can be safe. The problem is that its crystalline structure can fail instantaneously without any ability to detect beforehand. In this case the sub was likely improperly manufactured and improperly stored and damaged from previous dives and from transport. The company “planned” to inspect but as no non destructive testing was possible, they didn’t bother.

There is a YouTube channel that anaylzes the core problem in depth. Compression vs. tension is really a red herring because in a closed convex structure compression somewhere is tension elsewhere. The real problem is the carbon fiber maxtrix was wapped around the epoxy filler without tension like paper mache. So it had insufficient strength and non homogeneous strength. The sub was built up like an onion. Concentric layers of carbon fiber epoxy thermoset. I think it was something like 5 layers. Anyway because the layers were not wrapped tight before curing there were ripples in the surface of each layer. Subsequent layers were applied after sanding down high spots and applying a wrap of double sided adhesive tape between each layer (no joke). So not only were the carbon fibers not pretensioned but also they were cut in hundreds of spots. This is somewhat like if one were to pour layers of reinforced concrete by throwing a bunch of loose rebar in a hole, pouring concrete over it and then cuting pieces of rebar that stuck up before applying the next layer after putting a layer of plaster over it. For carbon fiber composites and concrete to be strong tension bearing elements need to be able to bear tension. If they are loose in the matrix or cut the composite will not be strong. Thus carbon fiber was not the problem but rather its manufacturing process. Anyone who has ever done drywall joints or autobody can understand the problem. It doesn't take an engineering degree to understand that if you wreck the tensile components of your composite it will be much less strong than if the composite is laid down properly!

This is the video https://m.youtube.com/watch?v=sE4uSjQoa3A

Their carbon fiber laying system sure looks an awful lot like the one used by oceangate. Can anybody here explain the nuances I'm missing?

> I tend to believe that Carbon Fiber is a fine material to use.

It's a fine material to use for unmanned submersibles!

>I tend to believe that Carbon Fiber is a fine material to use.

For deep underwater? Apart from the series of stupidities you go on to list, I'd love to hear your reasons as to why?

I'm a carbon f bike rider, even down to carbon spokes and I do not trust the material, knowing that pressure, or force, applied in the wrong direction will make it crack!. As for carbon in a circle...no way.

> I'd love to hear your reasons as to why?

It's been proven to work?.

A submersible constructed of carbon fiber went to depths that many metallic submarines and submersibles cannot.

If somebody constructs a submersible and then tests it to 5000m and finds it fails on the 200th run after exhibiting for the past 50 dives bad acoustic data. Wouldn't you think it's fine for them to take people on the same designed submersible that's only done 100th runs and still has good data?

Everything is a consumable in the long run. They didn't have data on what Titan looks like before a failure. Although in hindsight the acoustic data looks really bad, the issue really is just the specific design didn't have a known lifespan. A submserible without that defect is going to be a lot safer.

I've linked this elsewhere in thread, but here's testing results from a US Navy pilot project for carbon fiber unmanned subs. It looks like this found it pretty viable.

https://apps.dtic.mil/sti/pdfs/ADA270438.pdf

What's the issue with CF in a circle? My bike is mainly CF (mainly just brakes and drivechain are metal) and of course that means CF wheels which I think are great (CF means that you can have deep section "aero" wheels without much of a weight penalty).

Well designed carbon rims are surprisingly durable: https://youtu.be/VfjjiHGuHoc

When carbon fiber rims were new we still had not transitioned to disk brakes. You had to keep an extra eye out for misaligned brake pads to make sure they weren't dragging on surfaces not meant for friction contact. Now they make more sense. But also different loads on a wheel under braking than before, but also more like a wheel under acceleration, which is torsional force on the other side of the axle and pointed the opposite direction.

I think it's not ideal in the same way that plastics don't belong in an automotive engine bay and concrete doesn't belong" in tension. Add a little bit of fancy chemistry or some steel and fancy math and they both work fine for cheap.

With care and engineering trickery CF in a submersible (compression) probably can work. They still managed to make a few good dives with it despite comically bad decisions in just about every key area. The manufacturing process was primitive, the QC basically nonexistent and procedures didn't make any allocations for the materials (they beat on the thing like it was made of steel). Imagine what a well funded company with experience in CF, robust QC and careful operating procedures could do.

Trek 2100. The first carbon fiber bike affordable by upper middle class people.

Their trick was pre-formed carbon tubing glued to aluminum lugs. Sound familiar?

Good, because they had a massive recall because the carbon at the joinst started to chip and crack. Member of our club had to call a friend to come get him because his top tube came apart fifteen miles from town. Took em a while to replace it too. Eventually he ended up on a Serotta (Titanium with extra metalurgical tricks to make it lighter still).

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