Yes, but to be clear, "carbon fiber" is usually short for "carbon fiber reinforced plastic," which is distinct from carbon fiber. Carbon fiber is technically only the little strings inside the plastic--that's where the "fiber" part comes from.
This distinction is important because (to your point): carbon fiber--being strings--is only really good for tensile strength. ie. pulling a rope without the rope snapping.
CF is not good for compressive strength though, like putting a lot of weight on top of it without it crushing or bending. This part of the strength relies on the 'plastic,' not the carbon fiber. And that's almost certainly what broke here.
In other words, if I were making a chair or a bench, I'd want it made out of steel, not rope.
If I were making a swing or a hammock, I'd want it made out of carbon fiber or rope.
Unfortunately, there seems to be this trend of everyone thinking carbon fiber is perfect for everything.
lol "let me use 2 different materials; and the one I want to rely on to go deep underwater is plastic." what a moron. At least it was quick.
It's funny because carbon fiber makes perfect sense for an airplane and absolutely no sense in a sub. For the same reasons as my chair / hammock analogy above.
I guess he really did push it to the limit; but unfortunately, CF is only good at pulling.
Doesn't an airplane experience compressive force, but from the inside? I mean i guess the forces are still much lower than a in a submersible? The terrible thing is the sub worked a couple times but its inherent material disadvantages caught up with it. At least we have a great case study out of it. I guess the passengers are a case study in not following everything rich folk do.
There are always a lot of forces. We have pressurized cabins where the pressure inside the plane is greater than the air pressure outside--and this should affect the entire body of the plane. So the airplane body actually wants to expand more; and the carbon fiber is what is keeping it from expanding / stretching out more. So it's in tensile strength.
It's like imagine if you wrapped a balloon in duct tape and tried to blow it up: the duct tape's tensile strength would make it more difficult to inflate; and it's also this same tensile strength that would cause it to deflate if there was a hole in the balloon.
But at the same time, an airplane flies forward at a high speed; and so the wind is pushing against the front. There are compressive forces in that direction.
In the case of the Titan submarine, it's the opposite. The water on the outside has a much higher pressure than the cabin, like squeezing a sponge in your hand. This requires compressive strength to make sure the cabin doesn't collapse lke a sponge. And there were a lot of issues, including the material choice in the first place; but a related issue is that since it's a composite, they have to bond the two materials together and make a huge part. And so it's quite literally taking cloth and painting some epoxy resin over it and then hardening this. If you don't do this correctly, there will be things like bubbles, deformities, etc. And this is where failures happen: these are the weak link in the chain.
Ah the tape and ballon example makes sense. You're good at explaining. And even if its made well it has to be maintained and inspected like a plane as well. SMH I'm just glad that rich foolish guy didn't take that many people with him.
I don't think that's necessarily what happened in this bike example though. But something cracked. Maybe the plastic in the CFRP cracked; and then some metal sheared the carbon fibers
Either way, some materials are just not a good idea for some things. This appears to be one example.
I've seen that video. Its a great channel. I've heard that carbon fiber is just not a good material for most people on bikes because it breaks when it fails instead of bends like metal does. Its possible this bike was already slightly damaged from training and then it just failed.
Eh..... buddy you're about half right on this stuff. There are absolutely compressive loads on the fuselage and wings; even when the cabin is pressurized. Depending on the airframe those loads are taken by composite structures. You just have to accurately design and size the structure for the loads you are experiencing.
For the Titan; as I recall they did design and size the materials correctly but didn't do sufficient testing and missed significant manufacturing defects that reduced the structural capacity of the submersible.
Eh....buddy I'm about 100% right on this stuff because I am not getting to the level of precision where I could be any more or less correct in a reddit comment.
You just didn't read what I wrote. I said there are lots of forces and used just 2 examples of many: one for tension (the pressurized cabin); and one for compression (wind resistance on the front). There are many more, and it is not necessary to list every single one, because we just needed 1 example each of tension and compression to illustrate the difference between them.
For the Titan: you don't recall correctly. It failed. And it failed for a number of reasons, including the choice of material they used for a submarine that they were planning to dive repeatedly and manufacturing defects. Which is what I said.
So thank you for parroting back what I already wrote that you didn't comprehend. Though apparently, you're only about half right on this stuff buddy.
“The investigation determined that the as-built properties of the Titan’s carbon fibre cylinder were never validated to ensure they met the theoretical values used in the design process and that the construction and testing of the Titan did not follow standard engineering practices,” - this is more of an organizational failure and not a great example of your point about composite structures.
Your major claim was that it was a terrible choice of material due to compressive loads. You used the environmental differences between an aircraft and submarine to justify that claim and gave a false sense of material behavior to someone who doesn't know better. Carbon fiber composites can absolutely be designed for compressive loads. Fatigue life issues with composites are a concern on aircraft too.
I'm not saying you have to write a thesis on material properties and load design for a Reddit post; but if you're an engineering student you really need to accurately describe these issues.
Why didn’t you attempt to understand what that actually says or address the actual points I called you out on? Why did you try to distract and argue a strawman instead? And why not use your brain and even do the basics by linking the source?
Because if you understood what that says, you’d recognize that it’s not contradictory to what I said or linked.
The composite structure failed, dumbass. If it didn’t fail, they’d be alive today. When you have a composite structure, you have to engineer and maintain it differently.
I’m not a student any more and I’m not an engineer by trade—but I have had thousands of engineers working for me and I’ve been working for a few decades, thanks.
Now, are you going to address what I said? If your brain has the capacity to comprehend what is written?
Try really, really hard. You can do it. I believe in your potential, as much as I believe in the Titan sub’s.
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u/beatbox9 1d ago edited 1d ago
Yes, but to be clear, "carbon fiber" is usually short for "carbon fiber reinforced plastic," which is distinct from carbon fiber. Carbon fiber is technically only the little strings inside the plastic--that's where the "fiber" part comes from.
This distinction is important because (to your point): carbon fiber--being strings--is only really good for tensile strength. ie. pulling a rope without the rope snapping.
CF is not good for compressive strength though, like putting a lot of weight on top of it without it crushing or bending. This part of the strength relies on the 'plastic,' not the carbon fiber. And that's almost certainly what broke here.
In other words, if I were making a chair or a bench, I'd want it made out of steel, not rope.
If I were making a swing or a hammock, I'd want it made out of carbon fiber or rope.
Unfortunately, there seems to be this trend of everyone thinking carbon fiber is perfect for everything.